would this circuit work?

[Dimitree]

Hi everyone
I'd like to know if this simple circuit would work with no problems

I've designed it myself..I want a simple active feedback mixer.. I would use bipolar supply, so I guess I can remove any DC blocking cap, so no filters.. The first resistor should fix the impedance for the input buffer..but I believe I can remove the second 1M resistor on the output buffer..
I would put a delay and a pitchshifter in series on the send-return..that way on the output I would get no dry signal, just the first delay repeat (+ pitch), and this would mix back and pass again through it-self, so I would get another repeat (+ pitch on pitch) and so on.. The pot should attenuate the signal just like the feedback pot on delay circuits..
so my questions are:

1 - would the idea work?
2 - is the circuit right, or I need some more parts, modify something, remove something..?
3 - since I got half TL072 unused, where could I put it?
4 - will some part of dry signal pass through the bottom 10k, then through the pot and so to the output (I don't want dry signal on the output)?

many thanks
Dimitri

[Ripthorn]

I'm a bit out of practice on some of my circuits, but here are my thoughts:

It will probably work, but I think you would still get some dry signal on the output.  I'm not sure how much, you would have to try it out.

I would think you could use a single TL074 and just leave one opamp unused (connect the inputs to ground or something).

Other than that, I have not looked at it for too long, so I might be missing something, but it seems like it would possibly work.

[pjwhite]

What's the impedance of the circuit that will be driving the "RETURN" ?
The level pot will short the RETURN signal to ground when it's all the way down.  The level pot will change the output level as well as the feedback mix.  Are you sure that's what you want?

[Dimitree]

thanks guys
the impedance on the Return could be variable, I mean, I could plug there a Whammy, a Boss Pedal, I don't know..but most likely a whammy..
I want the pot to set the right mix of feedback..
If there are no other ways to do this, so no problems having some dry on the output..

[alanlan]

Here's what I'd do:

a) Just for a second, take the LEVEL pot out of the circuit completely.
b) Connect the pot input (i.e. top) to your OUT connection, this is a buffered version of RETURN anyway.
c) Connect the pot wiper to the 2nd 10K feeding the mixer stage.
d) Connect the pot bottom to ground (where it was originally)

So now, your return is buffered just like your input, and when you wind down the level to minimum, nothing is getting shorted to ground.

I would connect your unused stage as a unity gain inverter and connect it on the SEND output, so your SEND is in phase with IN and RETURN.

As you say, you shouldn't get any dry signal on your output - but how will you get a dry signal to your amp?  or does this not matter to you?

With the LEVEL pot halfway, and assuming a linear pot, you should get a level reduction of about 17dB which sounds reasonable.

[Dimitree]

wow many thanks! that should be perfect! I hope I've understood well:


yes it is true, I don't want any dry signal from this circuit if possible, since this is going to take a pre-splitted signal (and going to a dedicated amp)

[alanlan]

Cool.
I guess you have to think about other bits and pieces like power supply decoupling and coupling caps on inputs and outputs.  Like you say, you may not actually require the latter but it does assume a thing or two about what you are connecting the unit to.  It may also be a good idea to roll off the response of the unity gain buffers above a certain point just to limit bandwidth to audio signals and not RF!  200pF in parallel with the 10K feedback resistors would not be a bad thing.