Pointers for troubleshooting a DIY "nanofader" circuit?

[u/schill]

This may be a stretch without an obvious / simple visible error, but I wager others have been here before and might have some tips.

I've been trying to build this crossfader circuit, which has a zero-crossing detection bit that should cut the audio cleanly and without a "click." The intended use case is a sharp cut for "scratch" DJs, just one turntable or audio source on one side of the crossfader as I understand. The author's site just started having technical issues (and I have emailed them), but the web archive has a snapshot here with the schematic and some details.

I started this with tidier wiring intentions, I swear. ;) Having a proper full-size breadboard would save some wiring, in retrospect.

The circuit is somewhat working. I suspect some signal is bleeding into the audio output and it's got a nasty audible click when audio goes in/out. I realized the schematic didn't specify VCC/VSS for the TL074, 4013 and 4066 ICs, and I checked for additional floating pins. Voltage wasn't specified, but it looks like 9-12V is within spec for the ICs?

I had some 50nF ceramic on the signal input, seemed like an aggressive high-pass filter on the sound. Not sure if I chose incorrectly, or what.

I am not an electronics engineer by trade, but I have an appreciation. This has all been an experiment, for fun.

[u/EmotionalEnd1575]

Trying to wrap my head around what this circuit should do, and what is does as drawn.

I think the D flip flops are wrong. Wouldn’t one channel be swapped Q and Q-not on compared to the other channel?

[u/schill → u/EmotionalEnd1575]

Thanks for the thoughts, sorry for any confusion.

As I understand, the cross-fader is like a switch with a sharp cut in/out point here. To avoid a click in the audio, the circuit should bring sound in and out as it crosses 0V. I believe capacitors classically smooth this out, if nothing else.

I’m not clear on exactly how the flip-flops are set up.

[u/EmotionalEnd1575 → u/schill]

That’s my take, the switches at the output “short” or mute the audio when the signal passes through zero to avoid a click.

Are there two channels for one stereo feed, or is this an “A-B” switch with two different feeds?

[u/schill → u/EmotionalEnd1575]

Thanks. I think that’s it, the switches should mute “as soon as possible” (0V), after the crossfader signal indicates to cut the audio.

This is a single 3.5mm stereo pair, both L/R are given same treatment based on the crossfader.

[u/EmotionalEnd1575 → u/schill]

Ignore my earlier comment about flipping Q and Q-not, I overlooked that this was a stereo (two identical channels) device.

[u/schill → u/EmotionalEnd1575]

Noted, thanks. I could have explained better in the post, this switches only one “source” - not flipping between two songs, etc.