A rookie question re two amps, one pair of speakers

I just recently configured my system in the way the OP descibed. It can be done safely. My solution was to use an old Adcom speaker selector box, disconnection everything internally and installing a break before make switch along with some really good speaker wire. Total cost to me was about 8.49 for the switch since I already had the rest. Easy project. Be really really sure none of the wiring is shorting across poles on the switch or puff the dragon comes to visit.

Hello everyone, I hope someone might still be paying attention to this old thread. I've been scanning through a bunch of posts/threads about possibly connecting two amps to a single speaker...in my case for comparison of a Denon POA-2200 + Denon PRA - 1100 combo VS a NAD C372 integrated amp. I have no switcher unit available...all I have is the A+ B inputs of either Amp.

I am not clear on whether or not it's possible to use these switchers as a sort of substitute for an Amp A/B switcher. I don't mean using the switch to cycle between amps. I just mean using the switch to stop either amp from trying to driver the other's output stage, by turning off the A or B terminals of the amp not in use. Basically I am wondering if those A + B speaker terminals can be disabled effectively or is it the same as just turning off the HT receiver, the other amp will still detect and try to drive the output stage of the HT receiver. 

@imhififan how is that not good? You need to be able to switch A/B to disconnect the amp not being used. Unless I missed something...

It'll be fine if your careful, and make sure you switch one amp out before you switch the other amp in. Never have both switch in at the same time.

Cheers George 

This is always a very bad idea good luck!!

@imhififan how is that not good? You need to be able to switch A/B to disconnect the amp not being used. Unless I missed something...

Thank you all for the input.  You guys rock!

Or you can go the cheap way and use this one back to front.
http://www.ebay.com/itm/A-B-A-B-Switch-1-IN-2-OUT-2-Way-Stereo-Receiver-Speaker-Set-Selector-/152373329362?hash=item237a287dd2:g:Q9gAAOSwNSxVbL5-

I think it is not a good choice because of its A+B switchable.

Here is one that you can hook up two amps and two sets of speakers also if you want.
http://www.ebay.com/itm/TC-7220-2-Way-Amp-Amplifier-Speaker-Selector-Switch-Switcher-Comparator-Router-/391073502625?hash=item5b0dcc15a1:g:ccgAAOSwPhdU9yws

Or you can go the cheap way and use this one back to front.
http://www.ebay.com/itm/A-B-A-B-Switch-1-IN-2-OUT-2-Way-Stereo-Receiver-Speaker-Set-Selector-/152373329362?hash=item237a287dd2:g:Q9gAAOSwNSxVbL5-

Cheers George

Yes but, it needs to be said a speaker selection switch need to be used back to front.
Amps to the speaker connections terminals and speaker to the amp terminals.

The link of Niles SPK-1 has a connection diagram and instruction :

Common application: Two receivers sharing one pair of speakers. Receiver 1 speaker outputs are hooked up to A Default input of SPK-1 Receiver 2’s speaker outputs are hooked up to B Switched input. A 12-volt AC power supply is plugged in the Receiver 2 switched power outlet and connected to the 12-volt control input of the SPK-1. Receiver 1 plays through the common speakers until Receiver 2 is turned on. Receiver 2 is now heard through the Common output

Assuming you're able to switch back and forth properly, its completely OK to use your 2 channel amp with your HT setup. Just go through the speaker calibration setup on your receiver. It will match the gain to the rest of your speakers. A lot of people do the exact same thing.

Yes but, it needs to be said a speaker selection switch need to be used back to front.
Amps to the speaker connections terminals and speaker to the amp terminals.

Cheers George

George is right, do not connect two amp output to one pair of speakers! this topic had been discussed many times, best way to do it is using a speaker selector switch.
I had use a Niles SPK-1 years ago, it switch the connection automatically from the receiver 12V trigger.
https://www.google.com/search?q=niles+spk-1&ie=utf-8&oe=utf-8

One amp would be for my 2 channel system and the other (a receiver) would be for my home theater system. So long as I’m not powering both amps at the same time, is it safe/ok/advisable to connect both amps to one pair of speakers?

In one word NO!!
As one of the amps will be trying to drive the others output stage, even if not on.
Unless both amps have a speaker terminal disconnect relay when not on for both + and - terminals, only a tech will be able to tell you.

Cheers George

Thanks for the response.

Actually, up until recently, I had been doing just that.  It worked all right - my only issue would be that my front mains would be getting twice the wattage of the other channels in HT mode.  I've been having some issues with my NAD receiver lately though.  For some reason I get a humming from the preouts of the receiver when I connect it to my outboard Rotel amp. I've done some problem solving and I'm 99% sure it is the NAD preouts.  So at this point, I just want to completely remove the receiver from the 2 channel system (or as much as possible).   I have a separate DAC/Preamp that I can connect directly to the Rotel amp.  I just want to know if I can share just the front main channels with the NAD receiver and the Rotel amp.

Thanks again.

There might be a better solution. What amp are you using for your 2 channel listening? Does your HT Receiver have line-level pre-outs for the front speakers? 

You might be able to re-cable it using the 2-channel amp to power the front L&R speakers for both 2-channel listening and when listening to multi-channel HT from  the receiver.