MV abrupt taper change

[greiswig]

Hi all,

I tacked this on to the end of the thread about CTS pots, but hadn't heard back from that, so I thought I'd try giving it it's own thread:

I've got an issue with the master volume on my D'Lite build. The taper is quite even right up to about 1:00, which in my band ends up being about gig level (competing with another loud guitarist and a loud drummer on tight stages). At that point, the control gets as touchy as a rattlesnake. Tiny movements make big differences in volume. So at a gig, when you're trying to make changes while playing, it can be a real problem.

Not sure what pot in there...it's what was supplied by Brown Note.

Any suggestions for a taper or pot that might behave a bit more predictably at reasonable volumes?

[martin manning]

I believe the "log" taper in some pots is actually made up of two linear taper sections joined together. You may be sitting right at the point where it changes slope.

[greiswig]

I believe the "log" taper in some pots is actually made up of two linear taper sections joined together. You may be sitting right at the point where it changes slope.

Yup...I'd had the same thought, because that is exactly what it feels like. If so, any recommendations for pots that do not apply this technique of generating a taper?

[Structo]

George, after finding out I had several defective pots in my new 100w build I don't take anything for granted anymore.

I had bought some NOS pots and although I did measure the total resistance on the outside lugs, it was when they were adjusted that I found something was wrong.

These were two Allen Bradley pots and a NOS CTS pot.

For instance the pre gain pot was an Allen Bradley 1M pot that after about 1/4 rotation it was at max resistance.
I was not getting the clean head room that I should have been getting and after comparing notes with a couple other builders I dug into the pots.
Really scratched my head on that one until I pulled it out and measured the sweep and found the problem.

The pot I had for a master was the same way.

[greiswig]

Thanks, Tom. Yeah, nothing quite that off-spec here, but it isn't what I'd call a smooth taper.

So short of spending $15 on Alessandro's pots, is there a good alternative?

-g

[David Root]

PEC pots $9.95 at AES. 2W RV4, MILSPEC, short shaft for amplifier use.

Never had a bad one. Stainless case, you can't solder to it, other than that they're as good as it gets in my book. Oh, except 15% taper, not 30% like the old A-B J-types.

[Structo]

I've bought the expensive PEC pots as well as others and I keep coming back to Alpha pots.
Sure they are cheap but they are also pretty consistently good.

I do like the locking pots that PEC makes and I use those for adjusting bias current.
Because you can lock them down and the shaft won't drift.

But I have had a couple PEC lemons.

The tolerance on Alpha's isn't the greatest of all the pots but generally they are within what we need and you can always weed through a few if you need a tighter tolerance.

And for around $2 each, you can certainly get quite a few of each value to sort through.

[greiswig]

Thanks, all.

Have you found the Alpha and PEC pots to both have smooth tapers, rather than stacked linear tapers?

[Structo]

I have read about that but I don't really feel that in my pots.
I suppose it depends where your sweet spots are and if it happens to land where those two elements join.

For the most part I find the Alpha pots to work great and I see quite a few amp builders using them.

I have to say that while I also like PEC pots, I have had one get scratchy in short order and no way to clean it.

And I had at least one that was defective in the way it tapered. (an abrupt shift in resistance)
So in comparison a PEC costs $10 and an Alpha costs <$2 in most cases.

[ToneMerc]

Thanks, all.

Have you found the Alpha and PEC pots to both have smooth tapers, rather than stacked linear tapers?

PEC is a good pot, but still a 10% taper. I regretfully used them in MM ODS and I'm pulling them all out. I should have used Alpha. I like CTS, but I find you have to go through so many to get closer tolerances and they still don't have the correct taper.

[M Fowler]

So when are we going to have a pot buying party and get the correct taper pots available to everyone?

To get a large order we need the buying power of TAG members.

Mark

[NickC]

So when are we going to have a pot buying party and get the correct taper pots available to everyone?

To get a large order we need the buying power of TAG members.

Mark

Count me in.

[greiswig]

So when are we going to have a pot buying party ....

Soon to be contacted by the DEA...

But seriously, I'm interested in that as well. I've heard others say that the potentiometers really do make a big difference in the sound and behavior of the amp. And clearly I've got at least one issue that I'm aware of.

[David Root]

If we could get 30% taper I would be prepared to try Alpha or CTS again.

[M Fowler]

I agree and would like to try some 30% taper pots in a build.

Mark