The α10 stereo pre-amplifier

Before you start

Use the step-by-step procedure below to bring up your α10 stereo pre-amplifier. 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. Do not plug in any modules into the α10 backplane board until instructed.

This section assumes that your LCDuino-1 board has a microcontroller chip with the default bootloader and firmware from AMB.

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 voltages relative to digital ground or analog ground. 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.

Initial setup & adjustments

Digital power supply test



  1. Connect the power umbilical cable between the α10 main pre-amplifier chassis and the σ10 power supply box.
  2. Connect an AC power cord between the σ10 power supply box IEC power entry module and an AC wall outlet.
  3. Set your multimeter to AC V mode and measure the voltage across the AC input pads on the α10 backplane board, located at the σ25 board plug-in area (these are labeled "~ ~"). You should read approximately 13V AC. This is the T2 transformer's unloaded secondary voltage.
  4. Disconnect the AC power cord, and then plug the σ25 board into the backplane as shown in the photo above. Make sure all pins are aligned and seated fully, then fasten the board with four 1/4" #4-40 machine screws.
  5. Re-connect the AC power cord. The LED on the σ25 board should illuminate.
  6. Set your multimeter to DC V mode and measure the voltage across the DC OUT pads on the σ25 board. You should read very close to 5V DC.
  7. The digital power supply test is now complete. Disconnect the AC power cord to power off everything.

LCDuino-1 basic test



  1. Connect the five LCDuino-1 Molex harness plugs to the corresponding Molex headers on the backplane board (LJ3, LJ4, LJ5, LJ6 and LJ9). See the photo above.
  2. Re-connect the AC power cord. The σ25 board LED should glow again, so should the power LED on the LCDuino-1 board, and the LCD display backlight.
  3. The LCD display should briefly show a start-up banner then change either to the clock display or the main screen. If you cannot read the display, adjust the contrast control trimpot on the LCDuino-1 board.
  4. Set your multimeter to DC V mode and measure the voltage at LCDuino-1's +5V test point (near its power LED) relative to digital ground. You should read very close to 5V DC.
  5. 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 pre-amplifier (note that the LCDuino-1 itself does not turn off). The display will change to showing the clock when in the "off" state.
  6. When powered off, pressing the power/config switch will power up the pre-amplifier. The start-up banner appears briefly and then the display will change to the main screen.
  7. 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.
  8. After running the LCDuino-1 config mode to learn your remote control, you can test the following features. At this point you would only see the effect of the volume attenuator and I/O selector functions on the LCD display, because the δ1, δ2 and α20 boards are not yet in the system):
    • Power on/off
    • Volume up/down (slow, fine-resolution)
    • Volume up/down (fast, coarse-resolution)
    • Alternate volume up/down
    • Mute on/off
    • Change input source
    • Change output target
    • Toggle multi-output select mode
    • Select display backlight auto-dim, full bright, or dark mode
    • Enable/disable sleep timer
    • Change between main screen formats
    • Enter Menu Setup mode
  9. 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). For the reference AMB α10 pre-amplifier, the settings are shown in bold:
    • Number of relays on each δ1 (8)
    • The δ1 board dB-per-step setting (0.5)
    • Enable/disable the panel-mount potentiometer (Enable)
    • Enable/disable the panel-mount potentiometer's motor (Enable)
    • Enable/disable the real-time clock (Enable)
    • Number of δ1 and δ2 boards in the system (1 and 1)
    • Set the turn-on muting delay time interval (3 seconds)
    • Set the sleep mode time interval
    • Set the display backlight minimum/maximum brightness
    • The "Volume up/down (coarse)" step size
    • Set the volume control minimum/maximum limits
    • Customize the start-up banner (two lines)
    • Configure the δ2 ports and customize the port names
    • Set the clock
    • I²C address settings of each δ1 and δ2 board
  10. 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.
  11. 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.
  12. Pressing the miniature pushbutton switch (SW1) on the back of the LCDuino-1 board will perform a full reset and reboot.
  13. The LCDuino-1 basic functionality test is now complete. Disconnect the AC power cord to power off everything.

δ2 configuration and test



  1. Set the δ2 I²C address jumpers (JP1[ABC]+ and JP1[ABC]-) to match the LCDuino-1 configuration. Please refer to the LCDuino-1 and δ2 websites for details.
  2. Install a jumper shunt across the 2-3 pins of δ2's JP2 jumper block ("POWER_SEL").
  3. If your δ2 has the debugging LED arrays (LED+ and LED-), then install a jumper shunt across δ2's JP3 jumper block ("LED_ENB").
  4. Plug the δ2 board carefully into the backplane as shown in the photo above. Make sure all pins are aligned and seated fully, then fasten the board with eight 1/2" #4-40 male-female standoffs ("STANDOFF3" in the parts list).
  5. Re-connect the AC power cord. If your δ2 has the LED+ and LED- arrays, then the first LED on these arrays should light up.
  6. Set your multimeter to DC V mode and measure the voltage at δ2's +5V test point (between C1 and C3) relative to digital ground. You should read very close to 5V DC.
  7. Use your remote control to change input and output selections, you should hear the relays click, the δ2 LED arrays should flash, and the LCD display should show the new selections.
  8. The basic δ2 test is now complete. Disconnect the AC power cord to power off everything.
  9. You may keep the JP3 jumper in place, or if you prefer to disable the LED arrays, remove the jumper shunt.

