The γ1 modular miniature DAC

Before you start

This section assumes that you have pre-drilled your front and rear panels (for the jacks, switch, etc.). If you haven't done so, see the boards & panels section for details and work on that first.

You can print out an image of the circuit board silkscreen layer (PNG format | PDF format), to use as a guide for installing components.

Do not remove the integrated circuits from their sealed packaging until you're 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 DAC, one of the opportunities 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 γ1's small size and close approximity of parts, as well as the surface-mount device (SMD) integrated circuits, you should have the following tools and supplies to help you work on the board and case:
  • 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 Hammond, or Box Enclosures case only)
  • Imperial #6-32 or metric M3.5 tap (optional, if not using stock screws)
  • Multimeter with sharp probes

Circuit board assembly instructions





Important pre-assembly notes:
  • Some parts are not to be populated in each configuration. Be sure to check the Parts list section and make sure you're installing only the needed parts for the configuration you're building.
  • If you're new at soldering surface-mount devices, please view the following video, an excellent tutorial.

    Surface Mount Soldering 101
    by Curious Inventor

  • The DAC board and USB board are supplied as a single PCB, but it's "grooved" on both sides down the middle. If you are using a Hammond 1455C80x series case, you should break the board into two along the groove. Place the groove line along the sharp edge of a table or something similar and bend to break it apart. After they are separated, there may be some glass fiber strands at the edge but you could just run the edge along a sandpaper a few times to remove them.
  • If you are using the Box Enclosures B2-080 series case, do not break the board apart. Rather, you should carefully sand off approximately 0.015" (0.4mm) on each side of the board to allow it to slide into the case slot. Test-fit the board in the case as you work to avoid sanding off too much material. Be sure to sand off an equal amount on each side, in order for the hole locations shown on the Board & panels section to line up correctly.
  • If you are using the Hammond 1455C80x enclosure, or if you are building a γ2 board to mate with the γ1, then the 9P pin header (SIP-9) should be carefully cut apart into a 3-pin segment and a 5-pin segment (with 1 pin leftover). The 3-pin and 5-pin pieces are to be used as J2U and J3U, respectively. For the γ1 full++ configuration in the Box Enclosures B2-080, the 9P pin header is unused.
  • If you are building a γ2 board to mate with the γ1, and your γ1 is the full (A), S/PDIF-only (E) or full++ (F) configuration, then the "leftover" pin from the supplied 9P pin header (SIP-9) should be installed in JP1D pin 2 (round pad), to plug in to the matching receptacle at γ2's J3.
  • The PCB-mount RCA jack has two square pegs at the bottom of the jack body, along the front edge. These pegs must be cut off before you solder the jack to the board, or it will not sit level on the board.
  • The resistor networks are polarized. Pin 1 is marked on the part with a "dot" marker. The board has a square pad for pin 1, and round pads for the other pins.
  • Depending on which model of transformer you choose for T1D and T1U, pin 1 should be oriented to one of the octagonal pads marked with a round dot.
  • For the various jumpers (JPxU or JPxD), if you don't plan to change the settings, there is no need to populate them with pin headers and jumper shunts. You may leave an "open" jumper completely unpopulated, and you can solder a piece of clipped resistor lead to make a "shorted" jumper. See "Jumper settings" below.
  • The U4D, U9D reset manager chips should be installed very close to the surface of the board, so that they will not interfere with any parts on the USB board when the two boards are mated together. Similarly, all other parts should be mounted tight against the board for proper clearance. (The ferrite beads do not need to be elevated like they are in the Mini³ amplifier)
  • Take care not to mix up the fiber optic receiver and transmitter modules. They look identical except for the shutter color: The TORX147PL is black and the TOTX147PL is grey. The opposite is true for the Sharp modules: The GP1FMV31RK0F has a grey shutter while the GP1FMV31TK0F is black.
  • Similarly, do not mix up the SN74AHC1G02DBVR and SN74AHC1G08DBVR logic chips, or any of the voltage regulators. The markings on these SOT23-5 devices are coded as follows:

    PartDescriptionMarking
    U8DTexas Instruments SN74AHC1G02DBVRA02_
    U2UTexas Instruments SN74AHC1G08DBVRA08_
    U5D, U3UTexas Instruments LP2985AIM5-3.3L0RA
    Texas Instruments TPS79333DBVRPHUI
    U6DTexas Instruments TPS793475DBVRPHJI
    Texas Instruments LP2985AIM5-4.5LA7A

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

Clean both sides of the blank γ1 board with paper towel and isopropyl alcohol or electronics flux remover, then solder the components to the board, beginning with all the SMD integrated circuits for maximum access.

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 is correct. Most chips have a dot marking next to its pin 1. The board's silkscreen is also marked accordingly.

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.

When done, your solder joints should look something like this:

0

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).

Repeat the above procedure for all the SMD integrated circuits. When you are done with all of them, use a Q-tip and isopropyl alcohol, or specialized electronics flux remover to clean off the flux.

Now mount and solder the rest of the parts, starting with the lowest profile parts and work up, in the following order (see details below):
  • Resistors
  • Miniature inductors
  • Multilayer ceramic capacitors
  • Ferrite beads
  • DC power jack
  • Crystal
  • Resistor networks
  • Switch
  • Transformer
  • Reset manager chips
  • Transistors
  • Film capacitors
  • Electrolytic capacitors
  • RCA jack
  • Optical receiver or transmitter module
  • 3.5mm stereo mini phone jack
  • Pin headers/receptacles
  • LED, if applicable
Since the γ1 circuit board holes are plated through, with the exception of the SMD integrated circuits, you only need to solder the parts from 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 resistor networks, electrolytic capacitors, transformer, reset managers and transistors. For electrolytic capacitors, the positive lead should be the longer one.

