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2 amplifiers connected to 1 set of speakers

I’ve been in the hobby for a few years and my wife asked me a question that stumped me.

Can you have 2 amplifiers, connected via their own individual sets of speaker cables, connected to the same pair of speakers at the same time? I told her I didn’t think that would be advisable.

The question came about when she saw me disconnecting cables from my solid state amp and connecting the cables from my tube amp. (both were off of course). She asked me why it wouldn’t be ok and I started babbling that the signal from one amp would then travel through the other set of connected cables into the amp that was not in use. Even if the other amp was off that could be problematic. If the other amp happened to be on then it could prove catastrophic for both amps and potentially cause an electrical fire.

What is the correct answer fellow audiogon members? Ralph?
ghasley

Showing 3 responses by imhififan

imhififan's avatar
imhififan
2,125 posts
 
Instead of swapping cables, I think using a high quality amplifier selector is a safer way to switching amplifiers.

http://www.beresford.me/S/home_htm_files/TC-7220MKII.pdf
imhififan's avatar
imhififan
2,125 posts
 
@b_limo

That is one of the few units I custom built for my friend to demo amplifiers in his shop for his customers and his audio club.
His customers usually don't had time to wait an hours or two for setting up and compare tube amps, so these selectors can switch between amps, while one amp is playing the other amp still on with dummy load connected, it is the best compromise we can think of.

imhififan's avatar
imhififan
2,125 posts
 

Most (not all) SS amplifier has relay at the output for delay turn-on and protection. If both tube amp and SS amp are connected to the speaker and only the tube amp is on, it will do no harm to both amp because the SS amp output stage is disconnected by its built-in relay.
When the SS amp is on and the tube amp is off, then the SS amp will see the speaker as a load and also the tube amp output transformer secondary winding parallel to it. That will be bad for both amplifiers, there’s possibility fries the tube amp OPT and damage the SS amp or put it into protection mode.
Even though if the tube amp OPT secondary winding strong enough to stand the current from the SS amp, the speaker will definitely sounded weak with no bass because the inductance of the OPT secondary winding drained all bass energy through it.
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