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Old 5th February 2004, 02:09 AM   #1
tcpip is offline tcpip  India
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Default Inexpensive centre detent pots?

Where in the US or UK can I get ordinary, inexpensive, dual-ganged linear taper pots with centre detent? I and a few friends are building some preamps, and I'd really like to have centre-detent pots for the tone controls and balance. I need 100K linear dual-ganged ones for the tone controls and maybe 50K single (though I'll use dual-ganged at a crunch) for the balance one. And I'll be happy with ordinary carbon pots with their 10% accuracy and what not, though better ones, if affordable, would be great. Absolute upper limit: USD 5 per pot. I'm expecting to pay USD 1-2, actually.

Seems like lots of resellers have pots, but I can't find a centre-detent dual-ganged model with them. Farnell's online catalog seems to be the hardest site to search in the world. I have Digikey's printed catalog, but can't seem to find any centre-detent dual-ganged.

One of the threads here had a pointer to a most interesting site: www.potentiometers.com. Their Series 585 commercial grade stock pot seems to have a centre detent option. There are no prices online, so I guess I'll have to write and ask. Also, I've found a source of some spectacular knobs here in Bombay, but they have 4mm shafts, while these Series 585 things have 6mm shafts. Do you have any other pointers? Something with online prices?

Any help will be greatly appreciated, as they say.

Thanks,
Tarun
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Old 5th February 2004, 08:46 AM   #2
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Hi Tarun,

Are you really sure you want cheap pots? My experience with them (basically all I could get) is that the gang error tends to be terrible, and after a while they become scratchy. I gave up in the end and just bypassed my tone controls completely! (after about 10 different volume pots I got one that is barely acceptable, I used to go into Jaycar and ask them if I could borrow a multimeter to test the pots before I bought, Id go through the whole box, and walk out in disgust.

I'm eventually going to get an expensive pot or a stepped attenuator to replace my volume control, I hate having one channel become quiet (or cut out completely) while the other channel is still loud, makes it very difficult to listen at low volume levels.....

Just my opinion

Tony.
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Old 5th February 2004, 01:54 PM   #3
tcpip is offline tcpip  India
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Originally posted by wintermute
Are you really sure you want cheap pots? My experience with them (basically all I could get) is that the gang error tends to be terrible, and after a while they become scratchy.
Thanks, Tony. And I know about these problems. However, I've also seen a lot of systems last many years without any pot replacement. My Nak ZX-9 is twenty years old, and the guy who serviced it said that he rarely finds any need to replace any of the pots on Naks this old. (And my Nak was not exactly lightly used... it's a professional studio piece.) Similarly, my El Cheapo Cambridge Audio amp (it's apparently UKP 100 in the UK) has been behaving itself totally fine for three years now.

So, I guess I'll just have to take my chances. Even if I replace one or two pots every two or three years, it's still very inexpensive in terms of money. What else can I do? Even the simplest alternatives are more expensive than my entire preamp. Any suggestions?

You know, I've thought about trying out all these high-end volume control methods that people keep talking about. Somehow, I'd want a pot at the front-end, just because I find it "more natural to use" (purely subjective). Hence, even if I someday want to build a reed-relay based stepped attenuator, I'll probably use a linear pot on the front, use it to divide a reference voltage, pass the output through an A/D conv, and feed the data to a uC, which will then control the relays. Finally, I want the end-user to see a pot, with a fixed 300-deg rotation, not even one of those going-round-and-round-and-round rotary encoders. I find them non-intuitive, even a bit gimmicky when they are used to simulate a rotary pot volume control. Just me an' my prejudices.

And just curious... if you find good pots hard to get, have you tried getting something like, say, the RK50 range of Alps pots? They claim +/-1dB tracking accuracy from -100dB to 0dB. These pots have all the other audiophile trappings like large size, gold plated contacts, etc. I have no idea of the prices. Check here.

Tarun
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Old 6th February 2004, 02:02 PM   #4
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Hi Tarun,

I can get the RK27 from Farnell (It's the one I was thinking of getting) It costs about $50 Aus, which to me is on the expensive side, I was wondering whether I should get the motorised version, so that I could make a remote volume control but it's $80.... and when it comes down to it, I don't have to walk very far to do it manually

The RK50 looks even better, but I bet even if I could get it, it would cost a small fortune also wouldn't fit in my amp!!!(at least without modification)..

I find the gang error the most annoying thing, but I guess that is something that maybe could be "corrected" mechanically.....

It could be just here in aus that DSE and Jaycar only stock really poorly made pots (or maybe my expectations are too high) (but the scary thing is that these "cheap" pots cost about $6 each)..... I haven't tried any "cheap" pots from Farnell, they may in fact be fine. Although I don't think they have any with centre detents.

Tony.
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Old 7th February 2004, 05:09 AM   #5
tcpip is offline tcpip  India
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Quote:
Originally posted by wintermute
I can get the RK27 from Farnell (It's the one I was thinking of getting) It costs about $50 Aus, which to me is on the expensive side, I was wondering whether I should get the motorised version, so that I could make a remote volume control but it's $80....
You telling me!!! Sigh.... SIGH.... I asked www.potentiometers.com how much it would cost me, in very small quantities, for their Series 388MPLC stock pot, dual ganged, conductive plastic, motorised. Guess how much???? USD 140! And that's not Aussie dollars, it's the US kind.

