Can multiple amps be connected to a set of speakers?

[roadstarman]

I have a Nakamichi A/V receiver that I use for the TV surround. I want to use the same speakers to listen to music powered by a different system. The speakers are ADS L810's front, Infinity Qe rear, Martin Logan Vignette center and a PSB powered sub. To power these for music I use an Adcom gfa 555 for front, Mitsubishi DA A7DC for rear, HK Citation 19 for center. All these go through an Adcom GSP 560 processor and controled by a Sansui AU7700 in seperated mode as a pre-amp. The receiver, of course, would not be operating at the same time as the seperates. Will the speaker signal back feed into the system that is off and not being used causing undesired sound or damage?

 

[j_garcia]

The risk you run is accidentally turning both systems on and frying both amps - doesn't matter how careful you are. So basically not a good idea, however you might be able to connect the amps to the speakers via a speaker selector to isolate them being connected at the same time.

 

[roadstarman]

Do you mean running a speaker selector in reverse? If so wouldn't that be just as dangerous seeing as how they usually allow you to select more than one speaker, which in reverse would be amps?

 

[gmichael]

Even if one amp is off and the second one is driving the speakers, you run the risk of current feeding back through the first amp (even though it's off). The speaker selector would stop that, but as you pointed out, it's not fool proof either. I do know that audio shops have their systems set up to power any set of speakers by any amp in their system. Not sure where those switches are available or even if they are a great idea. Any time you add switches to your system you are adding another change to degrade the sound quality.

 

[j_garcia]

Yes, that's essentially what I am saying. You'd be going the opposite direction, but since a speaker selector is passive, it should work. Some switches allow simultaneous activation and others do not, so you'd want one that does not. OR connect it as you said before but get in the habit of disconnecting things manually before firing the systems up.

 

[lsiberian]

You should be fine with a speaker selector switch between the amp and speakers. Even if you had both on only one is feeding current to a speaker.

How would you get feedback into an open circuit? I'm really not following the thinking you guys have. I'm not an expert in electrical engineering, but I'm pretty certain you shouldn't have an issue. I'm not seeing the issue. Demo stores do this sort of thing all the time.

 

[j_garcia]

As mentioned, some speaker selectors allow multiple connections simultaneously, so that would mean both amps being connected. So, if you have an A-B selector, not all of them disconnect B when you press A, allowing both A and B. The switch in question should not allow this, and I think the good thing about that is the inexpensive ones typically don't.

 

[adwilk]

Curious- Even if both amplifiers were ON and connected to a speaker, both sending signals to the speaker, how would it fry the amplifiers? Its not that I don't believe you guys- I just want an explanation. I think I understand, but clarity is good...

 

[Grador]

Curious- Even if both amplifiers were ON and connected to a speaker, both sending signals to the speaker, how would it fry the amplifiers? Its not that I don't believe you guys- I just want an explanation. I think I understand, but clarity is good...

With the voltage differences being put out by the amplifiers they would try and drive each other. Imagine at some point in time one amplifier is trying to put 5 volts into your speakers, and one is trying to send a signal of -5 volts. This large difference between the amps would be effectively worse than a short circuit as they are actively opposing each other.

 

[lsiberian]

With the voltage differences being put out by the amplifiers they would try and drive each other. Imagine at some point in time one amplifier is trying to put 5 volts into your speakers, and one is trying to send a signal of -5 volts. This large difference between the amps would be effectively worse than a short circuit as they are actively opposing each other.

But the amp isn't doing that if it's off or the circuit is disconnected. Obviously you'd use the right tool.

I don't understand the OPs plan very well though. Why not run the receiver as a pre-amp. for both systems and use the amp to drive from both pre-amps.

 

[j_garcia]

But the amp isn't doing that if it's off or the circuit is disconnected. Obviously you'd use the right tool.

I don't understand the OPs plan very well though. Why not run the receiver as a pre-amp. for both systems and use the amp to drive from both pre-amps.

