Slam
 

Nick Gorham wrote:

Old Fart at Play wrote:

Jim Lesurf wrote:


Also, 2,200 uF is perhaps a tad on the small side if you want to support
sustained mean currents of the order of over 30 Amps per channel
(i.e. over
60 Amps total for stereo), particularly using a non-SMPS! The resulting
voltage ripple may be too high.




Where is all this current going?
Does this hypothetical amplifier provide 25kW per channel into 8ohms?

Roger.



FWTW 30amp into 8 ohm is 7.2Kw.


Yes, but we're playing with ball-park figures
and so for the PSU to average 30amp it is giving 60amp for half the time
then the other rail is giving 60amp for the other half.....

So it's four times the power you calculated.

Roger.

Slam
 

Old Fart at Play wrote:

Nick Gorham wrote:

Old Fart at Play wrote:

Jim Lesurf wrote:


Also, 2,200 uF is perhaps a tad on the small side if you want to
support
sustained mean currents of the order of over 30 Amps per channel
(i.e. over
60 Amps total for stereo), particularly using a non-SMPS! The resulting
voltage ripple may be too high.





Where is all this current going?
Does this hypothetical amplifier provide 25kW per channel into 8ohms?

Roger.



FWTW 30amp into 8 ohm is 7.2Kw.



Yes, but we're playing with ball-park figures
and so for the PSU to average 30amp it is giving 60amp for half the time
then the other rail is giving 60amp for the other half.....

So it's four times the power you calculated.

Roger.



Or not, but I can see what you mean :-) I wasn't thinking in terms of
double rail PSU's, too much time thinking about valve amplifiers maybe.

--
Nick

Slam
 

Old Fart at Play wrote:

Nick Gorham wrote:

Old Fart at Play wrote:

Jim Lesurf wrote:


Also, 2,200 uF is perhaps a tad on the small side if you want to
support
sustained mean currents of the order of over 30 Amps per channel
(i.e. over
60 Amps total for stereo), particularly using a non-SMPS! The resulting
voltage ripple may be too high.





Where is all this current going?
Does this hypothetical amplifier provide 25kW per channel into 8ohms?

Roger.



FWTW 30amp into 8 ohm is 7.2Kw.



Yes, but we're playing with ball-park figures
and so for the PSU to average 30amp it is giving 60amp for half the time
then the other rail is giving 60amp for the other half.....

So it's four times the power you calculated.

Roger.



Or not, but I can see what you mean :-) I wasn't thinking in terms of
double rail PSU's, too much time thinking about valve amplifiers maybe.

--
Nick

Slam
 

On Sun, 5 Oct 2003 10:45:25 +0100, Chris Morriss
wrote:

In message , Stewart Pinkerton
writes
On Sun, 5 Oct 2003 09:01:08 +0100, Chris Morriss
wrote:

In message , Jim Lesurf
writes
I'd agree that you need plenty of current available. For a 200Wpc I'd go
for well over 30Arms continuous, and bigger short-term available. However
soggy rails don't have to preclude this.

I used to be wary of stabilised rails, as this can lead to problems with
getting the stabilisers to work well. In effect, they end up becoming part
of the amp itself. My own preference was to spend the time and money on the
amp itself, working from a more basic PSU (old fashioned transformer,
bridge, and big caps with low ESR.)


The problem with the use of really big caps (22,000uF or so) is that the
current taken from the mains is in very short, high-amplitude pulses. My
new 200W mains SMPSU I've just designed at work needs a power-factor
correction stage converting the 90 to 260V rms into 400V dc before this
feeds the main islolating stage, to make the PSU look resistive to the
mains.

The law is now that any PSU over 85W needs PF correction. Does this
apply to amplifiers for domestic use?

It's easier to get a reasonable PF by using low value capacitors
(2,200uF or so) and tolerate the dc ripple by regulating down to a
stabilised output.

Or, if you have the money for it, you can use a choke-filtered supply
to maintain the rail voltage without active regulation. Musical
Fidelity use this in their better amps, as do most valve amps. It's
definitely the best electrical solution, since it gives a very quiet
power rail, but those big chokes are *seriously* expensive!


Funny you should mention that Stewart. I'm building a real 'Luddite'
single-ended Class A amp at this minute. (In fact I am wiring up the
Schottky rectifiers for the output stage PSU in between looking at the
emails).

And when I say Luddite, I mean it. Just to see if the 'zero overall
feedback' guys have any basis for their views, it's a single-ended,
emitter-follower output, choke loaded (125mH at 5A, not bought new of
course!) with a choke-input PSU.)

