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Thread: Peavey 112M Floor Monitor Attenuator

  1. #1
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    Peavey 112M Floor Monitor Attenuator

    Friends...

    A friend just bought 2 Peavey 112M Floor Monitors. This is a 65W, 8 ohm cabinet. It has a 12" speark and a dual horn. On the input jack, there is a "Attenuator" control. I looked at this thing and could not figure out if it is a big resistor or inductor. See attached photos.

    In any event, the control was frozen. Shooting some DeoxIt F5 solved the problem. But, I was wondering, what is that control and can it be bypassed? I always think it's better to control volume from the amp. I'd rather have a straight up crossover instead of dealing with a mechanical device in the speaker cab.

    Thanks, Tom
    Attached Thumbnails Attached Thumbnails img_0364.jpg   img_0365.jpg  

  2. #2
    Senior Member Enzo's Avatar
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    Let's say you have four floor monitors strung across the stage.. And let us say the singer likes hers nice and loud, while the bass player only wants it loud enough to hear for his changes. And the drummer wants his up loud for the couple songs he sings on, but likes to back ut off otherwise. How do you control that from the amp?

    The idea here is not we will go across stage and turn them all up and down, the idea is to allow each one to be tweaked for the guy listening to it.

    But you don;t have to use it, of course. And have we verified it as an overall level pot instead of a horn control?

    The part is a rheostat - a big power pot. In fact, if you demount it and look on the edge of the white ceramic base, it should be printed right on it, something like 50 ohms 50 watts, or whatever.

    On some simple floor wedges, PV just wired it in series with the speaker. It was wired as a variable resistor then. Two leads. COnsidering all three are wired here, it would be some different arrangement. it is part of the circuit. If you don;t want it, instead of replacing it with a large resistor, why not just leave it turned all the way up?

    The crossover is extremely simple, trace it out on a sheet of paper. You can then see where the rheo is wired in.
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    Enzo...

    I hear what you're saying about about having a chain of monitors and allowing someone to individually adjust theirs. But the way I run monitors, it is one monitor per single side of a stereo amp. So every monitor can be individually be controlled.

    The Rheostats become corrosive over time. For now, they are clean and working. But when they get dirty, the signal will not pass through the Rheostat to the speakers. This is why I was asking about removing it.

    I guess another simple alternative is to measure set the Rheostat at full volume, then figure out which side of the Rheostat is "0" ohms with respect to the center tap. I could then simply put a jumper across those two points on the Rheostat, while leaving the full value of the Rheostat in tact and in the circuit.

    Tom

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    Senior Member Enzo's Avatar
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    Well, nothing is more visually intuitive than that rheostat, the works are in plain view. Rotate the knob to full and see where the wiper goes. In your photo, I can easily see that it is almost all the way up. MAx it and the wiper will be on the lower left end cap.

    I have not found those to be unreliable at all. I replaced just one in the last 24 years. I had a spare in my drawer, and I recently had a customer come in wanting, of all things, a volume control box for his drummers monitor. I mounted my spare in a aluminum box with a couple jacks and voila! I suspect one wipe with Deoxit ever 5-10 years and it will be fine. To be honest, the jacks will be a lot more of a problem than that big pot. I am guessing that speaker is about 19 years old.


    But yes, you could easily replace it with a resistor. Really, look on the side of it and see if the value is printed. On some it COULD be up on top facing the panel.

    In fact, do trace out the little circuit, see if the resistor is really needed. If it isn;t, short the red and yellow wires together and lose the thing. Only I wouldn;t short the wires, I'd pull the molex off and short the two pins on the male header where teh red and yellow went.
    Education is what you're left with after you have forgotten what you have learned.

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    I just got one of these, was plaing my Classic 20 into it and it was very cool.... but I kept worrying about my C20
    Would these be okay to use like a regular attenuator for a guitar amp?

  6. #6
    Senior Member Enzo's Avatar
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    It won't hurt your C20, but that rheostat isn;t the best way to make an attenuator for an amp. It is well suited to what it is doing in that floor monitor, but less than ideal as a stand alone attenuator.
    Education is what you're left with after you have forgotten what you have learned.

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    Thanks, good to know I can use it without hurting the little amp.
    On the other hand, would running something like 50 watts be okay into it without melting the Rheostat?

    One of the coolest tones I ever heard was when I was running my 67 Marshall 45 watt amp into a drive in movie theatre speaker.
    Then one day I turned it up just a tad too much....

  8. #8
    Senior Member Enzo's Avatar
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    Obviously the C20 won;t make 50 wats. But a larger amp? Well the rheostat won;t readily mely because it is wire on ceramic. And it will only heat to the extent it has to dissipate anything. Somewhere on the rheost6at it should have its specs printed. May be around the edge of the ceramic, or you may have to dismount it to read what is on its face, now hidden. But lets say it is 50 watts. Your amp has to push 50 watts into it. it if is already in series with a speaker, the speaker will absorb a lot of the power. And if you have it dialed way down, the resistance will be at its highest, so its dissipation will be lower.

    I'd be less inclined to do that than your C20.
    Education is what you're left with after you have forgotten what you have learned.

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