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Phil Allison Phil Allison is offline
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Default Low Frequency Mains Noise

"Ian Bell = LIAR "


I presently have about 65uV of noise from the circuit under test.
Eliminating a 15uV component of it is worthwhile.

** Another ****ING RIDICULOUS unsupported assertion = typical
Bell puke.

FYI, you arrogant ****head:

Noise voltages DO NOT ADD !!!


No, their powers do. I made no statement either way about how they add.



** Yes you ****ing did !!!


No I did not. I said eliminating 15uV component was worthwhile.



Yes you ****ing did !!!

Do the math correctly as see what the REAL result is.

Then **** OFF


- you VILE LYING POMMY ****






........ Phil





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Ian Bell[_2_] Ian Bell[_2_] is offline
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Default Low Frequency Mains Noise

Paul G. wrote:
On Sun, 09 Nov 2008 08:07:26 +0000, Ian Bell
wrote:

Phil Allison wrote:
"Ian Bell"
Phil Allison wrote:
"Ian Bell"

One of the potential sources I have discovered is excess noise in the
anode resistors. This could account for 20uV or more of the total noise.
The solution seems to be to replace metal film resistors with wire wound
types.
** Where does this LUNATIC get these wacky ideas from ??

Metal film resistors are near as damn it free of voltage noise
Are they? Most metal film resistor suppliers that actually bother to spec
this usually put a figure of about 0.1uV/V for excess noise.

** What measurement bandwidth - eh ??

What resistance value - eh ??

Got no ****ig clue - have you.

You ****ING **** WIT

Sounds like you are back pedalling, Phil. You of all people will know
exactly how excess noise is specified (which includes the bandwidth). I
happen to have a 100K resistor in one anode which, from one
manufacturers graph, shows its excess noise is 0.1V/V.

As a said before, show me a manufacturer that quotes less.

CHeers

Ian


....... Phil








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, since I
can't find any details of what this standard uses (without paying for
it). That means the -40db would give you about .01uv/v (10 nv/v)
voltage noise. My guess is that this resistor is as good as you'll
get. I've been told that most wirewounds are typically -38db. Metal
film resistors often use this spec, and typical values for good
resistors (100kohms) are about -20 db using JIS C5202 5.9.


Thanks for the link. The data sheet itself says little more than the
current noise is -40dB, no graphs or further explanation.

From looking at other data sheets I get the impression that this type
of noise increases with resistance and decreases with increasing power
rating. The data sheet for Multicomp's MF series for example shows a
0.125W 1K resistor has a current noise of 0.01uV/V (-40dB) but the 100K
only achieves 0.1uV/V (-20dB). However the 0.5W version achieve -40dB
for values up to about 50K and the 100K is only a couple of dB worse.

From an article promoting Vishay resistors:
http://www.planetanalog.com/features...leID=177105460
"Current noise is the bunching and releasing of electrons associated
with current flow. The amount of current noise (or lack thereof)
depends largely on the resistor technology employed, and it is
measurable and is expressed as a function of the input voltage. The
magnitude is microvolts per volt applied. A noise index is expressed
in decibels, and the equation converting µV/V to dB is:
dB = 20 x log (noise voltage [in µV]/DC voltage [in V]).
For example, 0 dB equates to 1.0 µV/V, and 15 dB equates to 5.6 µV/V."
(end of quotation)
Read the article.... it answers a lot of questions, and poses some
possible audio nuttyness.


Yes, plenty of myth masquerading as science in that article.

Current noise has a 1/f frequency distribution. Bear that in mind when
you read the above article.... The frequency of the artifacts is very
low, and the oscilloscope pictures suggest a problem that is really
not as audibly bad as presented.

Carbon resistors have "contact noise", which is an additional very
significant noise. You should avoid carbon resistors, especially the
composition carbon ones (cheapo resistors).

The Johnson noise for the 100K resistor is about 41 nv (bw=1Hz),


That's 41nV per root Hz presumably?

or about 128 nv for the decade


Doesn't that depend on which decade?


(I don't know why manufacturers specify
a decade when 1 Hz is more specific).


Probably because it is 1/f noise.

It is wide band noise, not 1/f
noise. The different frequency distributions (1/f and wideband) make
judgements difficult, especially with the ear's sensitivity vs.
frequency. It's going to take a lot of 1/f noise to be noticed
compared to the wideband Johnson noise.


Good point.

Wirewound and bulk film resistors are considered best for noise,
even by Phil Allison http://sound.westhost.com/project66.htm "Metal
film resistors are about the best only bettered by wire wound which is
a bit impractical"

You must also be careful of wirewound resistors, since they can
inductively pick up AC magnetic fields, especially the precision
bobbin types of resistors.
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.
Considering typical gains of 10-100, that gives a noise (bw=1Hz) at
4.5uv to 45uv at the anode. The tube noise will completely swamp the
noise of the resistor! Make sure to use the correct bandwidth when
making the comparison.


That's a rather noisy tube. I currently see 65uV at the preamp output in
a 20KHz measurement bandwidth, which by my reckoning is about 460nV/rootHz.


