2 amps, 1 speaker.

Larry Behm · From: Mt Angel, Or 97362

Can you run 2 amps into a AB box and switch back and forth into 1 speaker without harming the amps?
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'70 D10 Black fatback Emmons PP, Hilton VP, BJS bars, Boss GE-7 for Dobro effect, Zoom MS50G, Stereo Steel amp, Telonics 15” speaker.

Phone: 971-219-8533

George Biner · From: Los Angeles, CA

I don't see why not but I would make sure the switch is a "break before make", i.e. it disconnects in between states. If it doesn't, you'll have both loads active which will load the amp down and will either fry the amp or make the protection kick in.

Also, you will probably have different levels between the two cabinets which may sound rude when switching.
_________________
Guacamole Mafia - acoustic harmony duo
Electrical engineer / amp tech in West Los Angeles -- I fix Peaveys
"Now there is a snappy sounding instrument. That f****r really sings." - Jerry Garcia

Larry Behm · From: Mt Angel, Or 97362

Would that be a on-off-on?
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'70 D10 Black fatback Emmons PP, Hilton VP, BJS bars, Boss GE-7 for Dobro effect, Zoom MS50G, Stereo Steel amp, Telonics 15” speaker.

Phone: 971-219-8533

Sandy Inglis · From: Christchurch New Zealand

Valve or Solid State?
Valves are a bit more forgiving than Solid State. I would put some kind of load resistor across each amp (output) before the A-B switch to give each amp a nominal load when switched off from the speaker load. This could be poss 20-30? odd ohms but you would probably need a high wattage resistor to do it (I haven't done the sums). This should not affect the amp as much as suddenly running it into no-load.
I would also mute the signal into the amp when it has no load?
Over-all I would not recommend it though.
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01'Zumsteel D10 9+9; Sho Bud D10 SuperPro; 6 String Lap Steel (Homemade); Peavey Nashville 1000; Fender Deluxe 85;
1968 Gibson SG; Taylor 710 CE; Encore Tele Copy; Peterson Tuner; HIWATT T40 C 40W/20W Combo

Dave Grafe · From: Hudson River Valley NY

You can, but your amps won't last long

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

If you're talking about a simple guitar/line-level A/B box, the answer to your question "Can you run 2 amps into a AB box and switch back and forth into 1 speaker with harming the amps?" is NO. There are several issues, but an important one is that switches in devices like this are often not designed to handle high power signals.

Beyond that requirement for high-power switching, it depends on exactly what amps you're switching between. With two solid-state amps, the amps are fine if they don't see a load. But a big issue is that the two amps should never be connected to the speaker cabinets simultaneously. So a circuit using a 3-way on-off-on or break-before-make relay/switch of the right power capacity should work. This way, both amps are completely disconnected before the switch is made. Radial used to make the Headbone SS for this purpose, but it is no longer in production.

Tube amps present a very different issue - they must see a load of the correct impedance at all times. There are a bunch of 'tube-head switcher' boxes out there like the Radial Headbone VT, the Weber Two-Head Amp Switcher, and others, which connect the amp to a dummy load when not connected to the speaker. I have the Radial Headbone VT, it works OK for this purpose. But this device apparently relies on a low-power dummy load for the 'off' amp, and relies on internal switching to mute any input signal to that amp. But if, for example, there is a delay connected to an effects loop which can generate signal at the output after the switch is made, there can be a problem. I really wish I had gotten the Weber unit, which uses a 200 Watt dummy load. Note that none of the tube head switchers I've seen are designed to work with solid-state amps.

Switching between a tube and solid-state amp presents yet different design issues. Radial used to make the Headbone TS to handle this exact use case, but it is also now out of production. I imagine one could put something together that uses an on-off-on switch/relay that connects the tube head to a dummy load in the off and other-amp mode, but I don't know anybody making anything like this right now.

There are other potential issues like the no sound while switching and switching noise or pops. IMO, you should think long and hard about what you really need before you act on this.

ajm · From: Los Angeles

"Can" it be done.
Yeah, I suppose so.
Given enough time and/or money, just about anything "can" be done.

But I'll cast my vote in a nutshell with a couple of other posters: No.

And I'll be the first to ask:

What amps are you talking about?

What speaker cabinet?

Why are you thinking about doing this to begin with?

George Biner · From: Los Angeles, CA

Yeah, I forgot about the fact that you shouldn't run a tube amp unloaded -- my bad. Shouldn't type late at night.
_________________
Guacamole Mafia - acoustic harmony duo
Electrical engineer / amp tech in West Los Angeles -- I fix Peaveys
"Now there is a snappy sounding instrument. That f****r really sings." - Jerry Garcia

Larry Behm · From: Mt Angel, Or 97362

Walker Stereo Steel and a Quilter Tone Block 202.
_________________
'70 D10 Black fatback Emmons PP, Hilton VP, BJS bars, Boss GE-7 for Dobro effect, Zoom MS50G, Stereo Steel amp, Telonics 15” speaker.

Phone: 971-219-8533

Clyde Mattocks · From: Kinston, North Carolina, USA

For years I used a Peavey Session 400 and a Fender Super Reverb amp head into the Black Widow Speaker in the Peavey. I used a Tele selector switch in box that I made, which I suppose was a break before make except when it passed thru the middle position, which I didn't leave it at. I never suffered any ill effect, but I didn't know any better then anyway.
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LeGrande II, Nash. 112, Fender Twin Tone Master, Session 400, Harlow Dobro, R.Q.Jones Dobro

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