The α10 stereo pre-amplifier

Assembly instructions

You should read through the entire page before starting work, so you'll have a broad overview of what to do. The documentation here assumes that you have already built the following modules:
  • α20 line stage amplifier (2 units)
  • LCDuino-1 display I/O processor
  • δ1 relay-based stepped attenuator
  • δ2 relay-based input/output selector
  • σ22 dual-rail tracking regulated power supply
  • σ25 single-rail regulated power supply
If you have not built all of them, refer to each of these project's websites for instructions, then return here to integrate them into the α10 pre-amplifier.

The following sections are arranged in the recommended order-of-work. Many of the photos and illustrations are mouse-clickable to display a larger, clearer version.

All hardware listed on this page are in US/imperial sizes, the Parts list shows Metric alternatives.

Several steps below require you to make wire harnesses to connect panel components to Molex connectors on the backplane board. You should measure the wire lengths so that they are consistent, and no longer than is necessary for strain-free connection.

Clean both sides of the α10 backplane board with paper towel and isopropyl alcohol or electronics flux remover before working with it.

1. Preparing the α10 enclosure

This section assumes that the front and rear panels on your enclosures are done (i.e., all holes and cutouts are drilled and the panel parts fit properly).

You should drill holes on the bottom of the enclosure for mounting the α10 backplane board (8 places). The locations of these holes should match to the backplane board mounting hole locations as shown in the illustration below. You can use the backplane board itself as a template to mark the hole locations. Adjust the backplane board position to allow enough room for the front panel components, the LCD display/LCDuino-1 board and its connectors, and for the rear panel jacks, etc.

The 1/4" #4-40 male-female standoffs ("STANDOFF1" in the Parts list) are to be used to mount the backplane board. After you are done drilling, install these standoffs in the holes, male side up, and secure them with 1/4" #4-40 machine screws on the bottom of the enclosure. Test fit the backplane board and then set the board aside for further work.

If you're using the Par-Metal 2" enclosure, then you will need to trim some material off the front and rear panel frames in order for the LCD display and RCA jacks to clear. See the photos below. You can use a nibbling tool, a flat file and a round file for this purpose, or a powered grinding tool as you see fit. The following photos illustrate the panel frames after modification:

You may install the RCA jacks and power umbilical connector at this time, but the wiring will be done in a later step. When mounting the RCA jacks, use their supplied washers to electrically isolate them from the panel. Do not install the front panel components (switch, LCD display, IR receiver, potentiometer) yet.

2. Install the plug-in module standoffs

The "plug-in" modules refer to the α20, δ2, σ22 and σ25 boards, which will be plugged into the backplane board. They will be supported by 7/16" #4-40 female-female threaded standoffs ("STANDOFF2" in the Parts list) on the top side of the backplane board.

Install these standoffs in the locations shown below (24 places). Secure the standoffs with 1/4" #4-40 machine screws on the bottom of the board.

3. Install the pin headers and receptacles

Follow the directions below to install the pin headers (male) and pin receptacles (female) that allows the various modules to be plugged into the backplane board. The pin headers should be cut from the "PH36" 36-pin strips (as listed in the Parts list) into the appropriate number of circuits for each location.

The mated pin headers and receptables should be soldered at the same time using the steps below to ensure correct alignment and proper electrical contact.

It is difficult to do all of the mated pin header/receptacles on the δ2 in one round, therefore you should repeat the following steps several times, each time soldering only a few mated pin header/receptacle assemblies.

  1. Before soldering, insert the male pin header into its associated female pin receptacle.
  2. Insert the mated pin header/receptacle assembly into the backplane board solder pad holes, with the male pin headers on the bottom.
  3. Align the plug-in board over the pin header/receptacle assembly until the receptacle's solder tails protrudes through its solder pad holes.
  4. Secure the plug-in board by fastening all of its screws into their corresponding standoffs, and check the pin headers and receptacles for proper fitment again.
  5. Solder the headers and receptacles on the bottom of the backplane board as well as the top of the plug-in board.
  6. Remove the screws and unplug the board.

The following illustration shows the locations (in red) where the pin header/receptacle assemblies should be installed, and their number of circuits.

Note: The σ22's terminal pads are on 0.2" centers, but the pin headers are spaced every 0.1", therefore you should cut off the solder tail of a header pin from every other position where it is not needed, and remove the corresponding contact from the receptacle.

If you are building the recommended separate power supply box to house the IEC power entry module, power transformers and solid state relay, then solder an additional 2P pin header into the location on the backplane board, labeled as "IG_CHASSIS" (teal blue in the illustration above). Install a jumper shunt in this location (which serves to connect the signal ground to the chassis via the center-rear backplane mounting standoff).

The following photo shows the bottom of the δ2 board with the pin receptacles. Other plug-in modules are similar.

