Peavey 400BH Need source for U2

[Tech. Tom]

Hello:
The part number on the schematic is 87478 which I can't find.
The numbers on the IC are M31AF 70413080.

I tried Mouser, Digikey and Encompass and can't find it.
Does anyone have a source for this part or a good sub.

Thank you.

Tom

[gui_tarzan]

According to a Peavey cross reference it's an LM-3080N.

[Enzo]

Is yours actually bad? You can remove it and the amp will work, but no longer have clip protection. But many times the problem is not the IC itself, but the fact it is being turned on by the other circuitry. It is controlled by the TL074. And fr that matter, if signal is being stopped at that point, Q17 becomes a suspect too.

[g1]

According to a Peavey cross reference it's an LM-3080N.

Yes, any 3080 should do, LM3080, CA3080 etc.

[Tech. Tom]

Thanks for the information.

[Tech. Tom]

The problem is there is very little output from the amp. At full volume you can hear it but it's very low. All supply voltages check ok. Actually I was checking the voltage on U1 when my probe slipped. I did have the proper plus and minus voltage but now with that ic in the circuit the -15V is down to -11V. It's normal with the ic removed. I haven't worked on one of these before.
I just wanted to have U1 and U2 on hand in case they were bad. It looks like I'll be needing U1. This amp is a pain to work on because there are no part locations on the pc board.
So Enzo is Q17 a high failure part in this amp? I haven't had a chance to get back on this since last week but I'll be doing so tomorrow. I'll pick your brain after that. Thanks for your input.
Tom

[Enzo]

The 400BH is one of Peavey's most widely used power amp boards. We have discussed it many times here. The schematic has been posted here, but customer service at the factory will send it to you. That includes a parts layout, which leaves no confusion as to what is where.

You have not yet revealed what you are working on, but U1 is a TL074, and PV used them a lot. There may well be some of them on the preamp board, steal one and put it in the power amp. Remove U2, that 87478. Now does the power amp work? We can replace the other TL074 later, and if you don;teally need a 87478, then why order one?

TL074 is a common chip, order from most any supplier, but if you are ordering, consider buying one at some local shop. For example, in my shop, in a repair, I charge $4 for one. They cost about 65 cents each at Mouser. But if you order from Mouser, you have at least $8 shipping. On a good day I might even charge a dollar or two.

Is Q17 a high failure part? No, nothing on this amp is a high failure part. I was troubleshooting. You asked after that 87478 IC, which led me to think you might be having a problem with low signal or blocked signal. That apparently is indeed the case. So I suggested taking the IC out, that will tell us instantly if it is the problem or at least involved. I mentioned Q17, because it is a totally separate circuit, but is able to shunt your input signal to ground like the compressor can.


Q17 is a power up mute, and U2 is a compressor used to eliminate clipping. Either one can pinch off your signal at the input, but both are also controlled by other circuits. Q17 by the Z signal, and the U2 by a couple sections of U1. So either one of those could be causing a diminished output, but not be defective or bad themselves.


The 400BH is a reliable, straightforward amp, and we can troubleshoot it without tossing parts at it.

[km6xz]

The biggest problem might be the one caused by the probe slip. The TL074, as Enzo said, is a very common part so no problem but the CA3080 is an out-of-production part that has no direct replacement. Some Chinese dealers on eBay claim they have them but I suspect they are not real. I needed a couple recently for DynaCord and found that only one shop in the US that I could find had some in stock. Unfortunately, ordering them and some additional parts, they never arrived. The link to the part on SmallBear Electronics IC CA3080AE

There are modifications which will allow other ICs but getting them to mimic the operation of a 3080 is not a casual "repair". Fine for new designs and will likely work better but not when a particular sound is expected to be that of the old one.

[g1]

You could check with Peavey for a sub or a workaround. They are still repairing those 400BH modules, so they must have some way of dealing with bad 3080's.

Edit: apparently they have (or had) something called "39095750 OTA adapter assembly" to replace those chips:
http://music-electronics-forum.com/t21008/#post175954

[52 Bill]

Edit: apparently they have (or had) something called "39095750 OTA adapter assembly" to replace those chips:
http://music-electronics-forum.com/t21008/#post175954

What chip are we discussing here the CA3080 or the CA3094.

I don't know if that board will work as a replacement for a 3080 family OTA, it was originally used for the replacement of the CA3094 OTA chip with the extra transistors.

[gui_tarzan]

Google is your friend...

Rochester Electronics

[g1]

What chip are we discussing here the CA3080 or the CA3094.

I don't know if that board will work as a replacement for a 3080 family OTA, it was originally used for the replacement of the CA3094 OTA chip with the extra transistors.

Sorry, I don't have first hand knowledge, just posting what I have found elsewhere. Best to contact Peavey.
Elsewhere it was said there was a note that the CA version of 3080 would not work in some peavey circuits. (http://music-electronics-forum.com/t9603/#post76047)
But the replacement board is supposed to work for either the 3094 or 3080 circuits:
"The following are replaced by the 39095750 OTA adaptor assembly from Peavey 14.99 each
403080 (70403080) Chips
87487 (70487487) OTA chip
CA-3094
LM-3080N "
http://music-electronics-forum.com/t28010/#post244783

[Enzo]

I am still waiting to hear if the part in his amp is even bad.

[gui_tarzan]

Agreed, I would definitely try your suggestion.

[Tech. Tom]

Hello Enzo: Sorry I took so long to get back to you.

It turns out that R48 was open. It wasn't cooked or anything, I guess it just died
of old age. So U1 and U2 were ok. Thanks for your help and every body else's.