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Old 15th March 2013, 08:08 AM   #1
Mooly is offline Mooly  United Kingdom
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Default Potentiometers. Cermet vs conductive plastic vs cost and other questions.

I've been looking at pots and am slightly shocked by the price range of parts on offer. So as a general kind of question to start with, what do you feel are the advantages/disadvantages of cermet vs conductive plastic tracks. I've seen reference to cermets not tolerating wear very well when compared to the conductive plastic types. Is there any truth or otherwise in that ? The cost of some of these parts is (imo) outrageous at 12-15 each. I'm thinking specifically of the Vishay/Spectrol types.

Which brings me on to these, which I've used as a "stop gap" before now and for experimenting, and tbh I haven't had any problems or any real concerns over quality in the limited use they have had. They are around 1/6th the price of the Vishays and use conductive plastic tracks.

Click the image to open in full size.

Anyone any thoughts on these cheaper "Omeg" types in particular ?
For example, for a pot that might receive very limited use (a tone control for example where it is adjust and essentially leave unaltered for long periods) would you be happy with pots like these.

Another question concerns crosstalk which I never see mentioned. With pots in the 10K region is this a real issue ?
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Old 17th March 2013, 07:42 PM   #2
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They sound quite good but they are mechanically fragile.
I had some that failed after hard use.
There are ones in metal cases from Ohmeg that seem to be more rugged.
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Old 17th March 2013, 07:52 PM   #3
Mooly is offline Mooly  United Kingdom
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Thanks for that Joachim. Its interesting to hear your experience of them.
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Old 18th March 2013, 02:05 AM   #4
EssB is offline EssB  United Kingdom
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Hi Mooly,
I just realised that I used one of those green Omeg CP pots in an oscillator (10K dual Log). The oscillator wasn't much cop but the pot worked fine. I thought the pot was causing some distortion so swapped it out for fixed resistors only to find the pot wasn't to blame.
I've used Omeg carbon pots a lot for general purpose and replacements and think they're fine for such use. The green ones feel stiffer but smoother than the carbon ones. I usually get them from ESR.
The elements in the green dual ones are about 7mm apart so I wouldn't expect crosstalk problems. Maybe the lack of metal screening might cause some problem with higher values. I bet a lot of people forget to ground the metal housing when they put them in an ABS project case.
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Old 18th March 2013, 08:01 AM   #5
Mooly is offline Mooly  United Kingdom
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Hi Essb,
its good to hear you found them OK. I know what you mean about the feel of those green ones, they feel to me like they are packed with really viscous grease but it certainly gives a great action to them.

Its really the long term durability of them that I wondered about, how they would be 3,5, 10 years down the line and whether they would still operate reliably. Actual use of them would be absolutely minimal and the values I'm looking at are all below 5K.

Thanks, that's helped me decide.... and I just can't see the value in those Vishay types
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Old 21st March 2013, 10:00 PM   #6
PChi is offline PChi  United Kingdom
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My understanding is that in general the cermet types have the lowest temperature coefficient and best stability.

The conductive plastic types have good life but less good stability and high temperature coefficients. The conductive plastic type drift badly in my crude notch filter.

Possibly the Vishay types will have a longer life, or possibly not.
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Old 22nd March 2013, 07:34 AM   #7
Mooly is offline Mooly  United Kingdom
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I can imagine a notch a filter is very critical on stability of the pot. Something to keep in mind, thanks.

(For the price I would hope the Vishays have a longer life )
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