Benchmark DAC2 DX Instruction Manual

Transcription

1 Benchmark DAC2 DX Instruction Manual Reference Stereo D/A Converter Native PCM and DSD Conversion Headphone Amplifier Dual Output Buses Asynchronous USB DAC2 DX Instruction Manual Rev A Page 1

2 Safety Information Fuses CAUTION: FOR CONTINUED FIRE HAZARD PROTECTION ALWAYS REPLACE THE FUSES WITH THE CORRECT SIZE AND TYPE (0.5A 250 V SLO-BLO 5 X 20 MM LITTELFUSE HXP OR EQUIVALENT). THE FUSE DRAWER INCLUDES TWO FUSES. ALWAYS REPLACE BOTH FUSES AT THE SAME TIME. Voltage Selection THE DAC2 IS EQUIPPED WITH A UNIVERSAL POWER SUPPLY. THERE IS NO VOLTAGE SELECTION SWITCH. AC VOLTAGE RANGE IS VAC, HZ. THE PRODUCT MAY ALSO BE OPERATED FROM DC POWER OVER A VOLTAGE RANGE OF VDC. Power Cord Modifications CAUTION: DO NOT SUBSTITUTE PARTS OR MAKE ANY MODIFICATIONS WITHOUT THE WRITTEN APPROVAL OF BENCHMARK MEDIA SYSTEMS, INC. MODIFICATION MAY CREATE SAFETY HAZARDS AND WILL VOID THE WARRANTY. NOTICE: CHANGES OR MODIFICATIONS NOT EXPRESSLY APPROVED BY BENCHMARK MEDIA SYSTEMS COULD VOID THE USER'S AUTHORITY TO OPERATE THE EQUIPMENT UNDER FCC REGULATIONS. Repairs CAUTION: DO NOT SERVICE OR REPAIR THIS PRODUCT UNLESS PROPERLY QUALIFIED. ONLY A QUALIFIED TECHNICIAN SHOULD PERFORM REPAIRS. CAUTION: ALWAYS USE A GROUNDED POWER CORD. THE PRODUCT IS EQUIPPED WITH A STANDARD IEC POWER ENTRY MODULE. USE AN IEC POWER CORD THAT IS EQUIPPED WITH THE APPROPRIATE CONNECTOR FOR YOUR LOCATION. CORDS ARE AVAILABLE FROM YOUR DEALER. DAC2 DX Instruction Manual Rev A Page 2

3 Contents Safety Information 2 Fuses 2 Voltage Selection 2 Power Cord 2 Modifications 2 Repairs 2 Quick Start Guide 5 Rear Panel 5 Front Panel 6 Control Functions 8 Applications 9 Professional Applications 9 HI-FI Applications 9 Computer Sound Card Elimination 9 Standalone Headphone Amplifier 9 DAC2 vs. DAC1 10 New Features 10 Performance Improvements 10 DAC2 DX Features 11 Feature List 11 Special DAC2 DX Features 12 Feature Details 13 DAC1 and DAC2 Product History 16 DAC1 Series History 16 DAC2 Series History 17 Digital Inputs 18 Input Formats 18 Limitations of Optical Inputs 18 Consistent Performance 18 USB - Computer Input 19 D1 and D2 - Optical Digital Inputs 20 D3 - AES XLR Digital Input 20 D4 and D5 - Coaxial Digital Inputs 20 D5 - Coaxial Digital Output 21 AES XLR to Coaxial Adapters 21 Analog Outputs 22 Main Output Bus 22 AUX Output Bus 22 Balanced Analog XLR Line Outputs 22 XLR Wiring 23 Unbalanced Analog RCA Line Outputs 23 AC Power-Entry and Fuse Module24 Fuses 24 Voltage Selection 24 Power Cord 24 Internal Settings 25 Jumper-Configured Options 25 Removing Top Cover 25 XLR Output Pads 26 Digital Pass-Through Function 30 Rack Mounting Options 31 Universal Rack Adapter Tray 31 ½-Wide Blank Rack Panel - Black 31 ½-Wide Blank Rack Panel - Silver 31 Connector Block 31 Benchmark Technologies 32 Hybrid Gain Control 32 Native DSD Conversion 32 Multi-Mode Asynchronous AdvancedUSB Audio 32 Jitter-Immune UltraLock2 33 High Head-Room DSP bit SABRE Conversion System 33 Diagnostic Display 33 Bi-Directional 12 Volt Trigger 33 Distributed Power Regulation 33 HPA2 Headphone Amplifier 34 Differential Amplifiers 34 UltraLock2 Clock System 34 USB Audio System Setup 38 USB Driver Installation - Windows XP, Vista, 7 39 Performance Graphs - DAC2 Series 45 Preliminary Specifications 61 Audio Performance 61 Group Delay (Latency) 62 Digital Audio Inputs 62 Jitter Tolerance 63 Balanced Analog Outputs 64 Unbalanced Analog Outputs 64 HPA2 TM Headphone Outputs 65 Status Display 65 AC Power Requirements 66 Dimensions 66 Weight 66 DAC2 DX Instruction Manual Rev A Page 3

4 Regulatory Compliance 67 FCC and RoHS Compliance Statements 67 FCC Notice (U.S. Only) 67 RoHS Compliant Information 67 CE Certificates of Conformity 68 Warranty Information 69 Benchmark 1 Year Warranty 69 The Benchmark 1 Year Warranty 69 Benchmark Extended Warranty 70 The Benchmark Extended 5* Year Warranty 70 The Benchmark s Extended 2** Year International Warranty 70 Notes on Warranty Repairs 70 DAC2 DX Instruction Manual Rev A Page 4

5 Quick Start Guide Rear Panel Analog Audio Outputs The DAC2 DX has three stereo analog outputs driven from two separate output busses. By default both busses are controlled from the front panel volume control. Either or both busses may be programmed to BYPASS the volume control. When an output bus is set to BYPASS, the output level is set to a calibrated maximum level. The XLR outputs can deliver +24 dbu. The RCA outputs can deliver 2 Vrms (8.2 dbu). The MAIN output bus drives a pair of balanced XLR outputs and a pair of unbalanced RCA outputs. The AUX output bus drives a pair of unbalanced RCA outputs. Digital Audio Inputs The DAC2 DX has six stereo digital inputs (1 USB, 1 AES XLR, 2 optical and 2 coaxial). The XLR, coaxial and optical inputs accept professional (AES) and consumer (S/PDIF) data formats at word lengths up to 24-bits. The optical inputs are limited to 96 khz sample rates. All other inputs support sample rates up to 192 khz. 12V Trigger I/O The 1/8 TRS jack on the rear panel is a bi-directional 12V trigger connection to enable power sequencing between the DAC2 DX and other audio devices in the signal chain. If the tip of the TRS connector is driven to 12 volts, the DAC2 DX will turn on. If the DAC2 DX is turned on locally, the DAC2 DX will drive the tip of the TRS connector to 12 V to turn on other linked devices. AC Power Input The DAC2 DX is equipped with a universal power supply. There is no voltage selection switch. AC voltage range is VAC, HZ. The fuse drawer contains two fuses, always use exact replacements. DAC2 DX Instruction Manual Rev A Page 5

6 Front Panel Power Switch Press once to turn on. Press once to turn off. IR Receiver The IR receiver for the remote control is located directly above the power switch. Do not block this opening. MUTE Switch and Light Press to MUTE all outputs. Press again to release. DIM Switch and Light Press to reduce the level of all outputs by 20 db. Press again to release. Input Selector Switches and Lights Press the INPUT buttons to select a digital input. If an input light is on, the corresponding input is selected and operating normally: U - USB digital audio input D1 - First optical digital audio input D2 - Second optical digital audio input D3 - XLR digital audio input D4 - First coaxial digital audio input D5 - Second coaxial digital audio input If an input light is flashing, the selected input is not connected or is not working properly: Slow Flashes (2 flashes/second) No input signal, transmission errors, or Non-PCM Rapid flashes Non-audio (input is flagged as data) Intermittent flashes Invalid sample (v-bit), unreliable connection DAC2 DX Instruction Manual Rev A Page 6

