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Thread: Amp Squeal

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    12.14.17 @ 07:32 PM
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    Amp Squeal

    ive got an old 100 watt lab series combo running to a marshall cab, and for some weird reason, the amp will sometimes freak out and go to a high pitched squeal. if i turn the amp off and then back on, it may or may not continue, but it usually just sticks around. someones gotta help me, i cant have this happening at a show, thanks in advance :Louis

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    03.30.13 @ 09:28 AM
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    The lab series amps are solid state. First off, are you matching the cab's impedance to the head properly? It's important with those amps.
    Also, are you running the cab as extension or did you unplug the main speaker and use the marshall cab as your main speaker?
    Is there a loop in your model and are you running effects through it?
    You didn't mention which model you have.

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    Quote Originally Posted by VanZeppelin667
    ive got an old 100 watt lab series combo running to a marshall cab, and for some weird reason, the amp will sometimes freak out and go to a high pitched squeal. if i turn the amp off and then back on, it may or may not continue, but it usually just sticks around. someones gotta help me, i cant have this happening at a show, thanks in advance :Louis
    VanZep, please forgive me for not knowing your proficency and for an elementary question, but do you have a speaker cable anywhere in the chain from the guitar to the amp input? If so, that could be the problem.
    Last edited by mk5; 01.07.05 at 10:06 AM.
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    Tribb, the head (lab series) can take a cab with an 8 ohm resistance or higher, the cab has a total of 8 ohms itself, i hope thats what you mean, the lab series is the L9, has 1 15 inch speaker, but its unpluged, and the cab goes in through that. there is no loop, all the effects ( two of em' ) are just going straight through. sorry i forgot to mention which model, i didnt think anybody would care, since lab series arent exactly the most common amps out there
    MK5, there is a cord that runs from my wah to my overdrive that may be a speaker cable, but its really small, like 6 inchs long (friend gave it to me) so im not sure
    Last edited by VanZeppelin667; 01.07.05 at 01:06 PM.

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    A speaker cable can cause some extraneous noise in front of the amp but shouldn't cause a squeal like you describe. As a rule you can tell a speaker cable from a guitar cable because a guitar cable will usually be round from the sheilding, where a speaker cable will look like the cable that runs from a lamp, with just 2 wires side by side.
    Just a couple of more questions. Have you plugged your guitar straight in, with no effects, and the regular 15" speaker only hooked up.
    If I'm not mistaken I believe your model has reverb but can't remember.
    If it does then turn the reverb right down/off and try it through the marshall speaker cab normally, but without the reverb turned on.
    If it doesn't have reverb then try what I suggested and try hooking it back to the 15" and remove your effects. Play it at fair volume for awhile and see what happens. The Lab series amps are actually great sounding amps, but since they're solid state they can't be checked like a tube amp would be. It sounds like internal feedback, which can be caused by an overloaded reverb circuit, especially if there are effects running through it to push the gain higher, or you could be just pushing the preamp a little to hard. A lot of SS amps are pretty fussy about what pedals they like and don't like.
    Also SS amps must never be turned on without a speaker load. They're more sensetive to load than tube amps. Have you ever accidently had it on without a speaker hooked up?
    Anyway, try what I've suggested and see what happens. Hopefully it's something simple.

 

 

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