Help with pots

[rizla]

Hello, I need a little help with pots. I'm trying to perform a feedback modification on an old synth, and I can't figure out how to wire the pot. I want the pot to be able to completely mute the feedback when turned down, and to raise the volume of the feedback when turned up.

No matter which pins I use on the pot to route the signal back into the filter, I can't get the signal to mute. What am I doing wrong?

I am using 100k resistor from the headphones output, a 100k (linier) pot going into the synth filter input.

I am indeed a newbee, so please excuse what is probably an amateur question!
     
thank you

[Circuitbenders]

try wiring the spare pin of the pot to ground and see if that helps

but i am fairly drunk right now so it may not work

[rizla]

Ah yes, that seems to do the job! There is still a bit of interferance when I touch the pot though. I'm gonna put it on a switch, so that I can put a jack socket on the filter input and use the same pot to control the filter input volume. I'll still have HISS though when my hands go near the pot. Is there any way to fix this?

Just one more question - I have found a resistor which when removed gives nice OVERDRIVE, what is the method of using a pot to replace the resistor?

Thank you Mr C.B.      sorry to hear about your hangover 

[Silas]

http://www.flickr.com/photos/26039450@N08/2460751359/

Just made this in paint, with my leet paint skills.. Just snip one of the resistors legs, or remove it completely. Then solder the pot to each side of the resistor. You connect leg A to one side and B to the other, optionally can connect leg B and C togheter, but it is not neccesary..

About interference from the pot.. Is it metal? Try using a plastic one. Do you got a knob on it? Try putting one on. If the casing is metal, is the pot completely isolated from it?

[rizla]

nice skills there, plastic caps seem to help a bit

thanks for help dude

[Circuitbenders]

Thank you Mr C.B.      sorry to hear about your hangover 

Not half as sorry as i am 

Wierd noise problems is always a tricky one and often theres nothing you can do about it. Trying a plastic pot is one option but they tend to be a bit unreliable in the long term. Alternatively try moving the wiring or the pot itself to a different position and see if that helps, it might be picking up some noise from the circuit itself. The other option is to try grounding the pot body itself by soldering a lead to the metal base or just wrapping the bare wire around the screw thread with the other end going to ground.

[Gordonjcp]

Just one more question - I have found a resistor which when removed gives nice OVERDRIVE, what is the method of using a pot to replace the resistor?

Sounds like it's setting the gain of an amplifier somewhere.  If you post the make and model of the synth, and a description of some of the components around this resistor, then I can probably help you find the appropriate circuit diagram.

In general if you use an opamp you have a resistor from the output to the inverting input to set the gain - the gain is then a function of the feedback resistor and the input resistor (massive generalisation, but go with it for now).  Because you're applying negative feedback, then the more you apply the lower the gain will be.  No resistor at all will give you no gain at all, ie. a gain of 1 - this is handy if you want to buffer a signal without amplifying it.

You could try putting a pot in series with the existing resistor.