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PA Mixer Cutting Out

Discussion in 'Pro Audio Equipment' started by tunzzz, Jul 4, 2003.

  1. tunzzz

    tunzzz Guest

    Hello all:

    I have a Peavey XR500C mixer/amp that just started acting up and it is getting worse.

    The symptoms: If the amp is working fine, at some point during a performance it kicks out. If I turn the volume all the way up, you can here scratchy sound at a very low level. The only way to get the sound back is if you turn the main up almost all the way and send any loud signal through it (guitar, vocal, whatever). At some point (30 sec - 1 min), the sound kicks back in (threatening to blow the speakers of course. It will perform fine until it kicks out at some other point. It is not blowing the fuse, but I can only guess there is some form of thermal overload is occuring. The weird part is that if I turn off the amp and allow it to cool down, the problem is still there when I throw the power back on. I then have to "force" the amp to output again by turning the main all the way up again. If this was a thermal problem, wouldn't the problem reset itself after the amp was turned off and cooled. It almost sounds like an electronics problem (solid state system). But the mixer is still outputting to my monitor rig as well as other output connections, so the electronics still appear to function, yet no output to the speakers.

    Now for some variables I have introduced to the amp recently. I just bought a small monitor system as well as upgraded the speakers from 8 ohm to 6 ohm. The speakers have been in place for months without the problem coming up and the problem came up BEFORE I bought the monitor system. Maybe something with the speaker impedance?

    It's a small mixer/amp and I'm thinking about replacing it. But, it has been a work horse and packs a surprising punch. I'd like to save it if not for posterity and to boost moniroing capability. Can anyone help? I'm a newbie at the elctronics piece, so have some patience with me.
  2. vinniesrs

    vinniesrs Active Member

    Tunzzz, I dont think your amp is at fault here. If it is it will be a bad connection in the input area. I think you could do fine to clean your mains faders. Keep in mind there are plastic components in there, so if you clean it, use a plastic friendly solvent, maybe even silicon based.
    If you want to rule out the amp(or confirm the amp as the culprit), do a tes run where you put an aux out directly to the amp input. If your prob continues then the amp needs to be repaired. You could check the circuit path at the input and see if an obvious short has occurred, but I dont think you'll need to worry, as I'm pretty sure the problem is those mains out on the board! Secondly(just to confirm your suspicions), send the mains out into a monitors amp, and see if your problem travels from mains to monitors. Then you will have an answer.

    If you have even the slightest inkling that you may F*(k it up, then send it to an authorized repair center.

  3. vinniesrs

    vinniesrs Active Member

    One more thing! i am just assuming that I don't have to tell you to check your cables.....right? :D :D :eek:
  4. sheet

    sheet Well-Known Member

    What is the sensitivity rating and power capacity of your speakers? How are you running your speakers, in series or parallel? That amp's speaker jacks are paralleled. The amp only puts out 150W TOTAL at 4 ohms minimum load. If you are running them in parallel, then you are dropping the impedance to 3 ohms. If you are doing that, the amp is going into protect mode. Plus, you probably are driving, no wait..you ARE driving the amp too hard, and need more power for your speaker systems.

    I do not think that it is your cables/connections, etc. You can check that, but I will be you money that it is your impedance.

    What the heck kind of speakers did you buy that are 6 ohms?
  5. vinniesrs

    vinniesrs Active Member

    Sheet, Tunzz mentioned that the system only comes back on when he cranks it! If overload was the problem then turning things down would solve his prob. What's happening here is a bad connection somewhere. Once the connection deteriorates the audio cuts out. Once the output signal becomes strong enough to pass through the bad connection, it does, and does so blaring loud! I have seen this in fader mechanisms, patch cables, and impedance adapters, usually being the result of a poor solder connect.

    I am not an electronics expert, but I would be stunned if amp overload or impedance mismatch was causing this issue.

    Steve. :c:
  6. sheet

    sheet Well-Known Member

    There could be a connection problem, but I think that running two speakers at 6 ohms each = 3 ohms, and then ANOTHER monitor with an undisclosed impedance in there is dropping the load to a dead short. The amp is heating up he said. I suspect that running the amp this hard may have done some damage, which has gotten worse over time. That little mono amp cannot crank at 1 to 0 ohms!
  7. vinniesrs

    vinniesrs Active Member

    Maybe I should have read the initial post twice. Tunzzz'z initial statement that the problem persisted on cooling, somehow stuck in my mind the most. After reading the article again I notice that he has already looked at the board and the problem is still in the amp.
    Even still, the problem is with the mainspeakers, and most of these amps(not sure on the peavey)will handle 2-16ohms, so 2 speakers, series or paralell, wouldn't drop past 2 ohms, and certainly could not drop the impedance to a dead short. As a matter of fact you will not create a dead short unless you melt all the voice coils down to zero ohms. I am not being sarcastic, simply pionting out that something which is inherintly resistant cannot be made to short without malfuction.

    Something has come to mind though! If one of the speaker wires was damaged it could be causing the amp to shut down.

    Tunzzz! In addition to checking your patch cables, exchange the speaker cables and see if this solves your problem.

    Sorry for not paying more attention before!

  8. Guitarman

    Guitarman Guest

    I am not familiar with that particular console... If it has a PFL or AFL can you still hear the main signal in the headphones when this happens? This could help in finding what part of the chain the cut out is.

    It sounds like a "cold solder" joint. If you are good with a soldering iron open the unit and check all the connections leading to and from the amp section. Although to have multiple points go bad is unlikely.... or is it? ;)

    Hey what do I know? Take it to a repair guy or call and b*tch to Peavey(if it's still under warranty).