7 Output Calibration Lights If a CALIBRATION light is on, the corresponding output bus is set to the calibrated maximum output level and the volume control is bypassed (BYPASS mode). If a CALIBRATION light is flashing slowly, the corresponding output bus is set to BYPASS mode, but the output is muted or dimmed. A - AUX analog output bus is in BYPASS M MAIN analog output bus is in BYPASS NOTE: If a bus is not in bypass mode, the corresponding CALIBRATION light will flash rapidly when the volume control is adjusted. This feature shows which busses are being adjusted. Word Length Display The DAC2 monitors bit activity to determine the input word length. This gives an accurate indication even when status bits are set incorrectly. 24 The word length is 24-bits. 16 The word length is 16-bits. 16 & 24 The word length is 17 to 23 bits. None - No input, DSD, or word length less than 16 bits. Sample Rate Display The DAC2 measures the incoming sample rate and uses 4 lights to indicate the rate and format Sample rate is 44.1 khz 48 Sample rate is 48 khz 44.1 & 2X Sample rate is 88.2 khz 48 & 2X Sample rate is 96 khz 44.1 & 4X Sample rate is khz 48 & 4X Sample rate is 192 khz 2X & 4X DSD Headphone Jacks The headphone jacks are driven by Benchmark s zero-ohm HPA2 headphone power amplifier. Both jacks can be used simultaneously. Both jacks are equipped with switches that can be programmed to mute the MAIN audio output bus when headphones are inserted. By default, the left headphone jack is programmed to mute the MAIN output bus while the right jack will not mute the audio. Internal jumpers can be moved to enable or disable the headphone switches. Other internal jumpers can be moved to adjust the headphone gain range. Volume Control The volume control is a motor-driven rotary potentiometer. The position of the control sets the 32- bit digital attenuation. Audio does not pass through the potentiometer. DAC2 DX Instruction Manual Rev A Page 7

8 Control Functions All DAC2 DX functions can be controlled from the IR remote control or from the front panel. In most cases, operation is identical (see table to the right for a summary of front panel and remote control functions). OFF (remote only) ON (remote only) Press once to turn the unit off. * Press and hold to turn off all devices connected to the 12V TRIGGER. Press once to turn the unit on. * If the unit is already on, pressing ON will cancel MUTE and DIM. POWER Press once to turn the unit on or off. (front panel only) * Press and hold POWER to turn off all devices connected via the 12V TRIGGER. VOLUME Press and hold to turn volume up or down. U/D * VOLUME UP will cancel MUTE. (remote only) DIM Press once to toggle the -20 db DIM function. *DIM will cancel MUTE. * Press and hold DIM for 10 seconds to toggle the AUX bus VOLUME CONTROL BYPASS function. MUTE Press once to toggle the MUTE function. * Press and hold MUTE for 10 seconds to toggle the MAIN bus VOLUME CONTROL BYPASS function. INPUT Press to change the input. U/D * Press and hold both front panel INPUT buttons while computer is connected to toggle between USB 2.0 and USB 1.1. USB Press to select USB digital input. * Press and hold remote USB button while computer is connected to toggle between USB 2.0 and USB 1.1. D1 Press to select 1st optical input (remote only). D2 Press to select 2nd optical input (remote only). D3 Press to select digital XLR input (remote only). D4 Press to select 1st coaxial input (remote only). D5 Press to select 2st coaxial input if enabled (remote only). ANALOG Not used on DAC2 DX (no analog inputs) DAC2 DX Instruction Manual Rev A Page 8

9 Applications The DAC2 DX is a professional reference-grade digital to analog converter with two independent analog output busses. It includes Benchmark's reference-quality HPA2 headphone amplifier, Benchmark's hybrid gain control system, and Benchmark's UltraLock2 jitter attenuation system. The DAC2 DX is designed to connect directly to power amplifiers and powered monitors. It is also capable of delivering +24 dbu studio interface levels. The DAC2 DX is available with an optional IR remote control which makes it equally well-suited for home applications. In a home Hi-Fi system, the DAC2 DX provides digital source selection, volume control, and direct drive to the power amplifier. The DAC2 DX is the only component required between digital sources and the power amplifier. The DAC2 DX has 6 digital inputs, 2 headphone outputs, a volume control, and 3 sets of analog outputs. It supports D/A conversion of PCM sample rates up to 192 khz, as well as direct DSD conversion. Professional Applications The DAC2 DX is designed for maximum transparency and purity. The sonic integrity of the DAC2 DX makes it well suited for critical playback in recording studio control rooms and mastering rooms. It includes features that are targeted at the needs of the audio professional. HI-FI Applications The versatility and performance of the DAC2 DX also makes it an asset to any high-end audiophile system. Digital signal sources may include HDTV, DVD, digital cable, music servers, digital radio, portable devices, etc. In a Hi-Fi system, the DAC2 DX replaces the low-performance D/A converters that are built into these low-cost devices. Computer Sound Card Elimination Benchmark s Multi-Mode Asynchronous USB interface makes the DAC2 an ideal output device for computer-based media playback, including: home media servers, digital audio workstations, desktop audio editing applications, and computer-based radio broadcast systems. Standalone Headphone Amplifier The zero-ohm HPA2 headphone amplifier delivers reference-quality performance. The full performance of the DAC2 is delivered to the headphones. Difficult loads are driven with ease. DAC2 DX Instruction Manual Rev A Page 9

10 DAC2 vs. DAC1 The DAC2 series builds upon Benchmark s highly successful DAC1 product family. Every DAC1 subsystem has been redesigned and upgraded to achieve higher performance. The DAC2 includes an updated version of Benchmark's highly-effective UltraLock jitter-attenuation system. New Features The DAC2 series introduced new features that add improve the listening experience while extending the versatility of the product. The DAC2 series introduced the following features: Native DSD conversion Asynchronous USB 2.0 Asynchronous USB 1.1 Volume-control bypass Digital pass-through Word-length display Sample-rate display Bi-directional 12V trigger More I/O than DAC1 Series Performance Improvements Lower Noise than the DAC1 An array of balanced 32-bit digital-to-analog audio converters are summed together to form each balanced output channel. The summing reduces noise. The result is that the DAC2 is about 10 db quieter than the DAC1. Low-level musical details are faithfully reproduced over a breathtakingly quiet noise floor. Lower Distortion than the DAC1 Benchmark s DAC1 converters are known for their very low distortion (THD and IMD). But, the DAC2 sets new benchmarks for clean and transparent musical reproduction. The DAC2 is designed to provide the cleanest possible path from digital to analog. Lower Power Consumption than the DAC1 The DAC2 complies with the latest international environmental regulations and consumes less than 0.5 W when turned off. The unit runs cool while providing substantial power to the headphone and output drivers. Power can be turned on or off from the front panel, from the remote control, or from the 12V trigger I/O port. DAC2 DX Instruction Manual Rev A Page 10