Quote:
The RK50 looks even better, but I bet even if I could get it, it would cost a small fortune also wouldn't fit in my amp!!!(at least without modification)..
Cool. You can actually claim that you had to reject it because wasn't "compatible" with your high-end amp. I just have to say it's incompatible with my wallet.

Quote:
I find the gang error the most annoying thing, but I guess that is something that maybe could be "corrected" mechanically.....
Does the answer lie in getting not one but two motor pots, one for volume and one for balance? I've been wondering about it too. There's a nice Xicor pot for about USD 10.00, dual ganged, linear, motorised. Maybe two of these will do for volume and balance, keeping all else (i.e. the IR remote circuitry, etc) the same.

Quote:
It could be just here in aus that DSE and Jaycar only stock really poorly made pots (or maybe my expectations are too high) (but the scary thing is that these "cheap" pots cost about $6 each)..... I haven't tried any "cheap" pots from Farnell, they may in fact be fine.
You know, you shouldn't have to spend these incredibly high figures for cheap and mediocre pots. We get similarly cheap pots here for INR 20, dual-ganged, non-motorised, 4mm metal shaft. (INR 45 is about USD 1.00). Send me your postal address, and tell me a few values of pots, and I'll just buy some and send them over to you. They're so inexpensive I won't feel a thing buying them for you. At least you can use them as disposable experimental things. Honest.

Tarun
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Old 7th February 2004, 07:36 AM   #6
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If you can get the exact manufacturers part number, try www.onlinecomponents.com (or was it componentsonline?) They don't seem to have a catalog, just a line card but they will sell small quantities. Minimum order is US$25, but that's better than US$140.
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Old 8th February 2004, 12:15 AM   #7
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Quote:
Originally posted by tcpip

You telling me!!! Sigh.... SIGH.... I asked www.potentiometers.com how much it would cost me, in very small quantities, for their Series 388MPLC stock pot, dual ganged, conductive plastic, motorised. Guess how much???? USD 140! And that's not Aussie dollars, it's the US kind.


Ouch!!!!!!!

Quote:
Cool. You can actually claim that you had to reject it because wasn't "compatible" with your high-end amp. I just have to say it's incompatible with my wallet.
I think though the wallet comes into it more

Quote:
Does the answer lie in getting not one but two motor pots, one for volume and one for balance? I've been wondering about it too. There's a nice Xicor pot for about USD 10.00, dual ganged, linear, motorised. Maybe two of these will do for volume and balance, keeping all else (i.e. the IR remote circuitry, etc) the same.
depends on how bad the gang error is. At one stage I had to use the mute switch on my amp to listen at low volumes (mute on my amp is crude resistor connected to earth switched in, drops volume 20db). The reason I had to do this was that at any volume less that too loud for nomal listening one channel was about 12db down and if you turned it down to what I would call low listening levels then one channel cut out completely! So even the Balance couldn't compensate! I guess the other thing is, that if your Balance pot has bad gang error (probably not so much of a problem in the middle of it's range) then it could fight with the volume pot and make things even worse

Quote:
You know, you shouldn't have to spend these incredibly high figures for cheap and mediocre pots. We get similarly cheap pots here for INR 20, dual-ganged, non-motorised, 4mm metal shaft. (INR 45 is about USD 1.00). Send me your postal address, and tell me a few values of pots, and I'll just buy some and send them over to you. They're so inexpensive I won't feel a thing buying them for you. At least you can use them as disposable experimental things. Honest.

Tarun
Yeah I gave up in the end, paying $6.50 for a piece of rubbish doesn't wash with me, If it was decent quality no problem but not rubbish...... I was going to replace the bass treble and balance pots in my amp cause they have died, but in the end I just bypassed that whole section of the preamp, and drove the power amp directly (via a 1uF cap) from the output of the NE5534 after the volume pot.

Thanks for the offer, I'm about to overhaul the amp, just got all the new caps, I'll see what I think after doing that

Just checked Jaycar and the price has dropped, now $3.50 for dual gang 50K log (or 100K linear), The thing that gets me is it says that they are built to their rigid engineering specifications...... Maybe I should go in again armed with a multimeter and check them out, you just never know.......

I think detents are what's giving you a hard time, I did a bit of a search on farnell UK, and all I could come up with in 100K linear dual gang was this http://www.farnell.com/datasheets/815.pdf

They state at the bottom, that they can do custom versions (detents etc) for DIY with "appropriate" volumes, I wonder how many is "appropriate" Other thing is they are carbon not conductive plastic and cost #2 so don't fit the cheap criteria either (sorry don't know how to get a pound symbol).....

Tony.
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Old 10th February 2006, 08:42 PM   #8
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I just found a company that _may_ be able to build a custom pot for me... http://www.potentiometers.com/ The guy I talked to seemed to think that their Series 70 might be able to be built to do what I need it to do... Once I get my service manual, I can find out what the exact specs on the pots are and see if they can do something for me.
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