using a combo as a cab

[Spitfire]

from time to time it would be convenient to be able to use my peavey classic 30 as a 1x12 cab... as standard it does not come with a jack to do this.. however it seems to me it should be an easy mod.

The speaker is hooked up simply as below... as they all are... if i was to drill a hole in the back of the cab, attach a jack socket... and then wire that with speaker cable to the additional lugs that come off the speaker without disconnecting it from the present cables (which connect the speaker to the peavey power section) would that cause a problem when running it as a cab... i.e. a signal coming through the new jack?? as i would be adding a current to an already complete circuit or would i have to disconnect the existing peavey speaker cables?



Thanks,
David.

[Twinfan]

I *think* you'd need to disconnect the Peavey amp otherwise the loads won't be right?

I'd drill a hole, fit a double switchable jack socket of some sort so you can switch between "combo" and "cab"?

[Frank]

You'll need to use a switched jack to make sure the existing power amp is taken out of the circuit when an external amp is plugged in.

[Frank]

Just a word about why it's important not to connect two power amps to one speaker - the driving amp will "see" an eight ohm speaker with the secondary of the unused amp's output transformer connected across it. So the actual impedance seen by the amp is anyone's guess.

Also the driving amp will be putting an AC voltage across the secondary of the unused amp's output transformer which is not a great idea. Transformers will transform a voltage in either direction and this would turn the OT into a step-up transformer, generating a large AC voltage on the primary windings with "unpredictable consequences" for the idle amp. Which in the case of tube amps usually means blue smoke and a repair bill.

[Spitfire]

You'll need to use a switched jack to make sure the existing power amp is taken out of the circuit when an external amp is plugged in.

thats a good idea.. i have done the odd bit of soldery in the past.. but id have no idea how to wire this.. can anyone advise what the best switchable socket would be and how to wire it??

[Frank]

Switched jacks have two moving contacts, just push a plug in and you'll see them move and open two contacts. These moving contacts need to connect to the speaker. Then the wires from the Peavey power amp go to the other contacts on the socket. This gives you a "normalised" socket like on a patchbay, the speaker is connected until a plug is inserted.

I'd do a diagram of this but it's rather tricky to draw!

I'll probably get panned by someone for recommending Maplin but you can get these if there's a shop near you

http://www.maplin.co.uk/1-4-mono-socket-withchrome-bezel-1263

The good thing with those is they're easy to work with when you do switching jacks, the construction is open and you can actually look and see them working. Helps a lot when you're trying to figure out where your signal disappeared to.

[Spitfire]

Switched jacks have two moving contacts, just push a plug in and you'll see them move and open two contacts. These moving contacts need to connect to the speaker. Then the wires from the Peavey power amp go to the other contacts on the socket. This gives you a "normalised" socket like on a patchbay, the speaker is connected until a plug is inserted.

I'd do a diagram of this but it's rather tricky to draw!

I'll probably get panned by someone for recommending Maplin but you can get these if there's a shop near you

http://www.maplin.co.uk/1-4-mono-socket-withchrome-bezel-1263

The good thing with those is they're easy to work with when you do switching jacks, the construction is open and you can actually look and see them working. Helps a lot when you're trying to figure out where your signal disappeared to.

Cheers, im very greatfull for your help..

I'll have to get the parts in and find my speaker cabling, sounds like it will be a simple mod