Switching preamps in and out

I'm going to put an email in to Kevin Hayes at VAC, and see what he thinks.

Mention to him that you are using the unbalanced RCA output of a source component that is solid state, for which the output impedance is 11 ohms.

I would expect that in general solid state components will have greater susceptibility to damage or degradation of long term reliability in this kind of situation than tube components.

Regards,
-- Al

Al, I think we are still not communicating. When the power amp's volume control is reduced to zero, its input connection is shorted to ground. Yes, it's true that the input jack is no longer connected to the preamp's ground once the i/c is disconnected. However, you are overlooking that in any modern amplifier, the power amp is still connected to an electrical ground reference due to the ground wire for the AC power connection. The amp is sitll referenced to ground when the input cable is disconnected. I agree with you that if the gentleman was using a vintage amp from the 1950s that used a simple 2-prong AC power connection, the amp would lose its outside ground reference if the input cable was disconnected and there might possibly be a momentary spike even with the inputs shorted. But not with a VAC or any other modern amp.

I agree, Salectric, that the chances of there being a problem in this particular situation appear to be slim.

I would note, however, that my own VAC Renaissance 70/70 Mk III amplifier has a 3-position switch controlling its ground configuration. One of those positions isolates circuit ground from chassis ground (except at RF frequencies), and hence from the AC safety ground that as you indicate would otherwise prevent circuit ground from floating to voltage levels that are significantly different than those of the upstream components, when the IC's are disconnected. I don't know if any sort of ground lift provision is included in any of Mike's components.

I would also note that two-prong power plugs were not just creatures of the 1950’s and earlier. The STAX and Tandberg components in my system, from the mid and early 1980’s, respectively, all have two-prong power plugs. And some people have cheater plugs on some of their components.

I would also re-emphasize that the front end situation has to be carefully considered, as well as the preamp-to-amp interface. Especially given that the source component is solid state, per my comment to Mike just above.

One of my basic motivations in this thread has been to dispel the impression, which threatened to be created early on, that in a situation where no signal can be propagated through the power amp one should necessarily feel free to do anything and everything with interconnects while power is on. As you appear to realize, but others may not, there are a whole lot of variables that can make that assumption risky. Including those I mentioned in my initial response to Wolf:

… what components are being used, what the designs of their input stages are, what effect a brief overvoltage might have on their long-term reliability, what their grounding configuration is, whether or not they provide a ground lift switch, whether or not he's using cheater plugs on any of his components, whether or not any of his components have two-prong power plugs, and whether the connections are RCA or XLR….

Regards,
-- Al

Salectric and I live as brave rebels unafraid to dare the electrons around us...go ahead obscure grounding issue...make my day.

Good summary Al. I overlooked your mention of cheater plugs and two-prong power plugs, so you had already covered that aspect. At the risk of beating an already dead horse, I would add that the concerns are probably still more theoretical than real even with an amp that is not referenced to the AC mains ground. In the old, old days, all of my amps were configured that way (Dyna ST-70, Mk. IV, and homemade tube and solid state amps) and on each one I wired an input shorting switch so I could mute the input in order to swap interconnects. I never had any problems with any of my amps in doing this. Of course, your point is there may have been a momentary spike when I removed the i/c cable and lost the ground reference, and I can't say that this didn't occur, only that I never had any problems.