Film-Tech Forum ARCHIVE: Peavey M 4000 Amps and 1/4 inch Jacks

This is topic Peavey M 4000 Amps and 1/4 inch Jacks in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by William T. Parr (Member # 677) on 02-15-2004, 09:21 PM:

Hey All,

I have inherited a Peavy M-4000 amp that has 1/4 inch Input and output jacks on it, but no documentation on how the 1/4 inch jacks are supposed to be wired. I plan on using balanced inputs so I need to know which part of the jack, Tip, Ring, Ground, gets the Hot (Red), Nuetral(Black) and Shield (Silever Exposed) part of the cable from the Crossover and like wise what part of the speaker feed goes to the Tip and Ring part of the jack. Thanks in advance for any info and I have already downloaded the spec sheet from Peavey, but it does not give this info in it.

Posted by Jack Ondracek (Member # 1466) on 02-16-2004, 01:27 AM:

Without specific knowledge of the amp, William, I assume you mention ring/tip/ground because you've already confirmed the amp has balanced inputs and is equipped to accept a "stereo" 1/4" phone plug. In this case, without a schematic, it might be difficult to know for sure without scoping the input/output of the amp to confirm polarity... or finding someone who's already figured this out. You won't have a problem unless you're mixing amplifiers. In that case, you probably ought to get a dual trace scope and confirm which polarity at the input gets all amps going positive at the output. That will tell you how to wire your ring and tip. The shield of your cable goes to the ground (lower) part of the plug... or not... depending upon which way gives you a lower noise floor.

As for the outputs to the speakers... it's the same issue. If you're mixing amps, you need to make sure you're sending the same polarity down the line to all speaker systems. If not, just make sure both channels are feeding their respective speakers in phase, one way or the other.

Posted by William T. Parr (Member # 677) on 02-16-2004, 01:30 AM:

You are correct Jack, The fact that it had Balanced inputs was part of the spec sheet, I just want to get the + and - on both the input and output correct the first time around and found nothing in the documentation of the specs as to which was what. It would be safe to probably assume that the Negative side goes to the part directly above the tip of the jack since both would be combined on the output. But I do not want to make that assumption and find out I was wrong.

Posted by Jack Ondracek (Member # 1466) on 02-16-2004, 01:34 AM:

If it's truely balanced, it won't matter. If it matters to you that a positive input to the tip causes a positive output at the other end, you'll need to scope it. Several people here have observed amplifier types that don't seem to follow any standard, though the channels should be consistent. If it doesn't matter, just make sure your polarity is not crossed at the inputs, then separately, at the outputs. At least this way, you won't be out of phase when you get to the speakers.

If you're feeding the amp with an unbalanced signal, it's another story altogether, and it also depends on whether the amp has a transformer-balanced or active input. Some active designs don't care for having one side grounded (as long as the shield is connected), and the output level will be effected by this issue.

Great question though... smart of you to wonder about that.