Every amp in one
 

Jim Lesurf wrote:



The second was that, although measured to deliver 50W into 8 Ohm loads,
this fell to 36W into 4 Ohm loads. Again, it was mentioned that the
distortion tended to rise as this level was approached. This implies that
the available current may also 'soft' clip at a value that may come into
play with speakers that don't maintain an impedance of about 8 Ohms across
the band. (In such cases the rated power may be misleading as significantly
higher powers may be available but with higher levels of distortion than
used to rate the max available power. Alas this is one of the many things
the HFW review fails to specify.)


Jim, I am confused here. I was under the impression that an amp will
deliver more power into a 4 Ohm load than into an 8 Ohm load.

If the amp delivers 50W into 8 Ohms,

then using P = (I^2) * R

I = sqrt (50/8) = 2.5 A


So, using a 4 OHm load, the amp should deliver

P = (2.5)^2 * 4 = 25 W


However if it was measured to deliver 36W into 4 Ohms,

then I = sqrt (36/4) = 3 A


So I take it the current the amp delivers can change with the load?
(apologies if this seems elementary, I haven't done these calculations
in a while!)

Every amp in one
 

In article , Tat Chan wrote:
JustMe wrote:
"Stewart Pinkerton" wrote in message
...
And Jim's research did indeed lead staright to
what's wrong with the Kraken - appalling current delivery! Into 4
ohms, it can only put out the voltage equivalent of 18 watts into 8
ohms. You just *know* that's going to be audible on peaks...........

In this particular setup (by my PC) it remains at a comparitively low
volume - I doubt I take it to anywhere near a level at which it'll clip,
even with variances from the speakers.

Again you say "what's wrong with the Kraken".

1) Do you know that this isn't by design?

(And I'm not asking for what *you* consider to be good design in an
amplifier, just whether you *know* if this is by design or not).

Excuse me for jumping in, but going back to Jim's finding that,
"although measured to deliver 50W into 8 Ohm loads, this fell to 36W
into 4 Ohm loads", wouldn't this mean the amp was improperly specced or
designed? I am under the impression that most amps would deliver more
power (not necessarily double) into a 4 Ohm load than an 8 Ohm load.

I guess it depends on your standards and how you look at things.

An "18 Watt/8 Ohm" amplifier which also drives 36 Watts into 4 Ohms
would achieve the usual modern standard [1]. Thus the Kraken could
be considered to be perfectly well designed to provide 18 Watts
into a nominally 6 Ohm loudspeaker (i.e. one with an impedance of 4
Ohms minimum).

It just wouldn't get the "50 Watt" label. However, that may be fine.
If the loudspeaker had a sensitivity of, say, = 93 dB at 1 metre for
a nominal 8 Ohm Watt then you could still get unclipped peak levels of
around 105 dB from an "18 Watt" amplifier - which would be fine for a
very reasonable range of music.

[1] Some amplifiers exceed this. The older Krells, for example, continue
doubling output power down to to 2 Ohms or even lower.

--
John Phillips

Every amp in one
 

John Phillips wrote:

In article , Tat Chan wrote:



Excuse me for jumping in, but going back to Jim's finding that,
"although measured to deliver 50W into 8 Ohm loads, this fell to 36W
into 4 Ohm loads", wouldn't this mean the amp was improperly specced or
designed? I am under the impression that most amps would deliver more
power (not necessarily double) into a 4 Ohm load than an 8 Ohm load.


I guess it depends on your standards and how you look at things.

as long as my amp can drive my speakers, I'm happy ... :)

well, that would be one criteria anyway.



An "18 Watt/8 Ohm" amplifier which also drives 36 Watts into 4 Ohms
would achieve the usual modern standard [1].


yes, that sounds right. I got thrown off by the "50W into 8 Ohms" figure


Thus the Kraken could
be considered to be perfectly well designed to provide 18 Watts
into a nominally 6 Ohm loudspeaker (i.e. one with an impedance of 4
Ohms minimum).

so a speaker with a nominal impedance of 6 Ohm has as its minumum
impedance, 4 Ohms? I thought it could go below that at certain frequencies.



It just wouldn't get the "50 Watt" label. However, that may be fine.
If the loudspeaker had a sensitivity of, say, = 93 dB at 1 metre for
a nominal 8 Ohm Watt then you could still get unclipped peak levels of
around 105 dB from an "18 Watt" amplifier - which would be fine for a
very reasonable range of music.


yes, the Kraken would be fine for driving very efficient speakers at a
"reasonable" listening level.



[1] Some amplifiers exceed this. The older Krells, for example, continue
doubling output power down to to 2 Ohms or even lower.

So the newer Krells might not do this? Cost cutting reasons, or they
don't make them like they used to?

Every amp in one
 

On Thu, 25 Nov 2004 10:15:48 +1100, Tat Chan
wrote:

Jim Lesurf wrote:



The second was that, although measured to deliver 50W into 8 Ohm loads,
this fell to 36W into 4 Ohm loads. Again, it was mentioned that the
distortion tended to rise as this level was approached. This implies that
the available current may also 'soft' clip at a value that may come into
play with speakers that don't maintain an impedance of about 8 Ohms across
the band. (In such cases the rated power may be misleading as significantly
higher powers may be available but with higher levels of distortion than
used to rate the max available power. Alas this is one of the many things
the HFW review fails to specify.)