At the very low level signal levels you seem to want, you will
probably get more satisfaction by using some of the more recent low
noise op-amps, and then amplify to get the voltage levels required by
your tube circuits. Vacuum tubes DO have considerable 1/f noise
(Johnson, John B, "The Schottky effect in low frequency circuits,"
Physical Review, July 1925, pg 71.). That's 1925! Not that I have much
against tube circuitry.... but they are not appropriate for low level
signal amplification (IMHO).


There we'll just have to disagree. ;-)

Cheers and thanks for the input

Ian
Paul G.



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Patrick Turner Patrick Turner is offline
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Default Low Frequency Mains Noise



Ian Bell wrote:

Patrick Turner wrote:

Ian Bell wrote:
Phil Allison wrote:
"Ian Bell"

Thanks for the input Patrick. I know about Johnson noise and in plate
resistors it is not much of an issue as it is swamped by other noise
sources. What I am concerned about is excess noise which is voltage
dependent. In the few places I have seen this specified it is typically
0.1uV/V so with a plate resistor with 150V across it there is possibly
15uV of noise due to this effect - enough to warrant a change of resistor
type.

** No it is not - you hee hawwwing ASS


Simple negation is no argument. I presently have about 65uV of noise
from the circuit under test. Eliminating a 15uV component of it is
worthwhile.

Cheers

Ian


OK, you have 65uV of noise. I think you said your amp has a gain of
about 15.

Suppose the input signal was 4.3 mV, then output signal would be 65mV,
and SNR = -60dB unweighted.

Removing 15uV of the noise won't make a significant SNR improvement.


Of course not. But it is just one of two such sources and I am simply
taking your recommendation of identifying each source in turn and
addressing them in turn.

Cheers

Ian

If the output signal is to be fed into a typical power amp needing 1Vrms
for clipping at 50W/6 ohms, then the power amp gain = 17.3x, 25dB,
and 65uV of applied noise will become 1.124mV not something that would
be improved by lowering to 0.87mV if 15uV was removed.

65mV of signal at the power amp becomes 1.124Vrms, enough to make 0.21
watts into a 6 ohm speaker, and if the 6 ohm speaker sensititivity is
90dB for 1 watt with 2.45Vrms, then the 0.21 watts gives about 83dB SPL
and is loud enough for most ppl, and allows a considerable headroom.

I suggest you work out the whole basic working of your system and amps
using a block diagram with signal levels or else quit mucking around
theorizing, and just build it and see if its quiet enough. After than
you can tweak things to make things more silent.


That is EXACTLY what I have done. The thing is on my bench now and the
output noise I quoted is as measured. You recommended I identify each
noise source and tackle them in turn which is just what I am trying to
do. I have fixed the low frequency noise as described in other posts and
now I am looking at other sources. Excess noise is just one of them.
From looking at metal film resistor specs it seemed they could be a
contributory factor and that wirewound types would be significantly
quieter. The only problem is finding them in the high values I need;
hence my original question on this topic, to which you and others
replied either that metal film resistors are not noisy or that the
noise they contribute is not significant.

Cheers

Ian


If you are worried by magnetically induced noise in WW R, then use a
pair of equal value and same brand with one reverse connected and close
to the other. Thus the magnetic noise of one cancels that in the other.

The excess noise isn't something so easily measured. I've never worried
about it because other sources of noise would always be greater. for
input stages of high gain amps I do like the cascode circuit using a
high gm j-fet like 2sk369 to drive a cathode of the triode with its grid
bypassed well to 0V. The triode load is usually a 22k R, and I will
typically use a pair of metal film 47k in parallel, and each 1W rated.
If excess noise exists, I ain't aware of it.

In the j-fet + triode cascode circuit made so famous by Allen Wright in
1988 in his FVP for MC, the gain at the anode of the triode is simply
fet gm x anode RL, and as the 2SK369 gm at 5mA = 40mA/V, if RL at the
anode = 20k, the gain = 800.
I have a source resistance fro local current FB to lower the gain to
about 250, and as this source R value is low, there is little added
noise from such an R.


So 0.4mV at the gate becomes 100mV at the anode. The first resistor to
shunt the amplified signal and able to add noise is the anode load
resistance, and afaik, the 20k does not significantly add any noise. In
the cascode case, the anode Ra is high because the effective Ra with a
an unbypassed cathode R = µ x Rk, and in the cascode with j-fet, Rk is
the very high Rd of the fet. So at the triode anode noise will be
determined by triode load value, and the j-fet gate input noise x the
cascode voltage gain. If gate ipnut noise was 0.2uV, then gain of 250
will increase it to 50uV. The reference signal will be 100mV, and SNR is
-66dB, unweighted, 20Hz to 20kHz.

If the gate noise was 0.1uV, SNR would be -72dB, and if the input signal
was 4mV instead of 0.4mV, then SNR would improve by 20dB.

In the case of my phono preamp, the RIAA filter improves the SNR.


