502HTA Hybrid Tube Amp Shield Hardware Reference Manual 2017 PI 2 Design PAGE 1
Table of Contents 1 Warranty... 4 2 Operating Specifications... 5 2.1 502HTA Operating specifications... 5 3 Overview... 6 3.1 Introduction... 6 3.2 Block Diagram... 6 4 On-Board Functions... 8 4.1 Overview... 8 4.1 PCM5102A 24-Bit 192Khz DAC... 8 4.1.1 PCM5102A 24-Bit 192Khz DAC Notes... 8 4.2 Dual Triode Amplifer... 9 4.2.1 Dual Triode Amplifer Notes... 9 4.3 Class-A MOSFET Buffer... 9 4.3.1 Class-A MOSFET Buffer Notes... 9 4.4 6.3V Heater Supply... 10 4.4.1 6.3V Heater Supply Notes... 10 5 RPi GPIO... 11 5.1 Overview... 11 5.1.1 RPi GPIO Notes... 12 6 502HTA Power... 14 6.1 Overview... 14 6.2 Software Controlled Power Hold... 14 6.3 Software Visible Power State... 14 7 502HTA Software... 16 7.1 Overview... 16 7.2 Driver Software Compatibility... 16 8 Connectors and Switches... 17 8.1 Overview... 17 8.1 J1 3.5mm Headphone Jack... 17 8.2 J2 3.5mm Headphone Jack... 17 8.3 W2 3-Pin Bias Adjust Header... 18 8.4 P2 40-Pin GPIO Header... 18 8.5 P2 DC Jack... 18 8.6 P3 3-Pin Heater Voltage Select... 18 8.7 RP1 and RP3 Trimpots... 18 8.8 RP5 Volume Pot with On/Off Switch... 18 8.9 SW1 Attenuation Switch... 18 8.10 SW2 Output Resistance Slide Switch... 18 8.11 W2 Bias Adjust Header... 18 9 Test Results... 20 9.1 Test Results summary... 20 9.2 Headphone Out, DAC Driven Test Results... 20 9.3 Headphone Out, Analog Line In Test Results... 26 10 Document Revisions... 33 11 Errata... 34 11.1 Overview... 34 List of Tables Table 1 502HTA Operating Specifications... 5 Table 2 RPi to PCM5102A Connections... 8 Table 3 CPU GPIO Pin Assignments... 12 Table 4 Document Revisions... 33 List of Figures Figure 1 502HTA Block Diagram... 7 Figure 2 502HTA Power Hold Circuit... 15 Figure 3 502HTA Connectors and Switches... 17 Figure 4 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, 0dB, 600 ohm... 21 Figure 5 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -3dB, 600 ohm... 22 Figure 6 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -12dB, 600 ohm... 23 Figure 7 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -60dB, 600 ohm... 24 Figure 8 502HTA Headphone Out, 11.025Khz, 16-Bit@44.1Khz, Jitter Test, 600 ohm... 25 Figure 9 502HTA Headphone Out, 12Khz, 24-Bit@96Khz, Jitter Test, 600 ohm... 26 Figure 10-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, 3dB, 600 ohm... 27 PAGE 2
Figure 11-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, 0dB, 600 ohm... 28 Figure 12-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -3dB, 600 ohm... 29 Figure 13-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -6dB, 600 ohm... 30 Figure 14-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -12dB, 600 ohm... 31 Figure 15-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -60dB, 600 ohm (Generator set to 50mV rms)... 32 PAGE 3
1 WARRANTY The enclosed product ("the Product"), a part of the PI2MEDIA Shield/Hat series, is warranted by Pi 2 Design for a period of one year for reasonable development, testing and use, all as further described and defined below. This warranty runs solely to the individual or entity purchasing the Product and is not transferable or assignable in any respect. This warranty is valid only for so long as the product is used intact as shipped from PI 2 Design. Any attempt or effort to alter the Product, including but not limited to any attempt to solder, de-solder, unplug, replace, add or affix any part or component of or onto the Product, other than components specifically intended for the user to