11 DAC2 DX Features Feature List HGC (Hybrid Gain Control) combines a motor-driven rotary control and a 32-bit digital attenuator with passive analog attenuators, to achieve state-of-the-art performance SABRE ES bit PCM D/A conversion system, multiple 32-bit D/A converters per channel SABRE ES9018 Native DSD D/A conversion system, multiple 1-bit DSD D/A converters per channel HPA2 reference-grade headphone amplifier - 0-Ohm high-current high-power outputs Dual Headphone Outputs jacks can be programmed to mute main output bus HPA2 gain jumpers - 0 db, -10 db, and -20 db - optimize headphone output levels to match a wide variety of headphone sensitivities Multi-Mode Asynchronous USB Audio bit/192 khz, DSD (DoP 1.1) Driverless Asynchronous USB Audio bit/96 khz Benchmark UltraLock2 Jitter Attenuation System eliminates jitter-induced distortion Sample Rate Display 44.1, 48, 88.2, 96, 176.4, 192 khz and DSD Word Length Display 16-bit, 24-bit 1 AES XLR Digital Input 24-bit/192 khz PCM, DSD (DoP 1.1) 2 Coaxial Digital Inputs 24-bit/192 khz PCM, DSD (DoP 1.1) 2 Optical Digital Inputs 24-bit/96 khz PCM 1 Coaxial Digital Output digital pass through from USB, XLR, Coax, and optical inputs Aluminum IR Remote - optional remote provides control of all functions 3 Stereo Analog Outputs 1 pair, balanced (XLR), plus 2 pairs unbalanced (RCA) 2 Stereo Analog Output Busses either or both busses can be set to fixed gain Low-Impedance Passive Output Pads 0, 10, and 20 db pads optimize output level to power amplifiers to maximize SNR over a wide variety of interface levels 12V Trigger I/O bi-directional 12V trigger can act as input, output, or both - links with power amplifier to sequence on/off functions Volume-Control Bypass places one or both analog output busses in a calibrated fixed-gain mode Mute Function accessible from remote or front panel, mutes all analog outputs Dim Function accessible from remote or front panel, reduces level of all outputs by 20 db Automatic De-Emphasis - responds to consumer pre-emphasis bit (44.1, 48 khz) Power Switch - accessible from remote or front panel, very low standby power - <0.5 W at 120 VAC High-Efficiency Low-Noise Power Supply only W, VAC, Hz Meets FCC Class B and CE emissions requirements Tested for immunity to radiated and conducted RF interference DAC2 DX Instruction Manual Rev A Page 11

12 Special DAC2 DX Features The DAC2 DX has some special features that set the DAC2 DX apart from the rest of the DAC2 product family: AES XLR digital input Dual Analog Output Busses Relay-Muted Analog Outputs These features are tailored to the needs of professional users but some Hi-Fi users may also find them useful. AES XLR Digital Input Many professional users have requested an AES XLR digital input. We have added this to the DAC2 DX without removing any of the other digital outputs. The DAC2 DX has: 1 USB audio input 1 AES XLR input 2 optical inputs 2 coaxial inputs (or 1 input and 1 pass-through) The DAC2 DX does not have analog inputs. Dual Analog Output Busses The MAIN and AUX busses can be programmed to BYPASS the volume control. When set to BYPASS the output is set to a fixed calibrated level. The MAIN and AUX busses are independently programmable for each digital input. This versatility is useful when one input (such as a digital console) has a digital level control while other signal sources do not. The console input could be set to BYPASS while an input from a CD player could be used in VARIABLE mode. The MAIN bus bypass function can be toggled by pressing and holding the MUTE button for 10 seconds. The AUX bus bypass function can be toggled by pressing and holding the DIM button for 10 seconds. This delay is intentionally long so that the function will not be toggled accidentally. The A light will be illuminated when the AUX bus is in BYPASS. The M light will be illuminated when the main bus is in BYPASS. Relay-Muted Analog Outputs The XLR and RCA analog outputs are equipped with mute relays that keep the outputs muted while powering on or off. These relays eliminate pops and clicks at the unit power up or down. DAC2 DX Instruction Manual Rev A Page 12

13 Feature Details UltraLock2 Clock System UltraLock2 provides the outstanding jitter attenuation of the older UltraLock system while providing a higher SNR. High-Headroom Digital Processing All digital processing includes at least 3.5 db headroom above an input level of 0 dbfs. This unique and important feature prevents all clipping in the digital processing, and provides clean, smooth, and transparent audio reproduction. Most competing products lack this important feature. Native DSD Conversion All DAC2 converters support native DSD conversion. DSD signals can be delivered to the USB or Coaxial inputs in DoP 1.1 format. The DSD signal is then routed directly to a bank of 1-bit DSD D/A converters. An array of balanced 1-bit converters are summed together to form each balanced output. Asynchronous USB 2.0 The USB interface supports DSD and 192 khz, 24-bit PCM. The DAC2 generates the conversion clocks and totally eliminates the USB interface as a source of jitter. No drivers are required for Apple operating systems. Drivers are provided for Windows operating systems at: Native Asynchronous USB 1.1 The DAC2 has a driverless USB 1.1 mode that supports 96 khz, 24-bit PCM with most operating systems. This mode provides quick and easy connection to a wide variety of computers and tablets. HGC Hybrid Gain Control HGC is Benchmark s unique Hybrid Gain Control that combines 32-bit digital attenuation with passive analog attenuation. The dual-domain HGC system combines the accuracy of digital control while preserving dynamic range through the use of passive analog output attenuators. HGC outperforms traditional analog or digital volume controls. Musical details are preserved over a very wide range of output levels. Digital inputs are controlled by a 32-bit DSP that feeds a 32-bit signal to the 32-bit conversion system. The output of the conversion system passes through low-impedance passive output attenuators that can be configured to match the output range to the sensitivity of the downstream device. The volume control is a motor-driven analog potentiometer that supplies a DC control signal to the 32-bit DSP system. The volume control rotates in response to commands from the remote control while providing the convenience quick and easy manual adjustments. This topology has the look, DAC2 DX Instruction Manual Rev A Page 13

14 feel, and convenience of an analog control while providing the accuracy, transparency, and precision of 32-bit digital control. MUTE Function The MUTE function mutes all analog outputs. The MUTE function does not mute the DIGITAL PASS-THROUGH. DIM Function The DIM function fades all analog outputs to a level that is 20 db lower than normal. This feature is intended to provide a convenient means to fade to and from a temporary background level without changing the volume control setting. DIM should not be used for normal listening. If DIM is required to achieve a normal playback level, this is an indication that the OUTPUT ATTENUATORS are set incorrectly (add more attenuation to fix this problem). Volume-Control Bypass (Calibrated Output Level) The volume control bypass function sets analog outputs to the maximum volume (BYPASS mode). In this mode, the 32-bit digital attenuator is bypassed and a full-level output signal is passed to the analog outputs. This is useful when volume is controlled before or after the DAC2. HPA2 "Zero-Ohm" Headphone Power Amplifier The HPA2 is one of the most transparent headphone amplifiers available. It also is able to deliver high current and/or high signal levels. This makes it well suited for cleanly driving virtually any set of headphones. The near 0-Ohm output impedance provides outstanding damping of headphone drivers. This damping reduces distortion, and maintains precise control of the frequency response. Headphone Mute Switches The left-hand headphone jack mutes the MAIN analog outputs. In contrast, the right-hand headphone jack allows simultaneous use of the MAIN outputs and headphones. The left-hand jack provides automatic switching between loudspeaker and headphone monitoring. The right-hand jack allows simultaneous use of loudspeakers and headphones. On the DAC2 DX, either or both headphone switches can be enabled or disabled using internal jumpers. The switches and jumpers control logic-level signals, no audio passes through these components. By default, the switch function is enabled on the left-hand jack but disabled on the right-hand jack. The high-power HPA2 headphone amplifier can easily drive two sets of headphones simultaneously. Both headphones should have similar voltage sensitivities. Direct Interfacing to Power Amplifiers All Benchmark DAC1 and DAC2 converters are designed to directly drive power amplifiers and powered studio monitors. For best performance, no additional devices should be inserted between the DAC and the power amplifier. A direct connection between the DAC and the power amplifier DAC2 DX Instruction Manual Rev A Page 14

