The ε12 muting / protect circuit

Wiring the ε12 to your amplifier

This section describes how to connect the ε12 v2 circuit to your amplifier.

Power supply

The ε12 must be powered from the amplifier's main power supply rails. Do not use a separate power supply for this circuit. If your amplifier has a separate power supply for each stereo channel, you should use two ε12 boards. Each one serves one channel only, and is powered the respective supply rails.

The following diagram illustrates the power supply connections to the ε12:

The switch shown in the diagram is optional, and is intended to be a second pole of the amplifier's main power switch (use a DPST ot DPDT switch for this purpose). This cuts off the power to the ε12 circuit and causes the relay to disengage at the same time you turn off the amplifier power. Without this switch, the turn-off muting ability of the ε12 depends on the turn-off characteristics of the amplifier. Many amplifiers have enough power supply rail capacitance such that after turn off, the voltage will drop slowly. If the voltage drops to below the relay open threshold before the amplifier produces any noise, then the turn-off muting function will work as intended. However, if the amplifier begins to emit noise prior to the relay open voltage threshold, or if the voltage drops too quickly (faster than the mechanical disengage time of the relay), then using the switch will make the relay open sooner, and help to prevent the turn-off noise from reaching the headphones.

Amplifiers split power supply, or single supply with virtual ground

Amplifiers that fall into this classification include the β22, M³, PPA, Kevin Gilmore dynalo and dynahi, Eaton, SDS Labs, Kumisa II & III and others. The minimum power supply voltage for this configuration is ±12V, and the maximum is ±30V.

Only the positive and negative supply rails from the amplifier should be connected to the ε12 board (to the V+ and V- pads, respectively). Do not connect the real or virtual ground of the amplifier to the ε12. This is because the ε12 contains its own virtual ground rail splitter, which is adjustable (see the Initial setup section for details).

For the M³ amplifier, the ε12's power is most conveniently tapped from the M³ board, at the location illustrated in the following diagram:


Amplifiers with single-supply, non-virtual ground

For single-supply amplifiers that do not employ a virtual ground splitter (i.e., Millett Hybrid, YAHA, Szekeres, etc.), the ε12 circuit provides turn-on/off delay muting functinality only. The minimum power supply voltage for this configuration is 12V, and the maximum is 30V.

For these amplifiers, the rail splitter and DC-offset sensing portion of the ε12 circuit should not be populated (See the Instructions section), and the power supply positive voltage should be connected to ε12's V+ pad and the power supply ground should be connected to the V- pad.


The ε12 should be inserted between the amplifier outputs and the headphone jack(s). The wiring scheme depends on the amplifier topology, as shown in the diagrams below. After you finish assembling the ε12 board, do not connect the amplifier output to the ε12 yet. That should be done as part of the Initial setup procedure.

2-channel (conventional passive ground) amplifier

These amplifiers use the power supply ground as a common reference for both the input and output. Examples of these are the 2-board β22, Kevin Gilmore dynalo and dynahi, Eaton, SDS Labs, Kumisa II & III, Millett Hybrid, YAHA, Szekeres and others.

3-channel (active output ground) amplifier

These amplifiers have an actively-driven output ground channel. Examples of these are the 3-board β22, M³ and PPA.

4-channel (balanced output, a.k.a. "bridged") amplifier

These amplifiers have a four-wire differential output, each wire is actively driven. Examples of these are balanced versions of the β22, M³, the Kevin Gilmore dynamid and dynamight.

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