Summer and Fall on the Breadboard

This week I ran across an email from July 30, telling Drew and Cory I’d started messing with a feedback loop circuit on my breadboard.  It’s taken until this weekend to get it soldered up.

Testing, from about a week ago
Testing, from about a week ago

Feedback loops can be simple and fun, but simple ones have a lot of limitations. Two big ones are that many pedals do nothing in them (because the pedals flip the signal’s polarity, so feeding them back just results in a quieter sound due to phase cancellation), and that they can get excruciatingly loud, fast, if the rest of your signal chain has enough headroom for it (like if your amp is running pretty clean).

Here’s a pretty straightforward feedback loop designed by Beavis Audio

I fixed those issues with a polarity inverter and limiting/hard clipping in the feedback loop.  I also added expression via treadle control of the feedback amount, and two modes for the loop: always-on (regardless of feedback on or off) and only-on-when-the-feedback-is-also-on.  (Mode names need work.)

Most pedals have one input, one output, and the circuit itself in a sort of loop within the pedal.  A feedback loop effectively has three inputs (main input, loop return, feedback circuit output) and three outputs (main output, loop send, feedback circuit input).  I hadn’t thought about all of that when I jumped into designing one, and all those signals crashing into each other results in a lot of parallel impedances and switching headaches I didn’t anticipate.  Given the challenges, I’m pretty happy with the performance of the design.

It’s not quite finished yet because I seem to have burned one of the footswitch connections, so I’m waiting for a replacement part to arrive.  I’ll do a video once it’s done.

That’s a lot of tech talk, but it’s pretty intuitive once it’s plugged in, I think; when you roll your heel back, you get more feedback.  It’s super-fun to play and useful for anything from freak-out noise to gentle washes of added delay or reverb.