Potentiometer Ohm rating as to volume control pot. I am replacing a cheap unlabeled pot, I'm curious as to application of the various ohm ratings for pots. Is there a audio standard for pot ohms and how does this apply to volume and also tone controls. 20k is what I am starting to find as a popular rating.
Please inform me as to values to use as Vol. and Tone controls.
Thank's Less Opinion
Please inform me as to values to use as Vol. and Tone controls.
Thank's Less Opinion
For volume it depends on the source impedance and load impedance. For tone it depends on the exact circuit.
A pot would have to be very cheap to be unlabelled.
A pot would have to be very cheap to be unlabelled.
The resistance values (in ohms) normally depend on the application circuit. Indeed, for volume you often see 10k or 20k, though tube gear generally has much higher values.
If the pot is unlabelled, but you have a multimeter, you can just measure the end-to-end resistance (after disconnecting the wires) to find the resistance.
But there is another attribute that is of importance to volume pots: they often have a logarithmic law. Meaning that equal turn angles not mean equal resistance value changes. In log pots, the resistance values change slower at the top of the range so you get a control law that matches better our logarithmic ear sensitivity. You can also measure that with a multimeter - the log effect is quite pronounced and you'll immediately see if constant speed turn does not change the resistance in a constant manner. Or, another even easier way: place the pot mechanically in mid position and measure resistance from wiper to each end. If the pot is log, the two values will be wildly different. In that case, go for a log pot.
Jan
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jan.didden, Now that's how one should answer a question, I am now educated in the laws of pot. Thank You! Now one other ? Could one assume that it is ok to use a log pot to replace a standard pot of the same ohm spec. My situation, I am pretty new to this and have bought a Lepai 2020A chip amp to use as a learning/play tool, I intend to cut modify and improve this thing to Death! and if that happens I'm out 25 bucks and I will have a box of parts to do it again. Thanks again that was very helpful.
Dave / Less Opinion
Dave / Less Opinion
If the original had a linear pot (and that is what the designer intended) then you should replace with a linear pot. You need to provide a whole lot more information before we can help you.
Pots are always labelled in one of the following ways:
a) plain language value and type stamped in metal back or side, such as "50k Log/Lin"
b) same but slightly more cryptic such as "A503" meaning "Audio 50+3 zeros" which means 50000
c) any of the above but silkscreened on the front, on a small exposed area of track Pertinax (brown phenolic paper) base which is good because label is on track itself, avoids Factory errors and bad because the pot shows no visible label while mounted on the front panel.
d) any of the above but printed on a small sticky paper label which *can* pulled with a nail tip, used thousands of such pots and never saw one label fall off on its own although *might* be possible (softened after soaking in a too generous application of pot cleaner or plain WD40?)
In any case, you can:
e) measure end to end value.
f) set it to "5" or halfway rotation and measure wiper resistance to each end:
g) both are roughly the same and around 50% of full value: Linear Pot
h) one is around 90% of full value, other is around 10% (in some cases might be 20% ): Log/Audio pot.
Well, we have covered all bases, post what you measure.
a) plain language value and type stamped in metal back or side, such as "50k Log/Lin"
b) same but slightly more cryptic such as "A503" meaning "Audio 50+3 zeros" which means 50000
c) any of the above but silkscreened on the front, on a small exposed area of track Pertinax (brown phenolic paper) base which is good because label is on track itself, avoids Factory errors and bad because the pot shows no visible label while mounted on the front panel.
d) any of the above but printed on a small sticky paper label which *can* pulled with a nail tip, used thousands of such pots and never saw one label fall off on its own although *might* be possible (softened after soaking in a too generous application of pot cleaner or plain WD40?)
In any case, you can:
e) measure end to end value.
f) set it to "5" or halfway rotation and measure wiper resistance to each end:
g) both are roughly the same and around 50% of full value: Linear Pot
h) one is around 90% of full value, other is around 10% (in some cases might be 20% ): Log/Audio pot.
Well, we have covered all bases, post what you measure.
Yes you could and electronically it would work just as well but your control of the volume would be awkward towards the top. Very small changes on the pot would make huge changes in loudness. That is why they invented log pots.
But there is a trick, if the only thing you have is a lin pot. That is to put a resistor from wiper to bottom; it's called 'faking a log law'.
There are some threads here about it.
Jan
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