Power amp phase response
 

I would be interested to know the phase response
of a high end SS amp (OK, I know, they are ALL high end:-)
at 20Hz and say 20kHz, or more points if the info is
available.

If someone can supply me with some figs (from say the
legendary Krell:-) I cold use these a benchmark for the
measurements of my own amp.

TIA

Iain

Power amp phase response
 

On Mon, 13 Dec 2004 23:27:18 +0200, "Iain M Churches"
wrote:

I would be interested to know the phase response
of a high end SS amp (OK, I know, they are ALL high end:-)
at 20Hz and say 20kHz, or more points if the info is
available.

If someone can supply me with some figs (from say the
legendary Krell:-) I cold use these a benchmark for the
measurements of my own amp.

It obviously depends on the bandwidth of the amp, which doesn't have
much to do with 'high end' credentials. A Naim amp for instance is
specifically designed to have limited bandwidth, and will have phase
angles of around 10-20 degrees at 20Hz and 20-30 degrees at 20kHz. At
the other extreme, a Spectral will have phase angles of less than five
degrees at these frequencies. My own Audiolab 8000P measures about 5-7
degrees at 20Hz and 8-10 degrees at 20kHz (approximated due to being
measured on a 'scope, since I don't have a vector voltmeter). The
Krell is about the same. Some SS amps are DC coupled, which will give
them zero phase angle at 20Hz.

The only thing 'legendary' about the classic Krells is that they
operate in Class A at their 8 ohm rated output, and that they double
that rated output for each halving of impedance down to 1 ohm.
Otherwise, they are not especially wideband or especially low
distortion. They are however, like most good SS amps and a very few
valve amps, sonically transparent.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Power amp phase response
 

In article , Iain M Churches
wrote:
I would be interested to know the phase response of a high end SS amp
(OK, I know, they are ALL high end:-) at 20Hz and say 20kHz, or more
points if the info is available.

If someone can supply me with some figs (from say the legendary Krell:-)
I cold use these a benchmark for the measurements of my own amp.

FWIW and IIRC: The response of the 730 amps I designed/use has -0.2dB
points at 20Hz and 20kHz [1] and it is effectively a first order rolloff
that is producing these results. (i.e. with the -3dB points well away from
20Hz and 20kHz). Can't recall the phase, but you can work it out from the
above. Can't say that this is a 'high end' amp, though, as I keep it on the
floor. ;-

Does this matter? Unless you are using something like ESL's in an excellent
room, I'd expect the phase effects of the speakers and room to dwarf any
amp phase effects in most cases.

Slainte,

Jim

[1] Assuming 8 Ohm resistive loads. Changes a bit at HF for some other
loads.

--
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

Power amp phase response
 

"Stewart Pinkerton" wrote in message
...
On Mon, 13 Dec 2004 23:27:18 +0200, "Iain M Churches"
wrote:

It obviously depends on the bandwidth of the amp, which doesn't have
much to do with 'high end' credentials.

Understood:-)
But I assumed the better the amp the better the performance.


A Naim amp for instance is
specifically designed to have limited bandwidth, and will have phase
angles of around 10-20 degrees at 20Hz and 20-30 degrees at 20kHz. At
the other extreme, a Spectral will have phase angles of less than five
degrees at these frequencies. My own Audiolab 8000P measures about 5-7
degrees at 20Hz and 8-10 degrees at 20kHz (approximated due to being
measured on a 'scope, since I don't have a vector voltmeter). The
Krell is about the same. Some SS amps are DC coupled, which will give
them zero phase angle at 20Hz.

Hmm! Thanks for the info. These are pretty impressive figs.
I have access to a phase shift generator/meter combination (digital of
course:-) made by Feedback Electronics in the UK.
That's why I was interested to obtain some kind of a yardstick.

An initial investigation of my 50W amplifier which has the first and second
stages DC coupled, shows -3 degrees at 10Hz, and -8 degrees at 50kHz.
So about the same as the Audiolab 8000P, and very close to the Spectral?
Not too shabby:-))

This amp has custom-designed Sowter transformers. A similar amp with
Hammond iron may not perform so well.

