Peavey Centurion no Auto mix input

[drewl]

So, A and B inputs for both channels work fine, the auto mix input does not.

Got the schematic from here, and on the one I have, the tip and ring of the auto mix input are grounded by the ch1 and ch 2 A and B inputs.


i checked the components connected to that input, no shorts from them.

The LED's light up when a jack is plugged into the auto mix input.

No way it can function if the jack is grounded. The jacks are stock, unless something is bent inside or Peavey used the wrong jacks when it was built.

Or am I missing something?

[glebert]

Are you using a footswitch with it?

[Jon Snell]

Try it with a T R S plug and the Ring not connected. If the Ring is ground there will be no change for the indicator switching transistors.
The Tip connects to both inputs and there is no reason, save broken sockets, that is won't work on paper.

[g1]

Automix ring is shown grounded. Tip should go to switch contacts of A & B inputs.
If yours is stock and not like that, maybe there is a different schematic.

[drewl]

Circuit looks the same as the schematic

But, as mentioned, A & B inputs 1 & 2 are grounded with switching jacks.

Not using a footswitch

Weird.

[g1]

But, as mentioned, A & B inputs 1 & 2 are grounded with switching jacks.

They only ground via switch of automix tip. As soon as a cord is (fully) in automix jack, they should not be grounded.

Are they board mounted jacks, or wired?

[Helmholtz]

But, as mentioned, A & B inputs 1 & 2 are grounded with switching jacks.

Weird.

A&B inputs are grounded via the automix switching jack. So inserting a plug there should lift the ground for the inputs.

[Enzo]

There are two switched contacts in the Auto jack. Your LEDs come on when you plug in so that contact is working. That leaves the signal path contact.

the tip and ring of the auto mix input are grounded by the ch1 and ch 2 A and B inputs

You have that backwards. The channel 1 and 2 input jacks are grounded through the Automix jack. Plugging into the automix should connect the guitar signal to both channel inputs. Stick a signal in there and follow it with a scope or tracer over to each input channel jack.

Why are we using the schematic for a Bass Mk3?

[g1]

Why are we using the schematic for a Bass Mk3?

That Centurion file you linked is another 'invalid'.

[Enzo]

Why don't they ever like my files? Are they THAT old?

Try this

[drewl]

There are two switched contacts in the Auto jack. Your LEDs come on when you plug in so that contact is working. That leaves the signal path contact.



You have that backwards. The channel 1 and 2 input jacks are grounded through the Automix jack. Plugging into the automix should connect the guitar signal to both channel inputs. Stick a signal in there and follow it with a scope or tracer over to each input channel jack.

Why are we using the schematic for a Bass Mk3?

Yes, on the schematic.
Looks like I had the Bass version, but the inputs are the same, Anyway:

On this preamp board, Ch1 & 2 A & B inputs are four connector jacks, with the tip of all four grounded, thus grounding the tip of the auto mix input.

These are pc board mounted jacks, and looking at some of the connections that were never touched, look to be original.
I'll take a pic and show you when I get home from work.

[Enzo]

I maintain my case. Look at the schematic. Look at the four channel input jacks. Where is there a ground connection? The ground connection is through the automix jack. Remove teh automix jack and the inputs are not grounded. The four input jacks have grounded bushings, but no grounded tip contact.

It is a clever circuit. If you plug into either channel in, the other channel remains grounded via the automix. If you plug into the automix, that common trace that was used for grounding becomes a common signal trace to split the signal into the two channels.

On the Bass layout, you can see the traces from the two input jacks connecting to the cutout on the automix.

[Helmholtz]

See post 7. Plugging into the automix jack removes the grounding of all inputs and routes the signal to A and B channels.

[drewl]

Yes, I see the way it's SUPPOSED to be.

Now picture the four jacks being four pin with the switch grounding the tip of all four input jacks also grounding the auto mix.

That is how this amp is set up.

[drewl]

We'll see if you can make out the picture.

I labeled the A jacks of channel one and two and you can see how they ground the auto mix jack.

If I plug a cord into A jacks of both channels it lifts the ground of the auto mix jack.

I need to remove them and take out the switch connector of both.