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previous: bill m. i know a lot of players like to... -- 2/9/2001 4:19 PM View Thread

Re: Vol. circuit-LIKE losing highs?

2/10/2001 6:15 AM
Mark Hammer
Re: Vol. circuit-LIKE losing highs?
Sure thing. It's a simple matter of doing the compensated volume control, except in reverse. Think of the compensated volume control as a kind of filter whose rolloff frequency, and relative contribution to the output, change depending on its setting. When the cap goes between the input to the pot and the wiper (we'll call that the "A" section of the pot), the cap and the other half of the pot between the wiper and ground (the "B" section) function as a kind of variable high pass filter.  
When you turn the volume up, the cap and resistance of the other half/side of the pot form a high pass filter with a rolloff that is pretty much beyond the range of the pickups and speakers, so you won't really hear it. Turn the volume down a hitch, and it turns into a high pass filter with a lower rolloff, whose output is effectively summed with that of the entire signal coming through the "A" half of the pot.  
Flip the cap to the "B" half of the pot, and it turns the "A" + cap into a variable lowpass filter whose rolloff is determined by the pot setting. At full volume, the cap WILL attenuate highs (in fact, it will function exactly like a tone control turned all the way down with the volume up full), but if you select the value appropriately, the rolloff will be so high up you won't be able to hear it. As the volume gets turned down, the rolloff frequency will start to descend so that more and more high end gets trimmed.  
So, what value cap? If you have 250k pots, start with the classic 220pf, and work from there. Higher values will give a more pronounced effect. Incidentally, given that you have a Strat, you can reap all the benefits of higher value pots without suffering the flaws with this mod. 500k pots *CAN* give you blistering highs with single coil pickups, but some folks find them a tad brittle sounding. With the suggested mod, and a well chosen cap value, all you need to do is to turn down the volume a tad, and all that nasty high end will magically disappear: from Nile Rodgers Johnny Guitar Watson to Stevie Ray at the touch of a knob.