That's a good point. If the Nakamichi has pre-outs, he should be able to run it in a configuration with both that would work.

 

[Grador]

But the amp isn't doing that if it's off or the circuit is disconnected. Obviously you'd use the right tool.

I don't understand the OPs plan very well though. Why not run the receiver as a pre-amp. for both systems and use the amp to drive from both pre-amps.

With the circuit disconnected you're obviously fine, but even with the amp off you can run into some issues. Applying voltage, even voltage within normal operating specs, in a manner a circuit isn't anticipating it can be catastrophic. When the amplifier is off circuit paths that may normally be open/closed could be in the wrong position causing some quite nasty issues. Additionally the amplifier that is not in use could act as a reactive load causing some acoustic issues.

 

[TLS Guy]

Curious- Even if both amplifiers were ON and connected to a speaker, both sending signals to the speaker, how would it fry the amplifiers? Its not that I don't believe you guys- I just want an explanation. I think I understand, but clarity is good...

Because the amps are Direct coupled to the output transistors. Even if one amp is off it will blow. It will look like a short and worse. The driving voltage is right on the collectors of the output devices, but the DC is balanced. Connecting the amp together will unbalance it, and then you have DC offset which flows through the output devices. This is absolutely the fastest way to blow two amps. It will do it every time instantly!

I think the whole scheme is a really bad idea and ripe for an expensive misadventure. We have had several posts since I have bee a member with the OPs asking what went wrong when they did this. Generally the cost of repair after this exceeds the value of the units.

 

[j_garcia]

I didn't know what was actually happening when this is done, but I have seen fried amps before (car audio) so I know that it is definitely a bad idea whenever I see it asked.

 

[lsiberian]

OP get a receiver with pre-amp outs and run the pre-outs to the amp. You can use a selector switch to choose the input between the adcom and the receiver.

You have a nice amp you might as well use it for movies and music.

 

[TLS Guy]

OP get a receiver with pre-amp outs and run the pre-outs to the amp. You can use a selector switch to choose the input between the adcom and the receiver.

You have a nice amp you might as well use it for movies and music.

That is absolutely the way to do it. Selector switches with modern high powered amps are just asking for trouble. It really requires a MOSFET switching circuit, as the currents are too high, likely to result in contact oxidation and quality downgrade or outright failure. I would never consider using a speaker selector switch with my high powered amps.

 

[roadstarman]

Thanks everyone for your input. I found these Speaker Selectors - Table Top, Dual Source Selector AB-2.2 Seems like a solution to my problems. They would do the trick but I would need 3 (front, center and rear).

 

[TLS Guy]

Thanks everyone for your input. I found these Speaker Selectors - Table Top, Dual Source Selector AB-2.2 Seems like a solution to my problems. They would do the trick but I would need 3 (front, center and rear).

No, your solution is to have one system for everything. Anything else is an unhandy dog's dinner.

 

[roadstarman]

No, your solution is to have one system for everything. Anything else is an unhandy dog's dinner.

Yes I can understand why you would say that, I visited your gallery! You are obviously (and enviously) very talented! I get a headache just thinking about the wiring nightmare behind the scenes

The Russound AB-2.2 mentioned above is manufactured 10 miles away from me so I'm going to take a drive over to see if they will sell to the general public.......maybe scratch & dent I am retired and don't have it in my budget to go out and buy a new receiver.

 

[lsiberian]

Yes I can understand why you would say that, I visited your gallery! You are obviously (and enviously) very talented! I get a headache just thinking about the wiring nightmare behind the scenes

The Russound AB-2.2 mentioned above is manufactured 10 miles away from me so I'm going to take a drive over to see if they will sell to the general public.......maybe scratch & dent I am retired and don't have it in my budget to go out and buy a new receiver.

That device will not work for your proposed problem. Electricity is a very dangerous thing when mishandled is your goal to burn down the house? I don't understand why you can drive the speakers with a the amp and use a selector switch between the sources instead of the amps.