"J" taper vs. "A" taper pots.

[dstrat]

I would like to thank you guys for the informative post, having just bought parts for a PR,
I didnt bother with the 2-35 pots just looked and cts wants 4.25 US for regular,
fender branded are 7.50 US I agree with theyare Market tricks and I dont care what number the settings are.
Just turn until sound is ok.

[pdf64]

J taper = 30% log;
standard audio taper = 10% log

As I see it, for ‘log’ to be meaningful here, it can only be applied to 10% tapers.
Note that some manufacturers seem to have a standard audio taper of 15%.
Or rather that’s the audio taper commonly available off the shelf from stockists.

[eschertron]

10% taper? 15% taper? meh. My tin ears can't tell the difference between -20dB at noon, or -16.5dB.

[Gregg]

There is also a "D" taper.

According to ALPHA RV16 series pots datasheet D taper is 10% log taper. Also note the G taper which is 5% log taper. Used as Gain pot in Mesa DR and Gain and Resonance in Peavey 5150.

[Helmholtz]

Seems that Alpha doesn't use the term J taper for 30% audio.

[Chuck H]

J taper is a marketing trick as helmholtz says, and in general works, straight using a linear one is stupid, it simply annoys users.

Yes, but it's a trick that's decades old now. Starting in the silver face era I think? In fact they still use the "J taper" in most of the HR series amps. And it's existence in older amps as well has pretty much made the J taper a standard thing. I knew the J taper was a 30% @ 5 even though I've never tried to find or replace one. I'm surprised, actually, that Helmholtz wasn't aware of it. As he seems to be so knowledgeable in most regards WRT classic designs. Maybe the J taper is just a little too far after the classic BF series to matter for some.

[Chuck H]

10% taper? 15% taper? meh. My tin ears can't tell the difference between -20dB at noon, or -16.5dB.

You might if you wanted to go from high gain to clean just by turning the guitar down. My max gain settings mean that I need to turn down to .75 to 1.5 on a 15% pot to get clean (it depends on the pots start tolerance). A 10% pot gives me an extra digit of adjustability. That's no small shakes working such a slim margin. Ibanez JS guitars (Joe Satriani series, if you wondered about gain levels) do use a 5% G taper pot. So there's a lot to be gained in adjustability with a given taper if you use your guitar volume as a gain control.

It goes the other way too. Some guys that play mostly clean or with only a little edge don't like 10% log pots because they seem too fast at the top of the adjustment. Just the opposite of what the gain players experience.

Whatcha gonna do.?.

[Helmholtz]

I'm surprised, actually, that Helmholtz wasn't aware of it.

Right, I wasn't aware of it. Meanwhile I confirmed that Fender specified J-taper in SF schematics. So I learned something new - good!

Now I tend to think of J-taper as a variant or subcategory of A-taper in agreement with Alpha's nomenclature ("30A").

Generally it's a good thing to be able to choose from different tapers.

[Chuck H]

Generally it's a good thing to be able to choose from different tapers.

Oh absolutely! Unfortunately potentiometer manufacturing has gone almost entirely to east Asia. Not that the pots are bad or anything like that. I just remember when I contacted a USA shop for some custom pots and they gave me a pretty reasonable bid for a low-ish minimum order. Now you have to order many thousands at a time, and that's if you only want small variations like a specific bushing or a logo stamp. If you want something like a custom taper or configuration you're into the tens of thousands for a minimum. And they won't even talk to you (or reply to email) unless you're already established and moving a shit load of pots.

I know this because I'm working on a project right now that involves the subject. What I'm faced with is trying to make things work with what's available, or not at all. Even a small variation in what's offered by the large manufacturers or venders seems impossible to coax. So product availability is limited to what's used by the largest buyers more than ever before.

[bsco]

According to ALPHA RV16 series pots datasheet D taper is 10% log taper. Also note the G taper which is 5% log taper. Used as Gain pot in Mesa DR and Gain and Resonance in Peavey 5150.

Just yesterday, somebody mentioned a G taper pot to me....I never heard of that one before but now I do..I usually just order pots form the amp manufacturers and use their part numbers to get the correct pot that I need...but this info is very interesting,,,,I always learn something new here...that is why I joined.....

[glebert]

I know this because I'm working on a project right now that involves the subject. What I'm faced with is trying to make things work with what's available, or not at all. Even a small variation in what's offered by the large manufacturers or venders seems impossible to coax. So product availability is limited to what's used by the largest buyers more than ever before.

If someone wanted to do a "custom" taper in a situation like this it seems like best path might be to externally tweak the taper with parallel resistors. http://geofex.com/Article_Folders/po...s/potscret.htm. I'm sure many of you guys already know this, but I didn't for the longest time so I like to share it often

[pdf64]

Higher % taper pots tend to work better as vol controls if the system gain is fairly low. I think Fender used them with many tweed amps, eg 5F6a with a 12AY7 input stage. It would become something of a trair trigger with a 12AX7 in V1. Hence Marshall using log vol controls when they copied it.
As system gain increases, it helps for the vol / gain pot % taper to be decreased, in order to get a good even range of control.

[Helmholtz]

Higher % taper pots tend to work better as vol controls if the system gain is fairly low.

Agree, but I think what makes the difference is actually signal compression/distortion (distortion/clipping typically means a lot of compression) produced by the following stages rather than linear gain. Of course more gain often means more compression.

But things are different if the compression/distortion is produced before the vol pot, e.g. by a pedal.

[J M Fahey]

According to ALPHA RV16 series pots datasheet D taper is 10% log taper. Also note the G taper which is 5% log taper. Used as Gain pot in Mesa DR and Gain and Resonance in Peavey 5150.

FWIW when I could make my own I made a special batch of "5% on 5" (similar to what you call G type, for me it was A05 or something) for exactly the same reason, I made high gain amps and "starting slow" gave me more of a usable "clean" or "low crunch" area.

Of course that factory is long gone, owner died, his son even before it closed had opened a small hotel at a beachside town and "earned 4 times as much than when making pots" , so now I have to use what´s available.

There is still one pot factory in Argentina but they will not make custom tracks for me, best I can get (which is important anyway) is them assembling special pots , whichever pad/taper/value/shaft/terminals they have on stock, which is not bad at all.

The only "weird" type I can get is A pots assembled "backwards" so they become C/reverse log ones, good for mixer input pad gain, MXR Dist+ and certain SS Fender amps.

Very good from people who take "small" 300 unit batches.

[Gregg]

Couple of years ago I spoke with a Song Huei distributor in Europe and they had a minimum of 200pcs for any custom taper, lead time 8 weeks but I don't have use for so many 5% pots which in preamps like the ones mentioned above are a must otherwise the useful range of the pot is very small.
You can still find original Mesa and Peavey 5% pots online but prices for one piece could be outrageous.
In UK Omeg can do small batches if the price is OK for you.