This simple module provides a true bypass function to isolate the connected effect unit from the main signal chain. Connect several of these in series to switch many effect units in or out of the signal chain.This module is used in the AXT-1250 microphone preamplifier to bypass inline effects (eq/compression etc) connected to the preamp.

The bypass module connection topology can be seen in the connection diagram. It shows 4 modules wired in series to support 4 effects units in a mono signal chain. If stereo is required then two chains will be required.


Bypass connection diagram













A single 5VDC power rail is required, for the signal relays. This can be a small 5VDC plug pack power supply.

ABM-1 Circuit (pdf) ABM-1 BOM (pdf)
ABM-1 PCB (pdf) Connection Diagram (pdf)


The module has a 2 pin connector for a LED, which is on when the relays are not in bypass mode, indicating that the effect is in the signal chain. A 2 pin connector for the bypass control switch is wired simply so that the pin pair is shorted by the switch when the effect unit is to be inserted into the signal chain. When off, the unit defaults to bypass mode and the LED will be off.


ABM-1 Module Rear view ABM-1 Front view