The γ3 high resolution DAC

Before you start

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:
  • γ24 high performance DAC core
  • α24 fully-differential line stage (2 units)
  • LCDuino-1 display I/O processor
  • ζ1 Audio Widget USB-I²S module
  • σ22 dual-rail tracking regulated power supply
  • σ11 single-rail regulated power supply (2 units)
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 γ3 DAC. Before proceeding further, you should have also unit-tested your σ11 and σ22 power supply boards to make sure they are producing the correct output voltages.

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.

Do not remove the integrated circuits from their sealed packaging until you are ready to solder them on the board. This is to protect them from electrostatic discharge and moisture.

While you look at the board layout, please also take the time to check the schematic diagram and associate each part with their location in the circuit. While this is not normally required to build a working unit, one of the benefits of DIY is to learn about how the circuit works. Try to determine what each part does and why the particular part or value is chosen. There are many web resources to help you with this, including the AMB DIY audio forum. You will find the overall DIY experience more rewarding as a result.

Due to γ3's use of surface-mount devices (SMD), you should have the following tools and supplies to help you work on the board:
  • A good soldering iron with fine tip, preferably with adjustable temperature. For example, a Weller WLC100 with ST6 tip. A more deluxe soldering station such as the Weller Weller WES51 or Hakko FX888 is nice, but not necessary.
  • Liquid flux or flux pen for electronics soldering/rework.
  • Thin gauge solder, such as 0.025". Your choice of 60/40 or 63/37 tin/lead. Avoid silver solder as it requires high heat. Lead-free solders also require higher heat and their durability is still in question.
  • Fine tweezer with sharp points, such as those from Wiha
  • Desoldering braid
  • Chip Quik® SMD desoldering kit (if needed).
  • Vision aid, such as magnifier lamp, loupe, magnifying eyewear (e.g., Fisherman Eyewear Flip-n-focus), etc.
  • Needle nose pliers
  • Diagonal cutter
  • Cotton Q-tips
  • 99% isopropyl alcohol or specialty electronics flux remover spray
  • Emery board or thin file (for black/blue/red Hammond cases only)
  • Multimeter with sharp probes
  • Oscilloscope capable of measuring at least 50MHz is highly recommended.

Assembly instructions

1. Build the γ3 backplane

You can view the γ3 backplane board silkscreen as a guide for installing components.

Important pre-assembly notes:
  • All parts should be mounted tight against the board for proper clearance.
  • Due to configurable input and output types, please take extra care to mount the correct parts associated with each digital input or output.
  • For the configuration jumpers JPn, you do not need to use pin headers and jumper shunts, because they are usually set once and never changed again. Just solder cut-off resistor leads across the jumper pads where they should be shorted together.
  • If you're new at soldering surface-mount devices, please view the following video, an excellent tutorial.

    Surface Mount Soldering 101
    by Curious Inventor

  • Do not mix up the SOT23 package logic chips and voltage regulators. The markings on these devices are coded as follows:

    U2, U4, U6, U8Texas Instruments SN74LVC1G125DBVC25_
    U10Texas Instruments TPS79333DBVPHUI
    Texas Instruments LP2985AIM5-3.3L0RA
    U17Texas Instruments SN74LVC1G00DBVC00_
    U18Texas Instruments SN74LVC1G80DBVC80_
    U20Texas Instruments TPS22929DDBVNF4F

    Note: The "_" character denotes a variance code or for the manufacturing facility and could vary.

Clean both sides of the blank γ3 backplane board with paper towel and isopropyl alcohol or electronics flux remover, then solder the components to the board, beginning with the SMD components. Apply liquid flux to the board solder pads, and place the chip over the pads. Use the tweezers to pick and nudge the chip until it is centered and aligned perfectly. Be sure that the pin orientation or polarity is correct. Most chips have a marking next to its pin 1. For SOIC packages, the top edge of the package where pin 1 is located is usually beveled. For SOT23 packages, pin 1 is at the lower left corner if you are viewing the top of the package, with the markings oriented for reading. For the Scientific Conversion SC947-02LF pulse transformer, there is a small red dot near pin 1.

Press the tweezer tip on the top of the chip to keep it from shifting while soldering. Apply only a tiny amount of solder to the tip of your iron, and tack down one corner pin of the chip. It helps to use a "wiping" motion of the tip on the pin and pad. If necessary, make small adjustments while heating that pad and pin again. If all is well, do the pin on the diagonally-opposite side. Then, do the remaining pins one at a time, reflow any pin that needs a bit of touch-up. If necessary, use the desoldering braid to remove any excess solder, and be sure there are no solder bridges between the pins.

