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Thread: Peavey XR-600C Mixer Head Noise

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    Peavey XR-600C Mixer Head Noise

    Hi All, I'm new to the forum and hoping I can get an answer to my problem. I bought this Peavey XR-600C 6 channel PA head a few weeks ago, and when hooked up to the SP3 Cabs that came with it
    there's an aggravating noise coming from the speakers. The best I can describe the 'Noise', is that someone had their guitar plugged into an amp with it on, unplugged their guitar and let the cord lay on the floor. Not a hum per se' , sounds like an open ground somewhere or something. This XR600 head uses a 400BH Power amp module. I saw on another thread here a guy that was having a similar problem.
    I believe it was Enzo? that suggested that it could be a TL074 Op Amp gone south, and to swap it out with another from the front end. Well I have the amp open and found the TL074 however, there isn't another one anywhere in this amp that I could swap out with it. There are a ton of RC4558 Op Amps. I did however, find 20 some odd solder connections that I desoldered and resoldered. All of the 1/4" inputs had bad solder connections, which I resoldered. I hooked it all back up and that noise is still present. I'm going to use this amp and SP3's to DJ small parties and weddings etc.. Any help would be greatly appreciated.
    I do have an electronics background. Hakko soldering station, Fluke model 75III Meter..etc.. I'm just stumped here..

    Thanks in Advance, PepsiMoon

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  2. #2
    Supporting Member Jazz P Bass's Avatar
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    First off, disconnect the speakers!
    Break out your meter & see if you can measure any dc voltage on the speaker jack.
    If so, the amplifier needs work.
    I always test the power supply.
    Both + & - rails should be the same.
    You can access them right on the case of the power transistors.
    Look for Vac ripple on the power rails & the opamp supplies.
    The power rails can have a small amount of ripple.
    The opamp supplies should see none. (pin 4 & pin 8)

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    Lifetime Member Enzo's Avatar
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    I agree^^^

    Sounds like you have DC on the amp output.


    I suggested someone steal a TL074 from the front end of a XR600C? The XR600B has a bunch in the front, but not the C. They are different amps. Suggestions like that are always in some context. Unless I was high, I would never suggest a bad TL074 for your symptom until I had already suggested isolating the problem to preamp or power amp, verifying all power supply rails, taking voltage readings and explored the likelihood of bad transistors and open resistors in the power amp.

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    Supporting Member Jazz P Bass's Avatar
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    How to troubleshoot the repair of an amp.
    "isolate the problem to preamp or power amp, verify all power supply rails, take voltage readings and explore the likelihood of bad transistors and open resistors in the power amp."

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    Lifetime Member Enzo's Avatar
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    (one two one two... I seem to be getting a little echo on my voice...testing testing...)

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    Supporting Member Jazz P Bass's Avatar
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    That's going in the Enzo book.

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    I'm sorry Enzo ..I didn't mean to offend you.. Well I hooked up the driver board/power amp and checked for DC on the speaker jack, there was none. I checked the DC on the TO-3 output trannys. On the Left hand 4 outputs the voltage was 52.6 VDC on each. On the Right hand 4 outputs the DC voltage was 0. Thinking maybe the ground from my meter had come loose, I switched my meter over to diode/ continuity test and checked. I had a good ground connection. I was called away for just a few minutes by my dear wife. When I came back, I forgot to put the meter back on DC and touched my hot lead to one of the right hand output trannys. Immediately the main 8 amp fuse opened up. Yes, of course I'm very embarrassed.. But what's done is done. I pulled all power from the chassis, and discharged the filter caps with my trusty 100 watt light bulb. All 4 right hand outputs checked shorted, as well as the large diode just above them. I pulled out the plug with the red, white and blue wires going to the right side, and the outputs checked good, as well as the large diode. I traced back to the 2 identical small blue transistors mounted on small heatsinks directly to the preamp board. One checked good , the other checked shorted. I desoldered the shorted transistor and removed it from the circuit and tested it again. It was shorted. I plugged in the red white and blue wire harness, and the 4 outputs on the right side checked good as well as the large diode.Now not only do I have to figure out why the right hand 4 output trannys checked 0 volts, I have to try to replace the small transistor I accidently shorted. As I said before this is the 400BH Power Amp Chassis. The transisor is blue with a 'M' 5322.. 'M' being Motorola I would venture to guess.Thanks for the help so far.. An Embarrassed....................PepsiMoon BTW how do I post pics here?