plug and unplug into appropriate sockets and/or Connectors to facilitate user programming, development and deployment, all as specifically described and authorized in this Product Hardware Reference Manual, shall void this warranty in all respects. Coverage under this warranty requires that the Product be used and stored at all times in conditions with proper electrostatic protection necessary and appropriate for a complex electronic device. These conditions include proper temperature, humidity, radiation, atmosphere and voltage (standard commercial environment, 0C to +70C, <60%RH). Any Product that has been modified without the express, prior written consent of Pi 2 Design is not covered by this warranty. The use or connection of any test or bus Connector, adapter or component with any device other than a Pi 2 Design Connector or adapter shall void this warranty and the warranty of all other components, parts and modules connected to the rest of the system. Pi 2 Design shall not be responsible for any damage to the Product as a result of a customer's use or application of circuitry not developed or approved by Pi 2 Design for use on or in connection with the Product. This warranty does not cover defects caused by electrical or temperature fluctuations or from stress resulting from or caused by abuse, misuse or misapplication of the Product. Any evidence of tampering with the serial number on the Product shall immediately void this warranty. This Product is not intended to be used on or embedded in or otherwise used in connection with any life-sustaining or life-saving product and this warranty is not applicable nor is Pi 2 Design liable in any respect if the Product is so used. Notwithstanding anything to the contrary herein, Pi 2 Design expressly disclaims any implied warranty of merchantability or implied warranty of fitness for a particular purpose in connection with the manufacture or use of the Product. PAGE 4
2 OPERATING SPECIFICATIONS 2.1 502HTA OPERATING SPECIFICATIONS The 502HTA conforms to the following specifications: Specification Dimensions Weight Value 65mm x 56.5mm Hat Compliant ~8oz (with tube) Storage Temperature 0C to +70C Operating Temperature 0C to +50C Humidity Input Voltage (VIN) Power Consumption 0% to 95% RH, Non-Condensing +24V +/- 5% 500ma Peak 8W Typical, 10W Maximum Table 1 502HTA Operating Specifications PAGE 5
3 OVERVIEW 3.1 INTRODUCTION The 502HTA, designed and manufactured by Pi2Media (a division of PI 2 Design), is a High Quality I/O Shield designed to bring Sweet Tube Sound to the Raspberry PI family of Single Board Computers. This HAT allows the Raspberry Pi SBC to drive Headphones from 32-300 ohm with ease and fidelity. The On-Board PCM5102A, 24-Bit @ 192Khz DAC drives the single stage Dual Triode Tube. The Class-A Output Buffer consists of the Audiophile grade IRL510 MOSFET and LM317A Constant Current Source. A dedicated 6.3V Heater supply insures lowest crosstalk. In addition, the 502HTA can be operated as a Stand Alone Headphone Amp via the 3.5mm Line In jack. The major features of the 502HTA are as follows: FORM FACTOR Raspberry Pi Shield w/40-pin Connector 24-Bit DAC The well regarded -112dB SNR PCM5102 is used to convert the I2S Stream to drive the Single Triode Tube Stage at 24-Bit up to 192Khz Frame Rate TUBE ROLLING The 502HTA supports both 6DJ8 (default is JJ 6DJ8) and 12AU7 type tubes. Individual Anode Bias Adjustment Pots plus selectable Series/Parallel Heater Configuration insure the perfect setup for virtually any tube! HEADPHONE OUT Rugged 