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AUDIO FORUMS >> D.I.Y. >> PEC pot on CD out?
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Message started by Brian on 08/03/10 at 23:17:47

Title: PEC pot on CD out?
Post by Brian on 08/03/10 at 23:17:47

A few years ago the PEC carbon pot received great applause on these boards as a volume control on power amps. Does the variety of potentiometer brands and types make a similar effect on the output of a source as they make on the input of an amplifier?

Title: Re: PEC pot on CD out?
Post by proud_indian on 08/04/10 at 04:46:55

I used it on the amp, and it did sound good. But after a very short time, the right channel got scratchy. As it is a sealed unit, I could not use it anymore, and moved on to a stepped attenuator. Even the tolerance was not god, so at low volumes it was a pain. Maybe I got a bum unit. I think it was Eli or Steve E who said that you could open it up in some thread, which I am unable to find. But, while it lasted, it did sound good. Takes about 150 hrs to break in.

shreekant :)

Title: Re: PEC pot on CD out?
Post by Brian on 08/04/10 at 06:54:29

Thank you for the warning shreekant. That rather turns me against them; but I am still wondering if the output end of a device is similar to the input, in that a volume control can sound better or worse depending on the brand and model and type.

Title: Re: PEC pot on CD out?
Post by proud_indian on 08/04/10 at 17:25:15

Yes, it can sound better or worse. Look at the pictures of the cd 200 that Steve has on the site. You will notice the stepped attenuators. Now unless you have a voltage gain problem ie if you are using the Zkit or some of the gain pre's I don't think you need it for a 2V output. If your CDP is a standard 2V, you may be better off looking at your RCA inputs ( female) most of them are junk.

shreekant :)

Title: Re: PEC pot on CD out?
Post by Brian on 08/04/10 at 20:48:36

It was Decware's model 200i I was thinking of. I wondered if I were to get one if I ought to ask for the PEC pots as an option.

Title: Re: PEC pot on CD out?
Post by proud_indian on 08/05/10 at 17:52:04

If you are buying it from Steve, then I guess you let him decide. I am sure he would have checked the PEC to the stepped.

shreekant :)

Title: Re: PEC pot on CD out?
Post by Brett on 04/03/11 at 00:40:17

I've been around a good share of PEC pots and they can be horribly mismatched channel to channel. So you really need to buy a few of them to get a good one.

And if that wasn't enough the 100K Ohm load resistance doesn't handle much current without causing the scratching. So sources that have a lot of output capacitance (.47uf in my case) can discharge and cause oxides that hamper conductivity and cause scratching. PEC Pots that are only driven by low voltage low current op amps for example don't develop this issue.

The cure for this is to buy the 1 Million Ohm version of the PEC and by pass the internal load resistance with a 2 watt 100K resistor (law faking resistor). That way the variable 1M Ohm series resistance is enough to lower the volume, yet the source still sees a 100K Ohm load parallel to signal and ground. But still you have to deal with the potential channel imbalance.

Shame because from a design standpoint it really is beautiful and they do sound very nice. Wish someone would take the time to manufacture one with more exacting standards.