Peavey Classic 30 Squeals Like a Pig

[misterc57]

You can cut a pin (previously soldered on top to facilitate its later connection) of C36 capacitor. It´s a 22uF electrolytic located next to the pair of 100 Ohm/5 watt resistors (accessible without disassembling the boards). That way you disconnect the feedback.

Your board nicely has the components printed on the board. Mine does not. You suspect the feedback. Looks like I could cut either side of C36 for a test?

Thank you

[Helmholtz]

If the OT primary wires ( brown and blue ) are reversed, the negative feedback (NFB) turns into positive feedback, causing oscillation.

[nosaj]

If the OT primary wires ( brown and blue ) are reversed, the negative feedback (NFB) turns into positive feedback, causing oscillation.

This was mentioned in post #3. Any time i get a squeal like that that's the first thing I check, easy to do and rule out a lot of needless troubleshooting if that is the issue.

nosaj

[nickb]

The squeal is so bad and piercing that I have yet to leave it on and try a guitar.

I bought the amp knowing it had this issue.

I now suspect that the OPT may have been replaced because all 6 wires at the molex connectors have heat shrink. Looks like they were spliced.

I had the following readings from the OPT when I pulled the molex connectors off the board.

Primary Brown to Red 74 ohms
Primary Blue to Red 100 ohms

Secondary White to Black 1.2 ohms
Secondary White to Black 0.9 ohms

I cannot get a stable reading on the primary from Brown to Blue. Should I be able to? The reading keeps jumping around.

On the primary the red is the center tap. I looked at some pics online and the wiring looks the same, with red in the middle of the molex connector.

Does it matter which way the primary molex is connected to the board? I would think not but a pic I saw online was reverse of the way mine is connected.

Attaching some images.

Thank you. MarkO

Here's another Classic 30 pic:


Spot the difference? Looking at your pic I see the OPT wires are swapped.


So it seems a repair has been attempted and caused the problem. Pity you weren't told about that.

[Pedro Vecino]

Your board nicely has the components printed on the board. Mine does not. You suspect the feedback. Looks like I could cut either side of C36 for a test?

Thank you

You can cut the most accessible side. Disconnecting the feedback you can check if the problem is associated with an inverted connection in the primary of the output transformer.
Although you can also reverse the connections in the primary and test.
In these cases I usually start with the first (simpler).

EDIT: Definitely brown and blue wires are inverted in mine.

[Enzo]

The OT is fine, though apparently wired backwards. If I recall, the molex with the red, blue, and brown wires can be easily turned around.

It ABSOLUTELY matters which way the OT is connected. It makes teh negative feedback into positive feedback if backwards.

[Enzo]

Your board nicely has the components printed on the board. Mine does not. You suspect the feedback. Looks like I could cut either side of C36 for a test?

The part numbers are on the layout drawing.

GAAAA. Don't CUT anything, just reverse the wires.

[misterc57]

I misunderstood post #3 when I read it. I was thinking it meant look for primary and secondary reversed. Clear to me now that is not what it said but that is what went through my mind.

Anyway, reversed the OPT molex connector and no more squeal. Another lesson learned.

Thank you all so much!!! I am a happy C30 owner now

MarkO

[misterc57]

No More Squeal

I misunderstood post #3 when I read it. I was thinking it meant look for primary and secondary reversed. Clear to me now that is not what it said but that is what went through my mind.

Anyway, reversed the primary OPT molex connector at the board and no more squeal. Another lesson learned.

Thank you all so much!!! I am a happy C30 owner now

MarkO