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Old 21st October 2004, 05:21 PM   #1
wrl is offline wrl  United States
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Default Problem with ALPS pots?

I have just recieved a set of alps blue motorized pots (model # RK27112MC030). These are supposed to be 100 k dual ganged motor driven units.

1) The maximum resistance is 84K on one resistor, 82 K on the other.

2) At midway through the rotation, one resistor has a 2K difference between gangs, the other has a 4K difference between gangs.

Is this normal? I mean these are 45 dollar resistors... the overall quality seems very high but I would have expected more precision.

-Wes
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Old 21st October 2004, 05:31 PM   #2
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Hi,
Where did you get your pots. Were they from Ebay- sourced from Hong Kong / China.
There are fakes out there of dubious quality.

Shoog
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Old 21st October 2004, 05:35 PM   #3
wrl is offline wrl  United States
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I got them from Michael Percy Audio. I was concerned with that after I have heard many reports of fakes, but these feel very high quality and MPA is a respected vender.

Hence my confusion when I broke out the multimeter (btw, this isn' a mutimeter issue as I have tried two seperate ones and gotten the same results)

-Wes
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Old 21st October 2004, 08:02 PM   #4
sam9 is offline sam9  United States
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You might give Percy a call and ask himm if this is "normal" tolerance. I looked on the Alps website and the spec calls for 20% resistance tolerance. 84k and are within that.

Are these linear or "audio" (log) taper. The common wisdom is that linear taper tends to be more consistant. On top of that using a resistor value equal to 15% of pot value and connected betwenn the wiper and ground pin of a linear pot results in a curve closer to the usual log taper (see sound.au.com. It is covered in one of the projects)

Lastly, what is most important is the resultant voltage divider ratioes. Calculate the the ratio for each of the coupled gangs in the middle range of the pot. The difference between these in dB will give an indication of whether you are likely to have a right/left mistracking you can hear.

PS: I prefer traditional mechanical pot to stepped attenuators or IC's, but certainly understand what drive some people toward these alternatives. I've also found cheap linear dual-gang pots don't seem to be any more inaccurate than expensive ones. I just zap them with ProGold or similar snake oil ever 2-3 years.
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Old 21st October 2004, 08:48 PM   #5
wrl is offline wrl  United States
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I spoke with Micheal Percy and he said that this is normal.

Checking ALPS websight, they do fall within the 20% tolerance. I guess I just figured that a resistor this expensive would be a little more accurate considering my 2 dollar radio shack alps pots were closer in tolerance.

I haven't installed them so I don't know if I'll hear any audible difference, but I can always adjust the gain on my crossovers to compensate if need be.

Any other comments or experience with these pots would be welcome.

Thanks
-Wes
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