The γ24 high performance DAC core

Before you start

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

You can print out an image of the circuit board silkscreen (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 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 γ24's use of surface-mount devices (SMD), 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
  • Multimeter with sharp probes
  • Oscilloscope capable of measuring at least 50MHz is highly recommended.

Circuit board assembly instructions

Important pre-assembly notes:
  • All parts should be mounted tight against the board. The axial lead ferrite beads do not need to be elevated like they are in the Mini³ amplifier.
  • 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:

    U5Texas Instruments SN74LVC1G00DBVC00_
    U9, U10Texas Instruments TPS79333DBVPHUI
    U11Texas Instruments TPS79318DBVPHHI
    Texas Instruments LP2985AIM5-1.8LAYA

    Note: The "_" character denotes a variance code or for the manufacturing facility and could vary.
Clean both sides of the blank γ24 board with paper towel and isopropyl alcohol or electronics flux remover, then solder the components to the board, beginning with the SMD components for maximum access. The following is the recommended order, starting on the top side of the board:
  1. TQFP-48 devices (U1)
  2. SSOP-28 devices (U2, U3)
  3. TSSOP-8 devices (U6)
  4. SOT23 devices (U5, U9, U10, U11)
  5. SOIC-8 devices (U8, U12, U13)
  6. SOP-20 devices (U4)
  7. Ferrite beads (L1-L6, if you are using SMD chip beads)
  8. Oscillator (X1)
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 dot marking next to its pin 1. For SOIC-8, the top edge of the package where pin 1 is located is usually beveled. That edge is represented as an extra white line on the board silkscreen. For the SOT23 package, pin 1 is at the lower left corner if you're viewing the top of the package, with the markings oriented for reading. The board's silkscreen is also marked accordingly.

For U6 (the CDCLVC1103PW), it may not be obvious which is pin 1. The following photo illustrates how it should be mounted:

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).

Repeat the above procedure for each of the SMD components.

Now proceed to mount and solder the though-hole parts, starting with the lowest profile parts and work up, in the following order (see details below):
  • Resistors (all)
  • Multilayer ceramic capacitors (all)
  • Ferrite beads (L1-L6, if using axial lead beads)
  • Reset supervisor (U7)
  • Electrolytic and organic polymer capacitors (all)
  • Board interface pin receptacles (Three 24P pieces, mount on the bottom of the board and solder on the top)
Since the γ24 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.

Before soldering the board interface pin receptacles, first plug them into their mating pin headers. The recommended orientation is pin headers on the DAC side and female receptacles on the γ24. Put the mated pins/receptacles assembly between the γ24 and main boards and work the solder pins into the holes on both boards. Do this for all three segments. Once they are all in, then solder them on each side to ensure good alignment.

Unplug the γ24 module from the main board, and clean up the solder flux residue on both sides of 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 after installation.

Install a jumper at JP1, between the 1 and 2 pads. You do not need to use an actual pin header and jumper shunt. Simply solder a cut-off resistor lead across these pads. Leave JP2, JP3 and JP4 open.

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.

Now the board assembly is complete, you could test the γ24 with the main board for functionality. If the main board is the γ3, use the instructions found at the γ3 website for initial sanity checking and testing.

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