"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 13:05:30 +0300, "Iain Churches"
wrote:

In tube power amps, the difference between wide
band and "A" weighted was often found to be 12dB,
and this was, IIRC something of a rule of thumb.

Iain

Such a difference would suggest a great deal of 1/f noise.

Indeed, and of course noise beyond the top end of
the audio band.

The amp that I mentioned had 100Hz audible
from the listening position The owner said
"All tube amps hum like that!"

"Ahaa!", sez I.

Iain