Patrick Turner.
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Patrick Turner Patrick Turner is offline
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Default Low Frequency Mains Noise



Ian Bell wrote:

Patrick Turner wrote:

Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
snip

If you have 50uV of noise at the output and gain is 15x, and input is
grounded, then you could have a total of 2uV grid input noise if the
input tube is a real good one. 2uV gets amplified to make about 30uV at
the output, and some of that is LF noise. where does the rest of the
noise come from? By observation you should be able to see where the
noise is being generated and how, and find ways of stopping it without
much complexity and cost.
One of the potential sources I have discovered is excess noise in the
anode resistors. This could account for 20uV or more of the total noise.
The solution seems to be to replace metal film resistors with wire wound
types. However, I am having trouble finding sources for 100K and 39K
wire wound types at anything less than 5W rating which is something of
an overkill. Do you know any good sources of high value low wattage wire
wound resistors (preferable non-inductive of course)?

Cheers

Ian
Suppose you had 30uV of noise due to the input tube at the output of
your amp with gain = 15x.

And total noise = 50uV. Say you have Ra of the input tube = 20k, and the
load resistor for dc in parallel to the following stage bias R might be
50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by
Ra = 20k and thus attenuated. The excess noise would also be shunted,
but unlikely to be as high as the V1 tube noise, even if its a poor
quality R. Its the value of R in ohms which gives rise to noise, and
usually 90% of the noise at the output of a mic amp is due to the
broadand noise of V1, and all following R and tubes have little
contribution unless the output of V1 is a tiny voltage.

I think you should just build it and then try things to make it silent.
Wire wound would appear to be blameless, and getting a high value one
may mean you series a few. A 47k WW type will at least make the
predicted amount of noise because its the ohms than make the noise.
Any other type of R, metal film, carbon film also will make similar
noise you should find unless they are faulty.

Read up from RDH4 about noise and equivalent input resistance and noise
in R and summing of noise voltages.

Thanks for the input Patrick. I know about Johnson noise and in plate
resistors it is not much of an issue as it is swamped by other noise
sources. What I am concerned about is excess noise which is voltage
dependent. In the few places I have seen this specified it is typically
0.1uV/V so with a plate resistor with 150V across it there is possibly
15uV of noise due to this effect - enough to warrant a change of
resistor type.

Are you saying that regular metal film resistors do not suffer from
excess noise?
I've never noticed it in amps i have built. If I'd found that the noise
measurements didn't seem to add up, then I'd have been the one to reason
why.

I've usually used Welwyn or Beyshlag metal film R for most circuits.
Noise is negligible.
I'll check out Welwyn and Beyshlag specs, thanks

Cheers



Noise is mainly the product of the resistance value. It should not
matter what the R is made from. If properly made from any resistive
material the number of ohms is the main issue, then temperature. I don't
expect Welwyn or Beyshlag or Mills or Cadock or anything else from the
Vishay Resistor Mafia to be much different.


I hear what you say Patrick but Morgan Jones and the manufacturers data
sheets I have seen do not support that view.

For example the Johnson noise in a 20KHz bandwidth at room temperature
for a 39K resistor is ABOUT 3.6uV. If it is in an anode circuit with
150V across it then the excess noise of a typical metal film resistor
will be about 15uV per decade.

In low voltage circuits I agree Johnson noise predominates but I am not
sure it does in anode circuits.

Cheers


The Johnson noise values given sound about right.

In experiments when testing batches of triode tubes like 12AX7, 12AT7,
12AU7, and to view the noise voltage on a CRO, I amplify the anode noise
signal with the grid grounded with a short link. And with dc applied to
the heaters. In my case I am using cheap carbon film R,
and the noise measured appears to be the grid input noise x tube gain.
If the gain = 15 for 12AU7, 2uV of grid noise in agood sample becomes
30uV at the anode and when amplified 1,500 times by an opamp,
you have 45mV of noise which is easily displayed on the CRO. The test
load for the 'AU7 is variable, but say it was 100k.
according to you the excess noise might be about 5uV, but the 100k noise
is shunted by the Ra of the tiode at about 10k, so the excess noise
is much attenuated and would be 0.5uV, a tiny amount compared to 30uV
because of amplified grid input noise.

In j-fet such as a 2sk369 with fully bypassed source, and with the same
gain as the 'AU7, load = 15 / 0.04 at 5mAdc, so load = 375 ohms.
Excess noise and Johnson noise indeed be low, and drain noise = 15 x
0.14uV = 2.2uV approx. The fet looks like it has about 1/14 of the
triode noise.

Where is any need to consider any noise of RL?

Patrick Turner.



Ian

Metal film do have low noise, and noise below old fashioned carbon
composition types. I have a box full ot NOS from the mid 1930s which are
carbon rods with brass end shells clamped on and painted. They are in
good condition but I doubt they will be noiser than later carbon
compostion types which were notorious for change of value and moisture
ingress and chemical corrosion and decomposition over time. Quad used
these horrible R in the Quad-II and 22 control units. All may have been
fine when installed. I'm sure Peter Walker would have checked all this
out. But maybe they were not so quiet after 55 years...