The SPICE simulation shows remarkably good performance, so it'll be
interesting to see how it measures and sounds in real life.

I'm working in Leicester now, and driving every day from Nottingham to
Leicester, so if it seems to work well, you'll be welcome to see how it
works on any speakers you have. (Being SE Class-A it will only give
about 15W into 4 Ohms though before running out of current.)

I have Apogee Duetta Signatures (3ohms - 84dB/W/M) and Tannoy 633s (8
ohms - 90dB/W/M), so I think I can accommodate you at either end of
the conventional sensitivity spectrum.

You're very welcome to drop in any time.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Slam
 

On Sun, 5 Oct 2003 10:45:25 +0100, Chris Morriss
wrote:

In message , Stewart Pinkerton
writes
On Sun, 5 Oct 2003 09:01:08 +0100, Chris Morriss
wrote:

In message , Jim Lesurf
writes
I'd agree that you need plenty of current available. For a 200Wpc I'd go
for well over 30Arms continuous, and bigger short-term available. However
soggy rails don't have to preclude this.

I used to be wary of stabilised rails, as this can lead to problems with
getting the stabilisers to work well. In effect, they end up becoming part
of the amp itself. My own preference was to spend the time and money on the
amp itself, working from a more basic PSU (old fashioned transformer,
bridge, and big caps with low ESR.)


The problem with the use of really big caps (22,000uF or so) is that the
current taken from the mains is in very short, high-amplitude pulses. My
new 200W mains SMPSU I've just designed at work needs a power-factor
correction stage converting the 90 to 260V rms into 400V dc before this
feeds the main islolating stage, to make the PSU look resistive to the
mains.

The law is now that any PSU over 85W needs PF correction. Does this
apply to amplifiers for domestic use?

It's easier to get a reasonable PF by using low value capacitors
(2,200uF or so) and tolerate the dc ripple by regulating down to a
stabilised output.

Or, if you have the money for it, you can use a choke-filtered supply
to maintain the rail voltage without active regulation. Musical
Fidelity use this in their better amps, as do most valve amps. It's
definitely the best electrical solution, since it gives a very quiet
power rail, but those big chokes are *seriously* expensive!


Funny you should mention that Stewart. I'm building a real 'Luddite'
single-ended Class A amp at this minute. (In fact I am wiring up the
Schottky rectifiers for the output stage PSU in between looking at the
emails).

And when I say Luddite, I mean it. Just to see if the 'zero overall
feedback' guys have any basis for their views, it's a single-ended,
emitter-follower output, choke loaded (125mH at 5A, not bought new of
course!) with a choke-input PSU.)

The SPICE simulation shows remarkably good performance, so it'll be
interesting to see how it measures and sounds in real life.

I'm working in Leicester now, and driving every day from Nottingham to
Leicester, so if it seems to work well, you'll be welcome to see how it
works on any speakers you have. (Being SE Class-A it will only give
about 15W into 4 Ohms though before running out of current.)

I have Apogee Duetta Signatures (3ohms - 84dB/W/M) and Tannoy 633s (8
ohms - 90dB/W/M), so I think I can accommodate you at either end of
the conventional sensitivity spectrum.

You're very welcome to drop in any time.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Slam
 

On Sun, 05 Oct 2003 16:07:47 +0100, Old Fart at Play
wrote:

Jim Lesurf wrote:

Also, 2,200 uF is perhaps a tad on the small side if you want to support
sustained mean currents of the order of over 30 Amps per channel (i.e. over
60 Amps total for stereo), particularly using a non-SMPS! The resulting
voltage ripple may be too high.

Where is all this current going?
Does this hypothetical amplifier provide 25kW per channel into 8ohms?

Not necessarily, but it will maintain a 56 watt/channel at 8 ohms
rating into a 1 ohm load. As it happens, I own such an amplifier.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Slam
 

On Sun, 05 Oct 2003 16:07:47 +0100, Old Fart at Play
wrote:

Jim Lesurf wrote:

Also, 2,200 uF is perhaps a tad on the small side if you want to support
sustained mean currents of the order of over 30 Amps per channel (i.e. over
60 Amps total for stereo), particularly using a non-SMPS! The resulting
voltage ripple may be too high.

Where is all this current going?
Does this hypothetical amplifier provide 25kW per channel into 8ohms?

