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Old 1st December 2007, 02:10 PM   #1
jol50 is offline jol50  United States
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Default How to ID volume & fader pots?

This is a long story so I'll be brief and tell you the situation I am in with this project. I have an old piece missing the volume and fader control. After a long wait I have managed to procure a similiar one temporary to ID them and find a substitute. But I find they are mounted and such that I can't get a number off them or see what pins go where, but can test them disconnected with some hassle. That is as far as I dare hack apart this other one. They are square just over 1/2" body, should be high quality. I'd guess they are dual/stereo and audio taper.

Is there a quick/standard way to test them? Any suggestions for common high quality brands/etc? Also going to panel mount these and will just run extension wires to them the way I want to do this, need to fit small knobs to them. Thanks for any tips!
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Old 1st December 2007, 07:50 PM   #2
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Aw c'mon, if it's cool enough for this much time and patience you gotta tell us what it is! Someone may already know the answers you seek.

The typical analog car audio volume control is a dual pot with on/off switch, and balance or tone controls added as well. The volume pots are usually two rows of 3 pins, one row per pot. Two of the three pins will read a constant resistance regardless of shaft position. That resistance value is the pot value you’re looking for. The third pin is the wiper, which will read between shorted and full pot value depending on the shaft position. Make a note of whether that value increases or decreases as you turn the shaft clockwise.

The fader has the same caveat, other features may be integrated in that unit. The fader pots may be a dual with one pot per side like the volume with one wiper connected as “R input” and the ends of the corresponding pot connected as RF and RR “outputs”, and likewise for the left. Other situations could be possible, but if your pot doesn’t have other controls or switches added, you can read it this way.

Typical analog car audio volume/balance/fader potentiometer values were in the 10kohm to 50kohm range, and most volume pots I encountered were 10k.

BTW, I have a few of these units leftover from the old days.

Tim
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Old 2nd December 2007, 01:12 AM   #3
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Volume controls can have 3 or 4 terminals per channel. If the control has 4 terminals, the 4th will tap onto the resistive element at approximately the 2:00 position. If you want to know the resistance of the pot, you have to measure across the outside terminals (not including the tap if it's in line with the other terminals).


The fader is probably going to have 3 terminals per channel. It's generally used to drive one output (front/rear) to ground when faded fully either way. You'd read the resistance across the outside terminals. In some faders (and balance controls), when the control is centered, the center terminal is shorted to one of the outer terminals.
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Old 2nd December 2007, 05:50 AM   #4
jol50 is offline jol50  United States
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You are going to make me tell you.... man you are mean. You might know the answer anyway but I was going to learn it the hard way. It is a pa 2 r, they heatshrinked the pots onto the cables with some huge stuff, and I don't want to cut into 20yr old (new, unused) cables that are not mine. So the static value, makes perfect sense now that I think about it. The volume/gain has an off switch, the fader is different, the rest look the same- the tone controls. Also have to figure out the pinouts to DINs. They are awesome stuff for old school, but I guess today there are digital tools that do the job. I was going to have the place make it for me, but thinking I will have a go at it myself now that I have another one to look at, other fund eating projects, and winter spare time. In the old days we drove LP amps into overdrive with these, what an amazing difference they made...but expensive!
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Old 3rd December 2007, 04:59 AM   #5
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So you have a rare old PAII remote without the volume and fader? And you can't use it. You know, when you turn your back it sticks out its tongue and mocks you!


Quote:
They are awesome stuff for old school, but I guess today there are digital tools that do the job.
Analog stuff of this quality can get most any job done if the installer has the know how to implement it. Digital equipment may be easier to manipulate, but not necessarily better. IMHO, of course. A worthy cassette deck is welcome in my dash.

Quote:
The volume/gain has an off switch, the fader is different, the rest look the same- the tone controls. Also have to figure out the pinouts to DINs
Finding an equivalent quality volume pot of the correct value with an on/off switch may not be a trivial task. You could break the on/off line out to a separate switch to make that easier and cheaper.

