True Bypass Looper with Send Control?

[test4echo]

Hey gang, I'm putting together one of those Beavis Audio True Bypass Loops and I was wondering how I would be able to add a send signal control pot that lets me control how much dry signal I'm sending to the feedback loop. Also, what ohm pot should i use for it? And what kind of switch?

Here's the schematic:


Thanks!

~first post~

[JohnForeman]

Have you checked this design?
http://www.guitarpcb.com/apps/webstore/products/show/3456364

[JohnForeman]

On the same page that has the layout you posted there is also another layou that includes a blend pot of the return signal. That may get you what you want
http://www.beavisaudio.com/projects/Looper-Switcher/index.htm

[ashcat_lt]

There's no feedback in the OP. 

Is there some important reason you need to attenuate the send?  Like you've got something in the loop which wants a smaller signal?  Or do you just want the loop to be quieter so it balances better with the bypass?  The attenuator on the return is probably better in most situations.

[test4echo]

Is there some important reason you need to attenuate the send?  Like you've got something in the loop which wants a smaller signal?  Or do you just want the loop to be quieter so it balances better with the bypass?  The attenuator on the return is probably better in most situations.

On the same page that has the layout you posted there is also another layou that includes a blend pot of the return signal. That may get you what you want
http://www.beavisaudio.com/projects/Looper-Switcher/index.htm

Basically cause I've noticed different pedals react differently to different levels of feedback so it would be nice to control how much signal it's getting. Also, I've seen that other Beavis schematic but again I'm wondering how to install a sort of PRE fader, unlike the Beavis schematic where the return has a POST fader of sorts.

I just found this which is based off of one of the Beavis schematics and it's basically what I'm getting at

[ashcat_lt]

Now that one has feedback.  Note that it does not ever bypass the loop, though.  The switch connects the feedback path, but the signal always goes through the pedals in the loop...except for the part of the signal which takes the feedback path to "get around" the pedals.  Yes, as you turn up the feedback you get more and more dry signal mixed in.  On top of that, whatever is plugged into the input will see a lower and lower impedance until at max feedback it sees the (probably extremely low) impedance of the output of whatever is in the loop as its load.  You can get around that by putting a buffer in front of the looper. 

I'm not trying to say that this is not an effective scheme, I'm just not convinced that it's what you want.

[test4echo]

ashcat_lt thank you so much for your reply. How could I make it true bypass?

[ashcat_lt]

ashcat_lt thank you so much for your reply. How could I make it true bypass?

Keep looking?  I've seen versions of this thing with a switch to bypass the loop and a second to enable the feedback.  In mine, I just cut the track on the pot at the minimum feedback end so that the switch is the TB for the loop and to disengage feedback I just turn the knob all the way down.  None of this changes the fact that when the loop is selected, the feedback knob also acts as a clean blend.  There have been threads about how to get around that, and I'm sure there's a scheme around that does, but it requires active circuitry.