True bypass loop in expression pedal

[Slugacannaduff]

Hello all.  Been lurkin' and searchin' for awhile... time to say hi and ask my question.

This might be a worn topic, but I tried searching and didn't find anything right on what I'm looking for.

I would like to have an expression pedal controlled true bypass loop. Pedal fully toe down, 100% wet (loop) signal, toe up 100% dry signal, and (obviously!) a mix in between.  It could have a switch to active the loop, or not.

I think this would be a tremendously fun tool -- lots of different effects in the loop could be brought in/out slowly, or blended with the dry to just the right degree.  For instance, a reverb pedal in the loop could be set to huge levels, and you could dial in the right amount with foot.  I also am wanting to pick up an octave down pedal, and that I think would be really cool to control in this way (plus I could just get an OC-2 and not have to worry about tone loss).

So... it seems strange to me that this isn't more of a common thing.  Seems like a simple idea, and (to me) seems like it would add a ton of flexibilty to one's rig.  Does this concept get kicked around here?

I've only found 2 commercial items.  One is made by a shop called Wounded Bear, and looks exactly like what I have in mind.  And Morley makes an FX Blender pedal that looks like the concept, although I haven't been able to tell much about how the switching works.

I have an old shell that I could use to make one... and in my simplistic mind (with rudimentary electronics knowledge)*, it seems like it would be pretty simple to wire up.  Like maybe as simple as a blender pot and a couple of jacks?  :sheepish questioning grin:

Thanks for any input.

* - I can solder, have done fair amount of guitar wiring, but never have never delved into effects or things more complicated than pots and capacitors!

[ppatchmods]

you could just use a volume pedal last is the looped chain to control the amount of effect looped. it would look like: loop send>tremolo>delay>volume>loop return

if that is not your goal, you can add another jack to the return and place an expression there. you  would have to wire it like so: loop return tip>exp jack tip>to bypass switch...that way you could still use it as a loop without the exp pedal. i think that will work ok. let us know and if you blow something up, forget my name....

[MikeH]

I'd do it with a simple mixer.  Active would be a much better way to go; basically you want something like a 'buff-n-blend' or a run off groove splitter blend built into an expression shell.

[Slugacannaduff]

I'd do it with a simple mixer.  Active would be a much better way to go; basically you want something like a 'buff-n-blend' or a run off groove splitter blend built into an expression shell.

Yes, I think that is what I am after.

Now for an embarassingly elementary question, why is active better?

[MikeH]

Any passive mixing device is going to have issues with signal loss, "tone sucking" etc etc.  An active mixer will keep your signal strong and keep it from sounding 'dull'.

[valdiorn]

if you want true bypass that switches the effect completely off when you put the expression pedal to zero you'll need to use a relay (buffering the signal or somehow having it connected at all =/= true bypass). But then again, true bypass is highly overrated as a good buffer has the potential to have input resistance up of the 10 megaohm degree (you could daisy chain 20 pedals and not feel the effects).

I'd start by buffering the input signal. From there, connect the buffer to one end of your mixer and also connect it to the pedal input (of the effect you want to "control"). Connect the output of the effect pedal to the other end of the mixer.

The Mixer itself could be as simple as a potentiometer (wah-wah style). Some expression pedals are very simple and only have a pot inside so you could just connect it straight. Others have a strangely tapered sweep and are not suitable for this. Personally I'd use OTAs (operational transconduction amplifiers) to do this, but that's just me. Another possibility would be vactrols (light-dependent resistor + LED). google around, let us know if you build something