Ssssh, is your tube preamp really that quiet?

Err Ralph, when I started the thread, i was actually talking about both phono and line stages; however, it quickly became evident that the phono stage is more of a factor. BUT, I think that Tube Line stages seem to suffer from the same problems, perhaps less obviously so, but nonetheless not totally quiet at all volume levels with no input signal. Is that not a fact with all Tube Line stages as well?

It is. Usually line stage noise is negligible unless you have speakers with high efficiency- 96 db or so and you may have to think about it. When loudspeakers get up to 104 or more, quite often the amplifier noise can be an issue too.

With most line sections the position of the volume control has little to no effect on noise. But I do know of some where the volume control is post-gain stage (the Dude, for example); such line sections are affected by the volume control position.

Why would a volume control (attenuator) after the gain stage affect the level of noise? Wouldn't that be true only of a volume control that is before the gain stage? Or have I somehow got this backwards in my head? I sense that I still have much to learn!

Hm.. To be true.. Realized after my last posting that I have not been quite fair to the Ref3.. The powerchord I use with my SS integrated is better and does make an obvious difference when it comes to create a darker background. The difference between the amps should be smaller to some grade than I experienced..

Why would a volume control (attenuator) after the gain stage affect the level of noise? Wouldn't that be true only of a volume control that is before the gain stage? Or have I somehow got this backwards in my head? I sense that I still have much to learn!

You do have this backwards. Think about the volume control as a valve of sorts that lets the sound through the circuit. The circuit is going to make a fixed amount of noise. So if the volume control precedes the line stage it will have little effect on the noise of the line section. If it occurs after the line section the noise will be reduced as you reduce the setting of the control.

The reason the latter is not done more often is that there is a price paid for having the volume control be the last thing the signal sees in the preamp- and that is that it can raise the output impedance substantially, and make the preamp highly susceptible to artifacts in the interconnect cable.

So to allow the preamp to drive longer cables without artifact, and to be able to make bass easier into transistor amplifiers, most designers put the volume control at the input of the line section (which has the additional advantage of preventing overload of the line section by a strong input signal).

Does this help your understanding?