The circuit resistances in most old ancient tube amps including Quad
junk and others was always on the high side. EG, Quad 22 volume control
is 500k.

Using say 100k instead of 1M to bias a tube reduces noise by 1/3.16, but
is true only if there isn't anything else shunting such R.

Noise in smaller R is proportional to 1 / sq.rt of the reduction of
resistance.

Or if you had 1uV noise in 1k for a given bandwidth, then noise with 10k
= 3.16uV, 100k gives 10uV, and 1M gives 31.6uV.
10M gives 100uV, and is a typical value used to bias a tube with grid
leak biasing as in a radio.
But there is usually some other R shunting the 10M, like a 1M volume
control, so noise is less at the output.


Patrick Turner.


Patrick Turner.
Cheers

Ian
Patrick Turner.

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Ian Bell[_2_] Ian Bell[_2_] is offline
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Default Low Frequency Mains Noise

Phil Allison wrote:
"Ian Bell = LIAR "
I presently have about 65uV of noise from the circuit under test.
Eliminating a 15uV component of it is worthwhile.
** Another ****ING RIDICULOUS unsupported assertion = typical
Bell puke.

FYI, you arrogant ****head:

Noise voltages DO NOT ADD !!!


No, their powers do. I made no statement either way about how they add.

** Yes you ****ing did !!!

No I did not. I said eliminating 15uV component was worthwhile.



Yes you ****ing did !!!

Do the math correctly as see what the REAL result is.

Then **** OFF


- you VILE LYING POMMY ****



No I did not. Nowhere in my original post did I use the word add.

Cheers

Ian




....... Phil







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Phil Allison Phil Allison is offline
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Default "Ian Bell = LIAR "

"Ian Bell = STINKING LIAR "


I presently have about 65uV of noise from the circuit under test.
Eliminating a 15uV component of it is worthwhile.
** Another ****ING RIDICULOUS unsupported assertion = typical
Bell puke.

FYI, you arrogant ****head:

Noise voltages DO NOT ADD !!!


No, their powers do. I made no statement either way about how they
add.

** Yes you ****ing did !!!

No I did not. I said eliminating 15uV component was worthwhile.



Yes you ****ing did !!!

Do the math correctly as see what the REAL result is.

Then **** OFF

- you VILE LYING POMMY ****


No I did not. Nowhere in my original post did I use the word add.



** Do the math correctly as see what the REAL result is !!!!!!!!

************************************************** **********


Then **** the HELL OFF

- you VILE LYING POMMY ****







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Ian Bell[_2_] Ian Bell[_2_] is offline
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Default Low Frequency Mains Noise

Patrick Turner wrote:

Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Phil Allison wrote:
"Ian Bell"

Thanks for the input Patrick. I know about Johnson noise and in plate
resistors it is not much of an issue as it is swamped by other noise
sources. What I am concerned about is excess noise which is voltage
dependent. In the few places I have seen this specified it is typically
0.1uV/V so with a plate resistor with 150V across it there is possibly
15uV of noise due to this effect - enough to warrant a change of resistor
type.
** No it is not - you hee hawwwing ASS


Simple negation is no argument. I presently have about 65uV of noise
from the circuit under test. Eliminating a 15uV component of it is
worthwhile.

Cheers

Ian
OK, you have 65uV of noise. I think you said your amp has a gain of
about 15.

Suppose the input signal was 4.3 mV, then output signal would be 65mV,
and SNR = -60dB unweighted.

Removing 15uV of the noise won't make a significant SNR improvement.

Of course not. But it is just one of two such sources and I am simply
taking your recommendation of identifying each source in turn and
addressing them in turn.

Cheers

Ian
If the output signal is to be fed into a typical power amp needing 1Vrms
for clipping at 50W/6 ohms, then the power amp gain = 17.3x, 25dB,
and 65uV of applied noise will become 1.124mV not something that would
be improved by lowering to 0.87mV if 15uV was removed.

65mV of signal at the power amp becomes 1.124Vrms, enough to make 0.21
watts into a 6 ohm speaker, and if the 6 ohm speaker sensititivity is
90dB for 1 watt with 2.45Vrms, then the 0.21 watts gives about 83dB SPL
and is loud enough for most ppl, and allows a considerable headroom.

I suggest you work out the whole basic working of your system and amps
using a block diagram with signal levels or else quit mucking around
theorizing, and just build it and see if its quiet enough. After than
you can tweak things to make things more silent.

That is EXACTLY what I have done. The thing is on my bench now and the
output noise I quoted is as measured. You recommended I identify each
noise source and tackle them in turn which is just what I am trying to
do. I have fixed the low frequency noise as described in other posts and
now I am looking at other sources. Excess noise is just one of them.
From looking at metal film resistor specs it seemed they could be a
contributory factor and that wirewound types would be significantly
quieter. The only problem is finding them in the high values I need;
hence my original question on this topic, to which you and others
replied either that metal film resistors are not noisy or that the
noise they contribute is not significant.

