Preamp power supply assistance.

[theadamsykes]

I have a preamp from an older Peavey Max bass system.  This amp was basically a CS-800 with a bass preamp together in a rack from the factory.
The power amp is dead on this and I would like to be able to use the preamp with a more modern power amp.  The problem I have, is that I do not know what this preamp requires in terms of voltage, etc.

The preamp has been apart from the power amp for sometime.  My plan was to measure what was being fed to the pre amp from the original power supply, but the fault in the power amp was preventing me from being able to power things up to take a measurement. 

Any ideas?

[J M Fahey]

Never seen one of these in the flesh, but the transformer seen on the picture looks too small to power a power amp, let alone a CS800 class one (unless perspective cheats me), so I think your preamp has it's independent power supply.
Draw a simple sketch of wires and color in that transformer and trace to see whether a couple of them go to the mains power in / power switch/main fuse.
You might only have to provide some independent mains connexion.
Of course it *might* be a, say, 50VAC to 15+15VAC, powered by some big transformer secondary
In that case you should have to find a similarly rated one, but with a 120VAC primary.

[Enzo]

No, the CS800 power transformer is the size of a cantelope.  And I see the power tramsformer right there in your photo anyway.

Is this the preamp from a MAX?  Or does it say "Max Bass Preamp" on the front panel?  They did sell the preamp as a stand alone too, you know.

The schematic can be had from PV customer service for the asking.

I suspect the preamp inot and the preamp section of the Max share the same board. 

Yours is dead.  Zero sign of life?  is mains voltage getting to the transformer primary leads?  The red secondary is the high voltage.  I don;t know what it is, but if it makes 100-200vAC or something, I bet it is OK.  And the orange wires are for the +22,-22 rails.

If secondary voltages are present, then are the DC supplies they serve working?   

And so on...



And you can unplug the power module and see what happens that way.

[Enzo]

Rather than edit the previous.

I think I am wrong.  The Max Bass Preamp includes a tube.  I see no tube in your photo, so the stand alone and combo preamps do differ,

In any case, the feed from the power amp is just mains voltage, so 120VAC in the USA.  That transformer has a splpit primary anyway, so it can be used either way, 120 or 240.

The preamp runs on +/-15v rails, so the power supply is simple.

The testing remains the same though.  Is mains getting to the primary?  is the center tapped secondary providing AC to the rectifiers?

I can;t post the files here for size limits.

[theadamsykes]

No, the CS800 power transformer is the size of a cantelope. 

Right, the CS800 power transformer is in the bottom half of the assembly. 

And I see the power transformer right there in your photo anyway.

I see that as well, but I am not sure what that transformer is seeing at it's primary.

Is this the preamp from a MAX?  Or does it say "Max Bass Preamp" on the front panel?  They did sell the preamp as a stand alone too, you know.

It's from a MAX.  It's the early version of the Max Bass Preamp

The schematic can be had from PV customer service for the asking.

I sent an email out to them and am waiting with my fingers crossed that they have it.

I suspect the preamp inot and the preamp section of the Max share the same board. 

I don't understand this part

Yours is dead.  Zero sign of life?  is mains voltage getting to the transformer primary leads?  The red secondary is the high voltage.  I don;t know what it is, but if it makes 100-200vAC or something, I bet it is OK.  And the orange wires are for the +22,-22 rails.

If secondary voltages are present, then are the DC supplies they serve working?   

And so on...

I'll head back and dig deeper.  Thanks for the help, thus far

[Enzo]

Confused?  Peavey made the Max Bass amp, which you have.  There is a preamp and a power amp, all of which together make the Max Bass amplifier.   Peavey ALSO made a product called the Max Bass Preamp.  it was a stand alone preamp, based on the Max Bass, but the Max Bass Preamp had a preamp tube in it, while the preamp from the Max Bass did not.

We might informally call what you are looing at the "Max Bass preamp", but that is different from the "Max Bass Preamp.'  If you follow me.

Sorta the same idea as this:  An English Muffin is not the same thing as a muffin from England.  or French Toast is not the same as toast from France.

SO I originally thought the Max Bass Preamp used the same board as the preamp in the Max Bass, but that was not the case.


Bottom line is that your preamp is a separate unit, and it just runs off 120VAC fed into that wires you point out.