Noise Weighting Curves
 

In article i,
Iain Churches wrote:
Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

That's not typical.

--
*If you think nobody cares about you, try missing a couple of payments *

Dave Plowman London SW
To e-mail, change noise into sound.

Noise Weighting Curves
 

On Thu, 4 Oct 2007 20:16:02 +0300, "Iain Churches"
wrote:


"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 18:51:36 +0300, "Iain Churches"
wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
Don Pearce wrote:
In tube power amps, the difference between wide
band and "A" weighted was often found to be 12dB,
and this was, IIRC something of a rule of thumb.

Iain

Such a difference would suggest a great deal of 1/f noise.

Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

http://www.kolumbus.fi/iain.churches...em/C50_002.jpg


Not a misconception, Dave is right - yours is hardly a typical valve
amp. My impression of the huge majority of the valve amps I have come
across is that you just know when they are switched on; there is
always that "liveness" about the speakers, usually a mixture of hum
and noise.

Of the thirty or so members of the "gramophone society" to which
I belong, more than half have valve amps. I cannot think of a
single member who has a system where one can even hear a
hint of hum/hiss at the listening position. Most systems are
silent with ear against speaker.

With the exception of the Cheepies, the quality of valve amps
offered by the many bespoke builders is very high indeed.
I would say the performance of my own is typical.

Iain

Typical of bespoke. To assess typical you need to include all valve
amps in the sum. The average valve amp hums.

Members of a gramophone society really aren't going to own typical
valve amps.

d

--
Pearce Consulting
http://www.pearce.uk.com

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

That's not typical.

I have a Lowther LL26 (EL 34's PP) 26W at 0.1% THD.
It is half the power of my PPP amp, but still the noise
floor is only 120µV a very presentable -98dB.
It cost £46 in 1968 and was a *very* typical amplifier
of the period.

Both my Radfords (STA 25 and STA 100) are silent,
ear-to-speaker, as are the TL12s.

Don't confuse them with the Dansette:-)

Best regards
Iain

Noise Weighting Curves
 

In article i,
Iain Churches wrote:
Most systems are silent with ear against speaker.

I'm willing to bet they're not.

--
*What boots up must come down *

Dave Plowman London SW
To e-mail, change noise into sound.

Noise Weighting Curves
 

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
Most systems are silent with ear against speaker.

I'm willing to bet they're not.

You are welcome to listen for yourself.
Bring a packet of chocolate Digestives - you
will lose the bet:-)

Iain

Noise Weighting Curves
 

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 10:00:34 +0300, "Iain Churches"
wrote:

My thanks to all those, both on and off list, who
provided useful info on the noise weighting curves.

The two ITU curves are similar but
ITU-R ARM is a later Dolby Labs
proposal which moves the whole curve
1kHz to the right.

Thanks also to my pal Richard in the UK,
I now have a chart in Excel showing all three
IEC curves, A,B and C, plus the two ITU curves.

http://www.kolumbus.fi/iain.churches...se/ABC+ITU.jpg

Comparison is interesting. One can also see why
the old IEC "A" weighted curve is still popular:-)


Iain, I've just looked at the curves, and I don't see the ARM curve
being 1kHz to the right of the 468 - it looks like identical
frequencies but 6dB lower to me. Hard to see from the graphs, but they
appear to peak at the same frequency.


Don. A bit more news has just filtered in. (Posting on UKRA
often results in informative e.mails from interesting sources)

It seems that the "Dolby shift" for ARM was implemented,
in the sense that 468 crossed 0dB at 1kHz, and ARM crosses
at 2kHz.

468 is intended as a professional standard with ARM a
commercial equivalent.

Best regards
Iain

Noise Weighting Curves
 

Don Pearce wrote:
On Thu, 4 Oct 2007 20:16:02 +0300, "Iain Churches"
wrote:

"Don Pearce" wrote in message
...
On Thu, 4 Oct 2007 18:51:36 +0300, "Iain Churches"
wrote:

"Dave Plowman (News)" wrote in message
...
In article ,
Don Pearce wrote:
In tube power amps, the difference between wide
band and "A" weighted was often found to be 12dB,
and this was, IIRC something of a rule of thumb.

