Switching preamps in and out

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.

Al and Salmetric,

Here are Kevin's responces to some of your assertions. See below and following posts.

Yes, you can get transient snaps, hum, or (in some cases) oscillations when 'hot swapping' single ended interconnects. We do it all the time at the factory, but generally speaking it's a bad practice. Some solid state amplifiers have been known to self destruct.

On 2/5/2013 9:43 PM, Mike Bauer wrote:
Kevin,

Just in case it matters: the source will be Playback Designs MPS5 SACD player with 11 ohm output impedance. The IC's are single ended. Someone said something about a grounding issue with the single ended connector.
see below. Is this a concern?

The problem with RCA connections is that during insertion the signal on the center pin is applied before the ground connection on the shell is made, and during removal the ground connection is removed before the center pin connection is broken. So there will be moments during insertion and removal when the zero volts that should be present on the center pin when no music is being played will not have a defined ground reference, and therefore may be seen as a very large and conceivably damaging voltage.

Thanks for your thoughts

More from Kevin,

The first sentence is true, and the core of the procedure I've suggested to you. The rest of this poster's theory has some flaws, and I would not rely upon his assumptions or assertions.

On 2/5/2013 11:10 PM, Mike Bauer wrote:
Kevin,

So here is the other counter argument about RCA connectors. I didn't want to bother you so I put the question on Audiogon and seemed to have started an argument. See below.

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.