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Old 18th February 2013, 09:35 PM   #1
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Default Peavey Renown 400 Issues

I have a Peavey Renown 400 212 amp here.

Here is the problem. Sometimes when I turn it on, the volume is VERY low (even with controls set to full) then it blasts and is normal.

Also with nothing connected to the input, there is an annoying hum and a static sound. It sounds like a dirty pot, although all pots were cleaned and make no noise when adjusted.

All solder joints are great. The previous guy replaced the several 4558 OP amps with a TL082CP. Not sure if that is a good idea. I believe the 4550 can be subbed with a better 4580 OP amp.

The problem is in the preamplifier section. I plugged in my iPod into the Power Amp input, and the jack disconnects the preamp internally. Unit is DEAD silent. It sounds fine and all is well. I then (just to make sure) plugged the preamp into another amp, and sure enough the hum and static was back. It isn't a grounding issue, a pot issue, or a solder joint issue.

My guess is either a bad OP amp, noisy transistor or a leaky capacitor. I am placing a Mouser order soon for my other stuff, so mind as well order any needed parts.

Any advice or suggestions?

Peavey Renown 400 Schematic & Board Layout
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Old 18th February 2013, 10:06 PM   #2
Enzo is offline Enzo  United States
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Most likely thing is a dirty cutout contact on either the power amp in jacki, or an FX reutnr jack. Plug a cord from preamp out right back to power amp in. ANy help?

If it is in fact in the preamp, don't start throwing parts at it, FIND the problem. If it is noisy and distorted, the problem is much more likely a defective op amp, than it needing an engineering uopgrade of some sort.

Use your controls, what controls have ANY effect on the noise? COntrols that turn the noise up and down or change the tone of the noise are after the source of the noise.

Go down the row of ICs, check the output pins - pins 1 and 7 on the dual op amps. Do any have a substantial DC offset? Talking volts here, not millivolts.

Use a signal tracer or scope and follow the signal path and see where the noise ooriginates.
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Old 18th February 2013, 10:35 PM   #3
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No difference when I use a cable to join the preamp and power amp together. Plus I replaced the jacks before hand.

Shorting the inputs or disconnecting the molex connector to the board. No difference. Disconnecting the molex connector connecting the effects pedal jack on the back to the board. No difference.

One thing that annoys me, is the turn on and turn off thumps are extremely violent, and cause the Scorpions to actually bottom out. But once running it is fine. Those thumps and pops occur regardless of the preamp being connected or not.

I will take voltage measurements soon.


EDIT: The TL082CP doesn't seem like a sub for the 4558. The TL082CP is a JFET design, and the 4558 isn't. Perhaps this is why it acts odd?

Wouldn't it be moot to take voltage measurements then? The pinouts don't even seem identical.

In my old Peavey CS-800 thread, someone mentioned that the 4580 is better than the 4558. Is this true?

Because I'm going to be replacing the OP amps with the correct type, should I just "upgrade" and go with these?

RC4580IP Texas Instruments | Mouser
Or stick with these?
RC4558IPE4 Texas Instruments | Mouser

And will those actually work? They confuse me by adding RC and IPE4 to the end.

Last edited by ouimetnick; 18th February 2013 at 10:59 PM.
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Old 19th February 2013, 12:11 AM   #4
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Hi, I have A Renown 400 as well, Mine does have a noisy channel but I have not taken the time to work on it yet.

But I was just curious if you like or dislike the sound using the TL082's in it.

I never much cared for the 4558 as it is too noisy and was thinking of swapping them out as well.

I had a Fostex 450 mixer that was loaded with them and I swapped them all out with TL072's and the thing was dead quiet and gave my Mackie 32-8 a good run for the money after that.

I believe the newer 4560 and 4580's series opamp's have a much better noise figure than the 4558's.

Quite frankly I despise the 4558's (any 45xx's) and could almost tell when a piece of equipment is using them.

The TL082 does have a faster slew rate than the 45xx series at 13v/us instead of 5v/us.
This is one of the reasons I like the TL0x2's better as well.
The TL072's have a lower noise rating the TL082's.

I have also considered using the NE5532's as well since they are not JFet types.
I used these in the Fostex mixer as well but it had problems with them in the filter sections (some would oscillate), so, I kept them in the signal path and used the Tl072's for the filters and this worked just fine.

All of these opamp's have the same pinout so there shouldn't be any problems as far as that goes.

There is a thread about one trying to use different opamp's in a crossover and had similar issues I had in the filter sections oscillating.
I am not sure if it was ever solved but it seemed to be an issue of the driving capability of the opamp being swapped with instead of the original and/or required some different/or more supply bypassing techniques to get them to work properly.

Don't remember what the numbers were but they were of the 45xx series of opamp's.
I believe that they were the original parts in the unit.
You can probably do search and find it in these threads.
The 4580's have a higher drive capability and I think that the one it was swapped out with did not.
And this caused the filter to oscillate

FWIW

jer
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Old 19th February 2013, 12:30 AM   #5
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Surely, the guy who designed the system knows what was available and used them. A 5532 is a comparator.
Jug Fets are excellent and if they take off it is because they are more sensitive and have a better response. Use a 47pF cap to stop it from happening.
The effect return socket is the cause in the first part of the post.
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Old 19th February 2013, 12:54 AM   #6
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Even though the TL082CP is a Jfet design, and the 4558 is not, they are perfectly fine to interchange? I just want to make sure the TL082CPs in the thing aren't causing any possible harm.

There are still two OP amps that are 4558. The previous person just replaced all the OP amps with TL082CP (as thats what he had) except two. Two of them are still 4558s.
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Old 19th February 2013, 12:55 AM   #7
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Yes, it is.
I have swapped out nearly every 4558 that I have ever owned wth a TL082/72 and never had an issue with them!

The NE5532 is a dual low noise bipolar opamp not a comparator.
It had been an industry standard for many years for low noise audio circuits.
I was one of the very first of such low noise devices.
Although it is now quite old and dated it is still of great quality.

http://www.fairchildsemi.com/ds/NE/NE5532.pdf

jer

Last edited by geraldfryjr; 19th February 2013 at 12:57 AM.
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Old 19th February 2013, 12:56 AM   #8
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Quote:
Originally Posted by geraldfryjr View Post
The NE5532 is a dual low noise bipolar opamp not a comparator.
It had been an industry standard for many years for low noise audio circuits.
I was one of the very first of such low noise devices.
Although it is now quite old and dated it is still of great quality.

http://www.fairchildsemi.com/ds/NE/NE5532.pdf

jer
So I can simply replace all the OP amps that are suppose to be 4558 with NE5532 OP amps without an issue?
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Old 19th February 2013, 01:19 AM   #9
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I can't say for sure 100% but that was the plan I am planning on trying with my amp.
I don't anticipate any issue with the deisgn of it as it is very straight forward.
IF the IC's have been socketed then it is just an easy swap.
Do you know which ones in your amp have not been switched out?

There is one in the poweramp stage and I am assuming that this one may not have been change out in your amp and would be of no benefit if it was (I think ).

jer
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Old 19th February 2013, 01:24 AM   #10
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U1: TL082CP
U4: TL082CP
U5: TL082CP
U6: RC4558P
U7: RC4558P
U8: TL082CP
U9: TL082CP

Should I juggle them around to figure out if the noise stops, or just replace them all?
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