15 always provides the cleanest and shortest path from the digital source to the monitor outputs. This direct connection often produces a substantial improvement in sound quality. The DAC2 s XLR output is equipped with 0, 10 and 20 db output attenuators for optimal interfacing. The pads optimize the output signal level of the DAC2 to the input sensitivity of virtually any amplifier. Most power amplifiers and powered monitors require the 10 db or 20 pad setting. Use the 0 db setting with the Benchmark AHB2 power amplifier. The DAC2 DX output attenuators are factory-set to the 0 db. Direct Interfacing to +4 dbu Studio Gear If the DAC2 DX will be feeding other professional +4 dbu audio gear, the 0 db setting should be used. In this setting, the output will reach exactly +24 dbu at 0 db FS when the volume control is bypassed or to maximum. In other words, the calibration is +4 dbu at -20 db FS. Digital Pass-Through The second coaxial input (D5) can be reconfigured as a digital output. When operating as an output, any selected digital input is passed through to (D5) without any processing. Optical, coaxial, AES XLR, and USB inputs can be passed through to the (D5) connector. This even includes special digital signals such as DoP, DTS, and Dolby Digital. This feature is particularly useful for connecting digital devices to computers that are not equipped with coaxial digital outputs. The DAC2 can connect to the computer via USB and provide a coaxial digital output to another digital audio device. Bi-directional 12V Trigger The 12V trigger can be connected to other audio components so that an entire audio system can turn on and off in a sequenced fashion. The DAC2 trigger I/O could be connected to a preamplifier, power amplifier, or both. The DAC2 will drive the trigger I/O to 12 volts DC when the DAC2 turns on. If an external device pulls the trigger I/O to 12 volts, the DAC2 will turn on. If an external device pulls the trigger I/O to 0 volts, the DAC2 will turn off. The timing of the trigger system is optimized to minimize any transient pops and clicks during turn-on and turn-off sequences. Low-Noise Power Supplies The DAC2 uses high-efficiency low-noise power supplies. Each critical subsystem has at least one dedicated low-noise regulator. The unit runs cool while providing substantial power to the headphone and output drivers. Power can be turned on or off from the front panel, from the remote control, or from the 12V trigger I/O port. DAC2 DX Instruction Manual Rev A Page 15

16 DAC1 and DAC2 Product History The pristine audio performance of the award-winning DAC1 made it the Benchmark of stand-alone D/A converters. The DAC1 USB and DAC1 PRE, and DAC1 HDR added features and minor performance improvements. DAC1 Series History The classic DAC1 was the first member of the Benchmark DAC1 family. The DAC1 introduced: The 1/2-wide 1-RU form factor UltraLock Jitter attenuation Passive output attenuators Analog volume control HPA2 Headphone amplifier The DAC1 USB added: The first 96 khz/24-bit USB audio input Headphone switch Headphone gain jumpers High-current LM562/LME49860 output drivers Low-Impedance passive output pads The DAC1 PRE added: A stereo analog input 3 S/PDIF digital inputs LM4562/LME49860 opamps throughout Premium Teflon-insulated bulkhead-mounted RCA connectors The DAC1 HDR added: IR remote-control HDR motor-driven volume control MUTE feature DIM feature DAC2 DX Instruction Manual Rev A Page 16

17 DAC2 Series History The DAC2 series represents a complete redesign of the DAC1. Our goal was to improve every aspect of the DAC1 while adding many of the most requested features. The DAC2 HGC series introduced: HGC Hybrid Gain Control 32-bit PCM D/A conversion Native DSD conversion Multi-mode Asynchronous USB Sample rate and word length displays UltraLock2 jitter attenuation system Volume control bypass Bi-directional 12V trigger More I/O than any member of the DAC1 family Ultra low-noise high-efficiency power supplies Universal power supply Power Switch The DAC2 D was a lower-cost digital-only version of the DAC2 HGC Analog inputs were removed Trigger I/O was removed The DAC2 L is a lower-cost non-headphone version of the DAC2 HGC Headphone amplifier and jacks were removed The DAC2 DX replaces the DAC2 D and shares flagship status with the DAC2 HGC. The DAC2 DX adds these features to the DAC2 D: Dual output busses Output mute relays Dedicated MUTE and DIM buttons AES XLR input Bi-directional 12V trigger DAC2 DX Instruction Manual Rev A Page 17

18 Digital Inputs There are six stereo digital audio connectors on the DAC2 DX: USB - USB Audio 1.1 or 2.0 Input D1 - TOSLINK Optical Input D2 - TOSLINK Optical Input D3 - XLR Input D4 - Coaxial Input D5 - Coaxial Input or Output Input Formats The optical, XLR, and coaxial inputs can decode AES/EBU or S/PDIF PCM input signals. Professional or consumer data formats are automatically recognized. The USB, XLR and Coaxial inputs can also decode DSD when transmitted in DoP 1.1 format. This format transmits native DSD64 data over conventional digital audio interfaces. The DAC2 will not decode AC3, Dolby, or other compressed formats. The Status Display will flash when AC3, Dolby, or other compressed formats are connected to the selected digital input. Limitations of Optical Inputs TOSLINK optical connections are generally limited to sample rates up to 96 khz. Sample rates above 96 khz, and DSD inputs may not work through TOSLINK connections. The optical inputs do not accept ADAT format. Consistent Performance The Benchmark UltraLock2 system removes interface jitter from all digital inputs (including the USB input). The result is that all digital inputs have identical jitter performance. DAC2 DX Instruction Manual Rev A Page 18

19 USB - Computer Input The USB input supports 44.1, 48, 88.2, 96, 176.4, and 192 khz sample rates at word lengths up to 24-bits. The USB also accepts DSD. Mac operating systems support all sample rates and formats without drivers. Windows operating systems require drivers for DSD and PCM sample rates above 96 khz. The USB input accepts a male B-type male USB connector. An A-B type USB cable is provided with the DAC2. The USB cable connects the DAC2 directly to a standard 'A-type' USB port on the host computer. USB Audio Modes The USB input can be toggled between two different modes: USB AUDIO PCM sample rates up to 96 khz USB AUDIO PCM sample rates up to 192 khz, and DSD64 in DoP 1.1 format. USB 1 ports only support the USB Audio 1.1 mode. USB 2 and USB 3 ports support both modes. USB Mode Indication The 2X or 4X lights will flash once when the USB input is selected. This flash indicates the USB mode: The 2X light will flash if the DAC2 is set to USB AUDIO 1.1 mode. The 4X light will flash if the DAC2 is set to USB AUDIO 2.0 mode. Changing the USB Mode The USB MODE can be changed using the front panel or the remote control. To change the USB MODE from the front panel: 1. Select the USB input 2. Press and hold the lower INPUT button for 10 seconds 3. When the mode changes, the 2X or 4X light will flash once to indicate the new mode To change the USB MODE from the remote control: 1. Press and hold the USB button for 10 seconds 2. When the mode changes, the 2X or 4X light will flash once to indicate the new mode USB AUDIO 1.1 MODE (Factory Default) The USB AUDIO 1.1 MODE provides a plug-and-play solution that works with many different operating systems. In most cases, the DAC2 can begin streaming high resolution 24-bit/96 khz audio bit-transparently within seconds after being plugged into a computer for the first time. Little or no software or hardware configuration is required in this mode. DAC2 DX Instruction Manual Rev A Page 19

20 The DAC2 s USB AUDIO 1.1 MODE provides driverless operation with Windows XP/Vista/7/8, Mac OS X, and many Linux operating systems. USB AUDIO 2.0 MODE The DAC2 s USB AUDIO 2.0 MODE provides driverless operation with Mac OS X. It is compatible with Windows XP/Vista/7/8 if the Benchmark driver is installed. It has been tested on Mac OS X versions 10.6, 10.7, and For the up-to-date information about more recent operating systems and suggestions for optimization, go to: D1 and D2 - Optical Digital Inputs The optical input connector is commonly known as a TOSLINK connector. The TOSLINK optical connector used on the DAC2 is designed to work well at sample rates up to 96 khz. Maximum word length is 24-bits. All sample rates between 28 and 96 khz are supported. The optical input will accept professional AES/EBU data formats or consumer S/PDIF data formats. The optical inputs do not accept ADAT format. In some cases, TOSLINK connections will operate at sample rates above 96 khz, but the connection is usually not reliable. Many MAC computers have a TOSLINK optical output hidden in the 1/8" headphone output. A special 1/8" optical connector is required to access this cool feature. Benchmark sells the appropriate cables. D3 - AES XLR Digital Input The AES XLR digital input is transformer isolated. Input impedance is 110 Ohms. Maximum word length is 24 bits. All sample rates between 28 and 195 khz are supported. The AES XLR input is DC isolated, transformer coupled, current limited, and diode protected. The XLR body and pin 1 are both bonded directly to the chassis to prevent currents in the internal ground system. This direct bonding also maximizes RF shielding. TIP: Shielded 110-Ohm digital audio cable is required for stable performance. Do not use analog XLR cables. D4 and D5 - Coaxial Digital Inputs The coaxial inputs use female RCA connectors that are securely mounted directly to the rear panel. The input impedance is 75 Ohms. Maximum word length is 24-bits. All sample rates between 28 and 195 khz are supported. DAC2 DX Instruction Manual Rev A Page 20

