Phil Allison wrote:
"Paul Goose "
Vishay sells bulk foil resistors
http://www.vishay.com/company/press/...08/080507foil/ , and
according to "JIS C5202 5.9" method of measurement, they are at -40db,
where 0db is 1 uv/v, and I assume it is for 1Hz bandwidth,
** No way it is for 1Hz bandwidth.
It is almost certainly for a decade of frequency range and this relies on
the noise being exactly " pink " in nature to make mathematical sense.
The Johnson noise for the 100K resistor is about 41 nv (bw=1Hz),
or about 128 nv for the decade
** Huh ?? That is just plain nuts.
Johnson Noise is WHITE noise - so magnitude ( in rms voltage or current)
goes with the sq. rt. of bandwidth in Hz.
Pink Noise however, has the same magnitude in any octave, fractional part of
a octave or any decade range of frequency.
(I don't know why manufacturers specify a decade when 1 Hz is more
specific).
** Cos they are NOT the same - pal.
It is wide band noise, not 1/f noise.
** That is what makes them different.
It's going to take a lot of 1/f noise to be noticed
compared to the wideband Johnson noise.
** Not true - when you allow that there may be hundreds of volts in that
uV/V calculation and that is a linear simple relationship.
Double the DC voltage and you double the rms ( excess) noise generated.
You must also be careful of wirewound resistors, since they can
inductively pick up AC magnetic fields, especially the precision
bobbin types of resistors.
** Gross exaggeration.
Film resistors are made with spiralled conductors too.
I've never seen much induced hum in any anode supply resistances.
The resistor noise voltage generated, is on the anode circuit for
your tube, if you use the input noise voltage for a typical low noise
tube (12AX7), you have about 450nv (bw=1Hz) effectively at the grid.
** uh ????????
The EIN of a 12AX7 is in the order of 2uV in the audio band.
I'd agree with this alright. But not all samples are that quiet.
The noise at the anode will be 180uV if the AX7 is in µ-follower mode.
If the input signal is 2mV, SNR = -60dB at the input.
But the source resistance might add more noise.
But a 2sk369 j-fet has far lower EIN, maybe 0.1uV.
The SNR with a j-fet can be 26dB better than a 12AX7, but source R must
be very low to take advantage of the low noise of the j-fet.
Patrick Turner.
This equates to only **14nV ** per rt Hz !!
Snip rest of this complete fool's tedious drivel.
Wot a Goose.
..... Phil