3.5mm Jack plus selectable output resistance between 1.5, 47 and 100 ohms. VOLUME POT AND GAIN SELECT High Quality ALPS Potentiometer and dual Gain settings allow the user to adjust the output voltage to the optimal level for each Headphone. SINGLE POWER INPUT OPTION A Single 24V @ 2A input powers the 502HTA and delivers 5V@3A to the Pi via Low Pass Noise Filter. Power can also be isolated between the 502HTA and the Raspberry Pi for the lowest possible noise. STAND-ALONE OPTION The 502HTA can also be operated in stand-alone mode using the 3.5mm Line In Jack. A dedicated stand-alone version, 502HTA-SA, without the Raspberry Pi interface or the PCM5102A DAC is also available. 3.2 BLOCK DIAGRAM Refer to the following figure for a block diagram of the 502HTA. PAGE 6
24V @ 2A Power Brick 5V @ 3A LDO WIDE INPUT 6.3V SWITCHING SUPPLY SERIES/ PARALLEL HEATER SEL Volume Control On/Off Switch ANODE/ CATHODE BIAS ADJ USB-A HOST USB-A HOST USB-A HOST USB-A HOST Backpower Protection Circuit ULTRA-LOW NOISE LDO S ½ DUAL TRIODE IRL510/ LM317A OUTPUT RESISTOR SELECT 40-Pin Expansion Header 10/100 RJ45 w/transformer +5V I2S GPIO 40-Pin Socket ANALOG LEFT ANALOG RIGHT I2S INPUT HW CONTROL LOW JITTER PLL PCM5102A 24-Bit 192Khz DAC GAIN SWITCH & VOLUME CONTROL ½ DUAL TRIODE IRL510/ LM317A 3.5MM Headphone Jack OUTPUT RESISTOR SELECT 3.5MM Stereo Input Jack Raspberry Pi w/40-pin GPIO Header HDMI 502HTA BLOCK DIAGRAM Figure 1 502HTA Block Diagram PAGE 7
4 ON-BOARD FUNCTIONS 4.1 OVERVIEW The 502HTA interfaces to the RPi via the 40-Pin GPIO Connector. This section describes in detail the functionality located on the 502HTA. 4.1 PCM5102A 24-BIT 192KHZ DAC At the core of the 502HTA is the Texas Instruments PCM5102A 24-Bit 192Khz DAC. This device interfaces to the Raspberry Pi via the I2S. The signals used to interface with the PCM5102A are shown in the following table. PCM5102A Signal RPi Signal Description MCLK - Grounded at PCM5102A BCLK BCLK I2S Bit Clock from Pi LRCLK LRCLK I2S Word Clock from Pi SDIN SDOUT I2S Serial Audio Data from Pi DEMP GPIO13 Pulled High to Enable De-Emphasis, Drive Low to Disable FILT GPIO6 Pulled High to Enable Digital Filter, Drive Low to Disable *MUTE GPIO5 Pulled Low to Mute, Drive High to Enable Table 2 RPi to PCM5102A Connections 4.1.1 PCM5102A 24-BIT 192KHZ DAC NOTES 1. The PCM5102A is not populated on the 502HTA-SA. 2. The 502HTA is designed for the Raspberry Pi to operate in master mode, supplying the Bit Clock, Word Clock and Audio Data to the PCM5102A. In this mode the PCM5102A derives its master clock from an internal PLL using the Raspberry Pi Bit Clock (BCLK) as the source. The PCM5102A automatically detects the incoming frequency of BCLK and adjust its PLL accordingly. 3. The PCM5102A is Hardware controlled and thus has no direct SW visible functionality. But, three GPIO s (5, 6, and 13) are connected in order to PAGE 8
control various options as described further below. 4. Although GPIO5 (MUTE) has a default pullup on the RPi of about 75K, which over-rides the 1Meg pulldown on the 502HTA, SW should drive this pin high. 5. Software should drive GPIO13 high to enable the Low Latency Filter if desired. It is set to normal latency by default with a pulldown resistor. 6. Software should drive GPIO13 high to enable the 44.1Khz De-Emphasis function if desired. It is disabled by default with a pulldown resistor. 7. The DAC, when at maximum level, outputs 2Vrms to the Dual Triode Tube Amp. 4.2 DUAL TRIODE AMPLIFER A Dual Triode Amplifier provides the voltage amplification of the input signal (DAC or Line In). This circuit designed to provide 10dB (3.3x) of overall gain (with volume control at 100%). 