The γ3 high resolution DAC

Initial check

Use the step-by-step procedure below to bring up your γ3 DAC. Read through all steps first and familiarize yourself with what you're about to do before proceeding. Do each step in order, and don't proceed to the next step until you have successfully completed each step.

This section assumes that all the mechanical assembly and wiring is done for both your γ3 DAC and power supply enclosures. It also assumes that all modules (γ24, α24, ζ1) are plugged in on the backplane board, and your LCDuino-1 board has a microcontroller chip with the default bootloader and γ3 firmware from AMB.

Your σ11 and σ22 power supply boards should be unit-tested before you proceed with the following steps, to make sure they are producing the correct output voltages.

You will need a multimeter for this procedure (a digital multimeter is preferable). If at any point your measured voltages do not match what is described, immediately remove power and check the board and wiring for errors.

In some steps you will need to measure resistances or voltages relative to ground (G) or isolated ground (IG). These refer to one of the two ground planes on the backplane board as shown in the photo below. You may use any of the small square pads that run along the border of the appropriate ground plane for your multimeter's negative (black) probe.



Since there are two σ11 power supply regulator boards, the rest of this document refers to the one that's "always on" to be σ11 #1, and the other one to be σ11 #2.

Basic sanity checks

  1. Do not connect the power umbilical cable between the γ3 DAC chassis and the power supply chassis until after performing this procedure.

  2. Set your multimeter to Ohms mode and measure the resistance between the following points. These should show no connectivity (infinite resistance).

    • G (backplane) and IG (backplane)
    • IG (backplane) and chassis (backplane)
    • LVDD (backplane) and G (backplane)
    • GVDD (backplane) and IG (backplane)
    • AVDD (backplane) and IG (backplane)
    • AVSS (backplane) and IG (backplane)
    • IN+ (α24 L) and G (α24 L)
    • IN- (α24 L) and G (α24 L)
    • OUT+ (&alpha24 L) and G (α24 L)
    • OUT- (&alpha24 L) and G (α24 L)
    • OUT (&alpha24 L) and G (α24 L)
    • IN+ (α24 R) and G (α24 R)
    • IN- (α24 R) and G (α24 R)
    • OUT+ (&alpha24 R) and G (α24 R)
    • OUT- (&alpha24 R) and G (α24 R)
    • OUT (&alpha24 R) and G (α24 R)
    • V+ (σ11 #1) and V- (σ11 #1)
    • V+ (σ11 #2) and V- (σ11 #2)
    • V+ (σ22) and V- (σ22)
    • V+ (σ22) and G (σ22)
    • V- (σ22) and G (σ22)
    • V+ (σ11 #1) and chassis (PSU)
    • V- (σ11 #1) and chassis (PSU)
    • V+ (σ11 #2) and chassis (PSU)
    • V- (σ11 #2) and chassis (PSU)
    • V+ (σ22) and chassis (PSU)
    • V- (σ22) and chassis (PSU)
    • G (σ22) and chassis (PSU)
    • IEC live and neutral (PSU)
    • IEC live and chassis (PSU)
    • IEC neutral and chassis (PSU)

  3. Measure the resistance between the following points. These should show connectivity (near 0Ω).

    • G (backplane) and chassis (DAC)
    • AES/EBU digital input/output XLR Pin 1 (backplane) and chassis (DAC)
    • V+ (α24 L) and AVDD (backplane)
    • V- (α24 L) and AVSS (backplane)
    • V+ (α24 R) and AVDD (backplane)
    • V- (α24 R) and AVSS (backplane)
    • AVDD (γ24) and AVDD (backplane)
    • AVSS (γ24) and AVSS (backplane)
    • GVDD (γ24) and GVDD (backplane)
    • J3 pin 3 (LCDuino-1) and LVDD (backplane)
    • G (LCDuino-1) and G (backplane)
    • IEC earth and chassis (PSU)

  4. Now connect the umbilical cord between the DAC chassis and power supply chassis, but do not plug in the AC power cord yet.