21 The Coax inputs are DC isolated, current limited, and diode protected. The RCA body is bonded directly to the chassis to prevent currents in the internal ground system. This direct bonding also maximizes RF shielding. TIP: Shielded 75-Ohm coaxial cable is required for stable performance. Do not use 50- Ohm cables or twisted pair cables, or any non-coaxial cables. The Coaxial inputs accept AES/EBU or S/PDIF digital audio formats. AES3-id and SMPTE 276M standards specify 75-Ohm 1 Vpp professional format digital audio signals and these are commonly used in video production facilities. IEC specifies 75-Ohm 0.5 Vpp consumer-format digital audio signals (commonly known as S/PDIF). The coaxial inputs on the DAC2 are designed to accept either type of signal. D5 - Coaxial Digital Output Coaxial connector D5 is a bi-directional port. D5 is factory configured as a digital input. Internal jumpers can be moved to configure D5 as a digital output. When configured as an output, D5 acts as a digital pass-through. Any selected digital input will be routed to D5 without any processing. PASS-THROUGH MODE can be use for: USB to Coax conversion Toslink to Coax conversion AES XLR to Coax conversion Coax to Coax buffering Digital routing Pass-through to slave DAC2 converters AES XLR to Coaxial Adapters Transformers are available to match adapt balanced 110-Ohm AES connections to unbalanced 75- Ohm coaxial connections. Our experience is that these work well. Coaxial to XLR adapters should be located near the XLR connector when possible. DAC2 DX Instruction Manual Rev A Page 21

22 Analog Outputs The DAC2 DX has two independent stereo output busses. By default, both busses are controlled by the front panel volume control. Either or both busses can be set to bypass the volume control. When the volume control is bypassed the volume is set to a calibrated maximum level. The DAC2 DX features high-current output drivers that are capable of driving 300-Ohm loads without an increase in distortion. They are also well suited for driving long cables or highcapacitance loads. All connector pins have their own dedicated drivers. No pins are wired in parallel. Main Output Bus The DAC2 has one pair of balanced XLR outputs and one pair of unbalanced RCA outputs that are driven by the MAIN bus. AUX Output Bus The DAC2 has one pair of unbalanced RCA outputs that are driven by the MAIN bus. Balanced Analog XLR Line Outputs The Left and Right balanced outputs use Neutrik gold-pin male XLR jacks. The XLR shell and pin 1 (ground) are both directly bonded to the chassis to prevent currents in the internal ground system. This direct bonding also maximizes RF shielding. The XLR outputs have passive attenuators that allow direct connections to a wide variety of audio devices without a loss of dynamic range. The 10 or 20 db pads are usually required for direct interfacing to power amplifiers and powered speakers. The DAC2 DX ships with the pads disabled (0-dB setting). A full description of the output attenuators and instructions for configuration is located in the Internal Setting section of this manual. The XLR output level is 24 dbu at maximum volume (or in BYPASS mode) when the output attenuators are set to 0 db. The XLR output level is 14 dbu at maximum volume (or in BYPASS mode) when the output attenuators are set to -10 db. The XLR output level is 4 dbu at maximum volume (or in BYPASS mode) when the output attenuators are set to -20 db. DAC2 DX Instruction Manual Rev A Page 22

23 XLR Wiring The DAC2 uses industry-standard XLR wiring: XLR pin 2 = + Audio Out XLR pin 3 = - Audio Out XLR pin 1 = Cable Shield CAUTION: If the balanced XLR outputs are wired to an unbalanced input (using a special adapter cable), pin 3 must be left floating. Shorting pin 3 to ground will increase the temperature of the output drivers, will increase power consumption, and may cause distortion. Unbalanced Analog RCA Line Outputs The Left and Right unbalanced outputs use standard RCA style jacks. The ground connections are bonded to chassis ground at the location where analog ground is bonded to the chassis. This minimizes the effects of ground loops caused by AC currents in the cable shield. The XLR output level is 2 Vrms at maximum volume (or in BYPASS mode). This is the same as 8.2 dbu. Note: The XLR pads do not have any effect on the level of the RCA outputs. The RCA output impedance is very low (30 Ohms). This makes these outputs well suited for driving high-capacitance loads and/or high-capacitance cables. TIP: The RCA outputs are capable of driving cables as long as 1360 feet (see Table 1). But, long un-balanced cables will generally suffer from hum problems due to ground loops. We highly recommend using balanced interconnects for long runs. TIP: Mono summing with an RCA Y cable is not recommended as this will cause high amounts of distortion. Mono summing with a Y cable can be accomplished with the use of a modified cable by implementing a 1k Ohm series resistor in each leg of the Y. DAC2 DX Instruction Manual Rev A Page 23

24 AC Power-Entry and Fuses Fuses CAUTION: FOR CONTINUED FIRE HAZARD PROTECTION ALWAYS REPLACE THE FUSES WITH THE CORRECT SIZE AND TYPE (0.5A 250 V SLO-BLO 5 X 20 MM LITTELFUSE HXP OR EQUIVALENT). THE FUSE DRAWER INCLUDES TWO FUSES. ALWAYS REPLACE BOTH FUSES AT THE SAME TIME. Voltage Selection THE DAC2 IS EQUIPPED WITH A UNIVERSAL POWER SUPPLY. THERE IS NO VOLTAGE SELECTION SWITCH. AC VOLTAGE RANGE IS VAC, HZ. THE PRODUCT MAY ALSO BE OPERATED FROM DC POWER OVER A VOLTAGE RANGE OF VDC. Power Cord The AC power input uses a standard IEC type connector. One USA-compatible power cord is included with DAC2 converters. IEC style power cords in country-specific configurations are available in your locality. CAUTION: ALWAYS USE A GROUNDED POWER CORD. THE PRODUCT IS EQUIPPED WITH A STANDARD IEC POWER ENTRY MODULE. USE AN IEC POWER CORD THAT IS EQUIPPED WITH THE APPROPRIATE CONNECTOR FOR YOUR LOCATION. CORDS ARE AVAILABLE FROM YOUR DEALER. DAC2 DX Instruction Manual Rev A Page 24

25 Internal Settings Jumper-Configured Options The following functions are jumper configured: XLR Output Pads Headphone Switches Headphone Gain Digital Pass-Through Removing Top Cover The DAC2 top cover must be removed to gain access to the jumpers. Do not attempt to remove the faceplate or the rear panel. CAUTION: The DAC2 contains static sensitive components. Static discharge may cause component failures, may affect the long-term reliability, or may degrade the audio performance. Use a static control wrist strap when changing jumper settings. Disconnect AC power by unplugging the power cord at the back of the DAC2 DX. Remove only the 8 screws holding the cover (4 on each side). Do not remove any screws on front or rear panels! Never remove the power entry safety cover in the rear corner of the DAC2 DX. Always connect a static-control wrist strap to the chassis before touching any internal component. DAC2 DX Instruction Manual Rev A Page 25

