A-127BOM Breakout Module

The module is no longer in production.

The A-127 BOM is an extension for the A-127 Triple Resonance Filter. It supplements the module with individual inputs for each of the three filters, as well as separate outputs (per filter) for bandpass, highpass, lowpass and notch. The original A-127, on the other hand, only offered a common input for all three filters connected in parallel, as well as individual outputs for the three filters – these only in bandpass mode.

Honestly: In order to tease out the amount of functionality from the original A-127, you had to invest many hours as a “hobby solderer” (both in research into the possibilities and required soldering points as well as for the complex realization). Not to mention the optics of the often rather “hand-carved” looking result. Basically, the BOM turns the A-127 into three completely independent multimode filters. And that is quite a practical matter.

User interface

In the first production series, the labels on the “HP” and “BP” outputs for high-pass and band-pass filters were reversed. This has been corrected in the current production (as shown in the figure).

First production series until about 2015.

Inputs (3 times, separately for each integrated filter of the A-127):

  1. Single In: Audio input for the filter.

Outputs (3 times, separately for each integrated filter of the A-127):

  1. LP: Audio output for lowpass filter mode.
  2. BP: Audio output for bandpass filter mode.
  3. HP: Audio output for highpass filter mode.
  4. N: Audio output for notch filter (bandstop) mode.

All outputs are available for each of the 3 filters.


  1. Level: Attenuator for the “Single In” audio input.

A-127 required

Actually, this is self-evident with a “breakout module”: Without the underlying A-127 Triple Resonance Filter, the Breakout Module is of course completely useless.

Connection wanted

Unfortunately, there is a small drop of bitterness with the A-127 BOM. Unfortunately, the connection is only really “simple” on a newer A-127, which also has the corresponding socket for the ribbon cable of the A-127 BOM. You can recognize it on the circuit board by the imprint “Version 4”. With older versions of the A-127, four solder points between the filter and the breakout module must be connected manually. This is significantly less effort than with any self-build attempt, but you should have had a soldering iron in your hand at least once. At the right end, hopefully.

On the other hand, this is also useful in some cases, because the first edition of the A-127 BOM had an incorrect imprint on the front panel: HP and BP were swapped on all three filters! If you now have to solder yourself, then you can of course also solder the accesses to HP and BP correctly, so that the front panel is correct again.

Technical specifications

Width8 HP
Depth50 mm
Power requirements20 mA (+12V) / -20 mA (-12V)