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I am working on a Peavey Deuce and it seems to have quite a bit of hum. It's the B version w/ 4 inputs: Effects, Parallel, Series , and Normal. The hum seems to be the strongest in the effects section where the tremolo oscillator is located. Plugging it into my Furman power conditioner doesn't help. Is this normal?
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No it should be pretty quiet. Start with power supplies. are the preamp rails up to voltage and clean?Education is what you're left with after you have forgotten what you have learned. -
The voltages in the power supply are there and clean. It doesn't hum when I plug into the Normal input so it has to be in the "Effects" section. I have a schematic but it is tedious as none of the components are labled so I have to trace the circuit. It has a trim pot for biasing the tremolo circuit. Could it be biased too "hot" or does it sound more like a bad cap. The amp functions perfectly other than the annoying hum in the effects, series and parallel inputs.Comment
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If the power supply caps were failing, it would affect all channels.
In the older circuits lacking layout drawings, I usually use the controls as landmarks.
I'd be looking for DC where it didn't belong. All those little 2uf/35v electrlytics they use as couplers are suspect for leakage. If your drawer doesn;t have 2uf, 4.7uf is close enough, otherwise order something close.
Turn the trem intensity to zero, that should eliminate any trem influence. The bias control there just sets the operating point for the trem FET. Mis-adjust it and the trm vunction either gets choppy or goies away or you squeeze the signal out of existence. No hum there though.
DO ANY of the controls in that channel affect the hum - reverb perhaps? ANy control that affects the level or tone of the noise is AFTER its source.Education is what you're left with after you have forgotten what you have learned.Comment
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I noticed when I turn the gain knob and the treble knob ONLY in the "effects" section of the amp, it does affect the loudness of the hum. Also when I touch the power and standby switches in the back, it somewhat quiets the buzz. Not all the way. What are those .022 caps for that are on the power switch. There are two of them and one is connected to ground. I have found a few coupling caps with leakage and have changed them. It did ease up the hum a little. I'm going to check around the gain and treble pots. Thanks for your help.
I also noticed at the treble pot on the effects input, it doesn't give a pot value but shows the pot going directly into a 558 FET/transistor???? What's up with that. There is also a 2 micro farad cap down by the 15 k resistor.Last edited by Danglin' Fury; 10-29-2008, 03:54 AM.Comment
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If that 558 JFET were a triode, you wouldn;t think twice about that treble control going right to its grid would you? Same exact configuration here. And that cap in parallel with the source resistor? I bet if it were a cathode resistor it would look right at home.
If the amp only hums in this channel, then I suspect there are DC levels screwed up. The two channels ar almost identical, the effects channel added the one emitter follower transitor in the middle to give the trem a place to work. Otherwise. You can compare voltage readings channel to channel if you like.
When i work on older amps like this, I make a chart of the parts layout. Nothing fancy, a rectangle for the board and little circles in the approximate position of each transistor. Then I number them. Then on my schematic I add numbers as I figure out which one is which. That gets added to my files.
Seriously, I'd be looking to replace ALL those little 2uf caps. If anything screws up DC levels in an amp like this, it is leaky caps.Education is what you're left with after you have forgotten what you have learned.Comment
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That's a good idea. I like the way you put your Thang down, Enzo! Thanks for the advice. I'm 2 years out of electronics school and I have only 15 amps under my belt.
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I don't know what's under my belt, I can't see that far.Education is what you're left with after you have forgotten what you have learned.Comment
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I changed all those electrolytics and it made a drastic difference. It is pretty quiet but when I turn the individual gain upon both channels, it seems to get more noisy. Is that pretty common for amps made in the '70's? Other than that, if I leave the channel gains turned to about 8 or 9 o'clock, and turn up the master gain, it stays relatively quiet.Comment
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That is common on any amp, the more you turn up the more noise you hear. WHite noise/hiss? Gain and noise go hand in hand.Education is what you're left with after you have forgotten what you have learned.Comment
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