"John Phillips" wrote in message
...

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

Maybe not, but it is still fun to do:-)

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.

Manufacturers choose the weighting which shows there amp in the best
possible light, but it is important to compare apples with apples. If all
are
using the same weighting, then there is no problem.

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.

Indeed.

Iain

On Thu, 4 Oct 2007 21:43:04 +0300, "Iain Churches"
wrote:


"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.

I think that whoever came up with that bit of back-pedalling must have
been a politician.

d

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

Iain Churches wrote:
"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


Of course it does depend on the speakers used.

--
Nick

"Nick Gorham" wrote in message
...
Iain Churches wrote:
"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
Of course it does depend on the speakers used.

I have several options. Kef, Tannoy, JBL
The Kef K1 monitors have 18x13 inch drivers. If
there were any hum, it would be audible on those.

Iain

--
Nick

In article i, Iain
Churches wrote:

"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.

FWIW I had to do something similar with my pair of ESL63s, bought in the
1980s. Also to my old Meridian 200 CD drive... Love the Meridian 263 DAC,
but not really impressed in the end by the drive.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

Iain Churches wrote:
"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


Thanks Iain - the transformers are tucked away and last time I looked
they weren't readily accessible, and I suspect they're a fair size given
the amp weighs about 35kg. And if my fettle causes a problem, they're a
problem to replace - £500 each springs to mind.

In use, and for some reason, I'm more forgiving of noise from a valve
amp, although as I say, the ones I have/had are comparable with SS.

Still, next time I open it up I'll have a look.

Rob

In article ,
Iain Churches wrote:

"Nick Gorham" wrote in message
...
Iain Churches wrote:
"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
Of course it does depend on the speakers used.

I have several options. Kef, Tannoy, JBL
The Kef K1 monitors have 18x13 inch drivers. If
there were any hum, it would be audible on those.

Ah - have you now restricted it to just hum?

Iain

--
Nick

--
*Don't sweat the petty things and don't pet the sweaty things.

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

"Rob" wrote in message
...
Iain Churches wrote:
"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.

Thanks Iain - the transformers are tucked away and last time I looked they
weren't readily accessible, and I suspect they're a fair size given the
amp weighs about 35kg. And if my fettle causes a problem, they're a
problem to replace - £500 each springs to mind.

Rob. The Beard that I worked on (SP35 IIRC) had the
mains transformer mounted centre chassis under the rear cage.
Before removing it, check the tightness of the bolts through
the laminations. This might solve the problem completely.

If not, you will need to drill out the transformer mounting
holes to say M8 and then fit the grommets. Put a tab
washer top and bottom, and then ensure that the transformer
bell is grounded to chassis (a separate black wire may
be required with a solder tag at each end from one of the
lamination securing screws to the transformer fixing bolt -
clean off the varnish if required) Don't bolt the transformer
down too tight.

Best regards
Iain

"Dave Plowman (News)" wrote in message
...
In article ,
Iain Churches wrote:

"Nick Gorham" wrote in message
...
Iain Churches wrote:
"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
Of course it does depend on the speakers used.

I have several options. Kef, Tannoy, JBL
The Kef K1 monitors have 18x13 inch drivers. If
there were any hum, it would be audible on those.

Ah - have you now restricted it to just hum?

No. There is no audible hiss either.
Chocolate Digestive biscuit anyone? :-)

Iain

"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:

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

That's not typical.

Bear in mind that traditionally valve amps had AC heaters.
These days, by simply using DC, and biasing the heaters
above the cathode can make 10dB improvement in the
LF noise floor.

In the hey-day of valve amps, iron was cheap and large
electrolytics very very expensive. Now the reverse is the
case. When valve retifiers were used, the reservoir cap was
usually limited to 47µF. Now 470µF is often seen as the first
cap in a chain with one or more chokes of 10 or 20H.
This results in a PSU of low impedance with very
low ripple.

I can understand that it might suit the agenda of some
to try to maintain the idea that valve amps are plagued
with hum and noise:-)

Fortunately, this need not be the case.


Regards to all
Iain