Iain
Such a difference would suggest a great deal of 1/f noise.
Fairly typical of AF valve circuits. Hum.
A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

http://www.kolumbus.fi/iain.churches...em/C50_002.jpg

Not a misconception, Dave is right - yours is hardly a typical valve
amp. My impression of the huge majority of the valve amps I have come
across is that you just know when they are switched on; there is
always that "liveness" about the speakers, usually a mixture of hum
and noise.
Of the thirty or so members of the "gramophone society" to which
I belong, more than half have valve amps. I cannot think of a
single member who has a system where one can even hear a
hint of hum/hiss at the listening position. Most systems are
silent with ear against speaker.

With the exception of the Cheepies, the quality of valve amps
offered by the many bespoke builders is very high indeed.
I would say the performance of my own is typical.

Iain

Typical of bespoke. To assess typical you need to include all valve
amps in the sum. The average valve amp hums.

Members of a gramophone society really aren't going to own typical
valve amps.

d


FWIW the three bits of valve kit I have (Beard power, AI integrated and
EAR phono), and the one I had (Carmenta pre), are pretty quiet. The
Beard has a slight hum from the unit (transformers?), but less than some
SS amps I've had.

Noise Weighting Curves
 

On 2007-10-04, Iain Churches wrote:

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
Fairly typical of AF valve circuits. Hum.

A common misconception.
With a properly designed PSU C-L-C-R-C and with
attention paid to layout and ground buss, one can build
valve power amps with no hum or thermal noise even EAS
(ear against speaker) And it plays music to please the
most discerning ears.

My 50W PPP tube amp has a noise floor of 80µV
that's -106dB

That's not typical.

I have a Lowther LL26 (EL 34's PP) 26W at 0.1% THD.
It is half the power of my PPP amp, but still the noise
floor is only 120µV a very presentable -98dB.

Very presentable indeed. I guess I look on amplifier noise floors
as follows:

- specified WRT full power they indicate the absolute maximum dynamic
range available from a system. I'm afraid I'm keen on good dynamic
range.

- specified WRT the nominal 1 W into 8 ohms (2.83 V RMS) you can add the
speaker sensitivity and approximately check if the hiss will be
audible (at 1 m or at the litening position by correcting at 6 dB for
each doubling).

I have heard systems (SS systems) in the past, even at dealers, that
had quite audible noise from the 'speakers and wondered why. It seems
perfectly possible to do an engineering check to see if a system will
exhibit a number of avoidable limitations like this.

I fixed a system some years ago which had a Hafler DH-100 pre-amp with
20 dB of gain from the AUX input, connected to a Quad 405 with its high
gain - somewhat untypical of the US power amps with which the Hafler
might have been designed to work, and some high-ish sensitivity 'speakers.

The combination was noisy. I guess no-one designed it. It just got
assembled. I had to reduce the gain of the preamp (checking it for
stability) to 10 dB, when it just became silent at the listening position.

--
John Phillips

Noise Weighting Curves
 

On 2007-10-04, Don Pearce wrote:
Just done something similar on my DAW. I've also created an A curve.
Made a chunk of white noise and compared the average noise levels.

Flat -19.44dB
A wt -21.7dB
468 -12.59dB

So that is a 19dB difference. I only eyeballed the filters, so I could
be a bit out. This is all a bit odd. I can see there being differences
between two subjective curves purporting to be of the same thing, but
19dB? Something smells nasty.

[Noting Don's correction from 19 dB to 9 dB]. May I ask if this
comparison is relevant?

Weighting curves are relative. AFAICS you just can't compare the absolute
audibility of A-weighted noise with ITU-R 486-weighted noise from the
same source. You can only compare weighted figures with the same type
of weighting.

AFAICS, for each weighting the absolute threshold of audibility may be
rather different. What you may get from comparing 468-weighted noise
figures is a more valid comparison WRT human audibility of noise than
from comparing A-weighted noise figures.

--
John Phillips

Noise Weighting Curves
 

"Rob" wrote in message
...

FWIW the three bits of valve kit I have (Beard power, AI integrated and
EAR phono), and the one I had (Carmenta pre), are pretty quiet. The Beard
has a slight hum from the unit (transformers?), but less than some SS amps
I've had.

The Beard valve amps that I have seen perform well. They have fairly small
mains transformers, which are bolted straight to the chassis. Setting them
on rubber grommets (and also tightening the bolts that secure the
laminations)
gets rid of the transformer noise.

Iain