Aren't they min-DIN's? It might be easier to open the unit up, plug the cables in and read off the PCB terminals. Then, translate the DIN configuration through the jack.

How many pins?

I'd start by checking with Linear. They may actually tell you the values or send you a schematic. I've had schematics emailed, even snail-mailed by Zapco, Nakamichi, and (long ago) Rockford Fosgate. Nak sent mailed me the entire ~10 page set of schematics for my TD-700 at no charge!

BTW, if you haven't checked before, good pots that track well are expensive.

Tim
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Old 3rd December 2007, 02:38 PM   #6
jol50 is offline jol50  United States
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LP is gone, but there is the place that services them. I had a quote for them to do this but it is just not worth it, can ask about parts. I bought all new cables for it that will be cut down. The pots have a little board on them too but don't think any components are on there.

Maybe I should not have bid on it? Might be more of a pain than it is worth, but at the time wanted one bad enough I guess.

Anther point is I can turn the knob and adjust my sound driving, these new HU you can't do that stuff driving.
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Old 3rd December 2007, 03:47 PM   #7
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LP is supposed to begin production again. Unfortunately, they will not sell you parts. I had an LP amp that needed a gain pot and they would not sell it to me. To have it replaced, it had to be sent to the authorized repair center. The flat rate price was $150.

If the volume pot isn't part of the gain circuit (only used as a variable voltage divider), you could use virtually any value between 5k and 100k. Depending on the balance circuit, it may work with no balance pot installed. If it doesn't work without the balance pot, you should be able to use jumpers to bypass the balance control.
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Old 3rd December 2007, 04:45 PM   #8
jol50 is offline jol50  United States
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I didn't think they would sell parts, but I have asked. I have another one here to measure not had time yet. Really don't know what the off is for on the volume/gain, maybe off or it is a bypass. It is also a pre-amp/line driver, and typically you use this volume instead of the HU but don't have to. It has a 30v power supply in it. I think it puts out 5v max. Doubt I would ever turn it off anyway.

If I could find some big thermal tubing for it, I could cut them apart and find out what they are but suspect they have been subbed by now anyway. They are more narrow than I thought, maybe .5 inch and a little taller and squarish. Metal shaft with alum knobs. It also has 2 LED but figure I could measure output voltage to figure those. In fact, I need to run it and see if it works.

There is the master volume/gain, fader, then 4 EQ pots. I bought another NIB for not a lot more than the repair quote, but it is for a friend and he wants it....I said not until I figure it out since he is not going to use it now anyway (maybe in spring)...'or you can buy your own stuff,' and he has no PC, lol. This one I still have well under half into with cables and unit.
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Old 3rd December 2007, 04:58 PM   #9
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Mcmaster has large heatshrink tubing. Type "page 777" into the search field on their site. For more options, search for "heat-shrink tubing".

http://www.mcmaster.com/
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Old 3rd December 2007, 05:47 PM   #10
jol50 is offline jol50  United States
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I'll look at it thanks. I measured and they are about 7/16 H x 3/8 W x 3/4 long best I can tell with the tubing on them (volume one), it is glued on inside also and that is not counting the little board under them. I did figure out a couple things; the volume has a switch that goes on, clicks off, the rest is a dual 10K. The rest are the same I think, the plugs are same and no labeling different as the knobs are not mounted and have printing on them, can test later to make sure. They are 50K dual pots. You know how hard it is to probe those mini dins..... So how would I find out the quality these need to be? Aside from the fact that most I have looked at are singles.

Only thing like that I see are the ALPS 12mm on p579 mouser and the similiar panasonic at digikey. I did not check for taper yet. They are only a couple bucks, but that does not cover the switched volume. And would need to figure out how to put wires on them.

They should at least give you basic info to repair this ancient stuff they don't sell anymore, but some companies are not nice.
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