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

Showing 8 responses by kalali

kalali's avatar
kalali OP
1,977 posts
 

Thank you. It would have been nice to be able to select which (or both) main-out you'd like to be active at any given time especially for scenarios like mine where the amps drive speakers in different (but adjacent) rooms. I have a Schiit Sys passive pre that I can insert in the middle to control (or turn off) the volume for my stereo amp but mainly wanted to first make sure if this is normal before resorting to a workaround.

Like onhwy61's theatrical analogy.... makes good sense, I guess.

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. 

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.


kalali's avatar
kalali OP
1,977 posts
 
Thanks again for all the input. I think Al has put his finger on the cause for this seemingly unusual behavior. It appears that the Vincent mute feature is is not only on during warm up - roughly 30 seconds, but also active while the amp is powered down. Regarding the scenario for burning in a source with only the preamp on, I suppose one could disconnect the amp through the process. I do however suspect if this is considered a normal behavior or design for majority of the amps. Those of you who consider this normal, have you actually experienced this situation with your gear? I'm sure this is a fairly popular arrangement for the folks who bi-amp their speakers using a single preamp.
kalali's avatar
kalali OP
1,977 posts
 
I’ll take the measurement when I get home this evening. Sorry but I can’t make out much by looking at the schematic but it’s nice to have it so I appreciate you posting it.

P.S. Had to look up what "dog’s breakfast"..no clue what it meant. Cool slang and a fairly accurate description of how my cabling looks....
kalali's avatar
kalali OP
1,977 posts
 
shadorn's comment about input impedance triggered a question I've been meaning to ask: Can the generally published spec for amplifiers' input impedance, e.g., 47K ohms for the Vincent, be simply measured at the input ports, presumably with the amplifier turned on, or there's a lot more involved in taking this measurement? Thanks again for all the education.
kalali's avatar
kalali OP
1,977 posts
 

With the amplifiers off, I measure "continuity" at the input ports on the Vincent but not on the MC2200, using my very basic millimeter. Didn't feel comfortable sticking my meter probes inside the ports with the amplifiers turned on. I think we can surmise this is NOT normal behavior and is dependent on the amplifiers' input stage design. Thanks everyone for your help in explaining this behavior.


kalali's avatar
kalali OP
1,977 posts
 
Previous post should read "multimeter" not millimeter. Autocorrect in action...
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