4. Install the Molex KK headers

Solder the Molex KK headers (denoted "MHn" in the Parts list, where n is the number of circuits) into the locations on the backplane board as illustrated below.

5. Install backplane board

At this point you may clean the flux off the backplane board with high-purity isopropyl alcohol or special electronics flux remover. Then, install the backplane board into the chassis using #4-40 hex nuts (8 places). This is how things should look after installation:

6. δ1 and δ2 pin headers and receptacles

A 6P pin header and receptacle assembly should be installed on the δ2 and δ1 boards to allow them to be stacked. This is described as follows:

  1. Temporarily install 1/2" #4-40 male-female standoffs ("STANDOFF3" in the Parts list) into the δ2 board's mounting holes, male side down, and secure them on the bottom of the board with #4-40 hex nuts (8 places).
  2. Mate a 6P 0.318" header and a 6P receptacle ("PH6" and "PR6" in the parts list, respectively), and insert this assembly, pin header side down, into the top side of the δ2 board J2 pads.
  3. Position the δ1 board over the δ2 board, and align it so that the 6P pin receptacle's solder tails protrude through δ1's J2 solder pad holes. Fasten the δ1 board to the δ2 board by using 1/4" #4-40 machines screws on the standoffs (8 places).
  4. Solder the J2 pads on both the δ1 and δ2 boards, then unfasten all screws, hex nuts and remove the standoffs. Separate the δ1 and δ2 boards and set them aside for later installation.

7. Install panel components

Mount the LCD display, LCDuino-1 board and infrared receiver

Follow the steps below to mount the LCD display, LCDuino-1 and IR receiver. It is assumed that you are using the custom fabricated front panel as described in the Parts list section, or something similar.

  1. Install two 1/2" #4-40 male-female standoffs ("STANDOFF3" in the parts list) on the back side of the LCD display board, into two diagonally-opposite mounting holes. Secure the standoffs with #4-40 hex nuts.
  2. Install the front panel to the front panel frame. Place two 1/8" unthreaded spacers ("SPACER" in the parts list) over the two diagonally-opposite LCD display mounting holes that do not correspond to the standoffs in the previous step.
  3. Fasten the LCD display to the front panel, through the spacers, using two 1/4" #4-40 machine screws.
  4. Using 24 AWG hookup wires, make a 3-wire harness and strip the wire ends. Solder a 3P pin receptacle at one end and tin the wires on the other end. Use heat-shrink tubing to insulate the receptacle pins, and solder the wires to the LCDuino-1 board. Shorten the leads on the IR receiver and plug it into the receptacle.
    Note: Make sure the IR receiver wiring is correct or you risk damaging the IR receiver.
  5. Carefully align the two 6P pin header on the LCDuino-1 board to the matching receptacles on the LCD display, and plug the LCDuino-1 board into the LCD display. Fasten the LCDuino-1 board to the standoffs with two 1/4" #4-40 machine screws.
  6. Fabricate a mounting bracket for the IR receiver using thin sheet aluminum, and mount the IR receiver to the front panel with 1/8" #4-40 machine screws. The "dome" on the IR receiver should fit into the front panel hole.

Install the power/config pushbutton switch

  1. Mount the switch to the front panel with the supplied washer and nut.
  2. Using 24 AWG hookup wires, make a 2-wire harness and strip the wire ends. On one end, crimp or solder Molex KK crimp terminals to the wires and then insert them into a 2P Molex KK plug housing until they lock. On the other end, tin the wires and solder them to the normally-open switch terminals. Heat-shrink the switch solder joints.

Here is a photo of the mounted switch with its wire harness:

Install the motorized potentiometer

  1. Using 22 AWG hookup wires for the CW and CCW lines and 24 AWG for the others, make a 5-wire harness and strip the wire ends. On one end, crimp or solder Molex KK crimp terminals to the wires and then insert them into a 5P Molex KK plug housing until they lock. On the other end, tin and solder the wires to the motorized potentiometer. Heat-shrink the potentiometer solder joints. The illustrations below illustrates the connections for the Alps RK16812MG099 potentiometer.
  2. Mount the potentiometer to the front panel with the supplied washer and nut.

Install RCA jack harnesses

  1. If you haven't already done so, mount the RCA jacks to the rear panel with insulator washers and nuts (16 places).
  2. Using 24 AWG hookup wires, make eight 4-wire harnesses and strip the wire ends. On one end, crimp or solder Molex KK crimp terminals to the wires and then insert them into a 4P Molex KK plug housing until they lock. On the other end, tin the wires and solder them to the RCA jacks according to the illustrations below.

