Recommendation and source for quality volume potentiometers

Hello,

First I'm sorry if this topic has been discussed before; I haven't had much luck with the search feature.

I'm looking for some decent quality audio taper potentiometers and wondering what brand/source you guys are using? I've used the cheap 9mm alphas that you see in guitar pedals but they aren't cutting it for me in my G9 or Green pre. Specifically the tolerances are all over the place and the taper is inconsistant.

Can anyone recommend any specific brands and where to find them (I'm in the US btw). Specifically I need 10k and 47k or (or 50k) audio taper. I know it's possible to spend a lot of money on pots but I'm looking for something that's a step up from the cheap alphas. Less than $10 a piece.

Thanks!

Alps, bourns?

I used Alps for my kit company back in the '70s and they were very good quality, while they make different versions.  Even back then I had to buy thousands at a time, but I have seen some popular models available in small quantity from distribution.

JR

I like bournes & clarostat.
I like them more than omeg, which are plastic and seem to adhere to a location after sitting, in a strange way. Not sure if that is a problem or not, but I prefer the feel of the others.

If all else fails...

http://www.state-elec.com/

They will make you the best of anything but
open your wallet!

GARY

11 pos rotary sw. will get better taper than 25 dollar Alps cond. plastic, and they stay in the same place during transit or if cords brush up against them,

for expensive i love the feel of the $25 alps in the LA2a and the taper aint That bad, jus sayin...

The trouble with true log or audio tapers is that they are very hard to make. Most log/audio pots are really just two different linear tapers each occupying half the track length.  There is a variation is the resistance of each track so the exact attenuation at the mid point varies and so dual pot tolerances are often poor. End to end tolerances are often 20% but you can get better if you shop around. For a potentiometer this does not matter too much. There are some manufacturers who take the extra steps necessary to manage the law and its tolerances along the length of the track but they are few and far between. The ALPS  XXX Beauty range is one and of course P&G is another. But in both cases the penalty you pay is greater physical size.

Linear pots are easier to control in manufacture and therefore much better and if you want pots with repeatable laws and good tolerance between sections of multiple pots. If you can tolerate to variation in load resistance then very repeatable results can be obtained using slugged linear pots to obtain a non-linear law. At Neve we never used log pots for this very reason. All non-linear laws were obtained using slugged linear pots.

Cheers

Ian

ruffrecords said:

If you can tolerate to variation in load resistance then very repeatable results can be obtained using slugged linear pots to obtain a non-linear law. At Neve we never used log pots for this very reason. All non-linear laws were obtained using slugged linear pots.

Click to expand...

Just to clarify, the "slugging" is where you put a resistor between the wiper and one end of the pot?

-a

Thanks for all the info everyone. Does anyone have a source for any of these? I've been searching far and wide but have really only come across two types of web sites:

1. Sells a very specific kind of pot: stereo switched for hi-fi people, 250 or 500k for guitar people (too narrow)
2. Places like mouser where the selection is absolutely overwhelming.

I'm just looking for a few single gang pots that would fit in a 1U rack space. Doesn't have to be top of the line but a step up from alphas.

ruffrecords said:

The trouble with true log or audio tapers is that they are very hard to make. Most log/audio pots are really just two different linear tapers each occupying half the track length.  There is a variation is the resistance of each track so the exact attenuation at the mid point varies and so dual pot tolerances are often poor. End to end tolerances are often 20% but you can get better if you shop around. For a potentiometer this does not matter too much. There are some manufacturers who take the extra steps necessary to manage the law and its tolerances along the length of the track but they are few and far between. The ALPS  XXX Beauty range is one and of course P&G is another. But in both cases the penalty you pay is greater physical size.

Linear pots are easier to control in manufacture and therefore much better and if you want pots with repeatable laws and good tolerance between sections of multiple pots. If you can tolerate to variation in load resistance then very repeatable results can be obtained using slugged linear pots to obtain a non-linear law. At Neve we never used log pots for this very reason. All non-linear laws were obtained using slugged linear pots.

Cheers

Ian

Click to expand...

Not that this is much help for the poster, opinions vary regarding how best to execute difficult pot tapers.

I've enjoyed the luxury while working at Peavey of being able to tool up specials and that is pretty useful for some of the better high gain low noise preamp topologies. The first 45' of rotation may only be near 0 to only 20 ohms, while the total R is 25-30k Ohms . IIRC one special gain taper was something like a 4 step or 4 screen process, so instead of a single pass with conductive ink to make a pot taper, this special pot used 4 different conductive ink mixtures each with different resistive properties, screened using 4 different overlay patterns. When using a million parts a year this is still more expensive but maybe $0.40 instead of $0.25 for a single step pot. Worth the extra money so the pot delivers a good control law versus rotation at both ends of the pot. The customers don't notice so much when it's right, but they notice when it's wrong.

