The ε12 Muting / Protect Circuit

Amplifiers with split power supply, or single supply with virtual ground

Amplifiers that fall into this category include the M³, PPA, Pimeta, Gilmore dynalo and dynahi, SOHA, Eaton, SDS Labs, Kumisa II & III, Meier, Pawliw, Simpson and Balkishan. The ε12 provides muting delay and DC offset protection functionality for these amplifiers. All parts of the ε12 circuit board should be populated. The power supply voltage to the ε12 is ±12V to ±30V in this configuration. TO-92 clip-on heatsinks should be used on Q1 and Q2 if the supply voltage is greater than ±18V.

Amplifiers with a single supply, non virtual ground

Amplifiers in this category include the Millett Hybrid, YAHA and Szekeres. The ε12 provides muting delay functionality only. No DC offset protection is provided, but these amplifiers have an output coupling capacitor that blocks DC. The rail splitter and DC offset sensing portions of the ε12 circuit should be omitted, and a some other modifications should be applied as follows:
  • Do not populate the following parts:
    U1, U2, R2 through R10, VR1, Q2 through Q4, C4 through C6, D3, D4
  • Use a 12V zener diode (1N5242B) for D1
  • Install a wire jumper in place of R2
  • Install a wire jumper across the C-E pads of Q2
  • Install a wire jumper in place of C4
The power supply voltage to the ε12 is 12V to 30V in this configuration. A TO-92 clip-on heatsink should be used on Q1 if the supply voltage is greater than 18V.

Circuit board assembly instructions

Solder the components to the board, starting with the lowest profile parts. This means the resistors, opamp sockets, and diodes. Then solder the small capacitors, transistors, followed by the trimpot, large capacitors, relay, and connector header pins.

Since the ε12 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, transistors, the opamp sockets, as well as the orientation of the trimpots. For the tantalum capacitors, be mindful of the polarity.

The V+/V- DC power pads and the audio input/output pads accept 0.100" headers. These allow easy disconnection from the board using Molex plugs. You may also simply solder wires directly into the pads. The next section describes the wiring considerations.

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. Correct any mistakes before proceeding to the next phase.

Next, proceed to the Wiring section for details about wiring up the connections to the board.

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