26 XLR Output Pads The XLR outputs are equipped with low-impedance passive pads that may be used to reduce the output levels while preserving the full dynamic range of the DAC2 DX. The unit ships with the pads disabled (0 db setting). When the output pads are enabled, the output impedance changes slightly, and the maximum allowable cable length should be reduced as shown in Table 1 (assuming 32 pf/foot and a maximum allowable loss of 0.1 db at 20 khz). Balanced Output Drive Capability: Attenuator Output Maximum Loss in db Setting (db) Impedance Cable (ft) at 20 khz Unbalanced Output Drive Capability: Output Maximum Loss in db Impedance Cable (ft) at 20 khz TIP: To set the XLR outputs to typical professional studio levels, set the pads to 0 db. For most home installations, set the pads to 10 db or 20 db. Use the 0 db setting when driving the Benchmark AHB2 power amplifier. TIP: When directly driving power amplifiers and powered speakers, start with the 10 db pad setting. If necessary, change the pads so that normal listening levels are achieved with the Volume Control above the 11 o clock position. Use the 0 db setting with Benchmark's AHB2 power amplifier. Table 1 - Cable Drive Capability XLR Output Pad Selection (P8, P9, P10, and 11): Four 6-pin headers (P8, P9, P10, and P11) allow selection of the analog output level at the XLR jacks. One pair of 6-pin headers controls the output level at each XLR jack as follows: 0 db Attenuation = +24 dbu at full output -10 db Attenuation = +14 dbu at full output -20 db Attenuation = +4 dbu at full output Figure 1-0 db Pad Setting (Factory Default) 0 db - Jumper plug between pins 1 and 2 of each header Factory Default -10 db Jumper plug between pins 3 and 4 of each header -20 db Jumper plug between pins 5 and 6 of each header DAC2 DX Instruction Manual Rev A Page 26

27 Headphone Switch Configuration: The DAC2 is configured so that the MAIN analog outputs will mute when a headphone plug is inserted into the left-hand jack. This is convenient when the user wishes to switch between headphones and speakers. This feature can be changed or defeated by moving jumpers at P1 on the back of the front panel. Either headphone switch can be enable or disabled by moving the jumpers. Connect the bottom two pins with a jumper to enable the mute switch for the left-hand jack - Factory Default (see Figure 2). Connect the top two pins with a jumper to enable the mute switch for the right-hand jack. Add a second jumper if necessary. No Jumpers - Both switched disabled Top Jumper Only - Right-hand switch enabled Bottom Jumper Only - Left-hand switch enabled - Factory Default Top and Bottom Jumpers - Both switches enabled Jumper(s) rotated vertically - Storage of unused jumper(s) Unused jumper(s) may be stored vertically on either pair of pins. Figure 2 - Left Headphone Switch Enabled (Factory Default) DAC2 DX Instruction Manual Rev A Page 27

28 Headphone Attenuation Jumpers (JP3 and JP4): The gain range of the HPA2 can be set using jumpers JP3 and JP4: 0 db attenuation - see Figure 3 10 db attenuation - see Figure 4 (Factory Default) 20 db attenuation - see Figure 5 The attenuation is inserted before the HPA2 headphone amplifier. This attenuator location keeps the output impedance of the HPA2 constant and very near 0 Ohms. External attenuators should never be inserted after a headphone amplifier as this would change the output impedance. Proper attenuator settings are important for maximizing the SNR of the headphone monitoring system. With proper settings, the full performance of the DAC2 can be delivered to the headphones for critical monitoring tasks, or maximum musical enjoyment. When the headphone attenuation jumpers are set properly, a normal listening level will be achieved between the 10 o'clock and 2 o'clock volume-control positions. If a normal listening level is achieved below a 10 o clock volume-control position, the headphone gain is too high, and the attenuation should be increased. If the level is too low at a 2 o-clock volume-control position, the headphone gain is too low, and the attenuation should be decreased. Figure 3-0 db Headphone Attenuation DAC2 DX Instruction Manual Rev A Page 28

29 Figure 4-10 db Headphone Attenuation - (Factory default) Figure 5-20 db Headphone Attenuation DAC2 DX Instruction Manual Rev A Page 29

30 Digital Pass-Through Function Coaxial connector D5 is factory configured as an input. This connector can be reconfigured as a digital output by moving both P14 jumpers toward the faceplate. When re-configured as an output, the raw data from any selected digital input is buffered passed out through D5. The Digital Pass-Through is bit-transparent. No data is modified. MUTE, DIM, and VOLUME control functions do not change the data in any way. The Digital Pass-Through function can be used for the following purposes: USB to Coaxial Transfers Optical to Coaxial Transfers AES XLR to Coaxial Transfers Coaxial to Coaxial Buffering Slaving another DAC2 When the Digital Pass-Through function is enabled, D5 cannot be selected as an input. If D5 can be selected, the Digital Pass-Through function is disabled. Figure 7 shows the factory default position (Digital Pass-Through function disabled, D5 is an input). Figure 7 Digital Pass Through - Disabled (Factory Default) DAC2 DX Instruction Manual Rev A Page 30

31 Rack Mounting Options Call us, visit our website ( or contact your dealer to purchase accessories for your DAC2. Universal Rack Adapter Tray The Universal Rack Adapter Tray is a tray that mounts up to two ½-wide Benchmark products in a standard 19 inch wide 1-RU rack space. The tray accepts any combination of ½-wide Benchmark products (with or without rack-mount type faceplates). ½-Wide Blank Rack Panel - Black The Blank Rack Panel is a ½-wide 1-RU black-anodized aluminum panel for covering an unused slot in the Universal Rack Adapter Tray. It can also be used with a connector block and a DAC2 DX with a rack-mount type faceplate. ½-Wide Blank Rack Panel - Silver This premium blank panel includes an engraved Benchmark logo, and matches the finish on the silver rack-mount version of the DAC2 DX. Connector Block The connector block joins two ½-wide Benchmark products with rack-mount type faceplates. The joined units fill a standard 19 inch wide 1-RU rack space. The connector block can also join a single ½-wide Benchmark product to a Benchmark ½-wide blank panel. DAC2 DX Instruction Manual Rev A Page 31

32 Benchmark Technologies Hybrid Gain Control "HGC" is Benchmark's unique Hybrid Gain Control system. The DAC2 combines active analog gain control, passive lowimpedance attenuators, a 32-bit digital gain control, and a servo-driven volume control. All inputs are controlled by the rotary volume control. This volume control moves in response to commands from the remote control. Analog inputs are never converted to digital, and digital inputs never pass through an analog potentiometer. Digital inputs are precisely controlled in the 32-bit DSP system. The DSP system preserves precise L/R balance, and precise stereo imaging, while avoiding any source of noise and distortion. Benchmark's unique passive output attenuators provide distortion-free gain reduction without reducing the dynamic range of the converter. The attenuators optimize the gain staging between the DAC2 and the power amplifier. This optimization is absolutely essential for maximizing the dynamic range of the entire playback system. Much of the success of the DAC1 converters can be attributed to the passive output attenuators. Musical details can be obscured by system noise whenever a preamplifier and power amplifier are improperly matched. The "HGC" system will make full use of your power amplifier's dynamic range. Experience the new details in your favorite recordings. Native DSD Conversion The digital coaxial, XLR, and USB 2.0 inputs on the DAC2 DX support native DSD conversion. DoP 1.1 is automatically detected on all digital inputs, and the system seamlessly switches to native DSD conversion. DoP 1.1 is supported by many media players, and DSD downloads are now available from several sources. Visit our website for an up-to-date list of DSD and PCM high resolution download sites. Multi-Mode Asynchronous AdvancedUSB Audio Benchmark's USB system supports USB Audio 2.0, DSD, and USB Audio 1.1. It is frequency agile, and will follow sample rate changes initiated by the computer and/or the media playback software. In all modes the USB communications are asynchronous in order to eliminate unnecessary sources of jitter. The DAC2 has a low-jitter master clock which controls the transfer of audio data from the computer to the USB sub-system. The computer asynchronously transfers audio data to a buffer in the DAC2. The contents of the buffer are then asynchronously transferred to the D/A conversion sub-system. This second asynchronous transfer eliminates any traces of jitter that accumulate as the data is transferred between the USB and conversion subsystems. No traces of jitter-induced distortion are measurable to our measurement limits (better than -160 dbfs). This truly represents the state-of-the art. Enjoy the convenience of computer playback without compromise. The Asynchronous USB system supports USB Audio 2.0 for high-resolution 192kHz, and DSD playback. No drivers are required for MAC operating systems. An easy-to-install driver adds 192 khz and DSD capabilities to Windows operating systems. You can download the latest drivers from: drivers An asynchronous driverless USB Audio 1.1 mode supports sample rates up to 96 khz. This USB mode can be selected from the front panel or from the remote control. The driverless USB Audio 1.1 mode allows quick plug-and-play connections to Windows, MAC, ios, and Linux operating systems without installing drivers. Just plug in the USB, and the DAC2 becomes an available audio device. DAC2 DX Instruction Manual Rev A Page 32