Install power umbilical connector harness

  1. The power umbilical connector has seven circuits that should be split into three groups: T1, T2 and SSR, each of these terminating in a Molex KK plug. See the Power supply schematic diagram
  2. for details. The schematic also shows the recommended pin assignment for the Amphenol Eco|Mate 6+PE series circular locking connector (as listed in the Parts list).
  3. For the T1 group, make a 3-wire harness with 22 AWG hookup wires, strip and tin each end. On one end, crimp or solder Molex KK crimp terminals to the wires and then insert them into a 3P Molex KK plug housing until they lock. On the other end, solder them to the umbilical connector. Heat-shrink the umbilical connector solder joints.
  4. The T2 and SSR groups are similar, except that they are two wires each, and go to 2P Molex KK plug housings. Make sure not to reverse the two SSR wires.
  5. Mount the circular connector to the rear panel. The following photo shows the mounted connector with its three wire harnesses.

8. Build the LCDuino-1 Molex harnesses

The LCDuino-1 needs to be connected to the backplane board via five wire harnesses, each one terminated with Molex KK plugs on both ends. The harnesses are described in the table as follows:

LCDuino-1 connector# Circuits (LCDuino-1 side)Backplane connector# Circuits (backplane side)

The pin assignments of these harnesses are all "straight-through" (i.e., pin 1 goes to pin 1, etc.). The only exception is the J3/LJ3 harness. This harness is 6P on the LCDuino-1 side but 3P on the backplane side. Simply connect pins 1 to 3 and omit 4 to 6.

Make the harnesses as follows (also refer to the backplane schematic):

  1. Cut the wires according to the table above. Use 22AWG hookup wire for any circuit marked GND, DG, VCC, MOTORPOT-CW and MOTORPOT-CCW. You may use 24 AWG hookup wire for the other signals.
  2. Strip and tin both wire ends, and crimp or solder Molex KK crimp terminals to the wires. Insert wires into the proper slots of each Molex plug housing until they lock into place.
  3. Each completed harness should then be plugged into its corresponding LCDuino-1 Molex header as shown in the photo below.

9. Mount the front and rear panels to chassis

The front and rear panels are now ready to be mounted to the chassis.

  1. Mount the front and rear panel/frame assemblies to the chassis bottom plate (for the Par-Metal cases, use four 3/8" #6-32 machine screws).
  2. Test-fit the Molex KK plugs from panel components to the corresponding Molex KK headers on the backplane board. See the photos below.
  3. Unplug the five Molex harnesses that connect the LCDuino-1 module to the backplane. These will be plugged-in again later in the initial setup phase.

10. Build the δ1 Molex harnesses

The δ1 board needs to be connected to the backplane via four wire harnesses after being stacked on top of the δ2 board, each of these harnesses are terminated with 2P Molex KK plugs on both ends. The pin assignments of these harnesses are all "straight-through" (i.e., pin 1 goes to pin 1, etc.). Use 24 AWG hookup wires. Otherwise, the instructions are the same as those for the LCDuino-1 Molex harnesses above.

After building these harnesses, plug them into the backplane as shown in the photo below.

At this point, you should plug the σ22 board into the backplane, and verify that the heatsinks and large electrolytic capacitors will not touch the top cover when it is closed. Remove the cover, unplug the σ22 board and set them aside when done.

11. Build the σ10 power supply box

  1. Mount the two power transformers and solid state relay into the external enclosure, install the IEC power entry module and the power umbilical connector to the rear panel, and install the LED on the front panel.
  2. Wire up the box according to the schematic diagram shown in the Power supply section. Use 18 AWG hookup wires for all transformer wiring, 24 AWG for the solid state relay trigger and LED. For the umbilical connector, use the same pin assignments as the one in the main pre-amplifier chassis. Note that the transformer primaries are to be wired differently depending on your AC mains voltage. Use insulated FastOn connectors for the AC mains connections at the IEC module, or use heat-shrink tubing to insulate them. Use heat shrink tubing to insulate the power umbilical connector solder joints.
  3. Double check your wiring for errors.
  4. Install the fuse in the IEC module.

12. Build the power umbilical cable

  1. Using 20 AWG stranded hookup wires, make a 7-conductor cable to your desired length. Strip and tin the wire ends.
  2. Cut the protective braided sleeving to the appropriate length, and run the wires through it.
  3. Assemble the cable-mount connectors and solder the wires, making sure that the pin assignments match on both ends. If you're using the Amphenol Eco|Mate 6+PE series locking circular connector as listed in the Parts list, please refer to the datasheet for cable assembly instructions. Make sure that there is good strain-relief for the wires in the connectors.
The basic α10 platform is now done. Install the rubber feet on both enclosures. Do not install any of the plug-in boards (α20, δ2, δ1, σ22 or σ25) at this time. Check your work thoroughly, then proceed to the Initial setup section to continue the bring-up of each module.

Main: α10 Main | Prev: Parts list | Next: Initial setup