Cheers

Ian


If you are worried by magnetically induced noise in WW R, then use a
pair of equal value and same brand with one reverse connected and close
to the other. Thus the magnetic noise of one cancels that in the other.


Interesting idea. Unfortunately it means finding WW resistors of double
the value and it's hard enough finding ones of the original value.


The excess noise isn't something so easily measured. I've never worried
about it because other sources of noise would always be greater. for
input stages of high gain amps I do like the cascode circuit using a
high gm j-fet like 2sk369 to drive a cathode of the triode with its grid
bypassed well to 0V. The triode load is usually a 22k R, and I will
typically use a pair of metal film 47k in parallel, and each 1W rated.
If excess noise exists, I ain't aware of it.


I have come to the conclusion that higher wattage metal film resistors
have significantly less excess noise and I have found one by Multicomp
that has nearly 10 times less excess noise in its 0.5W version than the
0.1uV/V typical value for other makes.

In the j-fet + triode cascode circuit made so famous by Allen Wright in
1988 in his FVP for MC, the gain at the anode of the triode is simply
fet gm x anode RL, and as the 2SK369 gm at 5mA = 40mA/V, if RL at the
anode = 20k, the gain = 800.
I have a source resistance fro local current FB to lower the gain to
about 250, and as this source R value is low, there is little added
noise from such an R.


Indeed.


So 0.4mV at the gate becomes 100mV at the anode. The first resistor to
shunt the amplified signal and able to add noise is the anode load
resistance, and afaik, the 20k does not significantly add any noise. In
the cascode case, the anode Ra is high because the effective Ra with a
an unbypassed cathode R = µ x Rk, and in the cascode with j-fet, Rk is
the very high Rd of the fet. So at the triode anode noise will be
determined by triode load value, and the j-fet gate input noise x the
cascode voltage gain. If gate ipnut noise was 0.2uV, then gain of 250
will increase it to 50uV. The reference signal will be 100mV, and SNR is
-66dB, unweighted, 20Hz to 20kHz.

If the gate noise was 0.1uV, SNR would be -72dB, and if the input signal
was 4mV instead of 0.4mV, then SNR would improve by 20dB.

In the case of my phono preamp, the RIAA filter improves the SNR.



Cheers

Ian

Patrick Turner.

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Default Low Frequency Mains Noise

Patrick Turner wrote:

Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
snip

If you have 50uV of noise at the output and gain is 15x, and input is
grounded, then you could have a total of 2uV grid input noise if the
input tube is a real good one. 2uV gets amplified to make about 30uV at
the output, and some of that is LF noise. where does the rest of the
noise come from? By observation you should be able to see where the
noise is being generated and how, and find ways of stopping it without
much complexity and cost.
One of the potential sources I have discovered is excess noise in the
anode resistors. This could account for 20uV or more of the total noise.
The solution seems to be to replace metal film resistors with wire wound
types. However, I am having trouble finding sources for 100K and 39K
wire wound types at anything less than 5W rating which is something of
an overkill. Do you know any good sources of high value low wattage wire
wound resistors (preferable non-inductive of course)?

Cheers

Ian
Suppose you had 30uV of noise due to the input tube at the output of
your amp with gain = 15x.

And total noise = 50uV. Say you have Ra of the input tube = 20k, and the
load resistor for dc in parallel to the following stage bias R might be
50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by
Ra = 20k and thus attenuated. The excess noise would also be shunted,
but unlikely to be as high as the V1 tube noise, even if its a poor
quality R. Its the value of R in ohms which gives rise to noise, and
usually 90% of the noise at the output of a mic amp is due to the
broadand noise of V1, and all following R and tubes have little
contribution unless the output of V1 is a tiny voltage.

I think you should just build it and then try things to make it silent.
Wire wound would appear to be blameless, and getting a high value one
may mean you series a few. A 47k WW type will at least make the
predicted amount of noise because its the ohms than make the noise.
Any other type of R, metal film, carbon film also will make similar
noise you should find unless they are faulty.

Read up from RDH4 about noise and equivalent input resistance and noise
in R and summing of noise voltages.

Thanks for the input Patrick. I know about Johnson noise and in plate
resistors it is not much of an issue as it is swamped by other noise
sources. What I am concerned about is excess noise which is voltage
dependent. In the few places I have seen this specified it is typically
0.1uV/V so with a plate resistor with 150V across it there is possibly
15uV of noise due to this effect - enough to warrant a change of
resistor type.

Are you saying that regular metal film resistors do not suffer from
excess noise?
I've never noticed it in amps i have built. If I'd found that the noise
measurements didn't seem to add up, then I'd have been the one to reason
why.

I've usually used Welwyn or Beyshlag metal film R for most circuits.
Noise is negligible.
I'll check out Welwyn and Beyshlag specs, thanks

Cheers

Noise is mainly the product of the resistance value. It should not
matter what the R is made from. If properly made from any resistive
material the number of ohms is the main issue, then temperature. I don't
expect Welwyn or Beyshlag or Mills or Cadock or anything else from the
Vishay Resistor Mafia to be much different.