33 The USB sub-system remains active when the DAC2 is powered down. This prevents interruptions to the computer playback operations and eliminates the need to reconfigure the computer every time the converter is turned on. Jitter-Immune UltraLock2 UltraLock2 is an improved version of the UltraLock system used in the DAC1 product family. DSP processing is 32-bits, DSP headroom is 3.5 db, sample rate is 211 khz, and jitter-induced distortion and noise is at least 160 db below the level of the music - well below the threshold of hearing. Benchmark's UltraLock2 system eliminates all audible jitter artifacts. High Head-Room DSP All of the digital processing in the DAC2 is designed to handle signals as high as +3.5 dbfs. Most digital systems clip signals that exceed 0 dbfs. The 0 dbfs limitation seems reasonable, as 0 dbfs is the highest sinusoidal signal level that can be represented in a digital system. However, a detailed investigation of the mathematics of PCM digital systems will reveal that inter-sample peaks may reach levels slightly higher than +3 dbfs while individual samples never exceed 0 dbfs. These inter-sample peaks are common in commercial releases, and are of no consequence in a PCM system until they reach an interpolation process. But, for a variety of reasons, virtually all audio D/A converters use an interpolation process. The interpolation process is absolutely necessary to achieve 24-bit state-of-the art conversion performance. Unfortunately, inter-sample overs cause clipping in most interpolators. This clipping produces distortion products that are non-harmonic and non-musical. We believe these broadband distortion products often add a harshness or false high-frequency sparkle to digital reproduction. The DAC2 avoids these problems by maintaining at least 3.5 db of headroom in the entire conversion system. We believe this added headroom is a groundbreaking improvement. 32-bit SABRE Conversion System Four balanced 32-bit D/A converters deliver audio to Benchmark's low-impedance current to voltage converters. The MAIN bus uses 3:1 redundancy to reduce noise and distortion to insignificant levels. The conversion system at the core of the DAC2 is as good as it gets. The analog circuits that follow the D/A converter are carefully designed. Benchmark has leveraged its long history of building reference analog audio equipment to create an outstanding output stage. Diagnostic Display Ever wonder why that 192 khz 24-bit download on your computer just doesn't sound right? Your media player may be down-sampling to 44.1 khz and/or truncating to 16-bits. Many media players apply poorquality sample rate conversion and truncation. Fortunately these problems can be eliminated with the selection of a good frequency-agile media player. The samplerate and word-length displays on the DAC2 confirm the proper operation of your media player. Bi-Directional 12 Volt Trigger Benchmark re-invents the 12 volt trigger. The trigger connection on the DAC2 can be used as an input or output or both, and is compatible with any common 12 volt trigger input or output. The trigger can be used to turn a power amplifier on or off automatically. The DAC2 will also respond to a 12 volt trigger and follow the actions of another audio component. Distributed Power Regulation To achieve the lowest possible noise, the DAC2 uses distributed power supply regulation. Each critical sub-system has at least one dedicated low-noise voltage regulator. DAC2 DX Instruction Manual Rev A Page 33

34 HPA2 Headphone Amplifier The DAC2 headphone output is driven by Benchmark s signature HPA2 headphone amplifier. This high-current, high-output amplifier has an output impedance of near 0- Ohms. It is designed to drive loads as low as 30 Ohms without any increase in distortion. It also has sufficient amplitude to drive lowsensitivity 600-Ohm headphones. The HPA2 includes current-limiting circuits that fully protect against damage from short circuits. This is important because the right channel of a headphone amplifier will experience a short whenever a mono phone plug is inserted into the stereo headphone jack. Shorts may also occur when a plug is partially inserted. '0-Ohm' Output Impedance Most headphone amplifiers use series resistors to maintain stability and protect against short-circuit conditions. These resistors are usually at least 30 Ohms, and have a negative impact on performance. A headphone amplifier with series resistors may measure very well when driving resistive loads. However, the same amplifier will measure very poorly when driving a headphone load. Unfortunately, most manufacturers do not specify headphone amplifier performance with anything other than ideal resistive loads. Our measurements show that headphones do not behave like resistive loads. Headphone Performance In our tests we have measured substantial distortion across resistors that are wired in series with headphones. We conducted measurements with a variety of headphones. In general, distortion increases as headphone impedance decreases. This distortion can be eliminated with a properly designed 0-Ohm headphone amplifier. The performance of the HPA2 does not change when headphones are driven. THD+N measurements for no-load, 30-Ohm resistive loads, 30-Ohm headphone loads, and 600- Ohm headphone loads are virtually identical. The HPA2 will substantially improve the sound of 30 and 60-Ohm headphones. It will make very noticeable improvements with 600-Ohm headphones. Differential Amplifiers Differential amplifiers remove common-mode distortion components from the D/A converter outputs. This feature is critical for achieving low-distortion in down-stream devices. Benchmark addresses common-mode distortion so that it will not cause distortion in power amplifiers and other connected devices. Common-mode distortion can cause audible distortion while escaping the scrutiny of an audio analyzer. The balanced and unbalanced outputs on the DAC2 deliver very similar performance. Many D/A converters omit the differential amplifiers after the converters. Specifications usually ignore common-mode distortion. A balanced signal with high common-mode distortion can measure just fine when feeding a precisely balanced input on a high-quality audio analyzer. However, any imbalance in a downstream device will expose the common-mode distortion. UltraLock2 Clock System Accurate 24-bit audio conversion requires a very low-jitter conversion clock. Jitter can very easily turn a 24-bit converter into a 16- bit converter (or worse). There is no point in buying a 24-bit converter if clock jitter has not been adequately addressed. Jitter is present on every digital audio interface. This type of jitter is known as interface jitter and it is present even in the most carefully designed audio systems. Interface jitter accumulates as digital signals travel down a cable and from one digital device to the next. If we measure interface jitter in a typical system we will find that it is 10 to 10,000 times higher than the maximum allowable level for accurate 24-bit conversion. DAC2 DX Instruction Manual Rev A Page 34

