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.
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.
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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.Take a look at the INPUT of the SP331 in the schematic!!! https://elektrotanya.com/PREVIEWS/63463243/23432455/egyeb/vincent_sp331-pwr_sch.pdf_1.png |
kalali, Can you use a ohm meter to check the input of the SP331 when it is power down to confirm that the input is shorted? |
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.... |
Yes, thanks for posting the schematic, imhififan. And yes, it is of course hard to read. But it appears that what is most likely a relay is connected directly between the signal pin and the ground sleeve of the RCA input connector on each channel. Presumably when the warmup period concludes a control voltage is applied to the relay which causes its contacts to open up, allowing the input signal to proceed to the input stage. And presumably when the amp is turned off that control voltage goes away and the contacts close, resulting in a short across the input. Unless perhaps there is some means by which the design causes the contacts that are opened during normal operation by the application of that control voltage are somehow also kept open when the amp is off. And then immediately closed at turn-on, for the duration of the warmup period. In which case a defect in the relay might be responsible for the issue. But I can’t envision how that scenario could occur, with the amp still able to operate reliably. So most likely the issue is caused not by a flaw in the relay but by a flaw in the thinking of the designer. Best regards, -- Al |
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