Iain

Power amp phase response
 

On Tue, 14 Dec 2004 11:25:59 +0200, "Iain M Churches"
wrote:


"Stewart Pinkerton" wrote in message
.. .
On Mon, 13 Dec 2004 23:27:18 +0200, "Iain M Churches"
wrote:

It obviously depends on the bandwidth of the amp, which doesn't have
much to do with 'high end' credentials.

Understood:-)
But I assumed the better the amp the better the performance.


A Naim amp for instance is
specifically designed to have limited bandwidth, and will have phase
angles of around 10-20 degrees at 20Hz and 20-30 degrees at 20kHz. At
the other extreme, a Spectral will have phase angles of less than five
degrees at these frequencies. My own Audiolab 8000P measures about 5-7
degrees at 20Hz and 8-10 degrees at 20kHz (approximated due to being
measured on a 'scope, since I don't have a vector voltmeter). The
Krell is about the same. Some SS amps are DC coupled, which will give
them zero phase angle at 20Hz.

Hmm! Thanks for the info. These are pretty impressive figs.
I have access to a phase shift generator/meter combination (digital of
course:-) made by Feedback Electronics in the UK.
That's why I was interested to obtain some kind of a yardstick.

An initial investigation of my 50W amplifier which has the first and second
stages DC coupled, shows -3 degrees at 10Hz, and -8 degrees at 50kHz.
So about the same as the Audiolab 8000P, and very close to the Spectral?
Not too shabby:-))

This amp has custom-designed Sowter transformers. A similar amp with
Hammond iron may not perform so well.

Iain


I wouldn't get too bothered by the phase response of an amplifier,
other than as an indicator of bandwidth (in a competently designed
amplifier where rolloffs are defined by single poles, -3dB = 90
degrees). Do remember that a speaker follows, with phase shifts that
are all over the place by comparison.

d

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

Power amp phase response
 

In article , Iain M Churches
wrote:


Hmm! Thanks for the info. These are pretty impressive figs. I have
access to a phase shift generator/meter combination (digital of
course:-) made by Feedback Electronics in the UK. That's why I was
interested to obtain some kind of a yardstick.

An initial investigation of my 50W amplifier which has the first and
second stages DC coupled, shows -3 degrees at 10Hz, and -8 degrees at
50kHz. So about the same as the Audiolab 8000P, and very close to the
Spectral? Not too shabby:-))

Are the above values with an 8 Ohm load from an 8 Ohm tap?

If you are concerned about this, I'd suggest you also check with reactive
and/or mismatched loads. FWIW Naim amps have tended in the past to have a
series resistor (about 0.2 Ohms IIRC) in their output, and then tell the
user to employ about 10 microH worth of special cable in series. (Which is
conveniently omitted from magazine measurements but is in place when using
the amp as recommended.)

Whereas many non-Naim SS amps either have direct output or have a small
series inductor. These can affect the phase response at 20kHz and mean that
values obtained into an 8 Ohm resistor are not always a good guide.
Similarly, if your valve amp has any reactance or an impedance much above
0.1 Ohms, this may interact with reactive loads and give a distinct change
in result.

How much this matters is a different matter, though. The figures you quoted
look - in themselves - perfectly respectable. Hence unless your amp has a
particularly high output impedance and/or is reactive at HF/LF I'd doubt
this matters compared to the way most speakers and rooms will affect the
phase of what reaches the listener. :-)

This amp has custom-designed Sowter transformers. A similar amp with
Hammond iron may not perform so well.

Since you are doing this, I'd be interested to know the complex output
impedance you get across the audio band as this seems to be the kind of
measurement that rarely gets done and published for *any* amp these days...

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

Power amp phase response
 

"Iain M Churches" wrote in message


I would be interested to know the phase response
of a high end SS amp (OK, I know, they are ALL high end:-)
at 20Hz and say 20kHz, or more points if the info is
available.

