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Messages - Enzo

#1936
What do you mean the fender doesn;t have outputs?  Both the Fender Princeton CHorus DSP and the older Princeton Stereo CHorus have a stereo FX loop.  The FX sends are line outs.  The jack is a single TRS for both L and R, so you'd have to use a breakout cord,  but there are your left and right sends.  The return is also TRS, so you have access to stereo comong and going.
#1937
Peavey usually uses blue and yellow for its main speaker leads, and yellow is the positive lead.  I would assume the blue to be negative here as well.  With the speaker not connected, check which wire is closest to ground.  That would be the negative wire.
#1938
Well, then, I don;t care if you want to mod your stuff either, go right ahead.

In your drawing, you highlight one half of the channel switch, but ignored the other half.  The other half of the switch selects which volume control is in use, and by extension whether the extra gain stage is in the circuit.

In clean mode, R48 is added in to reduce the signal feeding into the OD stage, that is SW1-B.  And in clean mode, SW1-A selects the clean volume.  Switching to dirt channel, R48 is shorted across, removing it from the circuit, and SW1-A selects the OD volume control, which uses the signal from the extra gain stage.

Your schematic is partial, so I don;t know if there are more things SW1 controls, I suspect there are no more sections to it.  SO SW1 is a DPDT switch.  The most straightforward way to do this in my view is with a relay.  Get a little DPDT relay, and wire the contacts in place of the switch.  YOu lose the switch on the control panel, so you must always use a footswitch for channel switching, but there you go.   We could wire up something so the panel switch remains and we have footswitching, but that would add to the complexity of the circuit we invent.  I suppose we could retain SW1, after reusing its solder pads, and have it controling the relay.

I can;t see the power supply other than to spot +15v.  I am guessing that derives from 20-25v somewhere?  ANyway, a 12v relay coil with a series ressistor would run fine off 15 or maybe a 24v relay off the 20-25v.  Tiny 12v relays are more common, but you can source anything.  A simple stomp switch would turn it on and off.

Alternatively, you could use three JFETs in place of the switch, and control their gates with a footswitch.  Same discussion about the panel switch being used or not..
#1939
This may sound more complex than it really is.  All we want to do at this point is determine if the power transformer primary winding is open or intact.

Imagine you have a table lamp.  A mains plug and cord, a switch, a socket for the bulb.  Imagine we know a good bulb had 100 ohms resistance.  If we put the bulb in the socket, unplugged the lamp from the wall outlet, we ought to be able to measure the resistance of the bulb itself out at the end of the power cord.  If you measure resistance between the prongs of the power cord with a meter and you get the 100 ohms, then we know the bulb is OK.  If we get an open reading, then either the bulb is burnt out or the switch and wiring is bad.   At that point we could unscrew the bulb and measure it direct - it is OK or it is open.

We are doing the same thing here, except instead of a light bulb, there is a transformer winding at the inner end of the power cord.


Imagine we plugged out table lamp into the wall and turned on the switch.  If we remove the bulb, we can set our meter on AC volts and probe the wall of the socket and the little bump in the center.   We expect to find 120VAC between the socket wall and the center bump.   Just so here.  If we unplug the transformer primary, there should be 120VAC (or whatever your mains voltage is) between the two wires it was connected to.  If that voltage is not getting there, then the transformer has nothing to run on.  If it IS getting there, then the transformer is suspect.
#1940
Well, first, those part numbers are Peaevy part numbers, so you are not going to find specs on them online.  $42.99 sounds very reasonable to me for that transformer.

The transformer works or it doesn;t.  The mains wiring in the amp works or it doesn;t.  SO look for the power transformer primary wires.  Most Peavey amps have connectors for this.  PLug the amp in and turn on the power switch.  Is there mains voltage between those primary wires or not.  If there is, then it is getting to the transformer, if there is not mains voltage there, then the mains wiring is bad.

Unplug the amp from the wall.  Disconnect the primary wires of the transformer from the mains wiring in the amp.  Use an ohm meter to measure continuity - resistance - through the primary.  it will either have some fairly low resistance, or it will be open.

The idea behind JM's test was that if you measure resistance between the mains plug prongs with the amp power switch ON, then your meter is measuring the resistance up one side of the mains cord, through the fuse and switch, through the transformer primary and back down the other mains cord wire.  If the transformer winding is intact, you would be measuring its resistance through the powr cord.

Since you seem to get an open that way, you need to determine if it is the transformer primary that is open or the mains wiring to it.

Yes, you can apply power to the transformer with the secondaries unloaded.

If the primary is OK AND getting voltage, then see what is on the secondary wires.
#1941
What would be an example of such an amp?
#1942
SCope?  Scope the power amp power rails to see if a filter cap has gone soft.   otherwise, measure them, and hte plus and minus sides about the same, and set the meter to AC and see if the ripple is about the same.

Whatever op amps might be in hte power amp stages, check THEIR power rails as well, the same way.
#1943
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.
#1944
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.
#1945
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.
#1946
And at the risk of sounding like an old fogey, one shouldn't be feeling around in the dark when setting up the gear.  if it is dark, get a flashlight or a work light.  And pay attention to what you are doing.
#1947
The Newcomer's Forum / Re: KUSTOM MODEL 1-L AMP IC'S
February 15, 2010, 08:01:54 PM
PC5129
#1949
The Newcomer's Forum / Re: KUSTOM MODEL 1-L AMP IC'S
February 13, 2010, 12:52:03 PM
I'm thinking the 14 pin chip is Kustom part 007-7015-00, which is calle out as a 739 on the schematic.

It is an old school dual op amp, the three extras pins per section are used for compensation caps.   +12 to pin 14 and -12 to pin 7.

Outputs are pins 1 and 13.  Inputs +9, -8, and +5, -6.

A quick look finds them in boards like PC5093, PC5102, PC5104, PC5128
#1950
The Newcomer's Forum / Re: KUSTOM MODEL 1-L AMP IC'S
February 12, 2010, 11:44:06 PM
What is the board number?   Look on the solder side for some number like PC5068.

A 1458 and a 4558 should both have the same pinout, and pin 8 would be V+ on either one.