When soldering the DC power jack, RCA jack and 3.5mm stereo mini jack, you should heat the solder tabs and pads sufficiently to allow solder to fill the entire hole. Remove heat immediately and cool the joint by blowing air at it as soon as you achieve a good fill. This assures that the jacks will be mechanically-secure.

If you're installing LEDU, bend the LED leads 90°, paying attention to the polarity and which way it will face through the front panel. Adjust the mounting height so that it is aligned with the front panel hole and solder one pin first. Heat the pad and make further adjustments if necessary. Then, solder the other pin.

If you're using the Box Enclosures B2-080 casing, the USB and DAC sections of the board are not physically plugged into each other as they are in the Hammond 1455C80x, so they must be connected with wires. For the "full++" configuration (F), only 5 wires are needed (to connect the DATA, VCC, VBUS, and two GND lines): J2U pin 1 (VBUS) -> J4D pin 1
J2U pin 2 (VCC) -> J4D pin 2
J2U pin 3 (GND) -> J4D pin 3
J3U pin 1 (GND) -> J5D pin 1
J3U pin 5 (DATA) -> J5D pin 5

The following picture shows an example of a 5-wire ribbon cable hard-wired to the bottom side of the board and soldered at the top side pads.

NOTE: If you're building a γ2 board to be mated to the γ1, then you do not need to add any wires. The γ2 board will provide this connectivity.

Clean up the solder flux residue from the board with isopropyl alcohol (or electronics flux remover) and a brush. Using your diagonal cutter, trim all protruding pins, leads, solder tabs, etc., on the bottom side as close to the board as possible to prevent a short circuit to the case after installation.

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. Correct any mistakes before moving on to the next phase.

Jumper settings

Set up the jumpers according to the following table, based on your build configuration.

γ1 Configuration JP1D JP2D JP1U JP2U-1 JP2U-2 JP2U-3 Note
Full configuration (A) open see below short 1-2 open open open -
Lite configuration (B) closed see below short 2-3 short short short -
USB-to-S/PDIF converter (C) - - short 1-2 open open open DAC board not used
Also short J2U pins 1 and 2
USB-to-I²S converter (D) - - short 2-3 short short short DAC board not used
Also short J2U pins 1 and 2
S/PDIF DAC only (E) open see below - - - - USB board not used
Full++ configuration (F) open see below short 1-2 open open open -

NOTE: If you're building a γ2 board to be mated to the γ1, do not install pin headers and jumper shunt on JP1U. Solder a clipped resistor lead across the appropriate pads on JP1U instead (see table above). Otherwise the two boards will not fit properly.

All positions of JP2D should be left open unless U1D is not installed. It is recommended that you install U1D, unless you have a good reason to omit it. If U1D is not present, then you may use JP2D to "hard-wire" the power source, as follows.

5V power sourceJP2D
Auto-switch (U1D installed)open
External power onlyshort 1-2
USB power onlyshort 2-3

After circuit board assembly is complete, proceed to the initial check section to test the DAC before connecting to the computer USB port or any other component. When you are done with testing, continue to the section below for preparing and mounting the board in the case.

Preparing the case

This section assumes that you have already done the initial checks of your assembled board(s).

You may use the panel screws supplied with your Hammond or Box Enclosures case, but they aren't as attractive as socket cap screws. Also, the supplied screws are self-tapping, and are not designed to be removed and installed for many cycles. Eventually the screw threads would wear out.

For this reason imperial #6-32 or metric M3.5 flat-head socket cap screws are recommended. These screws should be at least 3/8" (9.5mm) long but no longer than 3/4" (19mm). Flat-head screws are recommended for the front panel to avoid possible interference with oversized connectors.

If you use the screws supplied with the case, installing and then removing the screws before the final assembly keeps you from getting pieces of aluminum all over the board.

If you use #6-32 or M3.5 screws, you must first tap the case to match. Taps for your portable electric drill or drill press could be purchased from a tools and hardware store.

If you're using the Hammond 1455C801 case (metal end panels), it is recommended that you mount the panels directly to the case without the plastic bezel rings. This eliminates a gap between the panel and the board, which may prevent the Toslink plug from fully seating in the optical input module.

If you have a black or blue anodized Hammond case, or the Box Enclosures case (all colors), it is recommended that you grind away some of the anodizing from the board slots, in order for the exposed ground plane strips on the boards to make contact with the case. This provides RFI shielding. You do not need to do this with Hammond's clear anodized version. Using the emery board or thin file, carefully grind along the board contact surfaces of the slots on each side, until you could see bare aluminum showing through. When you're done, clean the case of all metal dust and shavings.

Insert the boards into the slot. Be careful while doing this to prevent any part of the circuit from touching the case. Be sure that the solder joints on the bottom of the boards do not touch the case.

Use your multimeter to check the continuity between the sleeve ("circuit ground") of the inner 3.5mm stereo mini jack and a point where you could make good contact with the bare metal of the case (such as at the panel screw threads). You should get a low ohms reading. If not, remove the board, grind the slots further and repeat.

The board may be slightly loose in the front/back direction of a Box Enclosures B2-080 case. If this occurs, shim the end of the board (where it contact the rear panel) with a small piece of foam tape.

Install the front and rear panels and fasten the panel screws. You're now done.

Connect your digital source and connect the line out to your stereo preamp or headphone amp, and enjoy the music!




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