  5. Measure the resistance between the following points. These should show connectivity (near 0Ω resistance).

    • V+ (σ11 #1) and LVDD (backplane)
    • V- (σ11 #1) and G (backplane)
    • V+ (σ11 #2) and GVDD (backplane)
    • V- (σ11 #2) and IG (backplane)
    • V+ (σ22) and AVDD (backplane)
    • V- (σ22) and AVSS (backplane)
    • G (σ22) and IG (backplane)

Power-up voltage checks

  1. Connect an AC power cord between the IEC inlet and a live AC wall outlet.

  2. The LCD backlight should glow, and the USB UAC mode LED on the backplane board should also light up, either in red or green. If the UAC LED does not light up, the unit is probably in "powered off" state. press the power/config front panel pushbutton briefly to turn it on.

  3. Set your multimeter to DC V mode and measure the voltage between the following points (with red probe on the first point and black post on the second). The expected result is shown:

    • LVDD (backplane J7 pin 3) and G (backplane) → +5V
    • VREF (backplane) and IG (backplane) → +3.3V
    • VRXTX (backplane) and IG (backplane) → +3.3V or +5V (depends on JP10 jumper setting)
    • V+ (α24 L) and IG (backplane) → +10V
    • V- (α24 L) and IG (backplane) → -10V
    • V+ (α24 R) and IG (backplane) → +10V
    • V- (α24 R) and IG (backplane) → -10V
    • AVDD (γ24) and IG (backplane) → +10V
    • AVSS (γ24) and IG (backplane) → -10V
    • GVDD (γ24) and IG (backplane) → +5V
    • +3.3A (γ24) and IG (backplane) → +3.3V
    • +3.3B (γ24) and IG (backplane) → +3.3V
    • +3.3C (γ24) and IG (backplane) → +3.3V
    • +1.8A (γ24) and IG (backplane) → +1.8V
    • +5.0A (γ24) and IG (backplane) → +5V
    • +5.0B (γ24) and IG (backplane) → +5V
    • G_RESET (γ24 board connector pin 35) and IG (backplane) → +3.3V
    • G_PCMDSD (γ24 board connector pin 2) and IG (backplane) → 0V
    • ZVDD_5V0 (ζ1 board connector 28) and G (backplane) → +5V
    • ZVDD_3V3 (ζ1 board connector 2 and 27) and G (backplane) → +3.3V

  4. Set your multimeter to DC mV mode and measure the voltage between the following points (with red probe on the first point and black post on the second). These are the analog output DC offsets. They should be be near 0V (less than ±4mV).

    • OUT+ (α24 L) and OUT- (α24 L)
    • OUT (α24 L) and G (α24 L)
    • OUT+ (α24 R) and OUT- (α24 R)
    • OUT (α24 R) and G (α24 R)

Sanity checking with an oscilloscope

If you have an oscilloscope capable of measuring at least 50MHz waveforms, you may use it to perform further tests.

For the following tests, connect the oscilloscope ground probe to IG (backplane), set the Y-axis to 1V/div, and check the following points:
  1. Check the waveform at JP1 pin 2 (γ24), you should see a 24.576MHz clock. Adjust your oscilloscope X-axis to get the best view. The waveform may look distorted due to probe wire capacitance and inductance, and is a measurement artifact.
  2. Check the waveform at R10, R11 and R12 (γ24). It doesn't matter which side of each resistor you check. You should also see a 24.576MHz clock.
  3. Check the waveforms at the SCL and SDA (γ24 board connector pins 30 and 31). You should see some pulses indicating I²C bus activity.
Connect the oscilloscope ground probe to G (backplane) for the following measurements:
  1. Check the waveform at board connector pin 34 and 36 (ζ1). You should see either a 12,288MHz or 11.290MHz clock, depending on whether the ζ1 is currently in 48KHz or 44.1KHz (or multiples) mode.
  2. Check the waveforms at U19 pins 1 and 2 (backplane board) You should see pulses indicating I²C bus activity similar to #3 above.

