Peavey Classic 212 VT

[jammyget]

I bought this amp about 6 months ago and I have been using it happily. I finally got roun dto building myself a footswitch (thanks be to this forum and all its users). My problem however is not the footswitch but the automix channel itself. When I plug into it the "Normal" Channel all nbut disappears and sounds distorted(all be it in a good way). Plays O.K when I plug into the normal jack socket, it's only when I use the Automix jack socket. "Bright" channel is unafected. Any ideas folks?

[Enzo]

Hi, welcome.

I am guessing you have a "Classic VT", and the 212 part is your description, yes?

To review: If you plug into the Normal jack, it works OK? And if you plug into the Bright jack, that also plays OK?

When you plug into automix, it sends the signal to both channels. Or should. The tip contact of the automix jack is wired to the cutout contact in the bright jack. SO it feeds directly into that channel. If that contact is dirty, little or no signal will get into the channel. U1a is the first stage of the bright channel, and after it, the signal progresses on. But it also branches up through U2 to get to the normal channel first stage. If the bright channel works, we know U1a is OK.

U2 is an OTA op amp. 87478 type. The phasor uses four of them in a row. If we doubt the one at U2, swap it for one of the ones in the phasor. Make a difference?

U2 is controlled by two transistors and the ring cutout contact on the automix jack. Make sure the jack contacts are working. This is simple: the automix jack has 5 legs, and when nothing is plugged into the jack, ALL FIVE should read as grounded.

[jammyget]

Thanks for the tip mate Yes it is the Classic VT, I've not had a chance to try it out yet but I'll let you know how I get on when I do.

[jammyget]

O.K. I tried all that yesterday. The I.C's checked out O.K. But one of the pins on the connector wasn't grounded, the one that goes back to thetransistor and ultimately U2. The tip connector seems to be grounded O.K. but there is no continuity between that and the pin. I tried cleaning up the connector and get continuity between gnd and the tip connector. Would it be acceptable to solder in a jumper?

[Enzo]

No, that defeats the circuit.

The automix jack has two pairs of cutout contacts plus the bushing/ground. If one set is not making contact, then puyll the jack and see if the contacts can be cleaned or adjusted, otherwise replace the jack.