Wierd ALPS motorised Pot - diyAudio
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Old 4th May 2007, 02:02 AM   #1
jaycee is offline jaycee  United Kingdom
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Location: Norwich, UK
Default Wierd ALPS motorised Pot

I pulled this thing out of a Pioneer XR-P250 stereo system that the neighbour threw away when the CD player quit. I was planning to use it in my amp and figured it would just be an ALPS motorised pot (it looks similar to an RK168)

However when I measured the pins, it didn't correspond to any of the dual pots ALPS seem to have data on. It also had some wierd connections in the original Pioneer. Here is a rough idea of how one channel was connected:

Click the image to open in full size.

I measured the following:

Between 7 and 3 = 84K
Between 8 and 3 = 42K
Between 8 and 7 = 42K
Between 2 and 8 = 42K->0->42K (turning CW)
Between 2 and 7 = 84K->0 (turning CW)
Between 2 and 3 = 0->84K (turning CW)

Obviously I could just use the normal connections (2, 3 and 7) but 84K is a little high for a volume pot. I'm also intrigued as to how this arrangement is supposed to work. The pot was mounted on an individual board containing the pot, H-bridge IC, preamp based around a 4558, and muting transistors.

edit: The code sticker on the pot says
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Old 4th May 2007, 02:15 AM   #2
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Location: Sussex, UK
Does it have some kind of 'loudness' control built in for low volumes?
Just a guess
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Old 4th May 2007, 02:29 AM   #3
jaycee is offline jaycee  United Kingdom
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That was what I was thinking.. but 42K-0-42K thing coupled with what appears to be a filter makes me think its some kind of trick to keep the impedance constant across the whole range of the control.
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Old 4th May 2007, 04:47 AM   #4
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It has seven connections...
then it is a dual stereo pot with loudness connection.
What confuses is the ground connection and is shorted internally for both the pots.

Gajanan Phadte
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Old 4th May 2007, 05:25 AM   #5
jaycee is offline jaycee  United Kingdom
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Location: Norwich, UK
Cool, I get it now.

Just wondering how best to use this. Obviously, I don't want a "loudness" circuit in my hi-fi amp altering the sound!

looking at this helps. Hm, according to tests, this is a linear pot.
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