I hear what you say Patrick but Morgan Jones and the manufacturers data
sheets I have seen do not support that view.

For example the Johnson noise in a 20KHz bandwidth at room temperature
for a 39K resistor is ABOUT 3.6uV. If it is in an anode circuit with
150V across it then the excess noise of a typical metal film resistor
will be about 15uV per decade.

In low voltage circuits I agree Johnson noise predominates but I am not
sure it does in anode circuits.

Cheers


The Johnson noise values given sound about right.

In experiments when testing batches of triode tubes like 12AX7, 12AT7,
12AU7, and to view the noise voltage on a CRO, I amplify the anode noise
signal with the grid grounded with a short link. And with dc applied to
the heaters. In my case I am using cheap carbon film R,
and the noise measured appears to be the grid input noise x tube gain.
If the gain = 15 for 12AU7, 2uV of grid noise in agood sample becomes
30uV at the anode and when amplified 1,500 times by an opamp,
you have 45mV of noise which is easily displayed on the CRO. The test
load for the 'AU7 is variable, but say it was 100k.
according to you the excess noise might be about 5uV, but the 100k noise
is shunted by the Ra of the tiode at about 10k, so the excess noise
is much attenuated and would be 0.5uV, a tiny amount compared to 30uV
because of amplified grid input noise.


That is an interesting point. The current preamp circuit has an 8K2
unbypassed cathode resistor (as the feedback point) which means with a
tube mu of 35 the effective ra is nearly 300K so it does not attenuate
excess noise in the same way as you describe.


Cheers

Ian

In j-fet such as a 2sk369 with fully bypassed source, and with the same
gain as the 'AU7, load = 15 / 0.04 at 5mAdc, so load = 375 ohms.
Excess noise and Johnson noise indeed be low, and drain noise = 15 x
0.14uV = 2.2uV approx. The fet looks like it has about 1/14 of the
triode noise.

Where is any need to consider any noise of RL?

Patrick Turner.


Ian
Metal film do have low noise, and noise below old fashioned carbon
composition types. I have a box full ot NOS from the mid 1930s which are
carbon rods with brass end shells clamped on and painted. They are in
good condition but I doubt they will be noiser than later carbon
compostion types which were notorious for change of value and moisture
ingress and chemical corrosion and decomposition over time. Quad used
these horrible R in the Quad-II and 22 control units. All may have been
fine when installed. I'm sure Peter Walker would have checked all this
out. But maybe they were not so quiet after 55 years...

The circuit resistances in most old ancient tube amps including Quad
junk and others was always on the high side. EG, Quad 22 volume control
is 500k.

Using say 100k instead of 1M to bias a tube reduces noise by 1/3.16, but
is true only if there isn't anything else shunting such R.

Noise in smaller R is proportional to 1 / sq.rt of the reduction of
resistance.

Or if you had 1uV noise in 1k for a given bandwidth, then noise with 10k
= 3.16uV, 100k gives 10uV, and 1M gives 31.6uV.
10M gives 100uV, and is a typical value used to bias a tube with grid
leak biasing as in a radio.
But there is usually some other R shunting the 10M, like a 1M volume
control, so noise is less at the output.


Patrick Turner.


Patrick Turner.
Cheers

Ian
Patrick Turner.

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Phil Allison Phil Allison is offline
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Default Low Frequency Mains Noise


"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.


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.

This equates to only **14nV ** per rt Hz !!


Snip rest of this complete fool's tedious drivel.

Wot a Goose.



...... Phil




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Ian Bell[_2_] Ian Bell[_2_] is offline
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Default "Ian Bell = LIAR "

Phil Allison wrote:
"Ian Bell = STINKING LIAR "


I presently have about 65uV of noise from the circuit under test.
Eliminating a 15uV component of it is worthwhile.
** Another ****ING RIDICULOUS unsupported assertion = typical
Bell puke.

FYI, you arrogant ****head:

Noise voltages DO NOT ADD !!!


No, their powers do. I made no statement either way about how they
add.
** Yes you ****ing did !!!

No I did not. I said eliminating 15uV component was worthwhile.

Yes you ****ing did !!!

Do the math correctly as see what the REAL result is.

Then **** OFF

- you VILE LYING POMMY ****

No I did not. Nowhere in my original post did I use the word add.



** Do the math correctly as see what the REAL result is !!!!!!!!

************************************************** **********


Then **** the HELL OFF

- you VILE LYING POMMY ****



You are still back pedalling Phil.

Show me where my original posts uses the word add.

Cheers

IAn


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Patrick Turner Patrick Turner is offline
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Default Low Frequency Mains Noise



Ian Bell wrote:

snip,


If you are worried by magnetically induced noise in WW R, then use a
pair of equal value and same brand with one reverse connected and close
to the other. Thus the magnetic noise of one cancels that in the other.


Interesting idea. Unfortunately it means finding WW resistors of double
the value and it's hard enough finding ones of the original value.


