Before you startYou can print out an image of the circuit board silkscreen layer (PNG format | PDF format), to use as a guide for installing components.While you look at the board layout, please also take the time to look at the schematic diagram and associate each part with their location in the circuit. While this is not normally required to build a working amplifier, 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. Circuit board assembly instructionsIf you're building the 3-channel "active ground" configuration, please note that some parts have different values on the ground channel. See the Parts list section for details.If you use screw-mount onboard MOSFET heatsinks, they must be tapped for imperial #4-40 or metric M3 machine screws, or you may use self-tapping screws in order to secure them to the board. The screw holes for the heatsinks on the board will need to be enlarged slightly. You can either use the same tap or a drill bit for this purpose. 
Since each MOSFET's mounting tab is internally connected to the drain pin, it will carry live voltages and should not be shorted to the chassis, ground or other parts of the circuit. If your onboard heatsinks will be in close proximity to the top metal cover when the board is installed in your chassis case, then you should mount the MOSFETs to the heatsinks using TO-220 mounting kits. If you use offboard heatsinks, then TO-220 mounting kits are also required. Otherwise, you may mount the MOSFETs directly to the heatsinks using #4-40 or M3 machine screws and hex nuts, after applying some heatsink thermal paste to the mating surfaces. The MOSFETs are vulnerable to electrostatic discharge damage when you are handling them, so keep their pins plugged into anti-static foam while working with them until you're ready to solder them to the board. Set the heatsinks pre-mounted with the MOSFETs aside for now. R30 and R31 are marked as 0Ω. You should simply use a wire jumper in these positions. Clipped resistor leads are fine for this purpose. Please note that the Q1-Q4 silkscreen outline on β22 board layout were drawn for the Linear Systems LSK389B dual N-channel and the LSJ109B dual P-channel JFETs. Since the latter is not yet available, you must use matched pairs of Toshiba 2SK170BL N-channel and 2SJ74BL P-channel single JFETs for these positions. The correct mounting orientation for these single JFETs are shown in the following photos. Please do not mount them as marked on the silkscreen!
The board version number is silkscreened on the top side of the board, beneath the β22 logo. If in doubt, please check the datasheets for the 2SK170 and 2SJ74 against the G, D and S markings on the board. Note: Despite the PCB layout, do not use the LSK389B and LSJ109B JFETs (even if the latter becomes available) until AMB has qualified them for use on the β22 amplifier. The CRD positions (CR1-CR8) have pads to accommodate several case styles. See the illustrations below. 
Solder the components to the board, starting with the lowest profile parts. This means the resistors and zener diode. Then solder the small capacitors, CRDs, small transistors, trimpots, followed by the larger capacitors. Lastly, install the MOSFETs and secure the heatsinks to the board, then solder their pins. Since the β22 circuit board holes are plated through, 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. Pay attention to the polarity of electrolytic capacitors, diodes, CRDs, transistors as well as the orientation of the trimpots. Be sure not to mix up the N-channel and P-channel MOSFETs! Clean up the solder flux residue from the board with isopropyl alcohol (or electronics flux remover) and a brush. 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. As a minimum, you should verify that the V+ and V- DC inputs are not shorted to ground, or to each other, and that the output pad isn't shorted to ground. Correct any mistakes before proceeding to the next phase. Repeat the above steps for all other β22 boards in your amplifier. Next, proceed to the Wiring & ground section for details about wiring up the connections to the board. Main: β22 Main | Prev: Device matching | Next: Wiring & ground |
