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beans

Op Amp for Reverb circuit HD130

I have an early release Music Man HD130 Reverb with the tube inverter. Chassis 2275-130. My tech told me that the op amp that drives the reverb is bad. I found a replacement, but how do I know which one it is on the circuit board? (There are seven of them).

mm210
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You REALLY need to ask him

You REALLY need to ask him which one. There are more than one IC's in the reverb chain so "driver" may not be the right choice of words. Ask him if he meant the one that is directly before the tank. That would be IC-5. OOPS-forgot to ask if you had IC sockets or are they hardwired in? Mike.

beans

I'm no expert, but I see two

I'm no expert, but I see two LM307H IC's in what I think is the reverb circuit on the schematic. If I am looking at the guts of the amp from the front, there are seven LM307H cans -- from left to right, would that be the 5th one? I think I am just going to order 7 of these from littlediode.com and just repace them all. I will post what happens. This amp sat with hardly any use from 1980 until now. It was a beast for me back in the 70's. I had this fully recapped recently, but it still much noisier than I remember it being "back in the day". Hopefully changing out the op amps with do the trick...

mm210
mm210's picture

If it has sockets, did you

If it has sockets, did you try pulling them out and wiggleing them around to clean the pin? Slight corrosion can do the same thing. Mike.

OOPS-according to little diode, they ONLY have 1. You might look into the brown dog adapters and use current issue opamps. There have been discussions here about the use of the new ones a lot.

beans

Thanks, Mike. Will give that

Thanks, Mike. Will give that a try. I like easy and cost-free ideas.

mm210
mm210's picture

Here-look at this thread.

Here-look at this thread.

http://pacair.com/mmamps3/node/1671

mm210
mm210's picture

By the way, since you are

By the way, since you are having reverb issues, why not pull one of the LM307's that are running in the first channel, that you aren't using and use THEM to diagnose which one is bad. You can just sub and fine the bad one. Mike.

beans

Great idea. Will try it.

Great idea. Will try it.

RD112
RD112's picture

LM 107?

mm210
mm210's picture

Yes, they are available in

Yes, they are available in limited quantities but at usually a ridiculous price in some cases. Just my opinion but a couple of guys(Ok- mainly Ed Goforth-one nice guy) here have done the hard work and TRIED the available current opamps. In my case, if I have to do mine, it will get something current. They are only going to get harder to find. Just my 2c's worth. Mike.

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