δ1 configuration and test



  1. Set the δ1 I²C address jumpers (JP1[ABC]+ and JP1[ABC]-) to match the LCDuino-1 configuration. Please refer to the LCDuino-1 and δ1 websites for details.
  2. Install a jumper shunt across the 2-3 pins of δ1's JP2 jumper block ("POWER_SEL").
  3. If your δ1 has the debugging LED arrays (LED+ and LED-), then install a jumper shunt across δ1's JP3 jumper block ("LED_ENB").
  4. Plug the δ1 board carefully into the δ2 board. Make sure their J2 pins/receptacles are aligned and seated, then fasten the board with eight 1/4" #4-40 machine screws. Check to verify that the tops of δ2's C1 and C3 capacitors do not touch the circuit pads and traces on the bottom of the δ1 board. Apply insulating tape if necessary.
  5. Plug the four 2P Molex harnesses from the backplane (for INPUT[LR] and OUTPUT[LR]) into the δ1 board's corresponding 2P Molex headers. See the photo above.
  6. Re-connect the AC power cord. If your δ1 has the LED+ and LED- arrays, then the first LED on these arrays should light up.
  7. Set your multimeter to DC V mode and measure the voltage at δ1's +5V test point (between C1 and C3) relative to digital ground. You should read very close to 5V DC.
  8. Use your remote control and turn the front panel knob to change the volume. You should hear the relays click, the δ1 LED arrays should flash, and the LCD display bargraph and digital readout should also show the changes.
  9. The basic δ1 test is now complete. Disconnect the AC power cord to power off everything.
  10. You may keep the JP3 jumper in place, or if you prefer to disable the LED arrays, remove the jumper shunt.

Analog power supply test



  1. Plug the σ22 board into the backplane, making sure all the pins are aligned and fully-seated. Then, fasten the board with four 1/4" #4-40 machine screws as shown in the photo above.
  2. Re-connect the AC power cord. Either use the remote control or the front panel power/config switch, turn on the pre-amplifier. The σ22 board LED and the σ10 power supply box LED should both illuminate.
  3. Set your multimeter to DC V mode and measure the voltage at σ22's V+ and V- output pads relative to analog ground. You should read approximately +12V and -12V, respectively (or +15V/-15V if you had configured the σ22 accordingly).
  4. Use the remote control or hold down the front panel power/config switch to turn off the pre-amplifier. The σ22 board LED and the σ10 power supply box LED should both extinguish.
    Note: the σ22 is unloaded at this point and its LED may take some time to dim. Please wait for this LED to turn off completely before proceeding to the next step.
  5. The analog power supply test is now complete. Disconnect the AC power cord to power off everything.

α20 setup



  1. Plug the left channel α20 board into the backplane (where it's marked "JISBOS Buffer"), making sure all the pins are aligned and fully-seated. Fasten the board with four 1/4" #4-40 machine screws.
  2. Pre-set the α20 VR1 and VR2 trimpots as described in the α20 website "Initial setup" section.
  3. Re-connect the AC power cord.
  4. Set the volume to minimum using the remote control or the front panel volume knob.
  5. Continue to follow the initial setup instructions at the α20 website. Where the procedure calls for turning on the power, use the remote control or the front panel power/config switch.
  6. Turn off the power after you're done with left channel α20 board, wait for the σ22 board LED to extinguish fully, then repeat all the steps above for the right channel board.
  7. After both α20 boards are set up, keep the pre-amplifier powered on for some time, and re-check the bias and DC offset.
  8. The photo above shows both α20 boards mounted on the backplane board.

Wrap-up

You're now finished building the α10 pre-amplifier. Turn off the power, disconnect the AC power cord, close the top cover, connect your input sources and output targets, re-connect the AC power cord, turn on the system and enjoy the music!

Note: The 5V digital 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 α10 pre-amplifier, you should first disconnect the AC power cord, unplug the J3 Molex connector from the LCDuino-1 board, 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, δ1 and δ2 boards are powered by the computer's USB power. The LED on your σ25 board will illuminate, but its 7805 regulator is inactive. Do not re-connect the AC power cord while the FTDI cable is connected to your computer, or the σ25 power supply may "fight" against your computer's USB power.


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