Wiring and groundAfter you finish assembling the circuit board, it's time to work on the chassis case. When ready, mount the CK²III circuit board into the case. If you are using a Hammond 1455Q series case, the board will simply slide into the slots within the case. You can choose which set of slots to use, as long as no part will interfere with the top cover. You may secure the board using an appropriately-sized metal standoff through the star-ground "hole". Then, mount the input and output jacks, volume control potentiometer, IEC power entry module and power indicator LED.Wire up the IEC power entry module to the power transformer primary leads. If your IEC module has no built-in power switch, you may want to add an external switch (see below). The recommended Amveco toroidal transformer (and many others too) have dual secondaries to support various world AC mains voltages. For operation in countries with 120V mains, wire the two primaries in parallel. For 240V mains, wire them in series. See your transformer documentation for information. Before connecting the transformer secondary leads to the board, use your multimeter and check the resistance between each of the two 15V AC pads. There should not be any short circuits. Connect the transformer secondary leads, audio input/output jacks, volume control potentiometer, and power indicator LED according to the diagram below. Each signal and ground wiring pair should be twisted tightly together to improve its noise-rejection properties. The audio input jacks and headphone jack should be isolated from the case. The IEC power entry module's AC earth connection should be tied to the case if it's metal. If your amplifier chassis is non-conductive (e.g., plastic), then you should connect a short length of wire to the volume control potentiometer body and connect it to the star ground point on the board. For the Alps blue velvet potentiometer, you can simply loosen one of its screws, wrap the wire around it and re-tighten. On the circuit board side, you can use a ring terminal and screw it down. See below for the wiring diagram. Note that the volume control potentimeter connections are shown with the pins pointing "up". The green area in the illustration containing the power transformer and the IEC power entry module may be in the same case as the amplifier, or located in a separate box to minimize magnetic interference. For the latter solution, a 4-conductor umbilical wire and 4-contact connectors (such as mini-DIN style) can be used to link the two boxes together. 
Note that the digram assumes that the IEC power entry module contains a power switch. If not, a separate switch can be wired in. It is recommended that the switch be mounted to the rear panel so that wiring containing AC mains voltage will not need to be routed to the front panel near the volume control potentiometer where low level signals are present. Note also that for a single-enclosure solution (where the power transformer and IEC power entry module are located in the same case as the amplifier board), this wiring scheme ties the amplifier's signal ground directly to AC earth. While this is a common practice, it does present a potential ground loop problem if the audio source or another component in the chain also has its signal ground connected to the AC earth. You would have two ground paths of potentially differing potentials, one through the interconnect cables, and another through AC earth ground. To solve this problem, instead of connecting the CK²III board's star-ground to the chassis using a metal standoff, isolate it using a plastic standoff instead. Then, connect the star ground to the chassis through a ground loop breaker, which consists of a 10Ω 5W wirewound resistor in parallel with a 0.1µF film capacitor rated at least 250VAC. For safety this capacitor should be rated for class X or Y (good for across-the-line use) with flame retardant casing. Mount the resistor and capacitor in a secure manner so that it will not come loose and come into contact with other circuitry. A good way to do this is to use a terminal strip. Main: CK²III Main | Prev: Instructions | Next: Initial setup |