4.2.1 DUAL TRIODE AMPLIFER NOTES 1. There is an attenuation switch which, when enabled (up position) reduces the input to the Amp by 10dB, thus reducing overall maximum gain to ~0dB. The actual gain is set by the tube and it s cathode resistor. It may vary as much as +/- 1dB. 2. The Amp is driven from either the PCM5120A DAC or, when a plug is inserted, the 3.5mm Line In jack. 3. An ALPS 10K Dual Potentiometer provides volume control and a power on/off switch. 4. If the output is to be driven to a line level input on another device, the user should enable the high attenuation. With this enabled (switch up) and the volume control at 100% the overall gain is ~0dB. 4.3 CLASS-A MOSFET BUFFER A Class-A Buffer consisting of the IRL510 MOSFET and LM317 Constant Current Source provides up to 125ma (peak) of output current to drive Headphones from 32 to 600 ohm. 4.3.1 CLASS-A MOSFET BUFFER NOTES 1. A three position slide switch adds 0, 47 or 100 ohm in series with the output. This allows low ohm headphones to be driven with much lower PAGE 9
noise and overall power consumption. For the best experience, the user should start at the highest resistance and reduce only if the output levels are not satisfactory. 2. There is a 25 second delay from power up before the headphone output is enabled. This allows the tube to warm up and reduces power on thumps. The output is disabled immediately when power is removed. 4.4 6.3V HEATER SUPPLY A low noise, high performance switching supply provides the 6.3V for the Tube Heaters. This supply also feeds the 5V LDO used to power the RPi (up to 3A). 4.4.1 6.3V HEATER SUPPLY NOTES 1. A 3-Pin Jumper is used to select how the power to the Tube Heater is fed. In 6V mode a jumper is placed on pins 2-3, while in 12V mode a jumper Is placed on pins 1-2. Note that 12V mode only works with tubes that allow 6.3V parallel operation, such as the 12AU7, not true 12V heaters. The following circuit illustrates this: PAGE 10
5 RPI GPIO 5.1 OVERVIEW The 502HTA uses a number of signals from the RPi GPIO header for control and status purposes. This usage is defined in the following table. Note that on the 502HTA-SA the Raspberry Pi interface is not supported. RPi PIN DIR AF PUP/ PDN 502HTA Name Description/Notes 1 - - - - RPi +3.3V - Unused 2 - - - +5V +5V Power to/from the RPi 3 I/O Y PUP I2C_SDA I2C Bus Data - unused 4 - - - +5V +5V Power to/from the RPi 5 OUT Y PUP I2C_SCL I2C Bus Clock - Unused 6 - - - GND 7 - - - GPIO4 Unused 8 - - - GPIO14 Unused 9 - - - GND Unused 10 - - - GPIO15 Unused 11 - - - GPIO17 Unused 12 IN Y - BCLK I2S Bit Clock to pcm5102a 13 - - - GPIO27 Unused 14 - - - GND 15 Out - - GPIO22 Power Hold Drive high to keep power on 16 - - - GPIO23 Unused 17 - - - - RPi +3.3V - Unused 18 IN - PUP GPIO24 Power Switch Read state of power on/off switch. Low = on. 19 - - - GPIO10 Unused 20 - - - GND PAGE 11
RPi PIN DIR AF PUP/ PDN 502HTA Name Description/Notes 21 - - - GPIO9 Unused 22 - - - GPIO25 Unused 23 - - - GPIO11 Unused 24 - - - GPIO8 Unused 25 - - - GND 26 - - - GPIO1 Unused 27 - - - ID_SDA Unused 28 - - - ID_SCL Unused 29 OUT - PUP *MUTE GPIO5, 0 = Mute PCM5102A Output 30 - - - GND 31 OUT - PUP FILT GPIO6, 1 = Enable PCM5102A Filter 32 - - - GPIO12 Unused 33 OUT - - DEMP GPIO13, 1 = Enable De-Emphasis (44.1k only) 34 - - - GND 35 OUT Y - LRCLK I2S Left/Right Clock to PCM5102A 36 - - - GPIO16 Unused 37 - - - GPIO26 Unused 38 - - - GPIO20 Unused 39 - - - GND 40 OUT Y - SDOUT Pi I2S Serial Audio Data to PCM5102A Table 3 CPU GPIO Pin Assignments 5.1.1 RPI GPIO NOTES 1. DIR is from the point of view of the RPi. 2. Y in the Alternate Function (AF) column indicates that the use of this pin requires the pin to be assigned to the function as defined by the RPi specifications. 3. PUP/PDN indicates if the GPIO should have its associated Pullup (PUP) or Pulldown (PDN) resistor enabled. 4. An asterisk * at the beginning of the name indicates a low true signal. PAGE 12