I recall trying to game pot tapers as a small company using standard tapers and it wasn't easy. Even the steepest standard reverse audio still was too fast at the hgih gain end. I had a nice 50k dual I used in my old kit company that was a variant B (linear) taper, but with "s" curved characteristic at both rotation extremes. I guess this one might work ok slugged but I never tried it.

The only time I used "slugging" was as a small company making crossovers (early '80s) that required a 4 gang pot (to make a sweepable 4 Pole L-R crossover). I bought the best matching spec that Alps sold (around $3 per 4 section pot, back when $3 was worth something) then I paid a tech to measure and add resistors (slugging) to make the sections match each other perfectly at mid rotation. With the topology I used the pot bulk resistance (typically +/-20%) was out of the circuit at full up and full down, and dialed in to track at 12 o'clock.

    JR

Andy Peters said:

ruffrecords said:

If you can tolerate to variation in load resistance then very repeatable results can be obtained using slugged linear pots to obtain a non-linear law. At Neve we never used log pots for this very reason. All non-linear laws were obtained using slugged linear pots.

Click to expand...

Just to clarify, the "slugging" is where you put a resistor between the wiper and one end of the pot?

-a

Click to expand...

That's right.

Cheers

Ian

trying not to highjack, but what is the quick and dirty on slugging? "If you want a REV audio pot with end to end R of 'X', use 'y' ratio pot to slug resistance."

gemini86 said:

trying not to highjack, but what is the quick and dirty on slugging? "If you want a REV audio pot with end to end R of 'X', use 'y' ratio pot to slug resistance."

Click to expand...

The way to work this out is to think about what you want the pot to do at the half way point. With a linear 10K pot, for example, you get 5K above and 5K below the wiper giving 6dB of attenuation. For a log pot you typically want 20dB attenuation at the mid point which needs 9K above and 1K below. To get the same from a 10K linear pot you need it to be 5K above and  555 ohms below. So you slug the 5K from the wiper to ground with about 620 ohms to get the required 555 ohms. For the antilog equivalent you just connect the 620 from the wiper to the top.

You can now see why I made the point before about load variation. The 10K slugged log pot looks like 10K when fully I off and like 555 ohms when fully up.

Cheers

Ian

Not to be a "debbie downer" but if slugging pots worked perfectly, there would be no reason ever for pot makers to even make other tapers. The economy of scale to just sell the same pot for every application would be compelling, especially when you need to buy thousands of each variant.

Where slugging works OK is at the middle of rotation where the pot resistance is significant, where it can get challenging is at the extremes where pot behavior is less ideal. Pots have hop-off resistance, kind of like a dead band at the end before the pot wiper hits the resistive track. Slugging is clever and certainly attractive to improve inventory utilization, but there are limits to what it can do. To bend a taper some, sure. In fact loading on the wiper needs to be considered for all potentiometric (attenuator)  circuits.

The example I gave of a mic pre gain pot for a circuit with a Rf/Rg gain relationship, the gain gets increasingly fast as the pot resistance gets down into single digits and tens, while at the opposite low gain end, you want to provide a couple 10k ohms to accommodate low enough gain for larger signal handling. There is no way to slug a linear pot to get >20k max, and good adjustability and well behaved gain law at the low resistance end.  Even a reverse audio taper with acceptable adjustability at the fast end , suffers on the min gain possible ( as a small console  company I ended up using a 1kRA for mic preamp gain decades ago as an OK tradeoff, later at Peavey in much cheaper products I was able to do much better at both ends with a special part). 

The four step process I mentioned had at least one step or application of resistive ink just for the first few degrees of rotation, overlaying the hop-off region for smooth early gain instead of a huge jump. 

Like I mentioned customer don't notice so much when you get this right, but they will notice if you get it wrong. Sometimes it is easier to use a less optimal circuit topology, because standard pot tapers can work better. Control laws is part of the ergonomic or human factors of product design that separates some products from others.

I might be tempted to try to source a special pot from a manufacturer's service department for low quantity, while identifying exactly what you want may take some digging.

JR

JohnRoberts said:

Not to be a "debbie downer" but if slugging pots worked perfectly, there would be no reason ever for pot makers to even make other tapers. The economy of scale to just sell the same pot for every application would be compelling, especially when you need to buy thousands of each variant.
JR

Click to expand...

