Grounding volume pot questions

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Hey, I am working on an effect that is made from the delay/echo from a karaoke boombox that's been hacked/circuit bend, and put in a new enclosure.

I took a tap from the signal path in the boombox at the delay chip IC to get a 100% wet delay signal, and then have a dry signal running on the side, which comes straight off of a buffer I put at the input.

At the end there is a mini mixer (the one from GGG, but modified to have a little more gain (R10 decreased)), which has volume pots for each channel, and then an output volume pot. All of these pots are set up to split the signal to the mixer or ground.

Also, there is a delay gain pot from the boombox (which is also just a volume pot that divides the signal between the delay and ground).

Now here is the question. The mixer input pots are 10k and the mixer output is 50k. The delay gain pot is also 50k I believe. The mismatch is just because it is what I had around.

I am getting weird things with feedback when you turn certain pots up or down in certain combinations. The 50k pot makes regenerating delay feedback at about 1/5 of the way up (when it is almost turned down). Is it because of the value mismatch, and the signal is leaking back out from ground or something?

One other thing - I am finding that If I turn the mixer dry volume pot down, it cuts out the delay as well, I figure because the dry input signal is being shorted to ground - how could I set this up so that I could ground the straight signal without taking out the input signal to the delay part?

FYI, I also have a buffer right at the input to help keep the straight signal bright and to accommodate for the splitting between straight and delay inputs on the mixer.

[GibsonGM]

Hi,
Why don't you post the schematic of what you have so far?  Something obvious might jump out. I'm thinking of a couple of different causes for your glitches, but I'm not clear about how you have your signal path running.   Shouldn't be too hard to get that running right - sounds like a pretty cool circuit )

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I'll try to post one later... maybe more of a block diagram... trouble is that it is sort of half new circuitry, half hacked up karaoke boombox, which I have no idea about the schematic for... but I will do my best to depict it because I know it is confusing to describe it all.

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Ok here is a diagram... as you can see there is a lot going on there... there is actually more going on, but I don't think it is relevant and would just confuse the main question...

The main thing I am wondering though, is if there could be a conflict caused by the 50K and 10K pots to ground?

On the circuit, the delay input volume (from the boombox circuit) is essentially running in parallel with the dry mixer volume pot - it comes right at the start of the boombox input, before it has passed through any other components (this was the design built into the boombox, I just moved the pot from being circuit mounted to being panel mounted.



Also, FYI, the spring reverb part isn't even hooked up at the moment, so that should be ruled out in terms of the cause of the feedback/regen that I am experiencing.

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Really, 100 people have looked at this and no one knows if a mix of 50k and 10k volume pots is a potential problem? The diagram is complicated, but the concept is simple.

I'd just test it, but I am out of both now.

[slacker]

Using different value pots won't cause the problems you're having  

On your diagram your pots are connected wrong though, they should be connected like on the GGG mixer schematic, that could cause some strange interaction between the pots if it's really set up like that.

Do you have capacitors between the outputs of the buffer and delay and the pots? If not you might have DC on the outputs and certain settings of the pots could then short things out.

Also what voltages are you running everything off?

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Using different value pots won't cause the problems you're having  

Thanks

On your diagram your pots are connected wrong though, they should be connected like on the GGG mixer schematic, that could cause some strange interaction between the pots if it's really set up like that.

Ah, you mean with the output going to the wiper of the pot. I think I really DO have them wired that way... didn't catch that or think about the difference, it probably messes with the input impedance. Thanks.

Do you have capacitors between the outputs of the buffer and delay and the pots? If not you might have DC on the outputs and certain settings of the pots could then short things out.

I have one after the buffer, but not after the delay. The mixer has one at the input though. Should I put one before it gets to the volume pot anyway?

Also what voltages are you running everything off?

The boombox ran off of 6v, so I am running everything off that.

Thanks a ton for your suggestions!

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Swapped the pins on all those volume pots and that was that - all working great now.

Lesson learned!