2. amps-preamps
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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.

128x128kalali
kalali's avatar
kalali OP
1,977 posts
 

I guess ignorance is a bliss as I was disappointed that this behavior was normal, albeit my intuition seemed unconvinced. I'll double check my connections to make sure I didn't miss something obvious.

Thanks gentleman for providing the counter argument. 

bdp24's avatar
bdp24
9,821 posts
 
What I would do is disconnect the ic going to the amp/speakers not wishing to be heard, at the pre-amp end.
asvjerry's avatar
asvjerry
4,680 posts
 
Interesting the stated effect...having to run both or nothing...

I run outputs from my sources (TT thru a phono eq, the 'puter, CD, tapes) into a matrix which goes directly either into the main input of an amp and/or to a receivers' tape in.  Sometimes an outboard eq gets 'looped in' via the matrix for input level control and/or eq, depending on the source.

This routine cares less whether both or either are running.. there's a slight drop in input level if both are running, but it's nominal....

Maybe I'm just lucky, or I'm not experiencing the 'feedback' that onhwy61 notes...any thoughts on how this works vs. the OP's state?
kalali's avatar
kalali OP
1,977 posts
 

I just did an experiment. Powered everything down and disconnected the ICs going to my Vincent SP331. Turned on the preamp and the MC2200s and they sounded fine. Powered everything down and plugged the ICs back in SP331 without turning it on, and turned the MC2200s and the preamp and no sound. Did the complete opposite and I can play the Vincent without having to turn on the MC2200s. The only conclusion I can draw is something in the Vincent input stage - I'm guessing its tube input stage, is somehow "shorting" the preamp output signal on both paths. I can do what bdp24 suggested if I need to play music in one room. Now I know which one I need to unplug. I'm now curious if this is normal behavior for tube amps or amps with (at least) a tube input stage.


shadorne's avatar
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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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