Peavey Renown 400 Issues - Page 2 - diyAudio
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Old 19th February 2013, 12:39 AM   #11
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U6 is the input opamp and I am surprised that this one has not been changed out.

U7 is the reverb driver and preamp is a standard current boost circuit no specialties there.
And could be upgraded.

U4 is fine.

What about U3 this is the one that I am questioning about.

U3 and U2 appear to be some sort of peak/clipping detector and compression stage on the ipnut to the power amp.
I need to find my print and look up U2 as it looks like it has a control voltage input pin.

jer
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Old 19th February 2013, 12:51 AM   #12
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I have my print on another drive that is not hooked up right now.
But if U3's function is what I think it is, there would be no change to the quality of the sound as it is just a peak detector for the power amp.

jer
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Old 19th February 2013, 12:51 AM   #13
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No worries. U2 and U3 are NOT in this amp. The schematic shows that U2 and U3 were on certain revisions. This one doesn't have them.

Should I pull a TL082CP and try it in U6? The reverb is still in the cabinet, and I have the amp pulled out and on the bench. I don't really care about the reverb right now.

The schematic for the Renown 400 is in the first post. It has the board layout and schematic.
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Old 19th February 2013, 12:59 AM   #14
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The noise could be caused from anything such as a bad cap or FET or even a noisy socket.
Reseating them my very well fix it.

I get a crackling noise in my amp and it stems from the clean channel.
I don't have the footswitch for it so I am not sure if it is coming from one of the channel muting fets or some thing else.
It comes and goes so I think that it is a cap.
I have seen FET's do this as well in a old Philips Stereo receiver once.
I changed out the muting Jfet and the noise stopped and worked perfectly after that.
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Old 19th February 2013, 01:02 AM   #15
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Sure it wouldn't hurt!!
This is the very first stage and if it is noisy the rest of the good opamps after it wouldn't make a difference any how!!

jer
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Old 19th February 2013, 01:09 AM   #16
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U7 is the reverb op amp and you have stated that it is a 4558.
If you do pull this chip make sure that the reverb unit is not plugged in because it could shift the bias of the reverb driver transistors to one of the rails.
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Old 19th February 2013, 01:18 AM   #17
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Replaced U6 with a TL082CP

No change.

Still hum, and some scratching sounds like before.
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Old 19th February 2013, 01:28 AM   #18
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Ya,that is the same kind of sounds I get some kind of scratch noise that comes and goes and is after the clean stage but before the poweramps main volume control on the clean channel.
No hum though.

If you have a scope this can be easily traced as per stage.

jer
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Old 19th February 2013, 01:29 AM   #19
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Pin 1 and pin 7 are the opamp outputs on each chip.
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Old 19th February 2013, 01:31 AM   #20
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Quote:
Originally Posted by geraldfryjr View Post
Ya,that is the same kind of sounds I get some kind of scratch noise that comes and goes and is after the clean stage but before the poweramps main volume control on the clean channel.
No hum though.

If you have a scope this can be easily traced as per stage.

jer
No oscilloscope.

Kinda thinking of taking the shotgun approach. I know it isn't the way to do things, but what else do I do?

I'm thinking of replacing all the electrolytic caps in the preamp section along with all the transistors and OP amps in the preamp section.

The power amp section is fine as can be, so I'm not recapping or shotgunning it.

IF I had a scope, I assume I connect the ground probe to the chassis, and use the other to probe various parts of the preamp (like the OP amp output pins) and I will see a funny signal in the scope, and I narrow the section of components and test the said section of components to see whats wrong?


Probably feed it say a 1KHz and trace it to where it isn't so pretty and figure it out.

If only I had a scope.

Last edited by ouimetnick; 19th February 2013 at 01:34 AM.
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