    Bets wishes,

    JD( o}===;;;
  9. sheet

    sheet Well-Known Member

    Not 16 ohms, 6 ohms. Maybe a typo. The Peavey powered head has 150W Mono Maximum output @ 4 ohms minimum load, and it's connectors are parralleled. He is using these for his mains, and since this is a mono unit and he is powering a THIRD monitor, then yes, 6 ohms + 6 ohms + 8 ohms would appear as a dead short to that amp, and require more power than what he can provide with 150W.
  10. Davedog

    Davedog Distinguished Member

    Those frikkin Peavy's will operate(not clearly) with all their available power @ less than half an ohm...and at outside temps in the 100's as well as below freezing. This has all makings of an op-amp in the main outs being intermittant.Or it could be one of the mains sliders...

    Tunnnnz....have you tried running all of this on just the monitor bus out? how about one side of your mains or the other?Any other outputed buses?A separate effects bus? Hook it all up to one of these ...Does it do the same thing?
  11. sheet

    sheet Well-Known Member

    How can any amp operate with "all of it's available power" while it is clipping, and loaded down to 0 ohms? It cannot. Not at full bandwidth. These things are tough, but not tough enough to defy physics.

    At the time that this thing was relased, Peavey didn't make ANY 4 ohm boxes. It wasn't until the power wars in the late 80's that Peavey felt the pressure. So, they didn't need to handle lower impedance speakers.

    If you look in their owners manuals for this series, you will see that this thing is mono, so you can't try a left/right swap. The monitor send is line level only. If he wants to use the power amp with the monitor send, he has to jumper the monitor out to the graphic in. The graphic Eq cannot be bypassed.

    It could verywell be an op amp, I gree.
  12. Davedog

    Davedog Distinguished Member

    Hiya Sheet you Okie!....yeah thats what i said....(not clearly)..We've got one of those 680C's here and it was doing the same thing..Was a loose connection in the graphic in/out on the front...Isn't this kinda the same beastie??I thought at first this 500 model might be one of the little mixer style units...but may be its the amp-head style like ours
    As for physics, Ive seen these little guys run some weird loads for long periods of time without damage....sometimes without clarity either!!! :w:
  13. vinniesrs

    vinniesrs Active Member

    As I have said before, I am not an electronics gooroo. I believe I have a good grasp on the basics though. When you combine resistance in series the circuit becomes more resistant. When you combine resistance in paralell the circuit becomes less resistant. Right?
    Here are some figures using 8ohm speakers, in paralell as an example.
    Speaker Impedance /# of speakers = Total Impedance for chain:

    8 Ohm x 2 4 Ohm

    8 Ohm x 3 = 2.66 Ohm

    8 Ohm x 4 = 2 Ohm

    8 Ohm x 5 = 1.6 Ohm

    8 Ohm x 6 = 1.33 Ohm

    8 Ohm x 7 = 1.14 Ohm

    8 Ohm x 8 = 1 Ohm

  14. vinniesrs

    vinniesrs Active Member

  15. sheet

    sheet Well-Known Member

    Oops. Right on. I had my mind on 4 6 ohm cabs for some strange reason.

    In his set-up, unless all of the speaker connections are made from one point on the amp, they are in parrallel.

    6 + 6 = 3 + 8 = 5.5 ohms total

    But, even though the impedance with the third cabinet brought it up a hair, maximum voltage required exceeds the abilities of this amp.

    Thanks for pointing out my error. You beat my wife on thie one.
  16. cloey2007

    cloey2007 Member

    i have a behringer europower pmp 2000 power mixer and it cuts in and out... i dont want to send to a shop because if it cost to much for them to fix it i might as well buy a new one and i cant afford that if anyone has any ideals i would appreciate it thanx
  17. Boswell

    Boswell Moderator Distinguished Member

    We have plenty of ideals but unfortunately rather fewer ideas.

    The sort of problem you are having with your unit is just one of the reasons these forums try to steer people away from that particular manufacturer. I'm sorry to say you will have to buy another unit of a different make.

    If going for a new unit is too much of a financial stretch, similar-function powered mixers are often available second-hand from Ebay and elsewhere.
  18. dvdhawk

    dvdhawk Well-Known Member

    Hi cloey and welcome,

    The main bullet-points from this old thread:

    A) Check ALL of your cables and speaker connections.​

    2) Do the math and make sure your impedance is within range of what the amp can handle​

    ** The overlooked nugget of gold hidden in Davedog's post - where he writes:

    3) "We've got one of those 680C's here and it was doing the same thing..Was a loose connection in the graphic in/out on the front." ​

    Over the years I've repaired a lot of powered heads that had a bad contact, or bad connection in the patch-points on the front. On your unit, those jacks labeled "Preamp Outputs" and "Power Amp Inputs" are usually internally normalled 1/4" jacks that have to be making good contact internally [even when there's nothing plugged in to them] for the signal to pass reliably between the pre-amp and amp section. In which case, good contact cleaning spray (Caig DeOxit) and (while powered off) working a 1/4" plug in and out of each jack several times can often 'cure' it. Connecting the appropriate 1/4" cables (I assume TRS - check your manual) from the "preamp outs" to the "amp ins" is also a valid test to see if it cuts out while bypassing those problematic normalling contacts.

    D) If it's none of those things, it will have to go to the repair shop (or the dumpster)​

    And as Boswell has suggested - not a particularly reliable product to begin with, so you will have to pick your battles.

    Best of luck - please let us know how you make out.

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