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RE: Tubes in Pre-amps: your expertise and honest opinion.
>>A tube/load circuit creates a kind of filter. That warmth people often
>speak of is just high frequency attenuation.<<
agreed, but only if the designer has intended this effect..... which is
probably where the market-speak "warmth" really comes from- a slightly
wooly sounding top-end, especially when compared with a modern recording.
but I have a couple of valve tape-decks that meet or exceed the frequency
response of their nearest "solid-state" peers.
see, for the last twenty-odd years, producers & engineers have been
putting more & more top-end onto recordings, safe in the knowledge that it
will actually reach the ears of the end-user via digital media. this sort
of delivery couldn't be guaranteed with analogue tape or vinyl. (& before
all the howls of protest start, I said it couldn't be guaranteed, not that
it was impossible! I have witnessed the work of studer & shibata.)
so we've all got used to much higher energy levels in that part of the
spectrum.
now the marketing guys have created an artificial association between the
use of vacuum tubes & some mythical era in which there was a bit less
top-end listener-fatigue, & songwriting was generally of a higher quality,
life was simpler, gas was cheaper, tv shows were better, beer didn't have
chemicals in it......
warm = good, cold = bad. (beer excepted)
analogue = warm. digital = cold.
& so ironically we have arrived at a situation where on the one hand we
complain that 44.1kHz is nowhere near fast enough of a sampling rate to
preserve all the detail of real-life sounds, while on the other we're
using valve circuits that have been deliberately badly designed so as to
soften the transients & high-frequencies we were so anxious to save.
so if you want your songs to last forever, like one presumes
lennon/mccartney or brian wilson's will do, you have to use OLD EQUIPMENT.
or at least, equipment made the old way, with glass in it. this is why we
had to endure "the white stripes", this kind of marketing.... 2nd hand
cred....
& you can buy a plug-in to simulate tape-saturation! what's that all
about? no! buy a real revox!
I'm ranting, aren't I? :-)
ok.
back to the science.
running a valve at a low voltage won't make it glow less; the glow comes
from the heater & the cathode, to a lesser degree.
running a valve at a very high voltage will occasionally produce an
additional blue glow, especially if the cathode's almost stripped. the LED
installed by EH, behringer & korg (amongst others) is there because the
real glow wasn't bright enough to satisfy their designers, probably
because modern tubes have a little more suspension material in them, & it
hides the "interesting" bits.
d.