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ransom peek 26th October 2006 08:03 PM

Interesting! ALPS blue velvet pot test results....
I just purchased a blue velvet RK27112A pot from AMB, and have tested, at 7 points, the resistances of the two channels for tracking.

Here are the results in K ohms (using a high accuracy B&K meter) and calculated percentage deviation :

0.001 0.001 0.00%
0.621 0.613 1.29%
2.156 2.188-1.48%
7.500 7.400 1.33%
13.70 13.50 1.46%
33.40 32.84 1.68%
49.70 48.70 2.01%

The specs for the pot say:

-6.0 db to 0 db within 3 db,
-80 db to -60 db within 5 db possible

Is this pot a good choice for attenuation for a briangt lm3875 chipamp?

Is this pot within spec?

DcibeL 26th October 2006 08:57 PM

The Alps Blue Velvet are excellent potentiometers. AFAIK they are a conductive plastic type, and because of this will last a very long time without wearing out.

ransom peek 26th October 2006 10:27 PM

The two elements are over 2% off relative to each other in resistance readings at some points on the curve.

The question is, how does this affect performance when used as an attentuator between cd player and the chipamp...

And, would this be within spec, when the spec tolerance is defined in terms of decibel tolerance.

wrenchone 26th October 2006 11:30 PM

2% is a pretty close match for a ganged pot. I doubt you're going to do any better without going to a stepped attenuator with discrete resistors.

ransom peek 27th October 2006 03:44 PM

How would you relate the specs for a pot that are in db to the measured resistance values?

How noticeable would 2% resistance variation be to the ear?

SY 27th October 2006 04:22 PM

2% corresponds to about 0.17dB difference. That's pretty small. I'd want to do better, but I admit that it probably wouldn't be audible.

Stuey 28th October 2006 02:52 AM

Not probably I reckon; you won't hear that at all.

cocolino 28th October 2006 04:48 AM

Interesting! ALPS blue velvet pot test results....
I have measured a couple of those blue ALPS pots also and can confirm Your measurements. They all performed way better than specs.
The specifications are for worst case what means if You buy one You MIGHT have bad luck in getting one which actually has a tracking error of 3dB (according spes) between channels, what would be quite noticeable (I would say useless for good audio).
So it`s good to know they usually perform much better than this.

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