"Arny Krueger" wrote in message ...

These really aren't digital amps. They are switchmode amps. The buggar in
just about all of them is the analog low-pass filter at the output, which
causes the output impedance to rise over the top octave or two of the audio
band. Therefore, they are somewhat sensitive to speaker impedance variations
in the same range.

They also tend to behave vastly different when they clip. Some pick up a lot
of high frequency trash in the last dB of dynamic range before clipping.

I wonder what a digital amp is if it isn't a switchmode amp? Yes the
output filter increases the ouput impedance, which can be assisted
with a zobel network. They can still achieve lower output impedance
than a lot of valve amps, so what's the bother?

The way they behave when they get near clipping is up to the designer,
just like an analogue amp.

Some digital amps can do some things better than many analogue amps.
They can take a CD's input digitally, they can get better SNRs and
full power THDs.

On 19 Jan 2004 06:18:09 -0800, (Ian Smith)
wrote:

"Arny Krueger" wrote in message ...

These really aren't digital amps. They are switchmode amps. The buggar in
just about all of them is the analog low-pass filter at the output, which
causes the output impedance to rise over the top octave or two of the audio
band. Therefore, they are somewhat sensitive to speaker impedance variations
in the same range.

They also tend to behave vastly different when they clip. Some pick up a lot
of high frequency trash in the last dB of dynamic range before clipping.

I wonder what a digital amp is if it isn't a switchmode amp?

A digital amp is a switchmode amp, but a switchmode amp is not
necessarily a digital amp. It requires synchronisation to an incoming
data clock, rather than just free-running PCM conversion, to make a
digital amp.

Yes the
output filter increases the ouput impedance, which can be assisted
with a zobel network. They can still achieve lower output impedance
than a lot of valve amps, so what's the bother?

Valve amps are crap, that's what!

The way they behave when they get near clipping is up to the designer,
just like an analogue amp.

Yes, but the designer is limited by available devices.

Some digital amps can do some things better than many analogue amps.
They can take a CD's input digitally, they can get better SNRs and
full power THDs.

But can they get better *part* power distortion artifacts, since they
will be *averaging* less than 10% of full power, and often only 1% of
full power?
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...
On 19 Jan 2004 06:18:09 -0800, (Ian Smith)
wrote:

"Arny Krueger" wrote in message
...

These really aren't digital amps. They are switchmode amps. The buggar
in
just about all of them is the analog low-pass filter at the output,
which
causes the output impedance to rise over the top octave or two of the
audio
band. Therefore, they are somewhat sensitive to speaker impedance
variations
in the same range.

They also tend to behave vastly different when they clip. Some pick up
a lot
of high frequency trash in the last dB of dynamic range before
clipping.

I wonder what a digital amp is if it isn't a switchmode amp?

A digital amp is a switchmode amp, but a switchmode amp is not
necessarily a digital amp. It requires synchronisation to an incoming
data clock, rather than just free-running PCM conversion, to make a
digital amp.

Yes the
output filter increases the ouput impedance, which can be assisted
with a zobel network. They can still achieve lower output impedance
than a lot of valve amps, so what's the bother?

Valve amps are crap, that's what!



Comment noted, name taken.....

On Tue, 20 Jan 2004 16:08:35 -0000, "Keith G"
wrote:

"Stewart Pinkerton" wrote in message
...
On 19 Jan 2004 06:18:09 -0800, (Ian Smith)
wrote:

Yes the
output filter increases the ouput impedance, which can be assisted
with a zobel network. They can still achieve lower output impedance
than a lot of valve amps, so what's the bother?

Valve amps are crap, that's what!

Comment noted, name taken.....

Don't tell him, Pike!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...
On Tue, 20 Jan 2004 16:08:35 -0000, "Keith G"
wrote:

"Stewart Pinkerton" wrote in message
...
On 19 Jan 2004 06:18:09 -0800, (Ian Smith)
wrote:

Yes the
output filter increases the ouput impedance, which can be assisted
with a zobel network. They can still achieve lower output impedance
than a lot of valve amps, so what's the bother?

Valve amps are crap, that's what!

Comment noted, name taken.....

Don't tell him, Pike!



In confectionary terms that line was a particularly fine hazelenut in a bar
of the finest Cadbury's chocolate.......... :-)

On Wed, 21 Jan 2004 13:56:39 -0000
"Keith G" wrote:


In confectionary terms that line was a particularly fine hazelenut in a bar
of the finest Cadbury's chocolate.......... :-)

Cadburys dont make chocolate.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.

In article , Ian Smith
wrote:
"Arny Krueger" wrote in message
...

These really aren't digital amps. They are switchmode amps. The buggar
in just about all of them is the analog low-pass filter at the output,
which causes the output impedance to rise over the top octave or two
of the audio band. Therefore, they are somewhat sensitive to speaker
impedance variations in the same range.

They also tend to behave vastly different when they clip. Some pick up
a lot of high frequency trash in the last dB of dynamic range before
clipping.

I wonder what a digital amp is if it isn't a switchmode amp? Yes the
output filter increases the ouput impedance, which can be assisted with
a zobel network. They can still achieve lower output impedance than a
lot of valve amps, so what's the bother?

Depends upon the speakers and other aspects of the situation. With a
coventional power amp you can - if you wish - maintain a low output
impedance even at 20kHz.

The designs for 'digital' amps I have seen used a 10 microH series output
inductor. That is, I think, relatively high by modern standards. However
old SS amps used higher values at times.

Hence so far as I am concerned, the increased output impedance at 20kHz is
'unfortunate' but provided it is taken into account should be OK.

Personally, I am more concerned by the level of ultrasonic power that may
still be reaching the speaker unit. I have not been able to get meaningful
data on the actual output patterns the digital amps produce, so can only
make a general estimate of this. However the level might be of the order of
a watt when using a 100 - 200 W digital amp of the designs I have seen.
This seems to me to be to be quite a lot of ultrasonic hash to present to a
loudspeaker. I must admit I also wonder how much this might cause
interference if used with high inductance (i.e. wide spacing) cables...

Slainte,

Jim

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

"Ian Smith" wrote in message
om

"Arny Krueger" wrote in message
...

These really aren't digital amps. They are switchmode amps. The
buggar in just about all of them is the analog low-pass filter at
the output, which causes the output impedance to rise over the top
octave or two of the audio band. Therefore, they are somewhat
sensitive to speaker impedance variations in the same range.

They also tend to behave vastly different when they clip. Some pick
up a lot of high frequency trash in the last dB of dynamic range
before clipping.

I wonder what a digital amp is if it isn't a switchmode amp?

You've missed the point.

Yes the
output filter increases the output impedance, which can be assisted
with a zobel network.

A zobel is a parallel network. In order to reduce the output impedance of an
amp substantially, it has to substantially short out the output of the amp.

They can still achieve lower output impedance
than a lot of valve amps, so what's the bother?

Nice job of damning switchmode amps with faint praise.

The way they behave when they get near clipping is up to the designer,
just like an analogue amp.

I can't imagine a designer willfully designing in the sort of bizarre
behavior I've seen in some cases.

Some digital amps can do some things better than many analogue amps.

You've got the whole rest of the post to list what they are.

They can take a CD's input digitally,

Ironically, very few of them implement digital inputs, and many that do, do
so with a regular DAC chip.

they can get better SNRs and full power THDs.

Really? Got a real-world example?