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Is It Safe To Connect Speakers To Two Amps??

i've got a combined HT and 2-Channel rig whereby my mains and subs function in both. i'm currently using the traditional connection scheme whereby the HT processor sends signals to the mains via the pre outs to my preamp (in bypass mode) then on to my main power amps, then on to the speakers.

if i wanted to bypass my preamp and main power amps althogther (it's a shame to burn tube hours on movies), is it safe to simply connect my main speakers to the HT processor via speaker level connections if they are also connected to my main power amps concurrently? only one amp - HT processor OR main amps - would be running at a time.

any inputs would be greatly appreciated.
128x128srosenberg
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almarg
9,670 posts
 
No. The amp being used would see a load impedance equal to the speaker impedance in parallel with whatever output impedance the other amp has when it is turned off. That output impedance, in turn, is indeterminate, at least without detailed knowledge of the design. It may also vary unpredictably as a function of the signal level being applied to its output terminals at any instant of time by the amp that is being used.

Given that, both amps could conceivably be damaged -- the one being used due to excessive loading, and the one not being used due to application to its output terminals of voltages that are widely in excess of its internal dc voltage "rails," which would be zero in this situation.

And if both amps were ever inadvertently on at the same time, while one was playing music, the amp being used would be working into a near-zero ohm load impedance, corresponding to the output impedance of the other amp when it is powered up. That would result in very large amounts of current flowing, which could also damage both amps.

Regards,
-- Al
rayooo
70 posts
 
if both amps had automatic speaker disconnect relays in them, and you were extremely careful, presumably a setup like this could work. but it's an accident waiting to happen. As mentioned.. when accidentally both amps are powered on at once.

If you wanted to install a manual high quality A/B speaker selector switch... while a bit of a kludge, I guess it'd work.
rwwear
2,867 posts
 
Niles Audio makes a signal sensing automatic switch just for this purpose.
willland's avatar
willland
846 posts
 
06-19-11: Rwwear
"Niles Audio makes a signal sensing automatic switch just for this purpose."

Here is the Niles switcher that was referred to:

http://www.nilesaudio.com/images/PDF/SPK-1_Cutsheet.pdf

http://www.onecall.com/product/Niles/SPK-1-Black/Speaker-Switching-Device/_/R-867

Bill
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