Use your multimeter and check the resistance between each pin of the chip and the pad to make sure you don't have a cold joint (i.e., your meter should read close to zero ohms). Also check continuity between adjacent pins for solder bridges (meter should read infinity, except where the pins are supposed to be connected to each other, see the schematic diagram for verification).

Now proceed to mount and solder the though-hole parts, starting with the lowest profile parts and work up. Since the γ3 circuit board holes are plated through, through-hole parts should be soldered only on the bottom of the board. Do not drill or enlarge the holes because that would damage the through-plating.

Make sure the correct part goes into each position on the circuit board. Measure each resistor with your multimeter to ensure it's the proper value before installing it. Pay attention to the polarity of electrolytic and organic polymer capacitors. The positive lead is usually the longer one.

Do not solder the γ24, α24 and ζ1 module plug-in pin header strips yet. These will be done in a later step.

Inspect all solder connections carefully, using a magnifying glass, to make sure there are no solder bridges or cold solder joints. Use a multimeter in ohms scale to check for short circuits, and correct any mistakes found.

2. Preparing the γ3 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 γ3 backplane board (11 places). The locations of these holes should match 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 so that it's tight against the rear panel with no gap.

If you are using the ε31 bridge board, then the backplane board should be centered between the left and right walls of the specified Par-Metal enclosure.

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 are 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 rear connectors to clear. It also allows the backplane board to be mounted against the rear panel without any gap. 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 rear panel jacks and power umbilical connector at this time, but the wiring will be done in a later step. When mounting 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.

3. Install the plug-in module standoffs

The "plug-in" modules refer to the γ24, α24 and ζ1 modules, which will be plugged into the backplane board. The γ24 and α24s 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 (12 places). Secure the standoffs with 1/4" #4-40 machine screws on the bottom of the board.

The ζ1 module does not use standoffs.

4. 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 for the γ24 and α24 boards should be cut from the 36P pin header strip (as described in the Parts list) into the appropriate number of circuits for each location.

The ζ1 module will use the Sullins 2mm-pitch pin headers and receptacles.

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. The following illustration describes the steps to do so. A 2P pin header and 2P pin receptacle is shown, but the same method applies regardless of the pin-count.

  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. For the γ24 and α24, 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 where the pin header/receptacle assemblies should be installed, and their number of circuits. The red locations have 0.1" pitch, and the male pin headers are taken from the 36P strip. The blue locations have 2mm pitch and use the Sullins pin headers.

The following photo shows the bottom of the γ24, α24 and ζ1 boards each with pin receptacles, ready for installation.

5. Install the Molex KK headers

Solder the Molex KK headers into the locations on the backplane board as illustrated below.

Note the following:
  • The Molex KK header locations in green should be installed in all configurations.
  • Whether to install the Molex KK header locations in red depends on the digital input and output configuration, and whether unbalanced, balanced or both types of analog outputs will be connected to rear panel jacks.
  • J12 and J13 are combined into one 4P Molex KK header.
  • J14 and J15 are combined into one 5P Molex KK header.
  • LJ5 and LJ6 are combined into one 4P Molex KK header.

6. 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 (11 places). This is how things should look after installation:

You may now install the plug-in modules (γ24, two α24s and ζ1) now. Simply plug these modules into its respective board connector pin headers. Install 1/4" #4-40 machine screws into the standoffs for the γ24 and α24 boards to secure these boards.

7. Install front and rear 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 22 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 22 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.
  3. Connect the Molex KK plug to J6 on the backplane board.

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

Install the motorized potentiometer

  1. Using 22 AWG hookup wires, make a 5-wire harness and strip the wire ends. This wire harness should be long enough to go from the mounted potentiometer to J9 on the LCDuino-1 board. 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.
  3. Connect the potentiometer Molex KK wire harness to J9 on the LCDuino-1 board.

Note: J7 and LJ9 on the backplane board are unused.

