Switching preamps in and out

Thanks everyone for input. Here are components. Everything purchased here on Audiogon. I agree with long term listening but I want to enlist some other ears too, so we will be doing switching in and out on that night.

Amp is -VAC Phi 300.1a

Source is- Playback Designs MPS5

Preamps are:
-VAC Sig MKIIa
-Messenger
-Allnic L-3000

Cables are all single ended

So the power amp has dual level controls. What about just turning down to "0"?
Can I leave the preamps on when switching IC's? I can press the mute button-would that work? They are all tube preamps so constsantly turning off and on is not ideal.

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.

Peter,
Check this thread in three or four weeks. I will post which preamp I like the most and why. I have some initial thoughts, but I want to do more listening with a wider variety of music before I post any thoughts.

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

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

Final Word from Kevin,

If you switch it to the variable volume mode and turn the volume controls all the way down, yes.

With the volume controls at minimum, the "direct/level adjust" switch will act like a mute switch.

On 2/6/2013 10:01 AM, Mike Bauer wrote:
OK. Thanks Kevin. So just to be redundant: I can "hot swap" the IC's between the preamps with the Phi 300.1a if I turn the volume all the way down.

--- On Wed, 2/6/13, VAC wrote:

From: VAC
Subject: Re: Phi 300.1
To: "Mike Bauer"
Date: Wednesday, February 6, 2013, 5:28 AM

The version of the Phi 300.1 with a front panel meter have a mute switch at the right of the front panel; this may be used to mute the amplifier.

The Phi 300.1a (no meter) does not have a mute switch, but you can effectively mute the unit by switching the attenuators in with the back panel switch and turning the front panel volume controls all the way down; return to the 'direct' mode when you're ready to listen.


On 2/5/2013 7:51 PM, Mike Bauer wrote:
Kevin,

Hello. I'm very much enjoying my VAC Phi 300.1a and Sig. MKIIa preamp combo. I have some audiophile buddies that want to try out their preamp in my system to compare with the Sig. Can I just power up amp,SACD player and three different preamps and switch IC's between preamps without powering off anything if I turn the level controls on the Phi 300.1a down to "0" and have the mute button on the preamps engaged?

I'm hoping "yes" because powering everything off and on and going back and forth for a couple of hours between the three preamps seems like a lot of wear and tear on tubes and such.

Connections are all single ended.

Thanks,

Mike

Agreed. I thanked him for all of us.

I agree with longer term listening, but swapping in and out is helpful too, and the only way when you have friends over listening with you!

My wife gave me the house this Saturday. She taking the kids to a birthday party so that's when the testing begins!