doug wrote:

some people havent got ears that are trained very well
and while mine are from years of live sound reinforcement and PA system
finalizing, as well as recording and mixing engineer in some interesting
projects I still like to be able to look at a plot to see whether I am
hearing 2nd harmonic distortion or 3rd harmonic or IMD or what.

The RDH4 from 1955 spells out what distortion is audible or not,
rather better than I could, in the time and space available.
Its an interesting read.
Human ears haven't changed in 48 years.

Meanwhile, once you get the distortion low *enough*,
there is little benefit in lowering it by
adding yet another 20 dB of NFB.
But if you have 20 cascaded amplifiers each with 0.1% of noise and distortion,
then there may well be some degradation of the sound we hear.
If the sound arrives from our CD player with less than 0.1% of N&D,
then the amount added by our tube amp systems and speakers
won't change the sound much.

But what is inexplicable is the subjective sound change heard
between various amps, although we have the same source,
and low N&D, and all wev'e done is swap one tube for another
brand.
Perhaps the really subtle harmonic differences do matter a litle bit,
but as long as the sound is drinkable good wine, what's the concern?

Patrick Turner.



Doug

"Patrick Turner" wrote in message
...


Ruud Broens wrote:

"doug" wrote in message
news:UFLxb.513594$6C4.282925@pd7tw1no...
: very cool stuff
: nice to have the tools to measure it with too huh?
:
: Doug

Yep, Doug, all true
it's da tools puttin' da smile
on the scientists' face
even on
a rany day
Rudy

And some would wonder what change would the
positive feedback make on the sound.

Patrick Turner.


~~~~
: "Brian" wrote in message
: om...
: I hooked up my HP 141T/8552B/8556A spectrum analyzer to the
push-pull
: 6V6 amp today and measured the following harmonic levels at 10 volts
: P-P output (1.5 watts) into 8 ohms:
:
: 2nd 3rd
: feedback -64 -52 dB
: no feedback -55 -48
:
: So not only does the unusual feedback path increase the overall gain
3
: dB, it lowers the distortion.
:
: Brian
:
: