The Steel Guitar Forum

I'm hoping someone with much more electronics savvy than myself can help me here. I have a 4-ohm cabinet which I'd like to use with two amps simultaniously: a 4-ohm Nashville 400 head AND a 4-ohm blackface Fender Bassman. I play steel and guitar, (not at the same time, mind you) and would like to run the Nashville and the Bassman through the same cab. The cab has two jacks on the back, and is loaded with 2 8-ohm 15" EV's for a total 4-ohm load. Is there a way to do this? Will I blow up one or both amps if I have them both plugged into the same cabinet at the same time? Or, can a switch be fashioned to switch between the speaker outputs of each amp? I would think the latter wouldn't work b/c I know you're not supposed to run an amp without a load, and the switch would screw up the resistance factor. Obviously, I would like to be able to have both amps powered on, so as not to keep turning amps on and off (especially the Bassman). Seems like there ought to be a way to do this, but maybe not. Anyhow, any advice would be appreciated.

Thanks,
Craig

My experience is you would have to physically disconnect one amp while the other was "on line" to the speaker. If not you could have bucking voltages, impedences, etc. Eventually something will probably blow, if it even works at all.

Well, I figured it wouldn't work, but I thought I'd ask on the off chance.

Thanks--
Craig

Craig, You could get an A/B box and switch from one to the other if you didn't need both amps at the same time. They don't cost too awful much and will do the trick.

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1985 Emmons push-pull, Session 500, Nashville400, 65 re-issue Fender Twin, Fender Tele

I wouldn't use a A/B switch....

In general,they can't handle the current.
The A/B/switches are for switchin' low current signals,like VCR,TV antanas,etc,etc, Not speaker loads. the internal wireing is too small to handle such loads.

Your askin' for trouble here !!

Mesa makes a unit called the 'High Gain Amp Switch'. It allows you to switch up to four amps or pre-amps, but I'm not sure if the amps can share a cabinet. mesaboogie.com

Craig,
You cannot have two amps connected to the speakers at once, there's just no way, and like you so correctly assumed, the Bassman should NEVER be run without a load connected to it - no tube amp will survive that in the long run.

You'll have to have a special switch made for you, with heavy wiring and a dummy load of suitable power-handling capacity, that's switched to the output of the Bassman, when that amp is not playing.

This is not nearly as complicated as it may sound. I've made numerous custom switch-boxes for myself and my musician friends over the years, but then again, I have a formal education in electronics.

If you'd like any specific/detailed advice/instructions, I'll gladly e-mail it to you !

Ole

Bill Crook, I have a DOD AB box that I have had for years and it's made for switching guitars and such. Also amps. Though some are made for TV's this isn't one of them. Check it out I think DOD still makes them.

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1985 Emmons push-pull, Session 500, Nashville400, 65 re-issue Fender Twin, Fender Tele

The DOD A/B Box is not heavy enough for high power amplifier switching. It's only made for low level instrument signals.

To have two "hot" amplifiers and switch between the two would take a switch rated for high power and also a dummy load to be switched into the standby unit. Big and costly. The best way is to put up with the hassle and just manually switch things when needed.

I know that an amp that's powered on without a load is a no-no. I'd have to have some sort of power-soak device so I wouldn't fry the amp on standby. I would also figure that any switch hooked up to the speaker outputs of two amps would tend to make a mighty loud POP when switched between the two. I sorta already figured out for myself that it's more of a pain to figure it out than it's worth. Ole, I appreciate your offer to help, but I think I'm gonna leave well enough alone for now. i already carry around a steel, a guitar, a pack-a-seat, a briefcase with effects, and an amp. What's one more heavy thing to me?

I don't recall all the details but once when I was young, foolish, and daring, I pugged a cord into the extention speaker jacks of 2 different amps to see if either amp would drive both speakers. It worked like a charm. Maybe I just got lucky. I wouldn't do it again, though. And, I wouldn't recommend it to anyone.

John Paul Jones<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by John Paul Jones on 30 June 2001 at 11:59 AM.]</p></FONT>

Tube amps need to have a load connected to their speaker outputs at all times, for the safety of the amp. Also, if you connect two amps outputs together like that, a portion of the output from the amp that you're using may end up feeding back through the amp that you're not using and cause its output section to fail. This depends on lots of factors, of course, but it's not a good idea to put two amps into one cab without a suitable switch.

For a schematic of a suitable A/B switch, go to http://www.aikenamps.com/HeadSwitch.pdf

My two cents
Matt Farrow
Pharaoh Amplifiers



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Matt Farrow
Marlen 9-string 6+2
Kustom K150

http://surf.to/pharaohamps

Craig,
You say your cab has 2 speakers and 2 jacks. Why don't you wire the cabinet so each amp has its own speaker input(i.e. each jack only connected to one of the speakers)? I think either amp could handle the slight impedence mismatch, but I wouldn't make any claims as to how this might sound!

what Cris said or invest in another speaker cab for the nashville.I allso play guitar as well as steel and tried using one amp or cabinet for both but I find myself never getting quiet the right tone for both so I carry both to my gigs (session 500 and classic 50)

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sho-bud,session 500,american standard strat,shecter tele,peavy classic 50

Gary, you are right about two separate amps. Or in my case I solved the switching problem by going to a rack system with a Transtube Fex. When I want to use my Tele I just switch to the lead guitar program.

My Nashville 400 is great for steel but it just doesn't have the bite for lead.