Active effects loop with tails, feedback loop and stuff

[slacker]

Here's something I've been working on for a few days, started as an idea in this thread, but I thought It deserved one of its own.

Schematic's here, i won't link it as a picture because it's a bit big.
http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/album170/tailsloop_001.jpg.html?g2_imageViewsIndex=1

It's an active effect loop, switchable between having delay tails (assuming you're using a delay in the loop) or "hard" bypass. It's also got a switchable feedback loop that can provide in or out of phase feedback to the pedal in the loop. This is mostly so that if the pedal in the loop inverts the phase you can still give it in phase feedback, also lets you try out of phase feedback which may or may not be interesting. Sticking the feedback pot in the middle gives no feedback and turning it left or right give in or out of phase feedback.

Switch A is a latching DPDT stomp. and switch B is supposed to be momentary. Switch A switches between dry and the loop. Switch B does a couple of things, if switch A  is set to the loop it activates the feedback, if switch A is set to dry then it engages the loop and activates the feedback. If you set the feedback pot to zero then it just allows you turn on the loop momentarily.

It's still a work in progress so if anyone got any ideas on improving it or on adding more features let me know. I'm thinking a tone control for the feedback might be nice.

[ashcat_lt]

That is pretty cool!  Any reason at all this can't be a quad opamp like lm324? 

Stupid question:  If we don't need that momentary switch and always want tails, would it be wired in the position shown, or the other?

[slacker]

Thanks.

Yeah the way it is drawn shows the loop engaged in tails mode, so if that's all you want just wire it as shown. You also don't need the two 10k resistors after the return, just go straight to the 10n capacitor.

If you want to use a quad opamp a TL074 would be a good choice, LM324s are not great for audio.

[ashcat_lt]

Cool, thanks.

But now you've got me worried.  A used an LM324 in a pedal for my bass player and we both think it sounds fine, so i ordered a few more from mouser, but...  I saw RG say something like "Ug" in re: LM324 the other day.  What's wrong with 'em?  And (I could google it...) is the pinout the same as the 074?  I always socket my opamps, so I could build with what I've got for now and get the better ones next time I need something from mouser.

[slacker]

I think one of the problems with LM324s is that they can suffer from cross over distortion, which doesn't sound very nice. Depending on what you're using it for this might not be a problem though, or it might actually sound good.

The pinout is the same as for a TL074, so you could try it with an LM324 and if you don't like it just swap the chip.

[Alien8]

Pulling up an old thread to say thanks!  I built one using the schematic with a few tweaks and it works beautifully.  I didn't add anything fancy for my first crack at it, and the bipolar feedback idea is certainly useful.