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I have an old Crown D-75 amplifier that I acquired a while back and it works like a beaut except one of the volume pots is toast.

The pot has 2 different numbers stamped on it, both of which yield no results on Google.

Can I find out what value of pot to get by measuring with a multimeter?

Has anybody else had an experience doing a fix like this?

Is there a good place to buy parts like this? The pot doesn't look like the standard Radio Shack part (the post on the pot is pretty tiny) and I'd like to match the original as closely as possible.

Note: I do have proper electronic tools (like multimeter, wire strippers, soldering iron, etc) to be able to fix this issue.

Sidenote: This quesiton was spawned off of the question "Scratchy volume pot". Apparently, it's a common practice to clean out old pots when they start to make scratchy noises. Unfortunately, one of the two pots on my amp is completely toast so I need to replace it.

*Update: Sorry about the delay. Here's the pictures as promised. enter image description here

enter image description here

And the part numbers are 1378325, and D4688-4. I'm guessing that one is a part # and the other is a serial #.

Update:

After a close second look at the pictures provided I realized that the part number is actually D4688-4. After some googling I found out that Crown has a section on their site specifically for ordering replacement parts.

Here's the parts list. Turns out it's a 25K pot.

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@Kim If you look at the manuals for most studio quality production equipment, you'll usually see a wiring diagram. This stuff is expensive (the amp I have retailed for ~975 before it was replaced by a newer model) and (at least back in the day) equipment was built to be repaired not replaced when it broke. Check with google; these types of questions are pretty common on pro audio sites. I asked here because: 1. I really do need to replace one of the pots on my amp. 2. I thought this was an appropriate audience for such a common problem. –  Evan Plaice Feb 12 '11 at 2:55
    
I see your points. I think the jury is still out on repair questions: meta.audio.stackexchange.com/questions/96/… -- I'll be happy to follow the direction of the moderators and the majority, so fellow users, please up-vote or comment away :-) –  Kim Burgaard Feb 12 '11 at 5:19
    
can we please have a picture? –  jlebre Feb 12 '11 at 12:47
    
can't edit the above apparently - picture or the numbers please? –  jlebre Feb 12 '11 at 13:06
    
I don't see any outspoken opposition to repair questions, so I've removed my original comment. –  Kim Burgaard Feb 15 '11 at 23:22
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2 Answers 2

Chances are it'll be something like A10k, or A14. That means it's a log pot, 10k resistance, or 1+4(zeros) resistance, or something similar. On older equipment, A will be linear though, and C would be log. Also some pots do say Lin or Log. You would be looking for a single gang, single turn rotary potentiometer.

If you live in the uk, and use places like Farnell, these would help you narrow down a lot your choices on their catalog.

there is still 2 more factors which I'm not really sure how to find: resistance tolerance and voltage rating. Luckily I always had spare part at hands or was send the direct replacement so didn't had to look more in depth than this. Maybe some of the EE guys in this forum could fill me in as well.

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I uploaded the pictures and added the part numbers to the question. Apologies about the delay, I haven't been home (where my amp is) in a few days so I couldn't get the pics. –  Evan Plaice Feb 15 '11 at 23:53
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up vote 2 down vote accepted

If you have a multimeter finding out the resistance value of the potentiometer is trivial. Simply hook one lead to the left, or input lug, and another lead to the middle, or sweeper lug. Set your meter to ohms (resistance) and measure it out. I'm guessing it's likely a 10k like @jlebre mentions.

Once you know the resistance value for the potentiometer, next you need to figure out the taper. It's probably a standard logarithmic audio taper, but I'm not going to bet the horse on that one. I am unaware of any way to find that out other than calling up Crown and asking them what kind of potentiometers they use. Since it is a volume potentiometer, however, I would guess logarithmic audio taper.

As for the voltage rating on the pot, here's a good article on that. Most of the time the voltage rating is of no consequence on audio equipment--but I'm not sure if this is one of those cases.

That's about all you need to replace it :), oh and you'll need some good soldering skills. Hope this helps!

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Nice... This is more along the lines of what I was looking for. While I'm perfectly comfortable with soldering and using a multimeter, I figured there were some special considerations to make with audio equipment. The link you provided was a great read. –  Evan Plaice Mar 14 '11 at 22:29
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