Re: Current Noise


west wrote:
There are several different types of noise to avoid and reduce, if we can,
in designing tube circuits, from what I been studying. We can discuss these
different types of noises in general but for now I would like to concentrate
on 1 type of noise, current noise, the kind that is generated in a plate
load resistor. I believe that this is especially important in preamp
circuits.
Some tubies advocate that boutique components are all fluff and a waste of
money and I think they have a point, to a degree. However, will a low noise
resistor make a difference in reducing plate current noise? If yes, then
they can make a difference.
The question is ...can we quantify this difference and how? I think it would
be cool to measure this noise and simultaneously hear what difference a low
noise boutique resistor can make. I may be off base with this idea, if so
chalk it up to an inexperienced but eager to learn Rodent. Thoughts? Thanks.

Cordially,
west

West:

This thread has already spiralled off into contending experts ego-
tripping. The two items of useful information in it is where Patrick
states the practical problem and where I tell you how to solve it.

Here Patrick states the problem: "the number of ohms was what
determined noise, and it mattered not one bit what kind of resistor it
was as long as the contacts to each end were mechanically tight"

And here I show how to solve the problem: "The solution is not fancy
resistors (you usually can't get them in the right ratings) but to use
standard oversized metal films in smaller values in series, say 6x10K
rather than one 62K." Thus you get both the silence of the smaller
ohmic value of each resistor (6x10k makes less noise than one by 62K)
and the silence of the oversized resistors running cooler. *That* is
why on all my amps the power resistors are, in strictly cost-
accounting engineering terms, overspecified; ditto for all the best
audiophile-designed tube amps. (The idiot Worthless Wieckless made an
offensive song and dance about overspecced resistors in my T39 Ultra-
Fi once because he is bog-ignorant -- I very carefully didn't explain
the real reason to him; he's such a wretched little man that nobody
else helped him out either. But those big ballast resistors account
for a good part of the silence of the amp.)

All the rest is, as I say, audiophoolery or "experts" tripping over
each other in their eagerness to show off.

Nobody stops you experimenting for yourself though; discovering
whether you like one sort of component better than another is half the
fun of building your own tube amps. There was a time when I swore by
Dale "non-inductive" cathode resistors on 300B and 845; today I just
use the 50W ali-cased jobs out of the RS catalogue. And I still like
Solen polyprops better than any other kind; you can get Solens in the
widest possible range of values in high voltage ratings and they sound
right in my amps and don't take up as much space as the (more
expensive) motor run polys I can buy locally.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

.

Relevant Pages

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