Tube phono pre noise

[Karl5150]

Both my Bottlehead based home systems include vinyl playback, driven by an Eros and an integrated Reduction. I always read about systems describing "black background" with envy and some sense of failure. Both systems use short, decent cables and neither exhibit hum nor mains noise; but there is certainly not a black background. There is a difficult to describe low-level background hiss/buzz audible within about 6" of my speakers and in my headphones. It does not exist when using my solid-state phono preamp or a digital source.
As an experiment, a very expensive experiment, I built a respected board-based tube phono preamp. I built it "BH style" to drop into my systems, but with the PS in a separate, shielded enclosure.
Either I made the same mistake 3 times (actually 5 if you count the 2 rebuilds of my Reduction) or there is just some level of audible noise associated with all tube phono.
What is considered an acceptable level and how do I measure it?
The flip side is that it really doesn't detract from the fact that I think both systems sound d**n fine spinning vinyl!
Karl

[Doc B.]

Tubes generate something called 1/f or flicker noise. It's pink noise, a sort of "dull" static sound. It's an inherent characteristic of a lot of electronic devices. What you have to do (besides sitting more than 6" from your speakers...) is address the signal to noise ratio of the system. A higher output phono cartridge or LOMC with a larger ratio step up device is the way to accomplish this. More output from the cartridge means you turn the volume knob down, and hence you lower the noise floor.

This is why we specify a recommended minimum nominal output level for the phono cartridge used with our preamps. Minumum is 3mV with 5mV being optimal for the Reduction. One can get away with around 2mV with the Eros, but in any case a higher nominal output will always result in better S/N.

[Karl5150]

Doc-thanks for the quick reply...by the way how's the leg doing?
The pink noise description makes sense with what I hear. I'm using a 2M Blue and Red, so plenty of output. And I do sit 6-9 feet back so it is really a non-issue with the speakers.
I guess I just needed a hand on my shoulder and an "It's okay".  This all coming from the guy who doubled up the drywall in the lounge and built a false wall stuffed with Rockwool on the common wall of our bedroom in our condo. Noise sensitive maybe?

[Paul Birkeland]

You can definitely the "black background" by using a feedback equalized phono preamp.  This is the kind of design that you'd find in something like a Fisher tube receiver.  We aren't as big of a fan of the way these sound and they have some other performance issues that make me a bit less of a fan, so we avoid these designs.  The great misfortune about all of this is that once the needle touches a record, the black background isn't going to be there anymore!

[Doc B.]

You can spend some dollars buying a bunch of tubes and cherry picking the most quiet ones. That's how microphone tuners get the most quiet performance from tube mics.