Boooooring... but SUPER useful utility circuit: an active buffer+signal mute with optional boost and dedicated tuner out

 First post in a few months since I've been busy building a "DAW-less" rig to make sequenced/electronic music with. I'm also deliberately taking time off from soldering, since I use leaded solder and probably have more of the stuff in my blood than I should after 4+ years of almost daily circuit building.

BUT since I am currently having to build quite a few of these things (seven in total) to properly mute all the channel strips on my mixer (some of them pop when I feed them too hot of a bass signal), I thought I might share my layout.

This is, essentially, a standalone active mute switch with an optional dedicated tuner output. I adapted it from a GuitarPCB design, and if you fancy something neater than stripboard, you can buy kits from Müsikding or PCBs directly from GuitarPCB.

This drawing includes some suggested modifications from GuitarPCB - most notably, the gain boost pot - which can be omitted and replaced with a simple jumper for just slightly above unity. The 470nF capacitors are my preferred values for maintaining low end integrity. The original build doc calls for 220nF caps in those four positions.

Any dual op amp will do - TL072's work fine. I've been using NE5532's in order to keep it clean and safely allow for the jump to an 18v supply (just use caps that are rated to a minimum 35 volts!).

You can also use a 3PDT stomp switch, of course - but only two columns of lugs are necessary - which is why the drawing is for a DPDT stomp.

The original build doc calls for a common-anode, bi-color LED but I've no experience with those, other than I have read that they can be kind of on the dim side. I've got horrible peripheral vision and need my LEDs to be visible from space, so I went with two standard 5mm diodes for separate active and mute indicators.

Also - if you don't want the dedicated, always-on, tuner pedal out - you can just omit the polarized 2u2 capacitor, as well as the cut that is just to the right of the cathode of that cap. One less 1/4" jack to solder!

The original goal of the designer of this circuit was to allow you to still use your tuner while totally removing it from your signal path. While replacing it with a decent, modifiable buffer/signal driver. As it is designed, the tuner is always on and pitch detecting - you just choose whether or not you want your signal active or muted.

It's a pretty simple utility build that works great, with NO popping or signal bleed. It's definitely in the "I didn't realize how badly I needed one of these until I built it" category for me.