There's a preamp with tone controls I'd like to build but I'm frustrated that I can't seem to find any good quality linear pots.
Same problem when I've wanted to replace worn pots on old equipment.
Am I not understanding something, why is everything log?
Same problem when I've wanted to replace worn pots on old equipment.
Am I not understanding something, why is everything log?
One typical justification goes along the lines of "the ear itself is logarithmic, so a logarithmic volume control is a better match". And it is perceived there are more volume controls installed on final gear than other types of pots, so it is perceived that demand is greater for log potentiometers.
There are many good linear pots, and they vary less than logarithmic types. What resistance, dimensions and conductive substrate are you in need of?
This does not directly address the OP's question but I'll just drop my 2 cents anyway. I live in a remote corner of a developing world and, ever since I started teaching myself electronics a long time ago, one ever present problem was to source anything but the most widely used parts. Decades ago, It was almost impossible to find linear pots. Now it's the opposite. Log pots are now as rare as a hen's teeth. And that's with any brand, from $0.20 Chinese products to high quality ones.
I'm looking for a sturdy 50k or 100k panel mount stereo pot with a 6mm shaft. I don't want to spend over $100+ for a stepped pot but I'd like something better than a $3 carbon pot like you'd find on Digi-key. Like a blue velvet or comparable, but there are no linear bv's anywhere. Log is no good for a tone or balance control.
Taiwan Alpha makes nice linear pots. Mouser carries them. Price is reasonable.
I'll just note that Baxandall based tone controls give the most reasonable action if set up with reverse log taper. I'll assume that your tone control setup is some other arrangement besides Baxandall.
I'll just note that Baxandall based tone controls give the most reasonable action if set up with reverse log taper. I'll assume that your tone control setup is some other arrangement besides Baxandall.
I've used these Vishay P11 (cermet) many times in the past and they've always been very reliable. Independent linearity is very good at +/-3%, this particular one also has 10% tolerance. €23 + tax is more than I'm usually prepared to pay for a pot but it may work for you:
https://eu.mouser.com/ProductDetail/Vishay-Sfernice/P11L2V0FLSY00503KA?qs=QxrAdWTCGdzgYYzaSzZI6w==
@djoffe I've never seen a Baxandall implementation that calls for reverse log pots, maybe there are some, but if the topology he has calls for linear ones, a reverse log will cause the center position of the pots to be anything but flat...
https://eu.mouser.com/ProductDetail/Vishay-Sfernice/P11L2V0FLSY00503KA?qs=QxrAdWTCGdzgYYzaSzZI6w==
@djoffe I've never seen a Baxandall implementation that calls for reverse log pots, maybe there are some, but if the topology he has calls for linear ones, a reverse log will cause the center position of the pots to be anything but flat...
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@cabirio Thanks for the tip on the Vishay's. I had discounted those because they are so small but they're rated a at 2 million cycles so that's encouraging. I wasn't aware of cermet resistive material but it sounds very durable. Good price point too.
@djoffe A tone control should be flat at 12 o'clock and I'm pretty sure an anti-log pot would not be.
@djoffe A tone control should be flat at 12 o'clock and I'm pretty sure an anti-log pot would not be.
This sounds like market reality.
High-end equipment has only a volume (logarithmic) pot. Mass-market equipment has both volume and tone/balance (linear) pots. The intersection of "high-end" and "linear" is the empty set.
I used Alpha linear pots and an Alps log pot in my old designs.
Ed
Who says so?
Log or Lin depends on application.
For passive Volume or Tone controls you need log ones because perceived effect vs. rotation matches ear response better.
On active circuits in general Linear works better, if anything because both ends are symmetrical.
In fact, for active tone or EQ controls, best curve is neither 😲 but so called "S curve", starting with Log, ending with anti-log.
Yes, on the same track.
Those are as rare as hen's teeth.
When I needed them, I had to make them myself, and minimum order was 500 units, go figure.
And I had to prepay for 5000 S curve tracks which I never got to use.
Mind you, Alpha or any other manufacturer can make them, no big deal, but minimum order will be 50000 or 100000 units per value because "nobody else will buy them".
Yep, I did the same thing on my last build.
The ESP preamp I'm currently building, however, is logarithmic using a linear pot.
He's probably talking now about the volume pot in this project where Rod uses the loaded linear pot trick to get a log-ish response (fig. 4). I've done this a number of times (e.g. here) and it works well, dual linear pots do generally have better tracking than log ones.
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+1 for the Vishay P11 cemet. For audio a conductive plastic track is usually preferred for a softer feel and less crackling noise.
When you put a passive Baxandall in the feedback of a non-inverting opamp circuit you need revLog tapers but these circuits are rare as they have a lot of total gain, just like the passive one has a lot of attenuation.
For standard active Bax tone control with inverting opamp, linear taper is correct and total gain is unity. Normally with 10k pots, linear + center detent which are readily available. Conductive plastic types are a bit scarce, though.
When you put a passive Baxandall in the feedback of a non-inverting opamp circuit you need revLog tapers but these circuits are rare as they have a lot of total gain, just like the passive one has a lot of attenuation.
For standard active Bax tone control with inverting opamp, linear taper is correct and total gain is unity. Normally with 10k pots, linear + center detent which are readily available. Conductive plastic types are a bit scarce, though.
Try https://www.omeg.co.uk/. They do small batches of custom spec pots from 10pcs up, provided that the pots consist of parts they have stocked/pre-produced.
Some real good preamps use a linear volume pot in a Baxandall volume circuit which yields a very log-like response when correctly designed and usually has lower noise and distortion than a log pot followed by a gain stage.
The Baxandall volume circuit is basically the same design idea as the inverting opamp Baxandall tone, just that the max gain from the opamp is limited to a fixed low value like 4x or so.