The circuit working should not be that critical.

You may have 4 x 5W stacked together, with short leads, correctly phased
to minimise hum....

Using 5 x 220k parallelled metal films each of 1/2 a watt gives you 44k,
5W, and maybe excess noise is lower,
but Johnson is the same as a 44k single R.....

Patrick Turner.
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Patrick Turner Patrick Turner is offline
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Default Low Frequency Mains Noise



Ian Bell wrote:

Patrick Turner wrote:

Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
Ian Bell wrote:
Patrick Turner wrote:
snip

If you have 50uV of noise at the output and gain is 15x, and input is
grounded, then you could have a total of 2uV grid input noise if the
input tube is a real good one. 2uV gets amplified to make about 30uV at
the output, and some of that is LF noise. where does the rest of the
noise come from? By observation you should be able to see where the
noise is being generated and how, and find ways of stopping it without
much complexity and cost.
One of the potential sources I have discovered is excess noise in the
anode resistors. This could account for 20uV or more of the total noise.
The solution seems to be to replace metal film resistors with wire wound
types. However, I am having trouble finding sources for 100K and 39K
wire wound types at anything less than 5W rating which is something of
an overkill. Do you know any good sources of high value low wattage wire
wound resistors (preferable non-inductive of course)?

Cheers

Ian
Suppose you had 30uV of noise due to the input tube at the output of
your amp with gain = 15x.

And total noise = 50uV. Say you have Ra of the input tube = 20k, and the
load resistor for dc in parallel to the following stage bias R might be
50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by
Ra = 20k and thus attenuated. The excess noise would also be shunted,
but unlikely to be as high as the V1 tube noise, even if its a poor
quality R. Its the value of R in ohms which gives rise to noise, and
usually 90% of the noise at the output of a mic amp is due to the
broadand noise of V1, and all following R and tubes have little
contribution unless the output of V1 is a tiny voltage.

I think you should just build it and then try things to make it silent.
Wire wound would appear to be blameless, and getting a high value one
may mean you series a few. A 47k WW type will at least make the
predicted amount of noise because its the ohms than make the noise.
Any other type of R, metal film, carbon film also will make similar
noise you should find unless they are faulty.

Read up from RDH4 about noise and equivalent input resistance and noise
in R and summing of noise voltages.

Thanks for the input Patrick. I know about Johnson noise and in plate
resistors it is not much of an issue as it is swamped by other noise
sources. What I am concerned about is excess noise which is voltage
dependent. In the few places I have seen this specified it is typically
0.1uV/V so with a plate resistor with 150V across it there is possibly
15uV of noise due to this effect - enough to warrant a change of
resistor type.

Are you saying that regular metal film resistors do not suffer from
excess noise?
I've never noticed it in amps i have built. If I'd found that the noise
measurements didn't seem to add up, then I'd have been the one to reason
why.

I've usually used Welwyn or Beyshlag metal film R for most circuits.
Noise is negligible.
I'll check out Welwyn and Beyshlag specs, thanks

Cheers

Noise is mainly the product of the resistance value. It should not
matter what the R is made from. If properly made from any resistive
material the number of ohms is the main issue, then temperature. I don't
expect Welwyn or Beyshlag or Mills or Cadock or anything else from the
Vishay Resistor Mafia to be much different.
I hear what you say Patrick but Morgan Jones and the manufacturers data
sheets I have seen do not support that view.

For example the Johnson noise in a 20KHz bandwidth at room temperature
for a 39K resistor is ABOUT 3.6uV. If it is in an anode circuit with
150V across it then the excess noise of a typical metal film resistor
will be about 15uV per decade.

In low voltage circuits I agree Johnson noise predominates but I am not
sure it does in anode circuits.

Cheers


The Johnson noise values given sound about right.

In experiments when testing batches of triode tubes like 12AX7, 12AT7,
12AU7, and to view the noise voltage on a CRO, I amplify the anode noise
signal with the grid grounded with a short link. And with dc applied to
the heaters. In my case I am using cheap carbon film R,
and the noise measured appears to be the grid input noise x tube gain.
If the gain = 15 for 12AU7, 2uV of grid noise in agood sample becomes
30uV at the anode and when amplified 1,500 times by an opamp,
you have 45mV of noise which is easily displayed on the CRO. The test
load for the 'AU7 is variable, but say it was 100k.
according to you the excess noise might be about 5uV, but the 100k noise
is shunted by the Ra of the tiode at about 10k, so the excess noise
is much attenuated and would be 0.5uV, a tiny amount compared to 30uV
because of amplified grid input noise.


That is an interesting point. The current preamp circuit has an 8K2
unbypassed cathode resistor (as the feedback point) which means with a
tube mu of 35 the effective ra is nearly 300K so it does not attenuate
excess noise in the same way as you describe.


Just one of the problems one encounters when using unbypassed Rk.

Pentodes and cascodes have the same problem even with the Rk bypassed.

So for low noise the cascode or pentode must not have RL too high, but
then as R goes low, gain also reduces,
and THD increases. It does not matter too much in low level input tubes
if the Vo is below say 0.1V.

