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Help me ID this potentiometer?
Help me ID this potentiometer?
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Old 8th May 2021, 06:06 AM   #1
andrewhogge is offline andrewhogge
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Default Help me ID this potentiometer?

Hi there,

I have an old Cello Palette Preamp and the main level pot has a weird lull/jump at 5 (12 o'clock) - right around that point one channel drops out slightly and the at 6 (1 o'clock) the volume jumps MUCH louder. There is no crackling so I'm not sure it would be a dirty pot. I've only ever changed out an alps blue 100k pot before, but this one I'm not familiar with. Its a 50k 10% but small white box shape and appears it might be even soldered down to the board beneath. Any help appreciated!

IMG_2597.jpeg
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Old 8th May 2021, 06:16 AM   #2
andrewhogge is offline andrewhogge
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OK I think its Vishay surface mount but not seeing one that has connections on top like this. Flipping over this board to see how many pins go through.
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Old 8th May 2021, 07:32 AM   #3
Mooly is offline Mooly  United Kingdom
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Help me ID this potentiometer?
That does look a weird thing.

You have to look how many pins in total. Three along one edge is a normal pot, a fourth pin (the one on top??) could be a tapping for a loudness circuit.
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Old 8th May 2021, 08:52 AM   #4
johnmath is offline johnmath  Australia
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Looks like a Vishay P11 option J (see page 13 in the data sheet linked):

https://www.vishay.com/docs/51031/p11sp11a.pdf
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Old 8th May 2021, 09:06 AM   #5
H713 is offline H713  United States
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Definitely a Vishay / Sfernice pot, and I would guess that the top terminal is some sort of loudness tap.

I'm surprised it's bad. Those pots are extremely high-quality (and seriously expensive). I consider those to be among the best small form factor pots on the market. Mouser carries some, and I know AML (audio maintenance limited) carries some as well. In all likelihood though, it's a custom part.

You could try contacting State electronics. They tend to handle all of the custom modular potentiometer tasks and have for a really long time. You'll pay, but they might have an option.

What's the shaft size and pin spacing?
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Old 8th May 2021, 11:04 AM   #6
Lampie519 is offline Lampie519  Netherlands
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I also use these pots sometimes but not with a center tap.
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Old 8th May 2021, 11:50 AM   #7
Lampie519 is offline Lampie519  Netherlands
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Maybe the source of the problem is not the pot as mentioned earlier. It could be the signal offered on the taps. Check if this is not out of phase or worse...
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Old 8th May 2021, 12:49 PM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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I would scope the pot as you turn it and see if the signal jumps.
Could be a coupling capacitor gone somewhere and upsetting DC conditions.
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Old 8th May 2021, 05:03 PM   #9
H713 is offline H713  United States
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Okay, looking at the price / value of this piece of equipment, the cost of a custom pot from State maybe isn't as big an issue as I thought. That would probably be my next course of action if I were the OP.
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Old 8th May 2021, 10:57 PM   #10
andrewhogge is offline andrewhogge
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Right, thank you for all the input!

I'm always a bit out of my depth here, but I do have a hunch its not the pot, just figured I might try to replace that first see if it fixed the problem, but yes its not your typical oxidization issue. When the pot is about half way turned there is a a discrepancy between channels for a very small portion of the turn and then it jumps in volume significantly. Only and always in the same position, its not intermittent.

I don't own a scope unfortunately, but I do know the local service on Cello gear is quite pricey so hoped to DIY if I could. Figured changing out the pot was the first step before losing more money and listening time putting it in the shop.

That Vishay looks close but correct its missing the tap. I haver to do quite a lot of disassembly to get it removed and check the pin spacing, but the shaft measures 6mm.

IMG_2598.jpg

Pot is top right corner, but I will have to disassemble 4 more to flip the board.

Last edited by andrewhogge; 8th May 2021 at 11:17 PM.
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