You are quite right. Like every technique it has its limitations. It is ideal for pan pots where you want to tweak the -6dB point of a pair of pots to be -4dBor -3dB - its repeatability and tracking score in its favour here. And it is even fine for a level control with a -10dB mid point - typical for AUX sends on a mixer. However, at -20dB at the mid point you are really pushing it. There are very few situations where you really need very accurate tracking or attenuation when you have a pot providing 20dB loss. If your design is such that this is the normal operating point of the pot then you need to look at your gain staging. You clearly need it for master stereo faders and possibly studio monitor level controls but there you are not space constrained and a P&G fader or a stepped attenuator will do the job.

Cheers

Ian

Why don't you send an email to Colin at audiomaintenance.com?  He sells the values you seek and knows the parts so will be able to set you with the quality you need.
Mike

ruffrecords said:

The way to work this out is to think about what you want the pot to do at the half way point. With a linear 10K pot, for example, you get 5K above and 5K below the wiper giving 6dB of attenuation. For a log pot you typically want 20dB attenuation at the mid point which needs 9K above and 1K below. To get the same from a 10K linear pot you need it to be 5K above and  555 ohms below. So you slug the 5K from the wiper to ground with about 620 ohms to get the required 555 ohms. For the antilog equivalent you just connect the 620 from the wiper to the top.

You can now see why I made the point before about load variation. The 10K slugged log pot looks like 10K when fully I off and like 555 ohms when fully up.

Click to expand...

Not to be awkward, but I've most commonly seen the 10k LIN pots in Neve switching units slugged with 5k1 resistors.

These look like 3k4 when fully up, and 10k when fully down. Not so bad.

Clearly, these are designed not so much for a specific mid-point value, as for reasonable load variation in use. After all, there are usually a few of these in parallel as Aux Send pots - off/pre-fade/post-fade switchable too, so they are not always in the same circuit.

ianmgull said:

Thanks for all the info everyone. Does anyone have a source for any of these? I've been searching far and wide but have really only come across two types of web sites:

1. Sells a very specific kind of pot: stereo switched for hi-fi people, 250 or 500k for guitar people (too narrow)
2. Places like mouser where the selection is absolutely overwhelming.

I'm just looking for a few single gang pots that would fit in a 1U rack space. Doesn't have to be top of the line but a step up from alphas.

Click to expand...

You want ALPS RK27 - try Mouser: http://gb.mouser.com/Search/Refine.aspx?Keyword=alps+rk27

These pots are an industry standard in affordable stereo gear. They last well and typically match far better than their quoted tolerance. They are not as durable or quiet in operation as their predecessor, the RK40, but are superb value for money. In applications where they're not going to be thrashed daily, they're as good as an RK40. For, say, a monitor level in a studio, I'd suggest keeping spares - after a couple of yrs you might notice a little noise.

thermionic said:

ianmgull said:

Thanks for all the info everyone. Does anyone have a source for any of these? I've been searching far and wide but have really only come across two types of web sites:

1. Sells a very specific kind of pot: stereo switched for hi-fi people, 250 or 500k for guitar people (too narrow)
2. Places like mouser where the selection is absolutely overwhelming.

I'm just looking for a few single gang pots that would fit in a 1U rack space. Doesn't have to be top of the line but a step up from alphas.

Click to expand...

You want ALPS RK27 - try Mouser: http://gb.mouser.com/Search/Refine.aspx?Keyword=alps+rk27

These pots are an industry standard in affordable stereo gear. They last well and typically match far better than their quoted tolerance. They are not as durable or quiet in operation as their predecessor, the RK40, but are superb value for money. In applications where they're not going to be thrashed daily, they're as good as an RK40. For, say, a monitor level in a studio, I'd suggest keeping spares - after a couple of yrs you might notice a little noise.

Click to expand...

Hey thanks for the help. That's right around the price range I'm looking for. Do you know off hand if there is a mono version of the rk27? I suppose I could always just use half the pot but if there was a similar product in a single ganged version I assume it would be a bit cheaper.

Thanks!!

MagnetoSound said:

I've most commonly seen the 10k LIN pots in Neve switching units slugged with 5k1 resistors.

These look like 3k4 when fully up, and 10k when fully down. Not so bad.

Click to expand...

Is that looking forward from the source? Looking back from the load wouldn't a 555Ω source impedance be better? Or does the 555Ω look like 0Ω at the fully up position to the load?