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6 502HTA POWER 6.1 OVERVIEW The 502HTA is designed to be powered from an external 24V +/- 5% source via 5.5mm x 2.1mm Jack. 6.2 SOFTWARE CONTROLLED POWER HOLD GPIO22 allows the RPi to hold the power on even after the user turns the power switch to the off position. After initialization, software can drive PWR_HLD (GPIO22) high, thus holding the power on regardless of the state of the on/off switch. Driving this low removes this hold condition. Note that for proper operation this requires user software to disable the internal pullup for GPIO22. 6.3 SOFTWARE VISIBLE POWER STATE The 502HTA allows the RPi to keep the system powered for clean shutdown. As part of this, PWR_SW (GPIO24) is used to sense the state of the ALPS Volume Control Switch. When high it indicates that the user has turned the volume control all the way to the left (counter clockwise) and thus turning the unit off. For proper operation, this circuit requires user software to enable the internal pullup for GPIO24. The following schematic illustrates the Power Hold Circuit: PAGE 14
Figure 2 502HTA Power Hold Circuit PAGE 15
7 502HTA SOFTWARE 7.1 OVERVIEW Due to the various resources interfaced on the 502HTA, both internal and external to the Raspberry Pi, it is necessary to initialize a large number of CPU registers and external devices before correct operation can begin. These values and their proper sequencing are beyond the scope of this document. See our web site at http://www.pi2design.com or email us at support@pi2design.com for example operating and initialization code. 7.2 DRIVER SOFTWARE COMPATIBILITY The 502HTA is compatible with the standard Raspberry Pi PCM5102A driver. An example is the Hifiberry DAC. Using this driver will support all the audio functionality of the 502HTA, but will not enable the Power on/off control. The Volumio 2 Audio Player (www.volumio.org) supports the 502HTA by way of the 503HTA plugin. PAGE 16
8 CONNECTORS AND SWITCHES 8.1 OVERVIEW This section provides the type, location and pinout for the various connectors and switches on the 502HTA Top Side. These are shown in the 3D rendering below. SW2 Attenuation RP5 Volume Control & Power Switch J1 3.5MM Headphone SW1 RP3 RP1 T1 Dual Triode Tube J2 3.5MM W2 R G L Line In P2 5.5mm x 2.1mm DC JACK Figure 3 502HTA Connectors and Switches J1 is a 3.5mm Stereo Jack for Headphone Out 8.1 J1 3.5MM HEADPHONE JACK J2 is a 3.5mm Stereo Jack for Line In 8.2 J2 3.5MM HEADPHONE JACK PAGE 17
8.3 W2 3-PIN BIAS ADJUST HEADER W2 is a 3-pin.1 single row header. It allows access to the Left and Right Channel Bias points. The pins are marked R-G-L for Right, Ground and Left respectively. 8.4 P2 40-PIN GPIO HEADER This is a standard 40-Pin.1 Dual Row Female Header. It is designed to plug into the 40-pin GPIO Header on a Raspberry Pi single board and conforms to the standard Raspberry Pi pinout. It is located on the bottom side of the 502HTA. P2 is not populated on the 502HTA-SA. 8.5 P2 DC JACK This jack is designed to accept a 5.5mm x 2.1mm center positive plug for external power in. Voltage must be 24V +/- 5%, 2 Amp minimum. 8.6 P3 3-PIN HEATER VOLTAGE SELECT P3 is a 3-pin.1 single row header. It is used to select between 6V or 12V (in series mode) tube heaters. 8.7 RP1 AND RP3 TRIMPOTS RP1 and RP3 are the bias adjustment potentiometers for the Left and Right Channels respectively. 8.8 RP5 VOLUME POT WITH ON/OFF SWITCH RP5 is an Alps RK09 Low Noise, Conductive Plastic Volume Control with built-in On/Off Switch. 8.9 SW1 ATTENUATION SWITCH SW1 a Single Pole, Double Throw (SPDT) toggle switch that controls the attenuation relay. 8.10 SW2 OUTPUT RESISTANCE SLIDE SWITCH SW2 is a Double Pole, Three Position (DP3T) Slide Switch. It adds 0, 47 and 100 ohm headphone output resistance when in the Left, Middle and Right positions respectively. 8.11 W2 BIAS ADJUST HEADER W2 is a 3-pin right angle header. It carries the Left (L) and Right (R) Bias signals along with Ground (G). This allows the bias voltage to be measured while adjusting for the current tube. PAGE 18
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9 TEST RESULTS 502HTA test conditions were: 9.1 TEST RESULTS SUMMARY Raspberry Pi 2 running Volumio Version 2.23, 503HTA driver selected External 24V from low noise benchtop supply Raspberry Pi powered from standard USB 5V@2.5A supply All Test Files were encoded as 24-Bit@96Khz unless otherwise noted 0db reference = 2Vrms dscope IIIe Analog In Load resistance = 600 ohm dscope IIIe Analyzer FFT = 32K, THD w/no weighting, Residual Noise w/a- Weighting 502HTA-SA test conditions were: External 24V from low noise benchtop supply All Test Files were encoded as 24-Bit@96Khz unless otherwise noted 0db reference = 2Vrms dscope IIIe Analog Generator set to 2Vrms Out, Floating Ground dscope IIIe Analog In Load resistance = 600 ohm dscope IIIe Analyzer FFT = 32K, THD w/no weighting, Residual Noise w/a- Weighting 9.2 HEADPHONE OUT, DAC DRIVEN TEST RESULTS Using 1-meter 3.5MM to XLR Adapter cable. Attenuation Switch High, Volume at 50%. PAGE 20
Figure 4 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, 0dB, 600 ohm PAGE 21
Figure 5 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -3dB, 600 ohm PAGE 22
Figure 6 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -12dB, 600 ohm PAGE 23
Figure 7 502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -60dB, 600 ohm PAGE 24
Figure 8 502HTA Headphone Out, 11.025Khz, 16-Bit@44.1Khz, Jitter Test, 600 ohm PAGE 25
Figure 9 502HTA Headphone Out, 12Khz, 24-Bit@96Khz, Jitter Test, 600 ohm 9.3 HEADPHONE OUT, ANALOG LINE IN TEST RESULTS Using 1-meter RCA to RCA Cable and 1-meter 3.5MM to XLR Adapter cable. dscope IIIe generator set to 1Vrms unless otherwise noted, Attenuation Switch Low, Volume adjusted to desired output level. PAGE 26
Figure 10-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, 3dB, 600 ohm PAGE 27
Figure 11-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, 0dB, 600 ohm PAGE 28
Figure 12-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -3dB, 600 ohm PAGE 29
Figure 13-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -6dB, 600 ohm PAGE 30
Figure 14-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -12dB, 600 ohm PAGE 31
Figure 15-502HTA Headphone Out, 1Khz, 24-Bit@96Khz, -60dB, 600 ohm (Generator set to 50mV rms) PAGE 32
10 DOCUMENT REVISIONS Date Revision Change 08/31/2017 P3 Preliminary Release Table 4 Document Revisions PAGE 33
11 ERRATA 11.1 OVERVIEW There are currently no known errata for the 502HTA Rev. P1. PAGE 34