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Old 9th September 2004, 01:19 PM   #1
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Default So I did try all those different potentiometers

Recently I've been experimenting a bit with different pots. Here's what I tried (from left): Taiwan Alpha, Panasonic, Nobel, PEC carbon, discreet switcher based on fixed series Vishay/tantalum and switching Holcos for shunt.

None of those pots is completely neutral and all of them show their sonic signature when placed at amp's input.
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Old 9th September 2004, 01:29 PM   #2
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Default Re: So I did try all those different potentiometers

Quote:
Originally posted by Peter Daniel
None of those pots is completely neutral and all of them show their sonic signature when placed at amp's input.
I suppose that you are comparing pots/switches with the same impedance?
Let's say, are they all 50k log?

With no input buffer (just a pot as a "passive pre") what works best is 10k.
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Old 9th September 2004, 01:34 PM   #3
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So deciding on using one or the other will greatly depend on personal taste (and the rest of the system).

Panasonic was the first one I evaluated. It has very natural sound and it is a rather musical pot. It's signature reminds of Panasonic FC capacitors: involving presentation. The only reservation I had here was the way it was softening the top end. But again, in some systems it may be desirable.

Nobel sounds cleaner than Panasonic and has more high frequency extention, however it's not as musical. If you fancy musicality, you'd better suited with Panasonic, if detail and speed is your thing, Nobel may be the right choice.

Two days ago I received this Alpha pot from Jaycar in New Zeland. As you see, it's very tiny and it could easily fit in a Walkman. It made very favourable first impression. It's not completely neutral, as it shows some slight coloration in upper midrange, but it's not very obvious. Also the detail is very good, but not as good as straight wire.

What I noticed comparing to Nobel, was slight loss of clarity and a bit less of separation and layering of instruments. It seemed that Alpha may had touch more bass

None of those pots was better than a switching volume attenuator built from discreet resistors.
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Old 9th September 2004, 01:35 PM   #4
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Default Re: Re: So I did try all those different potentiometers

Quote:
Originally posted by carlosfm


I suppose that you are comparing pots/switches with the same impedance?
Let's say, are they all 50k log?

With no input buffer (just a pot as a "passive pre") what works best is 10k.
Yes indeed. All of them are 50k, log.
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Old 9th September 2004, 02:04 PM   #5
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I left the best for last.

Recently, a forum member suggested to me trying the carbon pot from Precision Electronic Components. Digi-Key carries mono versions of the pot, but since the company is located in Toronto, I didn't have problem with sourcing few samples of a stereo version.

After I substituted my previous reference (discreet switcher) with this carbon pot, I was simply blown away.

None of the previously described potentiometers, or even the switching attenuator, had the amount of musicality and coherence that this carbon pot presents. I like it a lot, as it actually sounds like music. The other attenuators are more mechanical in character, what makes music sound more artificial.

After longer periods of evaluation, I noticed that the signature of this pot is pretty strong. It shows some tubiness, or "mushy" sound. For instance, Nobel sounds much cleaner, but again, less involving. There is no loss in detail however, and the resolution in highs is very good.

I tried to eliminate somehow this signature and soldered 22k nude Vishay parallel to IN/ OUT pins on the pot. Indeed it reduced the tuby sound, made things more bright, but the musicality disappeared somewhat as well. I guess it's better to leave it as it is.

It is my current pot of choice, and actually I have a hrad time deciding if I prefer listening with ML380 premap, or just this carbon pot.

As good as the preamp is (it's a modified unit) it still has some traces of 'processed' music. Listening to pot directly makes the presentation more spontaneous and more involving.

After saying that, and after some cosultations with friends, nothing beats S&B TVC line stage so far, none of those pots and probably not even modified ML380 preamp

Here's the pic of the inside of PEC pot.
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Old 9th September 2004, 02:10 PM   #6
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This is what I've been told with regards to their build quality:

Quote:
Instead of cheap silkscreened resistive elements, they use a hot molded
carbon element, the same hot molded process used for making carbon comp
fixed resistors.

Instead of using silkscreened conductor paths with the terminals riveted to
them (because you can't solder to the silver-loaded epoxy), they use solid
one-piece terminals.

Instead of using spring metal for the wiper conductor, they use a solid
molded slug of carbon. It fits into a molded piece of plastic which is
attached to a spring metal disc to provide the contact pressure.
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Old 9th September 2004, 02:11 PM   #7
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Konnichiwa,

Quote:
Originally posted by Peter Daniel
None of the previously described potentiometers, or even the switching attenuator, had the amount of musicality and coherence that this carbon pot presents. I like it a lot, as it actually sounds like music. The other attenuators are more mechanical in character, what makes music sound more artificial.
Try this:

Use a 1M Linear law version of the Carbon track pot you use.

Use 33-47k Law Fake resistor across out & gnd, use whatever sounds best to you, Carbon composition would be my take.

If you where still using the IGC Circuit with a 10K input Impedance I'd recommend simply a 250K Lin version of this pot, input impedance lawfakes by itself....

Sayonara
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Old 9th September 2004, 02:18 PM   #8
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Everytime I put a good pre instead of the passive pot I hear improvements.
Clearer, more definition, real harmonics.
I've tested this too many times.
Last week again.
A pot as a passive pre.
Then, an op-amp after it.
Bingo.
An open window.
The pot was the same, I've just put a TPA6120 after it.
Yes, a good pre can be just as simple as using the right op-amp.
Too many parts and too long a signal path just throws it all away.
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Old 9th September 2004, 02:21 PM   #9
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Hello Peter,
Thank you for taking the time to share with us your findings. Funny enough, I was just thinking about getting some pots for my experimental rig with Behringer xover.
I always find your posts very interesting, detailed and informative, and I always enjoy reading them.
Stay well
AR2
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Old 9th September 2004, 02:25 PM   #10
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Quote:
Originally posted by carlosfm
Everytime I put a good pre instead of the passive pot I hear improvements.
Clearer, more definition, real harmonics.
I've tested this too many times.
Last week again.
A pot as a passive pre.
Then, an op-amp after it.
Bingo.
An open window.
The pot was the same, I've just put a TPA6120 after it.
Yes, a good pre can be just as simple as using the right op-amp.
Too many parts and too long a signal path just throws it all away.
It is my observation that a quality of the pot IS very critical (when placed at amp's input). It may make or brake the sound of the amp. When properly chosen it will will sound cleaner and more natural than even a very good active stage.

So far I didn't find the active stage I can live with in a long run. But I can live with a good pot. And as I said already, the passive TVC stage is probably most "pure" sounding of them all.

In closing, one can't argue about the value Alpha pot offers. For the money, it's a bargain, I think.
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