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Using my basic112 pre amp out to power amp

fnordlyone

fnordlyone

Jun 12, 2013
1,207
573
south Louisiana
www.talkbass.com
#1
My first amp/combo is the original Peavey Basic 112 without a send to ext. cab. I was disgusted with it farting out and was trying to sell it. Then… I heard about stuffing it with pillow stuffing, and it worked! No more farting from the cab. I always liked the tone of the head of the Basic combo and decided to send the pre amp out to my QSC RMX1450 to send the tone to my 2x12 and 2x10 cabs. Worked fine with an instrument cable from Peavey preamp out to input of power amp.
Weird thing: :help: The speaker of the Peavey combo was still working even though I sent nothing back to its power amp in; I sent only the Peavey pre-out to the QSC. Obviously, the Peavey pre amp sent another signal to the combo's power amp section to run the combo's speaker, Right? :beaver:
Or just… what the :chicken: is going on?
fnord!
 
#2
Correct! (hint: read the manual...) Plugging something into the Preamp Out does not interrupt the signal flow to the power amp side, nor does that cut the power amp off. The "Power Amp In" jack does interrupt the signal path ( there is a wire inside the amp going from the "tip" of the Preamp Out jack to the switched contact of the Power Amp In).

So this gives the user tremendous flexibility. You can use just the Preamp Out as a "send" to the PA's mixing board, or to another power amp, or to a tuner, or a tape recorder, or whatever, and the Basic 112's power amp will still merrily send the Preamp's signal to the internal speaker. Or you can plug something into the Power Amp In jack, that jack switches off the internal connection from the Preamp Out: the power amp will only amplify the signal that's coming into it through the Power Amp In jack.

You could verify this by plugging a short instrument cable or patch cable into the Power Amp In and leaving the other end unplugged, you won't hear anything (well you will hear an annoying hum or buzz being picked up through the unterminated end of the cable but you won't hear any signal). Plug the other end into the Power Amp Out jack and the signal path is restored. So you can use this to run an effects loop, the Preamp Out goes to the effects pedal input jack, and the effects pedal output jack plugs into the Power Amp In. Now all of the Basic 112's signal goes throught he effects pedal.

Or....you could bypass the Basic 112's internal preamp altogether and plug something else into the Power Amp In.
 
#3
Excellent! Thanks, Bill. I like the preamp on the Basic. It somehow makes my J sound much more P than my BDDI can :). I've closed off some gas for a P right now by rediscovering my starter combo :bassist:. Priceless. I don't mind the Basic's cab lighting up now that I've stuffed the fart out of it!

nice explanation of Basic's guts
much appreciated,
fnord!
 
#4
zombie reload:
Of course I did get a P any way. Here's hoping that nashvillebill can offer me some more help or any other Peavey Basic 112 vets can help me trouble shoot this problem.
I can plug into my Basic and go out from the pre amp out into an exterior power amp,
BUT, all of a sudden, I cannot get any sound out of the combo.. neither to its speaker or headphone jack anymore.
I've ripped it apart, but took a sanity break before pulling the card loose to look for some sorta bad solder joint. Any body out there?
fnord!
 
#5
If you know for sure you get sound out of the Pre Amp Out: Try plugging your cable from the Pre Amp Out into the Power Amp In. The Power Amp In is a type of jack known as a switching jack, and its internal contacts can get corroded. That can cause exactly the symptom you've described.

However, if that doesn't work, then something has gone caput in the power amp section. Since your headphones aren't working, that rules out a bad speaker or bad speaker connection...I'd have to trace the signal through the power amp to find the problem. This is a very simple power amp though and a competent tech should be able to sort through it easily.
 

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#6
nashvillebill said:
If you know for sure you get sound out of the Pre Amp Out: Try plugging your cable from the Pre Amp Out into the Power Amp In. The Power Amp In is a type of jack known as a switching jack, and its internal contacts can get corroded. That can cause exactly the symptom you've described.

However, if that doesn't work, then something has gone caput in the power amp section. Since your headphones aren't working, that rules out a bad speaker or bad speaker connection...I'd have to trace the signal through the power amp to find the problem. This is a very simple power amp though and a competent tech should be able to sort through it easily.
Click to expand...

I literally just read this after drinking beer and watching college football. I thank you for the response, and before I pull the board will try a direct pre out to power in… But,
Before, when I'd use Basic's pre amp out to my separate power amp for running a couple of cabs, the power amp section of the Basic (I have the older original version) would still engage the combo's speaker. Now, the pre out still runs into the qsc power amp (all eq settings work), but doesn't engage the speaker or headphones.
Frankly, I have an old Peavey Mark IV, so I don't need the Basic anymore, but I'd like to fix this thing and use it as a rehearsal combo, feasable.

f!
 
#7
Right, but if you look at the schematic, it will show what the Power Amp In jack does (note, in the schematic it's labeled Effects In, I think). This is a switching jack (the Pre Amp Out is NOT a switching jack). Ordinarily, the Power Amp In jack passes signal through it, unless there is a plug plugged into it. If there's a plug in the Power Amp In, it disconnects the contacts internally (inside the jack) so that signal doesn't pass from the internal connection that comes from amp's Preamp Out jack. So yes, if you plug a plug into the Preamp Out only, signal still goes through the contacts inside the Power Amp In, and the amp's power amp still gets signal. That's how it's SUPPOSED to work...but those contacts inside the jack are notorious for getting corroded. If they get the tiniest bit of dirt or corrosion, the Power Amp In jack acts just as if there is a plug plugged into it, the signal from the Preamp side is cut out.

So by plugging a cord from the Pre Amp Out into the Power Amp In, you bypass those nasty little internal contacts. Quick and easy check. I'd definitely check this out before tearing into the amp--these switching jacks are used all over the place in virtually every manufacturer's amps, and they are well known for being problematic.
 
#9
I tried it and it works! Thanks again Nashville Bill.
Full disclosure, I had already pulled the head out so I pulled the board to see how everything looked. Damn guts looked like they were installed yesterday, like a sealed tomb. Put it back together and did the pre out to pwr amp in and bass sounds came from the speaker again. Then I took the pre to pwr instrument cable off and Now it's functioning properly with just the instrument input… Maybe taking it apart and putting it back together again joggled the switches back to functionality? I'll know the bypass if this happens again.
f!
 

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