feedback loop/volume pedal

[smccusker]

For one reason or another I've had to give up building for a few months, but now I'm picking up where I left off. I had the idea to put an expression pedal on a feedback loop so I had easier control over the crazyness while I was playing (playing a few lines or whatever and then just diving into all kinds of crazy). So the more I thought about it, I wondered if I could add a switch of some kind that would let me change between the feedback loop and just a plain volume control when the pedal was in the on position.

Does anyone have any ideas about wiring this one up? On one hand I can't imagine that it would be too tricky, but on the other I've made that mistake before.

[chunks717]

this should help. there is a wiring diagram about half way down, or a full how to if needed
http://experimentalistsanonymous.com/board/viewtopic.php?t=134[/b]

[smccusker]

I've  had a bit of a think about this, so roughly it should go

Code Select Expand


(input)------(Volume)-----(switch)----(output)
             |            |      
(return)---               ---------(send)


Colin mentioned something about putting buffers in the pedal, to give it alittle more control, and since I was going to make this pedal active anyway (having a LED+LDR combo for the volume control), I'm wondering if it's just as simple as tacking two of these after the input and before the output?

Anyone shed any light on it? Am i making this unncessisarily complex?

[smccusker]

I'm sorry about the messyness of this schem, but it was a bit of a rush job. I've had a complete mental blank as to how to draw DPDT switches, so its wrong, but thats what i want to use to bypass the feedback loop.

So a quick runthrough,
A 3PDT switch controls the bypass of the entire effect. When it is engaged, the signal runs through the buffer (from GGG, with the output cap removed), and if the DPDT switch is bypassed, through the optocoupled LDR, which controls the volume of the signal, and finally through the output buffer (again with all the input buisness, like the pulldown resistor and the led, taken out).

If the DPDT switch is on, then the signal goes out to the send, and back in the return, with the LDR now controlling the ammount of feedback, and the original signal just running straight through to the output buffer.

Like i said, its messy, a bit confusing, and the DPDT switch is drawn incorrectly, but can anyone see why this wouldn't work?
Im not too sure whats happning witht he buffers, i just removed any components i thought might be unnessisary, but im not 100 sure what im doing.

I might pop down and get some breadboard tomorow and try and get something happning with this, but any feedback (pardon the pun) would be greatly appreciated, since im stabbing in the dark here.

[petemoore]

I don't see where 'it's' connected, I assuming the LED is going to need a min R set resistor, and that your tapping the send jack from after C2, and the return jack from before C1.
 I also think you may be wanting to set the minimum FB loop resistance higher than the LDR min.
 Other than that it looks like a basic plan.
 Little is known by me as I've read little on the subject.
 I think I'd make a daughter board of the LED/LDR arrangement with enough room to diddle with parts on both sides beyond hooking stuff to the R/S wire ends.
 Then I'd build a circuit with wire sticking up enough all over it that my small alliclamps can hook right on the inputs and outputs or wherever pretty easy.
 I might just start with a larger pot or pot/resistor instead of the LDR to see  'and whats what and where' as far as resistances are concerned, maybe try FBing the second half.
 IIRC it took Some diddling with.
 The LDR idea is interesting, if it's in a FB loop though, the amps'll probbly be topping out to whatever is limiting them when the FB loop is on, making it hard to not keep the LED lit brightly.
 LISaid... haven't messed with these but once [OT]. Might work good or provide a different approach using muting to dim the LED.

[petemoore]

You could run a buffer and a second channel for the LED, separating it from the FB loop signal path.