35 Fortunately, interface jitter has absolutely no effect on the audio unless it influences the conversion clock in an analog-to-digital converter (A/D) or in a digital-to-analog converter (D/A). Many converters use a single-stage Phase Lock Loop (PLL) circuit to derive their conversion clocks from AES/EBU, Wordclock, or Superclock reference signals. Single-stage PLL circuits provide some jitter attenuation above 5 khz but none below 5 khz. Unfortunately, digital audio signals often have their strongest jitter components at 2 khz. Consequently, these converters can achieve their rated performance only when driven from very low jitter sources and through very short cables. It is highly unlikely that any converter with a single-stage PLL can achieve better than 16 bits of performance in a typical installation. Specified performance may be severely degraded in most installations. Better converters usually use a two-stage PLL circuit to filter out more of the interface jitter. In theory, a two-stage PLL can remove enough of the jitter to achieve accurate 24-bit conversion (and some do). However, not all two-stage PLL circuits are created equal. Many two-stage PLLs do not remove enough of the low-frequency jitter. In addition, twostage PLL circuits often require several seconds to lock to an incoming signal. Finally, a two-stage PLL may fail to lock when jitter is too high, or when the reference sample frequency has drifted. UltraLock converters exceed the jitter performance of two-stage PLL converters, and are free from the slow-lock and no-lock problems that can plague two-stage PLL designs. UltraLock converters have extremely high immunity to interface jitter under all operating conditions. No jitterinduced artifacts can be detected using an Audio Precision System 2 Cascade test set. Measurement limits include detection of artifacts as low as 160 dbfs, while applying jitter amplitudes as high as UI, over a frequency range of 2 Hz to 200 khz. Any AES/EBU signal that can be decoded by the AES/EBU receiver will be reproduced without the addition of any measurable jitter artifacts. The DAC2 employs Benchmark s UltraLock2 technology to eliminate jitterinduced performance problems. UltraLock2 technology isolates the conversion clock from the digital audio interface clock. Jitter on a D/A digital audio input, or an A/D reference input can never have any measurable effect on the conversion clock of an UltraLock2 converter. In an UltraLock2 converter, the conversion clock is never phase-locked to a reference clock. Instead the converter oversampling-ratio is varied with extremely high precision to achieve the proper phase relationship to the reference clock. The clock isolation of the UltraLock2 system ensures that interface jitter can never degrade the quality of the audio conversion. Specified performance is consistent and repeatable in any installation with cables of any quality level! How does conversion clock jitter degrade converter performance? Problem #1: Jitter phase-modulates the audio signal. This modulation creates sidebands (unwanted tones) above and below every tone in the audio signal. Worse yet, these sidebands are often widely separated from the tones in the original signal. Jitter-induced sidebands are not musical in nature because they are not harmonically related to the original audio. Furthermore, these sidebands are poorly masked (easy to hear) because they can be widely separated above and below the frequencies of the original audio tones. In many ways, jitter induced distortion resembles intermodulation distortion (IMD). Like IMD, jitter induced distortion is much more audible than harmonic distortion, and more audible than THD measurements would suggest. Jitter creates new audio that is not harmonically related to the original audio signal. This new audio is unexpected and unwanted. It can cause a loss of imaging, and DAC2 DX Instruction Manual Rev A Page 35

36 can add a low and mid frequency muddiness that was not in the original audio. Jitter induced sidebands can be measured using an FFT analyzer. Problem #2: Jitter can severely degrade the anti-alias filters in an oversampling converter. This is a little known but easily measurable effect. Most audio converters operate at high oversampling ratios. This allows the use of high-performance digital anti-alias filters in place of the relatively poor performing analog anti-alias filters. In theory, digital anti-alias filters can have extremely sharp cutoff characteristics, and very few negative effects on the in-band audio signal. Digital anti-alias filters are usually designed to achieve at least 100 db of stop-band attenuation. But, digital filters are designed using the mathematical assumption that the time interval between samples is a constant. Unfortunately, sample clock jitter in an A/D or D/A varies the effective time interval between samples. This variation alters the performance of these carefully designed filters. Small amounts of jitter can severely degrade stop-band performance, and can render these filters useless for preventing aliasing. The obvious function of a digital anti-alias filter is the removal of audio tones that are too high in frequency to be represented at the selected sample rate. The not-so-obvious function is the removal of high-frequency signals that originate inside the converter box, or even originate inside the converter IC. These high-frequency signals are a result of crosstalk between digital and analog signals, and may have high amplitudes in a poorly designed system. Under ideal (low jitter) conditions, a digital anti-alias filter may remove most of this unwanted noise before it can alias down into lower (audio) frequencies. These crosstalk problems may not become obvious until jitter is present. Stop-band attenuation can be measured very easily by sweeping a test tone between 24 khz and at least 200 khz while monitoring the output of the converter. Put UltraLock converters to the test: We encourage our customers to perform the above tests on UltraLock2 converters (or let your ears be the judge). There will be absolutely no change in performance as jitter is added to any digital input on an UltraLock2 converter. Try the same tests on any converter using conventional single or two-stage PLL circuits. Tests should be performed with varying levels of jitter and with varying jitter frequencies. The results will be very enlightening. Jitter related problems have audible (and measurable) effects on A/D and D/A devices. Practitioners of Digital Audio need to understand these effects. Is it possible to eliminate all of the effects of jitter in an entire digital audio system? Interface jitter will accumulate throughout even the most carefully designed digital audio system. Fortunately, interface jitter can only degrade digital audio if it affects the sampling circuit in an analog-to-digital or digital-to-analog converter. Any attempt to cure jitter outside of an A/D or D/A will prove expensive and, at best, will only partially reduce jitter-induced artifacts. Dedicated clock signals (word clock, and super clock, etc.) are often distributed to A/D converters and D/A converters in an attempt to reduce jitter. Again, these are only partial solutions because jitter even accumulates in these clock distribution systems. Furthermore, a poor quality master clock generator can degrade the performance of the entire system (if converter performance is dependent upon reference clock quality). Jitter free A/D and D/A converters are the only true ensurance against the ill effects of jitter. UltraLock2 converters are jitter-immune under all operating conditions (they will never add audible jitter induced artifacts to an audio signal). DAC2 DX Instruction Manual Rev A Page 36

37 What UltraLock converters cannot do: UltraLock2 converters cannot undo damage that has already been done. If an A/D with a jitter problem was used to create a digital audio signal, then there is nothing that can be done to remove the damage. Jitterinduced sidebands are extremely complex and cannot be removed with any existing audio device. Therefore, it is very important to attack jitter at both ends of the audio chain. The DAC2 is a great start, as it will allow accurate assessment of various A/D converters. It is impossible to audibly evaluate A/D performance without a good D/A. The consistent performance delivered by the DAC2 eliminates one major variable: jitter. DAC2 DX Instruction Manual Rev A Page 37

38 USB Audio System Setup Plug it in and Start Listening Immediately Benchmark's Advanced USB Audio technology is truly 'Plug and Play'. When connecting to a USB port on a computer running Windows or Mac OSX, the computer will automatically and instantaneously recognize the presence of the Benchmark USB device in USB 1.1, playing tracks up to 96 khz 24-bit. Any audio played from the computer will then be routed to the Benchmark USB device immediately. There is no software to install or configure. To play tracks up to 192 khz or DSD, the DAC2 needs to be engaged in USB 2.0 mode. To engage it in USB 2.0 mode, hold down the USB button on the remote control until you see the 4X LED blink. If the 2X LED blinks instead of the 4X LED, hold down the USB button again on the remote control until you see the 4X LED blink. In Mac OS X, no driver is required to play tracks up to 192 khz or DSD. On Windows XP, Vista, or 7, a driver is required for 192 khz or DSD playback. To download the driver and get the instructions for Windows XP, Vista, 7, and 8, please visit: DAC2 DX Instruction Manual Rev A Page 38

39 USB Driver Installation - Windows XP, Vista, 7 Note: The DAC2 driver is available for download at: hgc/driver Before you install the driver, make sure the USB is unplugged before installation of the driver. 1. In the DAC2 Driver folder, double click setup.exe. DAC2 DX Instruction Manual Rev A Page 39

40 2. A welcome screen will pop-up. Click Next. DAC2 DX Instruction Manual Rev A Page 40

41 3. When you see the following screen, turn on the DAC2, and select USB as your input. By default, the DAC2 is shipped in USB 1.0 mode. You can enable your DAC2 in USB 2.0 mode in two ways. 1) Using your remote control, hold down the USB button on your remote control for 3-4 seconds until you see the 4X LED light up for 3-4 seconds. 2) From the front faceplate, hold down both input buttons until you see the 4X LED light up for 3-4 seconds. 4. You will be prompted to select a location to install the driver in. It will default to your Program Files folder. If you wish to install it another location, you can change the location. We suggest keeping it in the default destination folder. DAC2 DX Instruction Manual Rev A Page 41

42 Press Install DAC2 DX Instruction Manual Rev A Page 42

43 5. When the installation begins you will see the following screen. Please be patient while the driver installs. Installation time is between 1-5 minutes. 6. Once the installation finishes a message at the top will say Installation Complete. Press Next to continue. DAC2 DX Instruction Manual Rev A Page 43

44 7. Click Finish. The Setup will close automatically and this completes the installation process. You can now enjoy music up to 192 khz and DSD. DAC2 DX Instruction Manual Rev A Page 44