AudioFilter

Audio Multi Filter

Drawings and PCB (c) 2026 Andrew Martin, acramonics

This is an implementation of Jake Rothman's Audio Multi Filter described in Practical Electronics, May 2026.

This circuit provides High-Pass, Low-Pass, Band-Pass, Notch and All-Pass filters on a single circuit by combining combinations of High-Pass and Low-Pass outputs.

In addition to the hardware on the board, my design requires:

• a 3P6T rotary switch,
• a DPDT (or DPST) toggle switch,
• a 10K anti-log pot,
• a dual 100K anti-log pot.

Power Supply

The design includes power smoothing, but will need a dual rail power supply providing somewhere between +/-12V and +/-18V.

Hardware

3P6T rotary switch

The classical wafer switches are extremely expensive from UK suppliers, typically #30.00 upwards per wafer! However, I have found them at a very reasonable price (~#4.00) from AliExpress.

You could also use a 3P5T switch and replace the 1st straight through position ('Thru') with another toggle switch.

For a stereo version, either build two boards, or if you want the same output on both channels, you could use a 6P6T switch (if you can find one), or a 6P5T switch (which I have seen on AliExpress at ~#5.00) and a toggle switch to replace the Thru position.