Install rear panel jack harnesses

  1. If you haven't already done so, mount the input and output jacks on the rear panel. RCA and BNC jacks should be installed with their insulator washers and nuts, if necessary.
  2. For each digital input and output configured as AES/EBU or Coaxial, and for each left and right channel unbalanced analog output, make a 2-wire harness using 22 AWG hookup wires. For each balanced analog output, make a 3-wire harness. Strip all wire ends. On one end, crimp or solder Molex KK crimp terminals to the wires and then insert them into a Molex KK plug housing until they lock. On the other end, tin the wires and solder them to the jacks according to the schematic diagram.
  3. Pin 1 of each AES/EBU digital input should be connected to the chassis. On the recommended Neutrik XLR female panel connector, there is a "body" solder tab that could be bent and soldered to the pin 1 solder cup. When the jack is mounted on the panel, it will automatically make the chassis connection. This is shown in the third photo below.

Install power umbilical connector harness

  1. The power umbilical connector has eight circuits that should be split into four groups: LVDD, SSRTRIG, GVDD, AVDD/AVSS. These correspond to J12, J13, J14 and J15, respectively. However, J12+J13 are combined into a single 5P Molex plug, and J14+J15 are combined into a single 5P Molex plug. See the Parts list and Power supply schematic diagram
  2. for details.
  3. The schematic diagram also shows the Conxall Mini-Con-X 8P circular locking connector (as listed in the Parts list) pin assignment as used on AMB's reference build.
  4. These wiring harnesses should be long enough to run from the mounted circular connector to their destination J12-J15 connectors on the backplane board.
  5. Make the two wire harnesses. Strip and tin both ends on each wire, and crimp or solder Molex KK crimp terminals to one end of the wires. Insert the crimp terminals into the proper slots of each Molex plug housings until they lock into place.
  6. Solder the other end of each wire to the respective pin of the umbilical panel connector, use some heat shrink tubing at the end of these wires to prevent short circuits.
  7. Each completed harness should then be plugged into its corresponding Molex KK pin header on the backplane board.

8. Build the LCDuino-1 Molex harnesses

The LCDuino-1 needs to be connected to the backplane board via one of the following two options:
  1. Use wire harnesses with Molex KK plugs.
  2. Use the ε31 bridge board (only applicable when you have the same enclosure, LCD screen location, backplane board mounting location and standoff height as AMB's reference γ3).
This section assumes option 1. For option 2, please see the ε31 documentation.

You need to make six 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 _Dn harnesses, which do not have pin numbers on the LCDuino-1 side. Just make sure you connect them so that the same _Dn numbers get connected on both ends.

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

  1. Cut the wires according to the table above. Use 22AWG hookup wire. 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.
  2. Each completed harness should then be plugged into its corresponding LCDuino-1 header.
  3. The _Dn harnesses connect to standard pin headers rather than Molex KK pin headers on the LCDuino-1, therefore they do not have polarity indication. Be mindful of the plug orientation. Also, the connector does not lock, but pin/receptacle spring resistance and cable tension should be enough to hold them in place.

Note: LJ3 is unused on the backplane board.

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 for each enclosure).
  2. Plug in the Molex KK harnesses from the LCDuino-1 and panel components to the corresponding Molex KK headers on the backplane board.
  3. Plug in the six Molex KK harnesses that connect the LCDuino-1 module to the backplane.
  4. Plug in the power/config pushbutton switch Molex KK harness to the backplane.

10. Build the power supply chassis

  1. Mount the σ11 and σ22 boards in the power supply chassis using 7/16" tall #4-40 standoffs ("STANDOFF4") and machine screws (12 places).
  2. Mount the power transformers and solid state relay into the power supply chassis, install the IEC power entry module and the power umbilical connector on the rear panel, and install the LED on the front panel.
  3. Wire up the box according to the schematic diagram shown in the Power supplies section. For the umbilical connector, use the same instructions and pin assignments as the one in the main DAC 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 panel connector solder joints.
  4. Double check your wiring for errors.
  5. Mount the front and rear panels on the chassis base.
  6. Install the fuse in the IEC module.

11. Build the power umbilical cable

  1. Using 22 AWG stranded hookup wires, make a 8-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 are using the Switchcraft/Conxall Mini-Con-X locking circular connector as listed in the Parts list, please refer to the cable assembly instructions. Make sure that there is good strain-relief for the wires in the connectors. A large heat-shrink tubing at the end of each cable connector is also recommended.
The basic γ3 platform is now done. Install the rubber feet on both enclosures. Check your work thoroughly, then proceed to the Initial check section to continue the bring-up of the system.

Main: γ3 Main | Prev: Parts list | Next: Initial check