Active tone con. changes volume

[BRingoC]

I have built a modified ds-1 with active high and low tone controls following various schematics for these on the web.  I don't have the pedal/values in front of me so my best explanation of the problem is as follows.  First I had a set of resistors/caps in it that allowed only one tone control to work and at one extreme it caused motorboating, the other did nothing at all.  I changed the caps/resistors to another set of values to match another frequency point and now they both work to turn the volume down and do not effect the tone at all.  I have found several active eq's on the forum, some have resistors connected to ground, others to Vref, whats the difference, and how do I get the thing to change the tone.  Do the components need to be exactly the value stated, or is there allowance for slightly higher/lower values and still have the indicated frequency, or would that be causing the tone control to not work at all?  Thanks.

[JDoyle]

If the pot in a tone control is controlling the volume and not the tone, most likely you have either forgotten a series cap to block DC and differentiate between frequencies (a passive tone control is, after all, just a frequency dependent volume control), or said cap is faulty or has a solder short.

In terms of keeping the same corner freqency, you have to scale the resistor down by the same amount you scaled the cap up, or vice versa.

Beyond that, without seeing the circuit you are talking about, there isn't any way to help you...

[BRingoC]

can you explain the series cap better, where its placement is, and would filtering dc current depend on being polar/non-polar. I have a schem for a filter similar to the filter on http://en.wikipedia.org/wiki/Active_filter  the sallen key topology diagram on the wiki page, but the v/out is not connected to an 'out' and r2 is connected to Vref. the Vin is from the middle lug of a 100k pot and the outer lugs attached to an in-line op amp. I understand its hard to determin this without a schem, ill see what i can do with scanning my work to post.  Thanks.

[JDoyle]

can you explain the series cap better, where its placement is, and would filtering dc current depend on being polar/non-polar. I have a schem for a filter similar to the filter on http://en.wikipedia.org/wiki/Active_filter  the sallen key topology diagram on the wiki page, but the v/out is not connected to an 'out' and r2 is connected to Vref. the Vin is from the middle lug of a 100k pot and the outer lugs attached to an in-line op amp. I understand its hard to determin this without a schem, ill see what i can do with scanning my work to post.  Thanks.

Yeah, I've got to admit, I can't really figure out how your pot is wired from your post, sorry...

For a tone control the caps won't be polarized, in fact, unless you are dealing with a very low input impedence you will never really need to have polarized caps in the signal path. Polarized caps are large value and mostly used for bypass (meaning to filter the power supply or to bypass a emitter/source/cathode resistor to raise the gain of an amplifier stage).

You are going to need to post the schem because from your description you have a fundamental problem in the circuit that part values and type probably wont affect.

Regards,

Jay Doyle