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I keep meaning to get around to mine, although my arduino is built on vero with parts from Tayda...

My plan was to try to do a guitar tuner.  I think there's a project or two out there for that.

I just picked up some blue and first spray went on great.

Unfortunately I set my toaster oven way too high.  As a datapoint, this paint is flammable at 350F.

Wicked.  Unfortunately I'll have to take a pause in the fun since I need to grab a new tip for my desoldering iron.  The last tip actually cracked and crumbled on me which sucks (or doesn't suck, or sucks - but in all the wrong places).

All I've got on hand is one of those rubber bulb suckers which just doesn't ever seem to cut it with fabbed boards.

I'll post up once I've tried the workaround.  Until then, thanks for the help guys, and Merry Christmas

This look right?

I was hinting the design needs a reference buffer.

You can hack in a transistor based one if you don't mind it being a bit messy?

Nope, don't mind at all.  There's plenty of room lower in the box for me to stick an vero or perf voltage buffer.  Have one in mind?

I wonder how much current it draws...

I'm reading 20.4mA on, 18.8mA off.

Can you describe the pop? Is it high-pitched or a thump?

More of a thump than a click.

So I connected Vb to the tails through the DPDT when in the off position, but it seems to pull my Vb down to 3.58 (from 4.22).  Not as much of a jump/drop in voltage between its engaged/bypassed state as there was before, but the pop is still present.

I'm happy to true bypass this which would solve the issue, but if we want to troubleshoot further I'm game.

Try just removing R41. (Leave the Vb connection.)

Done, but no change.  Slight correction, the Vb is dropping to 3.88 when the pedal is not engaged (instead of my previously stated 3.48)

Clarification: I don't think it makes any difference, but for full disclosure my Vb connection that I've got running down to the footswitch is coming straight off pin 5 of that opamp (soldered to the underside of that IC socket).  I don't think it matters where I'm pulling the Vb from, but then again I don't know what I don't know...

I use a Black '65 clone for exactly this.  No real tube in there though.  Also no foot massage, but if you leave the cut resistor leads in the carpet it could be a form of acupuncture (without the "acu").

I don't know about where you are, but here in Ottawa loopers show up on the used market (kijiji and the likes) fairly often for cheap.  I grabbed a RC20xl for $120 if I remember right. 

So I connected Vb to the tails through the DPDT when in the off position, but it seems to pull my Vb down to 3.58 (from 4.22).  Not as much of a jump/drop in voltage between its engaged/bypassed state as there was before, but the pop is still present.

I'm happy to true bypass this which would solve the issue, but if we want to troubleshoot further I'm game.

Awesome, I've started Jon's workaround but now my kids are up and causing havoc so my soldering iron is going back in its holster for now.  I'll update tonight when I fire it back up

No worries at all Brian, I enjoy troubleshooting.  If you need any other measurements just let me know!

Measure the voltage on both lugs of your tails switch when on and off. If there's a difference in DC, that's the source of your click. (Pin 7 might be slightly higher than pin 3 ... also, when they're connected, R40 and R41 are in parallel which might be making the DC on BOTH change. I'm not seeing a good passive solution if that's the case.) If the voltage is the same and/or doesn't change, then it's most likely mechanical noise being picked up by the circuit, which is also kind of tough to do anything about.

Thanks Jon, I'm looking at:

Off:
Tails 4.04 / 1.27

On:
Tails 4.22 / 4.22

3V different! There's your problem. What's your Vb measure? Is it also 4.22? If so, we can use the other pole on your switch to make things better.

Vb (taken from the right side of R40) reads 4.20 off / 4.02 on.

Measure the voltage on both lugs of your tails switch when on and off. If there's a difference in DC, that's the source of your click. (Pin 7 might be slightly higher than pin 3 ... also, when they're connected, R40 and R41 are in parallel which might be making the DC on BOTH change. I'm not seeing a good passive solution if that's the case.) If the voltage is the same and/or doesn't change, then it's most likely mechanical noise being picked up by the circuit, which is also kind of tough to do anything about.

Thanks Jon, I'm looking at:

Off:
Tails 4.04 / 1.27

On:
Tails 4.22 / 4.22

Absolutely.  Working on finding some knobs tonight and will try to get some recording done tomorrow.