Look at the amp's frequency response curve and use what you know about the
Hibert transform or simply draw Bode diagrams to estimate the amp's phase
response. At low levels power amps tend to be minimum-phase.

Amps tend to have fairly well-matched response between the channels, so the
phase response isn't all that significant, anyhow. Phase response matching
between the channels is far more important.

Power amp phase response
 

"Arny Krueger" wrote in message
...
"Iain M Churches" wrote in message


I would be interested to know the phase response
of a high end SS amp (OK, I know, they are ALL high end:-)
at 20Hz and say 20kHz, or more points if the info is
available.

Look at the amp's frequency response curve and use what you know about the
Hibert transform or simply draw Bode diagrams to estimate the amp's phase
response.

As mentioned before, I have access to a phase measuring set
(generator and meter) In the past, I have made measurements
using an oscilloscope.

At low levels power amps tend to be minimum-phase.

So should I take measurements at different power levels?


Amps tend to have fairly well-matched response between the channels, so
the phase response isn't all that significant, anyhow. Phase response
matching between the channels is far more important.

Both channels seem very closely matched.
My increased interest in this parameter was fed by the fact that I now have
access to equipment to measure it, but I needed some figures on which to
base my judgement of the performance.

Iain

Power amp phase response
 

"Jim Lesurf" wrote in message
...
In article , Iain M Churches
wrote:
An initial investigation of my 50W amplifier which has the first and
second stages DC coupled, shows -3 degrees at 10Hz, and -8 degrees at
50kHz. So about the same as the Audiolab 8000P, and very close to the
Spectral? Not too shabby:-))

Are the above values with an 8 Ohm load from an 8 Ohm tap?

Yes, they are.

If you are concerned about this, I'd suggest you also check with reactive
and/or mismatched loads.

Not so much concerned as interested:-) The figs in themselves do not mean
much if I have no yardstick - hence ther question.



The figures you quoted
look - in themselves - perfectly respectable. Hence unless your amp has a
particularly high output impedance

The damping factor is 20, which for a valve amp very respectable:-)

and/or is reactive at HF/LF I'd doubt
this matters compared to the way most speakers and rooms will affect the
phase of what reaches the listener. :-)

Understood.

This amp has custom-designed Sowter transformers. A similar amp with
Hammond iron may not perform so well.

Since you are doing this, I'd be interested to know the complex output
impedance you get across the audio band as this seems to be the kind of
measurement that rarely gets done and published for *any* amp these
days...

Can you suggest the best way to ascertain these figs?


Iain

Power amp phase response
 

On Tue, 14 Dec 2004 11:25:59 +0200, "Iain M Churches"
wrote:


"Stewart Pinkerton" wrote in message
.. .
On Mon, 13 Dec 2004 23:27:18 +0200, "Iain M Churches"
wrote:

It obviously depends on the bandwidth of the amp, which doesn't have
much to do with 'high end' credentials.

Understood:-)
But I assumed the better the amp the better the performance.

That depends how you define 'batter'. The Spectral for instance has
megahertz bandwidth, so immaculate phase response at 20kHz, but is
notoriously unstable. The Naim OTOH has been highly regarded by
audiophiles for about thirty years, despite being sensitive to
capacitive lopads and demanding highly inductive speaker cable to
maintain its warranty. VCome to think of it, the phase response is a
lot worse if you include that cable, as you should since Naim consider
iot to be an essential part of the circuit driving the speaker.
Basically, there's a *lot* more to 'high fidelity' than sheer
bandwidth. Many decades ago, the brilliant Gilbert Briggs of
Wharfedale coined a very useful phrase - the wider you open the
window, the more the muck flies in!

An initial investigation of my 50W amplifier which has the first and second
stages DC coupled, shows -3 degrees at 10Hz, and -8 degrees at 50kHz.
So about the same as the Audiolab 8000P, and very close to the Spectral?
Not too shabby:-))

That's very impressive for a valve amp.

This amp has custom-designed Sowter transformers. A similar amp with
Hammond iron may not perform so well.

Impressive results explained! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering