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The ε27 volume control potentiometer mounting board


  • May 2008: ε27 blank circuit boards are available.


ε27 ("epsilon 27") is a volume control mounting board for the Alps RK27 series ("blue velvet") stereo (2-gang) potentiometers (also compatible with the Noble AP25 series) for volume control use. It is recommended for DIY pre-amplifier and headphone amplifier projects, where the potentiometer is not soldered directly to the amplifier board. The use of this board avoids the messy task of soldering wires to the thin potentiometer pins, and makes the wiring look neater and more attractive. Clearly-labeled input and output pads virtually eliminate the chance of wiring errors. The use of Molex connectors allow the potentiometer assembly to be easily removed, enhancing serviceability.

Note: This board should be used only for 2-channel stereo volume control purpose only. It should not be used for non-volume applications, such as balance control, tone control, or other applications. In particular, the ε27 is not suitable for bass boost control on the headphone amplifier.

The following is a photo of the top and bottom sides of the ε27 circuit board, and a photo of an assembled board.

Parts list

The following is the parts list to populate the ε27 board.

QtyPartdescriptionRecommended part(s)
1-Volume control potentiometer, stereo (Alps RK27112A or Noble AP25)AMB audio shop
2J1, J2Molex KK 254 4P header 22-23-2041Mouser 538-22-23-2041, Digi-Key WM4202-ND
2-Molex KK 254 4P crimp housing 22-01-3047Mouser 538-22-01-3047, Digi-Key WM2002-ND
8-Molex KK 254 crimp terminal 08-50-0114Mouser 538-08-50-0114, Digi-Key WM1114-ND

Note: The Molex headers and crimp terminals specified in the list above are tin-plated. Gold plated versions are also available under separate part numbers for a higher price.

The circuit board

The ε27 board is made of high quality FR-4 glass epoxy, single copper layer with top-side silkscreen and bottom-side soldermask. The dimensions of the board is 2.0" x 1.0" (50.8mm x 25.4mm). The thickness of the board is 0.062" (1.58mm). There are two screw holes which can optionally be used with a bracket to further secure the potentiometer/ε27 assembly. The following image shows the board layout:

Clean the bottom (copper) sides of the blank ε27 board with paper towel and isopropyl alcohol or electronics flux remover before soldering any parts on it.

Where to get help

Please visit AMB DIY audio forum for support.
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