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Preamps with two main-outs

Question for folks with two separate stereo amps driven by a single preamp. My preamp has two main outputs feeding two separate amps - one stereo and one pair of monoblocks, driving two pairs of speakers in two different rooms. Is it normal to need to turn on all the amplifiers to play any music? In other words, I can't just turn on my stereo amp to listen to music in one room. Its all or nothing. Fortunately the mono amps (MC2200) have volume control and I can turn them all the way down but can't do that for the stereo amp for the speakers in the other room. I was wondering if this is normal for all preamps with multiple pre-outs or its dependent on a particular preamp model. If it matters, the preamp is a NAD C165BEE. Thanks.

P.S. The second main-out has a little knob for gain control but its on the back of the preamp next to the ports and not practical to use for this purpose.

kalali

Showing 2 responses by shadorne

shadorne's avatar
shadorne
7,477 posts
 
+1 Al

looks like you found it! Nevertheless an active amplifier works as specified with input impedance as stated when powered up - I am not sure what happens to the input buffering on all amps when switched off - probably most remain high impedance but that is not a given hence my warning that amps are designed to be used when switched on.

Similary for line level inputs for different members of a band you can’t just branch all the inputs directly to one amplifier input - their gear is all connected to a MIXER that not only allows volume adjustments/effects but as a minimum the mixer buffers the outputs of individual instruments from affecting each other....
shadorne's avatar
shadorne
7,477 posts
 
This is quite normal.

The input of the amplifiers are active components and need to be switched on to do their job. Obviously when one amp is switched off it is providing low resistance to ground (or frequency dependent resistance) and affecting the line level signal adversely.

The fact is that this is rather a dogs breakfast approach to hooking up audio gear. It may kind of work with some gear depending on the different ways the input circuitry behaves when switched off (due to different designs)

Honestly you need a Zone Mixer between the output and the two separate zone amplifiers as it appears currently you are just connecting the same output to two amps (dogs breakfast approach)

The dogs breakfast approach could also lead to ground loop issues and other interference/noise but on the positive side perhaps different interconnects may sound different in such a setup - providing endless entertainment going down that rabbit hole. (as I have stated many times - well designed gear that is correctly setup won’t need special cabling)
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