LCDuino-1 basic test

  1. If you cannot read the display, adjust the contrast control trimpot on the LCDuino-1 board until you can see the text clearly, with the widest viewing angle possible.

  2. Set your multimeter to DC V mode and measure the voltage at LCDuino-1's +5V test point (near its power LED) relative to G. You should read very close to 5V DC.

  3. When powered on, a quick press of the front panel power/config switch will toggle "mute" mode. Pressing and holding the switch will power down the DAC (note that the LCDuino-1 itself does not turn off). The display will change to showing just the banner screen when in the "off" state.

  4. When powered off, pressing the power/config switch will power up the DAC. The start-up banner appears briefly and then the display will change to the main screen.

  5. If you quickly press the power/config switch while the LCDuino-1 is powering up, it will go into configuration mode, where you could revert all settings to "factory defaults" and/or learn your IR remote control buttons for specific functions. Refer to the LCDuino-1 website for more information about this.

  6. After running the LCDuino-1 config mode to learn your remote control, you can test the following features.

    • Power on/off
    • Volume up/down (slow, fine-resolution)
    • Volume up/down (fast, coarse-resolution)
    • Alternate volume up/down
    • Mute on/off
    • Change digital input source
    • Toggle amongst different filters
    • Enable/disable anti-clip mode
    • Select display backlight auto-dim, full bright, or dark mode
    • Change between main screen formats
    • Enter Menu Setup mode

  7. Press the Menu key on your remote control to enter Menu Setup mode, where you could go through a series of screens to set up the following (see the LCDuino-1 website for more details).

  8. If you enabled the panel-mount potentiometer during setup, turning the volume knob directly should also cause the volume bargraph and digital readout to change.

  9. If you enabled the potentiometer motor during setup, using the remote control to change the volume should also cause the volume knob to automatically turn to the new setting.

  10. Pressing the miniature pushbutton switch (SW1) on the back of the LCDuino-1 board will perform a full reset and reboot.

  11. The LCDuino-1 basic functionality test is now complete. Disconnect the AC power cord to power off everything.

Final functionality test

You're now finished building the γ3 high resolution DAC. Connect your digital input sources, connect the analog outputs to your amplifier and test the system for all its functionality and features. The full user's guide for the γ3 system is found at the LCDuino-1 website.

Please refer to the ζ1 website about setting up your computer, tablet or mobile device for USB audio playback on the γ3 DAC.

If any portion of the DAC does not seem to work properly, examine your build carefully, use the schematic diagram to help determine the cause and fix. If you have difficulties and do not know how to proceed, post questions on the AMB DIY audio forum for help.

If your γ3 works, congratulations! You've now completed a sophisticated, high performance DAC that took tremendous effort to design and develop, and will please your ears for many years to come. You should also be very proud of your skills, as this is not a trivial build. Relax and enjoy the music!

Note: The LVDD 5V power supply is always "live" when the AC power cord is connected. To prevent the top cover from causing a short circuit, always disconnect the AC power cord when opening or closing the cover.

Flashing new LCDuino-1 firmware

The procedures for flashing new firmware are described at the LCDuino-1 website. For the γ3 DAC, you should first disconnect the AC power cord, disconnect the power umbilical cable, and plug the FTDI TTL-232R cable into J3. Take care not to plug the cable in the wrong way, the green wire should be closest to the LCD contrast adjustment trimpot.

While the FTDI cable is plugged in and connected to the computer's USB port, the LCDuino-1 board and some other parts are powered by the computer's USB power. Do not re-connect the umbilical cable and the AC power cord while the FTDI cable is connected to your computer, or the σ11 power supply may "fight" against your computer's USB power.


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