Using different value pots?

[Dylan]

One of the pots on my amp is broken, but the pot is a B220K (Linear 220k right?). These are rarer than gold round here apparently and ones you do find are expensive/need to be imported. What effect would using a 100k or 470k resistor have on the circuit? Would it damage it? The control is for "Gain" on the clean channel, and the pot is PCB mounting, like this one;


Any help would be much appreciated.

[petemoore]

Very most likely won't hurt a thing...as far as a gain knob goes.
 The knob probably will alter gain differentlym depending on how it's used in what circuit.

[dolhop]

Depending on the gain stage circuit, it could change the amount of gain  - if the pot is used as the feedback resistor, then lowering the value will decrease the amount of gain you can achieve, while increasing the value will increase the amount of gain - but could also cause clipping, oscillation or overdriving the next stage.

If the pot is used at the output of the stage shunted to ground, then you won't affect your sound too much by changing the pot.  

Nevertheless, it is safe to change the value, but definitely try to keep it in the same range -  200k and 250k pots should be readily available.

[Dylan]

If someone could point me towards a source of pots that look exactly like the one above in 200k or 250k it would be very helpful. I can't find any.

[dolhop]

Have you tried radio shack?  They're more expensive than the local electronics shop, but easy to find.  Where are you located?

[Mark Hammer]

It is often the case that a pot value might be the closest one to what you or a manufacturer needs but only a portion of its range is really of any use.  That can mean that a very different pot value will be just fine (e.g., using a 100k distortion pot in a Dist+), or that a different value with either fixed resistors added in series with the input or output lugs (or both), or a different value with a parallel resistor between two lugs, will do just fine.

As noted, in many instances, the specific value of the pot may have no substantial effect (or at least not a black and white effect) on the tone.  What is critical in such cases is its action as a voltage divider.

[Dylan]

I'm in the UK and unusual pot values are very hard to come by, I have one of those 100k Alpha pots lying around I might try. What safety precautions should I take before desoldering the old pot in the amp?

[dolhop]

Do yourself a favour and get yourself a solder sucker for removing the old pot.  The most important thing is to not hold the soldering iron on the board for too long or the pad will lift, then you'll have to start jumpering.

250k is a fairly standard value pot, you shouldn't have much difficulty finding one.

Good luck.

[Dylan]

This is just an old Valvestate amp (early 90s I believe) is turning it off then removing the power cord enough to drain the charge in the amp to make it safe enough to remove the old pot?

[Samuel]

the answer is no - read up on discharging the power capacitors before you monkey with it

[Dylan]

I'm gonna take this to a tech with the pot I want installed, I don't really feel too comfortable messing about inside of an amp.  :shock: