Alpha's

[talbany]

After recently stumbling on a nice stash of NOS Allen Bradley pots the last few builds I did for myself using these pots have noticed quite a difference in how the amp performs.. Beside the fact that they are 30% taper (which I know makes a difference as posted by others) the tone seems more open the amp wants to run...touch sensitive and breaths better.. I don't find I have to turn things up as much to get the amp to come to life and the range increases substantially..Now I know why Dumble didn't use these in his amps and the settings on the clips I see posted throughout the net makes better sense..Personally I think there is more to it here than the taper.. Maybe the type of carbon they use on the trace..Anyway after going here on a few builds with the Bradley's I am a believer.. The CTS's are no doubt the same.. If you want to go the extra mile and hunt down the Bradley's or CTS they do make a big difference.. Check it out..

Tony

[Structo]

Interesting.

I wonder why they changed the taper on modern pots.

Are you saying that the CTS pots made today are 30%?

It makes sense that the material they are made from could have an impact on tone.

Great, now I have to buy all new pots for every piece of gear I have built in the last three years......

[talbany]

How do you really confirm it's material?..same with caps and resistors.. You just have to go there on several amps and use your ears...I do think it's more to do with trace material than taper..Gut talking!!

Tony

[David Root]

I see you just answered my question! I should have looked here first!

So I'll add in here the other aspects of this I asked you about in my e-mail.

"Is there a
difference between carbon and conductive plastic?

I have used only RV4 2W pots up to now, however I recently
bought some 1/2W Bourns open types from Steve Slater at Apex Jr. to use in
my Princeton #13 build. I did that because the RV4 pots are too close a fit
in the sloped chassis front apron because of their depth and diameter.

I don't know what they sound like but they sure have a very
smooth high friction feel when turned. I believe they are of Asian origin,
not made in USA."

Anyone used these pots yet?

Tom, I think 30% pots are custom order only these days. Why did the manufacturers fix that when it wasn't broken?

[talbany]

Sure!! why not!!.. A pot is a variable resistor.. Different resistors yield different sonic qualities.. carbon comp/Metal film/ RN65's.. Most builders here swear it's not a Dumble tone chirp on the top etc.. if you don't use the 65's on the plates and yet pass right over the type of pots.. There are more pot's in this amp than plate resistors...
Dave I've not yet used the Bournes.. However I have used the Clero's in various spots but not throughout the entire amp.. It wasn't until I used the AB's throughout the entire amp on the last 2 builds and a few other amps that it became obvious to me that these do make a difference...I wish I could be more specific about other type pots as the next build want to use the Clerostats or Bournes.. Maybe someone else here who has used different type pots can chime in and give some opinions..Anyone here ever seen a volume control on a Dumble here with an Alpha?

Tony

[Sonny ReVerb]

...Why did the manufacturers fix that when it wasn't broken?

I think the 10% pots are considered more 'accurate', i.e. half the knob rotation gives you half the available volume. They should provide finer control over the lower portion of the volume range. The 30% would ramp up more quickly with little perceived change over the last half of rotation.

HAD used 30%, so that's what everyone wants to use. It's just a variable resistor, so either will provide the same result but at different knob positions. Now the composition of the trace may be a different matter, which will probably lead to a carbon comp vs. carbon film miasma.

[ampdork]

Log pots today are actually two linear tracks spliced at an angle and joined....giving a pseudo audio taper.

Not answering anything really just pointing it out.

[Structo]

Where did you read that?
Can you cite a source?

It does make sense that the material of the trace would have an effect.

But in most all the locations it is low voltage right?
So maybe it doesn't matter that much.

I am not doubting what you hear Tony, just thinking out loud.

Aren't Alpha pots carbon traces?

[Bob-I]

Where did you read that?
Can you cite a source?

It does make sense that the material of the trace would have an effect.

But in most all the locations it is low voltage right?
So maybe it doesn't matter that much.

I am not doubting what you hear Tony, just thinking out loud.

Aren't Alpha pots carbon traces?

I read that here. http://www.geofex.com/article_folders/p ... tscret.htm

Not sure on the source but I've measured some alpha pots and I agree.

[Structo]

Thanks, I remember reading that a long time ago. Good information.

It does seem like the potentiometer is a crude, antiquated device.
But they work and most of the time they do what we want them to do.

I didn't recall that they may use different materials in the same arc for resistance.

I would think the quality of the wiper would also play into how well they track.

I used to use a lot of CTS pots in my guitars and amps and still do on most of my guitars.

But when I started getting ones with the white nylon shaft I thought that was a pretty cheap move.
I later found out they have several designs that they sell concurrently.
So it depends on the vendor or supplier as to what you actually get.
They can alter a lot of things in the manufacture of pots.
Such as rotation resistance, taper, etc.
It just depends on the stock that the supplier orders.

I know that CTS still makes the ones with the brass shafts but they seem to be harder to find than they used to be.

The PEC are nice but are about $10 a pop.

Haven't tried any of the Bournes yet.

[glasman]

I did some testing a while back on some CTS pots that I picked up from CEDist.

They exhibited a very pure log response. You can still order J Taper (30%) elements from CTS, but they are not cheap . I requested a quote for a J taper, 1M with push pull switch and they were ~$4.75/ea for 1000 quantity.

I ended up ordering a custom line of pots from Alpha. 30% taper with +/-10% tolerance. I honestly think, the 30% pots make a sonic difference. Who knows maybe it is only because I can run the input gain around 11:00 and that makes me feel better.

I am pretty sure that Alpha is making the elements for the current line of CTS pots, why, the construction is virtually identical, I have taken Alpha elements and grafted them into CTS housings (I wanted the switch ).

[David Root]

J taper Allen Bradley pots appear to have become unobtainium.

Hopefully the PEC and Clarostat RV4s are as good.

I did see a post on gearslutz.com that conductive plastic "is better than carbon", but no reason given.

Anyone have any experience/opinions?

[glasman]

J taper Allen Bradley pots appear to have become unobtainium.

Hopefully the PEC and Clarostat RV4s are as good.

I did see a post on gearslutz.com that conductive plastic "is better than carbon", but no reason given.

Anyone have any experience/opinions?

Not sure on the PEC's and RV4's. I had a local bring a TW clone by for me to see if I could find a hum and it had PEC's. Honestly, I didn;'t think they worth the $7 to $12 they get for them. I tried some Bourns and was not happy at all, 10% taper and the rotation felt like crapola.

Conductive plastic probably has a much lower noise figure than carbon, but probably imparts it own sonic signature, just as carbon does. Might be fun to try them in a project amp.

[fishy]

Mixed reports on the Bourns. Some have had no issues while others have. I know of one builder who had the pot physically fall apart...not good.

I have used the PECs.... I like those but pricey. If you are building something with a few pots it is easier to swallow.

Clarostats.....used those in my Express and I agree with Gary on those. They are poor value.

[greiswig]

I honestly think, the 30% pots make a sonic difference. Who knows maybe it is only because I can run the input gain around 11:00 and that makes me feel better.

Probably shouldn't discount that factor. Also, for my part the controls on these amps are often used more like they were boost controls (turning up) rather than cut (turning down). So being able to start hitting the "sweet spot" of a control earlier (11:00 versus 2:00) means that there is more room and resolution to fine tune the control up above that spot?