Not necessarily, but it will maintain a 56 watt/channel at 8 ohms
rating into a 1 ohm load. As it happens, I own such an amplifier.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Slam
 

"Jim Lesurf" wrote in message
...
In article , Andy Evans
wrote:
I am uncertain about the above for two reasons; 1) That you are
essentially telling us that 'slam' is an 'artificial effect', but then
only tell us what it does *not* mean,

I assume the above is quoted from myself, although the quoting is not
clear...

If it's an artificial effect, does it need to be defined, or indeed can
it be defined?

Well, if you use a word without giving me a definition, how can I know
what
you mean by it? If thr word has no definable meaning, can it be expected
to
convey any information from the speaker to the listener?

Your description seemed to be equivalent to saying "a koala bear is not a
kangeroo". This may tell me something, but does not really help me to
recognise a koala bear when I see one, nor know what you recognise as one.

If you said a "a koala bear is a small type of bear" this might be of some
use if I am aware of what some other bears look like. This would not be a
precise definition - allowing an unambiguous recognition - but would
perhaps be helpful. Unfortunately, giving an example of what something is
not may not tell me much at all.

**Just a small pedantic point:

A Koala is not a bear. In fact, the Koala is more closely related to the
Kangaroo, than it is to _any_ mammal. Koalas and Kangaroos are both
Marsupials. Both animals are strictly vegetarian. Until the arrival of the
Dingo, some 20-30,000 years ago, Australia had no large (predatory) mammals
of any kind.


--
Trevor Wilson
www.rageaudio.com.au

Slam
 

"Jim Lesurf" wrote in message
...
In article , Andy Evans
wrote:
I am uncertain about the above for two reasons; 1) That you are
essentially telling us that 'slam' is an 'artificial effect', but then
only tell us what it does *not* mean,

I assume the above is quoted from myself, although the quoting is not
clear...

If it's an artificial effect, does it need to be defined, or indeed can
it be defined?

Well, if you use a word without giving me a definition, how can I know
what
you mean by it? If thr word has no definable meaning, can it be expected
to
convey any information from the speaker to the listener?

Your description seemed to be equivalent to saying "a koala bear is not a
kangeroo". This may tell me something, but does not really help me to
recognise a koala bear when I see one, nor know what you recognise as one.

If you said a "a koala bear is a small type of bear" this might be of some
use if I am aware of what some other bears look like. This would not be a
precise definition - allowing an unambiguous recognition - but would
perhaps be helpful. Unfortunately, giving an example of what something is
not may not tell me much at all.

**Just a small pedantic point:

A Koala is not a bear. In fact, the Koala is more closely related to the
Kangaroo, than it is to _any_ mammal. Koalas and Kangaroos are both
Marsupials. Both animals are strictly vegetarian. Until the arrival of the
Dingo, some 20-30,000 years ago, Australia had no large (predatory) mammals
of any kind.


--
Trevor Wilson
www.rageaudio.com.au

Slam
 

In article , Old Fart at Play
wrote:
Jim Lesurf wrote:


Also, 2,200 uF is perhaps a tad on the small side if you want to
support sustained mean currents of the order of over 30 Amps per
channel (i.e. over 60 Amps total for stereo), particularly using a
non-SMPS! The resulting voltage ripple may be too high.


Where is all this current going? Does this hypothetical amplifier
provide 25kW per channel into 8ohms?

The difficulty is that some people may wish to use loudspeaker loads that
may have impedances that go down to the 1 - 2 Ohm region. (e.g. some
electrostatic or magnaplaner units) or use multiple speakers in parallel.
Hence in some cases you may need to be able to deliver over 30 Amps if you
want the amplifier to be able to assert output voltages in the 30 - 70 V
range into such loads without running out of steam...

If someone is building an amp privately for their own use, then they only
need to ensure it works well with their speakers. However when I was
designing a 'high power' amp for commercial sale I felt I had to ensure it
could deliver high currents for people who chose to use it with 'difficult'
loudspeakers. This may, of course, have been influenced by my own
preference for speakers like electrostatics. :-)

The result does imply 'quite high' powers may be available into low
impedance loads. However such loads are often inefficient (and reactive,
which adds to the desiger's headache) so this may be needed for people to
be able to enjoy music using such loudspeakers.

The alternative would be an amp that could deliver 200W into 8 Ohm light
bulbs, but which collapsed in a heap as soon as many real loudspeakers were
used. Since the purpose is to allow the user to listen to music, my
reaction was to ensure a fair amount of current was available if needed.

Slainte,

Jim

--
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