Arthur Quinn wrote:


** Taking some or even all NFB from the speaker side of the output
capacitor was pretty common with amplifiers using one DC supply. Doing
so however raises the issue of low frequency instability.

I recall seeing a Kenwood solid state receiver of late 60s vintage that
when connected to a Philips 8 inch low resonance woofer ( AD8065)
slowly went into oscillation at about 3Hz.

The trick was to use only a judicious amount OR have a capacitor or two
internally rolling off the gain of the power stage at low frequencies
- as is done with most valve amps.



Yes, the review says of the damping factor that "from about 2Hz to 50Hz
it tends towards slightly negative and infinity", implying that the
resistive component of the amplifier output impedance passes through
zero to negative within that frequency range.


** The get such test results implies the amplifier was being driven at its output with a varying frequency of known current while watching the voltage and phase at the terminals. It's a powerful technique that not many reviewers ever used.

BTW

The output stage of the 626 has very similar topology to the 40watt design published in the Philips "Audio Amplifier Systems" application book of 1970 - minus the regulated PSU.


..... Phil

On 09/11/2015 15:03, Dave Plowman (News) wrote:
In article . com,
Albert Zweistein wrote:
'And listening to Radio 3 or 4 using the FM tuner demonstrates how much
nicer these can sound via FM than via DAB.'
I quite agree but would you say this is a result of the low bit rate the
bbc uses or is an indication of the inherent superiority of analogue vs
digital sound reproduction?

Think you'll find that pretty well all of the chain from microphone to
transmitter is digital these days.

It's a very sad fact that it's all to easy to mess up a perfectly good
digital signal by simply reducing the data rate at the point of
transmission. They've done that with both radio and TV.


Yes reducing the transmission bitrate is easy to do and a lot of people
working in the industry who *should* know better either don't or don't
seem to care. Come the revolution I'll have them all shot.

On 09/11/2015 16:52, Jim Lesurf wrote:


Indeed. And so far as I know, the BBC still use NICAM for the distribution
for FM. Hence it is digital with a 32k sample rate and less than 16 bits
per sample. So nominally 'worse than Audio CD'. Yet can sound fine. People
ceased being able to hear an all-analogue FM chain decades ago.

Maybe fewer than 16 bits but it's almost a floating point encoding
so gives better resolution at low levels than you might think.

--
Eiron.

In article ,
Jim Lesurf wrote:
Indeed. And so far as I know, the BBC still use NICAM for the
distribution for FM. Hence it is digital with a 32k sample rate and less
than 16 bits per sample. So nominally 'worse than Audio CD'. Yet can
sound fine.

Dunno, Jim. The transmission side of the BBC was out sourced many years
ago. So may have changed things to commercial PCM equipment for
distribution too.

--
*Just give me chocolate and nobody gets hurt

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

In article . com,
Albert Zweistein wrote:
It's a very sad fact that it's all to easy to mess up a perfectly good
digital signal by simply reducing the data rate at the point of
transmission. They've done that with both radio and TV.


Yes reducing the transmission bitrate is easy to do and a lot of people
working in the industry who *should* know better either don't or don't
seem to care. Come the revolution I'll have them all shot.

It's not really up to those working in the industry. More a government
thing on how bandwidth is allocated. The more channels, the higher the
taxes.

--
*I don't feel old. I don't feel anything until noon. Then it's time for my nap.

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

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:
Indeed. And so far as I know, the BBC still use NICAM for the
distribution for FM. Hence it is digital with a 32k sample rate and
less than 16 bits per sample. So nominally 'worse than Audio CD'. Yet
can sound fine.

Dunno, Jim. The transmission side of the BBC was out sourced many years
ago. So may have changed things to commercial PCM equipment for
distribution too.

That's possible, yes. I've asked in the past but never been able to find
out for sure. Although more than one BBC person has told me they think it
still is NICAM for FM distribution.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Eiron
wrote:

Indeed. And so far as I know, the BBC still use NICAM for the
distribution for FM. Hence it is digital with a 32k sample rate and
less than 16 bits per sample. So nominally 'worse than Audio CD'. Yet
can sound fine. People ceased being able to hear an all-analogue FM
chain decades ago.

Maybe fewer than 16 bits but it's almost a floating point encoding so
gives better resolution at low levels than you might think.

Yes, this may help people who've not checked it out.

http://www.audiomisc.co.uk/BBC/PCMandNICAM/History.html

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article ,
Jim Lesurf wrote:
Dunno, Jim. The transmission side of the BBC was out sourced many years
ago. So may have changed things to commercial PCM equipment for
distribution too.

That's possible, yes. I've asked in the past but never been able to find
out for sure. Although more than one BBC person has told me they think it
still is NICAM for FM distribution.

The equipment would be getting on a bit by now. ;-) The department that
designed and had such things made was axed many years ago. But it could be
possible.

--
*Middle age is when work is a lot less fun - and fun a lot more work.

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

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:
Dunno, Jim. The transmission side of the BBC was out sourced many
years ago. So may have changed things to commercial PCM equipment
for distribution too.

That's possible, yes. I've asked in the past but never been able to
find out for sure. Although more than one BBC person has told me they
think it still is NICAM for FM distribution.

The equipment would be getting on a bit by now. ;-) The department that
designed and had such things made was axed many years ago. But it could
be possible.

The people who designed FM are probably also now all dead. :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article . com,
Albert Zweistein scribeth thus
On 08/11/2015 12:21, Jim Lesurf wrote:
Just to let people know I've put up a new webpage at

http://www.audiomisc.co.uk/Armstrong...iliconEra.html

This documents the 1973-4 period when they released the 600 range and it
got a lot of attention. Can be interesting to compare reviews to see when
they agree and when they conflict. :-)

FWIW I'm planning two more pages.

One to deal with the 1975-1985 period which covers the dissapearance of
Armstrong as a manufacturer. This is actually quite a complex set of events
so needs a lot of details. Also covers more reviews of the 600 and those of
the 700 amps, what happened with the tuner, etc. In some ways its also a
history of what went wrong in UK manufacturing and how equipment was
reviewed and sold by retailers, etc. Some skeletons will be dug up, and
oddities in 'reviews' examined. 8-]

The other page is to document more extensively the 'radio chassis era' from
1932 to about 1960. During this period Armstrong made a lot of different
models, some without their name or logo on the front! I'm still working
though old references, magazines, etc, to sort this out!

However I'm also doing some work to try and build a decent website for the
Museum of Communication, so it will take a while to do the above pages.



Below is a quote from your page at
http://www.audiomisc.co.uk/Armstrong...airandmod.html
'And listening to Radio 3 or 4 using the FM tuner demonstrates how much
nicer these can sound via FM than via DAB.'
I quite agree but would you say this is a result of the low bit rate the
bbc uses or is an indication of the inherent superiority of analogue vs
digital sound reproduction?


Around the best these days is the high rate net feed.

FM is still processed apart from the limitations of the FM system and I
think at the moment BBC R3 DAB is at 160 K instead of the 192K it ought
to be at!.

--
Tony Sayer