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How to select Volume pot rating?

nitrous

nitrous

pfm Member
OK, so I'm sure to many this is a silly question, but how do you know if a 10k, 22k 100k etc pot is best?

I have knocked together a basic pre-amp using the Vellemen kit (managed to reduce the input using 1m ohm resistors as it was overloading), and bunged an op200 chip op amp in and using a maplin dual 10k pot got it working. Quite pleased with how clear the sound is, and the sound overall. BUT, you only have to move the volume a tiny bit and it goes LOUD! VERY LOUD VERY QUICKLY!:eek:

I would consider using an alps blue pot, but don't want to buy 10k unless I can attenuate the output. I was thinking of a resister across gnd and output before pot, but would a 50k or 100k pot do the same and be better?

This is just a bit of fun in a second system, cheers for help:cool:
 
Value has nothing to do with volume.

If it is too loud, you should reduce the gain of the pre-amp.
 
Hi piglets dad. Ok, can do that but just so
that I understand what is the reason then
different values of volume pots?
 
Hi Pete, Linear pot 10k. It is working fine (considering the lowley nature of the parts), but it could just do with being a bit more gentle. If we talk using a clock face and say 7pm is no sound, by eight we have reasonable output (tuner as source) nine o'clock very loud, 10 way too loud.

Cheers nitrous
 
Pete MB&D said:
Hi, Nitrous

Thats your problem, you need a Log pot not a linear one.

Pete
Click to expand...

Hi Pete, thanks for reply. I thought that may have something to do with it. I'm still a bit unsure as to what rating I should get, if I do buy a new log pot; 10k 50k 100k etc. etc?

Regards Nitrous
 
The volume pot in a preamp sets the input impedance of the preamp and the optimum value depends on the impedances of the amplifier stages/components immediately before and after the volume pot.

Basically, a lower input impedance (= pot value) will give you less noise in the preamp circuit after the pot, but in return the preceding amplifier stage (= the output of the source) has to supply more current, which not all sources are capable of. 10-100k is the normal value for a volume pot and within that range you should be fairly safe. EDIT ...and any preference for one value over the other within this range would have to be decided case-by-case.


/U.
 
Unless I knew otherwise, 50k is a safe value - even really weedy sources can drive 50k, while some very gutless valve devices might struggle with 10K. You basically want the lowest value (for noise reasons) that doesn't cause the source any distress at all.

And you definitely want a log pot, otherwise volume comes up abruptly at the bottom.
 
Carrotman & Piglets Dad, Many thanks for taking the time to explain that for me, now I understand a bit better. I'll stick with a low value and get log pot, and I think I will be sorted then.

Many thanks.

nitrous
 
What's the current preference for sound quality, folks ? IIRC Panasonic are detailed - can't remember any others ...
 
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