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    Lifetime Member Enzo's Avatar
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    You didn't offend me, I was poking fun at Jazz for repeating something I wrote.

    Look at the schematic. This power amp is quasi-complementary. The collectors on the positive side transistors are at V+. But the negative side output transistors have the output bus on the collectors. The V- appears on their EMITTERs. It is thus normal for zero volts on the collectors of those transistors.

    You can get the exact 5322 and 5321 transistors from parts dept at PV. Get the schematics for the amp from customer service there.

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    Supporting Member Jazz P Bass's Avatar
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    Lifetime Member Enzo's Avatar
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    AH, and points out the typo. Those transistors are 5331 and 5332.

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    Thanks Jazz P Bass for the link to the schematic.. Thanks Enzo for correcting my typo.. I just talked to Sherri at PV and I ordered two of each of the 5331 and 5332 and 2- 8 amp fuses. They're shipping out today..
    I'm glad I have a new can of Deoxit 5, there are a lot of pots to clean while I wait. I'm in Oregon, so it'll be a few days till I get my parts. I wanted to add that I did some research on Bing, and found a free schematic for the XR-600C.. It's for the front end mixer section, and master board. Thanks for your help guys........... PepsiMoon

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  12. #12
    Lifetime Member Enzo's Avatar
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    Peavey will send any schematics you request.

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    Hello again!! I received the 5331's and 5332's and 2-8 amp fuses Saturday. I replaced both transistors and fuse and fired up the main amplifier section. I'm measuring +52VDC on the left hand transistors, and -52 on the emitters of the right hand transistors. 0 VDC on the output jacks. I switched off the unit and plugged in the Master Board from the front of the unit, switched on the Peavey and the noise has returned. Doesn't matter if the master volume is up or down , the noise stays the same regardless. I've checked various voltages using the schematic and all seems good. I found the main audio input wire and corresponding ground(after disconnecting the Master Board) and hooked up one side of my stereo pre-amp output to that, the hum, hiss, noise (whatever you wanna call it) gets louder, although I am getting good loud signal output. As I said before it sounds like there is a loose ground connection in the audio signal path somewhere. Anyway any help would be greatly appreciated....Thanks In Advance...PepsiMoon

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    Lifetime Member Enzo's Avatar
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    OK< so now the amp basically works, you can amplify music and it sounds OK. It just adds some noise, yes? No? And if you disconnect the cable to the preamp from the powr amp board, the noise goes away?


    SO you have some hummy noise, and turning the master to zero has no effect? OK, you have a graphic EQ on there, do those sliders affect the noise tonally?

    Plug a cord into the power amp in jack. On its free end, measuer tip to sleeve for DC, is there 15v there? If so, we have a shorted diode.

    PLug a guitar or other signal into the power amp in jack. Is the hum present now? And does it amplify OK to the speaker?

    Now plug the guitar/whatever into the graphic in jack. OK or not?


    I don't recall, have we checked that ther is CLEAN +15 and -15 at the chips on the mixer panel?

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    Quote Originally Posted by Enzo View Post
    OK< so now the amp basically works, you can amplify music and it sounds OK. It just adds some noise, yes? No? *YES* And if you disconnect the cable to the preamp from the powr amp board, the noise goes away? *Yes*


    SO you have some hummy noise, and turning the master to zero has no effect?*Right* OK, you have a graphic EQ on there, do those sliders affect the noise tonally? *Yes They do*

    Plug a cord into the power amp in jack. On its free end, measuer tip to sleeve for DC, is there 15v there? * No, 0 Volts Tip to Sleeve* If so, we have a shorted diode.

    PLug a guitar or other signal into the power amp in jack. Is the hum present now? *No* And does it amplify OK to the speaker? *Yes*

    Now plug the guitar/whatever into the graphic in jack. OK or not? *Yes ok, no hum, clean guitar sound*


    I don't recall, have we checked that ther is CLEAN +15 and -15 at the chips on the mixer panel?
    * No, we haven't*

    Thanks so far .. Pepsi Moon

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    Lifetime Member Enzo's Avatar
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    O)K, so sitting there the amp hums, plugging into the power amp in kills the hum, an plugging into the graphic in kills the hum? So unplugging from the graphic in returns the hum? AND... the master volume control has no effect on the hum? That doesn't leave us much. Between the master vol control and the main put jack/graphic in jack is U24b IC. See if the output pin is sitting at some DC voltage other than zero. And of course verify the power pins.


    And just to be sure, take a signal cord, plug into the power amp in jack, now the other end, plug it into the MON OUT jack. Hum? No hum?

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    Ok first off I was a little confused. Now.. With the main Amp Module sitting not hooked up to the master board or anything , there's no hum or " Noise"
    When I plug in the Master Board, there's a hum "Noise". When I turn up the sliders on the EQ, Main Master, Reverb To Main, Tape/Aux Level controls. The "Noise" gets progressively louder as I advance these controls.
    I checked U24b and found the + Vcc in was 15.89 VDC -Vcc in was -15.89VDC, the output pin was 0 VDC. After checking other IC's around the board, I found one that had DC on the output pin. This IC is located
    between the "Reverb to Master" and "Reverb to Monitor" Pots, and had a reading of +2.17 VDC. I did notice that when I touched the case of the Main Master Pot, I got a noise much like touching the hot pin of an RCA jack
    hooked up to an amplifier. Now, with the Amp on and the Master Board connected the EQ, Main Master, Reverb To Main, Tape/Aux Level controls turned up humming away,I plugged my guitar into the PWR AMP Input and the hum vanished, clean guitar sound. When I unplugged the guitar cord from the PWR AMP Input the hum returned. When I plugged my guitar into Graphic In the hum vanished once again, clean guitar sound.
    With the amp humming away I took a signal cord and plugged it into the Mon. Out jack and into the Power Amp In jack, the humming stopped. So that's where I stand with this thing.I appreciate all of your help and I'm sorry for the confusion...Thanks , PepsiMoon
    ** I thought I would add, that even though the Master Board is unhooked which results in no noise, when I connect anything to the 400BH Module Driver Board input, I get the same noise.
    I traced the plug going from the input of the driver board that connects to the Master board and found the + input and ground. I soldered in a female RCA jack, then connected one channel of my outboard carver pre-amp to it and you guess it! Humming noise!But had signal( Music) I ran pre-out of a Marantz 2226 to it, same noise, and had signal (Music) When I disconnected the RCA Jack the noise vanished**So maybe it's not the Master Board at fault here at all. My guess is there's a fault in the 400BH Driver board.**

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    Last edited by PepsiMoon; 07-23-2013 at 11:41 PM. Reason: Added More Info again

  18. #18
    Lifetime Member Enzo's Avatar
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    I doubt it. With everything connected, you can plug into the power amp jack - which is actually a circuit on the preamp - and the amp performs fine, right? SO if the fault was on the 400BH it would be there all the time, or it would magically know when you plugged into that jack.

    Going in the graphic in jack runs signal through a bunch of more circuitry, which all seems to work.

    The IC between those controls is U16, the reverb driver. I bet that 2v goes away when the reverb pan is plugged into the board.

    Your graphic is clean, so center the controls and forget them. You mention a bunch of controls, master, reverb aux/tape that increase the hum. DO they do it independently? Or must the master be up first. IN other words, with the master on 5 turning the reverb up increases hum. But if you turn the mast6er to zero, can you still hear hum when the reverb is turned up? The Tape/aux goes onto the main bus, so does the reverb to main. SO if the master can turn to zero and kill the hum, we know the hum is before the master.

    Are the ICs in sockets on this one? I am now suspicious of U24, and if socketed, it is easily swapped with a different one to see if it changes things.

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    Yes, The Master must be up before the other controls increase the " Noise" The IC's are all in sockets on this amp..Thanks ...PepsiMoon

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    That did the trick! I swapped it out with one on channel 4 ( which I'll never use anyway.) The Old SP3's wont handle a lot of really deep bass,so I tried to run a guitar cable from Monitor Out to my Behringer 450 watt bass head, to my 2-15" cabinet and got hummmm. So I grabbed a 12 foot RCA patch cable and soldered a 1/4" guitar jack on one end,and ran that from Tape Out on the PV to the Behringer, sounds great!!
    As I was cleaning all of the input jacks and such with Deoxit, I noticed that the Aux In female + connector tab was bent on the inside, touching the ground tab. So I desoldered it and tried to bend the tab back into position and it broke off. Now to figure out why the Monitor Out has hum...I'm wondering, since this amp can run at 2 ohms if I could maybe find 2 PV 8 ohm folded horn Sub Cabs to hook up to the other outputs on the back of the SP3's? Thanks for all of your help and patience.. A Nearly Deaf, PepsiMoon..LOL

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  21. #21
    Lifetime Member Enzo's Avatar
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    Peavey Parts dept will have the exact jacks.

    So your basic setup is hum free? Where does the monitor put hum? Plug a cord from MON OUT to power amp in, then apply signal to an input channel and send some to the monitor bus and bring up the monitor master, is the MON still hummy playing through its own amp? I suggest this test, because if you connect the MON out to some other amp, we COULD be facing a ground loop or shielding problem.

    You have the thing open, might as well fix it right. replace the bad IC. These are old 4558s, which used to be all over. Nowdays we have 4560 an 4580 as more common, either would work. A common TL072 would be fine, or even a NE5532. Just about any DIP-8 dual op amp will work.

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    Quote Originally Posted by Enzo View Post
    Peavey Parts dept will have the exact jacks.

    So your basic setup is hum free? Where does the monitor put hum? Plug a cord from MON OUT to power amp in, then apply signal to an input channel and send some to the monitor bus and bring up the monitor master, is the MON still hummy playing through its own amp? I suggest this test, because if you connect the MON out to some other amp, we COULD be facing a ground loop or shielding problem.

    You have the thing open, might as well fix it right. replace the bad IC. These are old 4558s, which used to be all over. Nowdays we have 4560 an 4580 as more common, either would work. A common TL072 would be fine, or even a NE5532. Just about any DIP-8 dual op amp will work.
    Hi Enzo, well,still a little hum in the background but not as bad as it was. I'm thinking seriously about shelling out the $$ for a brand new jacks and IC's for the Master Board, and Mixer section ( With the exception of the XLR's they seem fine) just to be sure..I got the hum from my Behringer 450 watt bass guitar amp head when connected to the "Mon. Out" on the PV. However, when I ran an RCA jack to a male guitar jack adaptor from "Tape Out" on the PV to the same Behringer bass amp head, I got good clean signal. No Hum at all. Weird. What do the 4560's and/ or 4580's usually cost? I counted 15 of the 4558's on the mixer board, and have to remove the EQ on the Master Board to count all of them. I'm going to pack toilet paper around all of the pots today and give them all a good healthy shot of deoxit 5. Most all of them have dead spots, are scratchy and a few are really hard to turn.

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    Last edited by PepsiMoon; 07-24-2013 at 11:38 PM. Reason: added letter to make plural

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    Lifetime Member Enzo's Avatar
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    DOn't bother replacing a million ICs, that isn;t where your hum is coming from unless one has a DC offset. I usually expect to pay like 40 cents for one of those ICs.


    Get a can of Deoxit D5 spray, and squirt up inside each control and spin it back and forth. I bet almost all if not all of them clean up just fine. DO that before ordering new pots. Spray some Deoxit on a Qtip and swab the jacks out well. Look at how black your Qtip is. Qtips are cheap, use as many as you need to. I bet that cures a lot of jack issues right there. Deoxit won;t hurt the circuit board.

    As long as your boards are out of the front panel use your ohm meter to verify the grounds of the jacks are connected. One output might be hummier than another due to a lost ground connections. Check the solder under all jacks.

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