But if RL is high, and shunt NFB is used, then the noise is fed back and
reduced by external NFB...
So with a CCS load on a pentode, you'd expect noise to be considerably
high. OK, but if the gain with CCS of say 1,000 is reduced to say 50
with the NFB, the noise should become 1/19 of the noise without NFB.
A cascode with j-fet and triode with gain of 250 would be probably
quieter though.

Even in a low µ triode with low Ra, the electrostatic internal anode
feedback is what gives the low Ra, and lower noise as a result.

Patrick Turner.
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Arny Krueger Arny Krueger is offline
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Posts: 17,262
Default Low Frequency Mains Noise

"Patrick Turner" wrote in message

Ian Bell wrote:

snip,


If you are worried by magnetically induced noise in WW
R, then use a pair of equal value and same brand with
one reverse connected and close to the other. Thus the
magnetic noise of one cancels that in the other.


Interesting idea. Unfortunately it means finding WW
resistors of double the value and it's hard enough
finding ones of the original value.


The circuit working should not be that critical.

You may have 4 x 5W stacked together, with short leads,
correctly phased to minimise hum....

Using 5 x 220k parallelled metal films each of 1/2 a watt
gives you 44k, 5W, and maybe excess noise is lower,
but Johnson is the same as a 44k single R.....


Interesting how 5 x 1/2 = 5.

I keep getting 5 x 1/2 = 2.5

What is wrong with me?


  #174   Report Post  
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Patrick Turner Patrick Turner is offline
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Posts: 3,964
Default Low Frequency Mains Noise



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

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Paul G. Paul G. is offline
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Default Low Frequency Mains Noise

On Tue, 11 Nov 2008 00:30:45 +1100, "Phil Allison"
wrote:


"Paul Goose "


grrrrrrrr



......snip......

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.

This equates to only **14nV ** per rt Hz !!



You're correct, 2uv is about right for a 12AX7, my figures are 1.8
uv from 25Hz to 10KHz (RCA manual). The question is.... is it pink or
white noise? Assuming it to be pink, normalizing to 1 Hz, means 4
decades drop, or about 400 nv. Assuming it to be white, means it is
reduced by roughly sqrt(10000), or 100, giving a value about what you
say, approximately 14nv.
White or pink is relevant to this thread, because the original
posting was concerned with low frequency.


Paul G.


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Ian Bell[_2_] Ian Bell[_2_] is offline
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Default Low Frequency Mains Noise

Patrick Turner wrote:

Ian Bell wrote:
snip,

If you are worried by magnetically induced noise in WW R, then use a
pair of equal value and same brand with one reverse connected and close
to the other. Thus the magnetic noise of one cancels that in the other.

Interesting idea. Unfortunately it means finding WW resistors of double
the value and it's hard enough finding ones of the original value.


The circuit working should not be that critical.


I just realised series connection would work just as well #:-)


You may have 4 x 5W stacked together, with short leads, correctly phased
to minimise hum....

Using 5 x 220k parallelled metal films each of 1/2 a watt gives you 44k,
5W, and maybe excess noise is lower,


Unlikely as the noise seems to get worse for higher resistances - on the
other hand using a couple og .5W in series might be worthwhile.

but Johnson is the same as a 44k single R.....


Of course.

Cheers

Ian

Patrick Turner.

  #177   Report Post  
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Phil Allison Phil Allison is offline
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Posts: 1,444
Default Low Frequency Mains Noise

"Paul Goose "


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.

This equates to only **14nV ** per rt Hz !!


You're correct, 2uv is about right for a 12AX7, my figures are 1.8
uv from 25Hz to 10KHz (RCA manual). The question is.... is it pink or
white noise?



** Well, that reveals the DEPTH of this fool's ignorance of tubes.


Assuming it to be pink, normalizing to 1 Hz,



** What insane nonsense.

First - it ain't "pink noise".

Second, you cannot " normalise" pink noise to 1Hz of bandwidth.

Cos there is a ***small problem** with where in the spectrum that 1 Hz is.

**** off !!!!

You ridiculous idiot.



...... Phil


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Eeyore Eeyore is offline
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Default Op-amp PSRR figure = fake



Phil Allison wrote:

On balance, why one *needs* 120 dB power supply rejection when $0.25 and
0.50 cent regulator chips produce DC power with just a few millivolts of
noise on it, makes this discussion kinda moot.


IME a few hundred microvolts.

Layout is everything.

Graham

  #179   Report Post  
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Phil Allison Phil Allison is offline
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Default Op-amp PSRR figure = fake


"EeySore the ****ing NUTTER "

Phil Allison wrote:


** No he bloody did not !!


On balance, why one *needs* 120 dB power supply rejection when $0.25
and
0.50 cent regulator chips produce DC power with just a few millivolts
of
noise on it, makes this discussion kinda moot.


** The above are all Arny's words.


Layout is everything.



** Learning to read is a pre-requisite to everything.




...... Phil


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