Jim, I am confused here. I was under the impression that an amp will
deliver more power into a 4 Ohm load than into an 8 Ohm load.

If the amp delivers 50W into 8 Ohms,

then using P = (I^2) * R

I = sqrt (50/8) = 2.5 A


So, using a 4 OHm load, the amp should deliver

P = (2.5)^2 * 4 = 25 W


However if it was measured to deliver 36W into 4 Ohms,

then I = sqrt (36/4) = 3 A


So I take it the current the amp delivers can change with the load?
(apologies if this seems elementary, I haven't done these calculations
in a while!)

It's simply that the amp has limits on both output voltage and ouput
current. 50 watts into 8 ohms represents the 20 Vrms limit of its
output voltage, while the 36 watts rating at 4 ohms indicates a low
current capability of only 3 amps.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Every amp in one
 

On 24 Nov 2004 23:56:20 GMT, John Phillips
wrote:

In article , Tat Chan wrote:
JustMe wrote:
"Stewart Pinkerton" wrote in message
...
And Jim's research did indeed lead staright to
what's wrong with the Kraken - appalling current delivery! Into 4
ohms, it can only put out the voltage equivalent of 18 watts into 8
ohms. You just *know* that's going to be audible on peaks...........

In this particular setup (by my PC) it remains at a comparitively low
volume - I doubt I take it to anywhere near a level at which it'll clip,
even with variances from the speakers.

Again you say "what's wrong with the Kraken".

1) Do you know that this isn't by design?

(And I'm not asking for what *you* consider to be good design in an
amplifier, just whether you *know* if this is by design or not).

Excuse me for jumping in, but going back to Jim's finding that,
"although measured to deliver 50W into 8 Ohm loads, this fell to 36W
into 4 Ohm loads", wouldn't this mean the amp was improperly specced or
designed? I am under the impression that most amps would deliver more
power (not necessarily double) into a 4 Ohm load than an 8 Ohm load.

I guess it depends on your standards and how you look at things.

An "18 Watt/8 Ohm" amplifier which also drives 36 Watts into 4 Ohms
would achieve the usual modern standard [1]. Thus the Kraken could
be considered to be perfectly well designed to provide 18 Watts
into a nominally 6 Ohm loudspeaker (i.e. one with an impedance of 4
Ohms minimum).

It just wouldn't get the "50 Watt" label. However, that may be fine.
If the loudspeaker had a sensitivity of, say, = 93 dB at 1 metre for
a nominal 8 Ohm Watt then you could still get unclipped peak levels of
around 105 dB from an "18 Watt" amplifier - which would be fine for a
very reasonable range of music.

[1] Some amplifiers exceed this. The older Krells, for example, continue
doubling output power down to to 2 Ohms or even lower.

On a point of information, Krells before the KAV series were always
specified as doubling rated power right down to 1 ohm. This isn't
repealing the laws of physics however, as my '50 watt' KSA-50 mk II
actually puts out 105 watts into 8 ohms, 195 watts into 4 ohms, and
does indeed drive 440 watts continuously into a 1 ohm load.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Every amp in one
 

On Wed, 24 Nov 2004 18:45:21 -0000, "JustMe" wrote:


"Stewart Pinkerton" wrote in message
.. .
On Wed, 24 Nov 2004 09:40:39 -0000, "JustMe" wrote:

The comparisons I made were using a PC's line out as a source (both CD
and
320kb/s MP3) and a pair of B&W LM1 speakers, at my desk, however I have
made
similar comparisons using more "hifi" sources and superior speakers.

The pre/power amps are currently driving a pair of original Mission 752s
which
together sound staggeringly good.

A fine speaker, indeed.

Whoops - I meant VM1s with regard to the B&Ws, although I doubt you were
referring to those as "fine" :o)

Correct - although they're fine as PC speakers.

And Jim's research did indeed lead straight to
what's wrong with the Kraken - appalling current delivery! Into 4
ohms, it can only put out the voltage equivalent of 18 watts into 8
ohms. You just *know* that's going to be audible on peaks...........

In this particular setup (by my PC) it remains at a comparitively low
volume - I doubt I take it to anywhere near a level at which it'll clip,
even with variances from the speakers.

Again you say "what's wrong with the Kraken".

1) Do you know that this isn't by design?

I don't care. Any SET amp is bad by design.

(And I'm not asking for what *you* consider to be good design in an
amplifier, just whether you *know* if this is by design or not).

See above. I'm using 'wrong' in the context of not sounding like any
other good amplifier. You may well like that 'wrongness', indeed you
have so stipulated.

2) If I like what the amp does, then what is wrong with it, to me?

Nothing, for you.

OTOH, the effects decribed would be not unlike one of the classic
nonlinearities of valve amps, so that may be why you like it.

I cannot comment on this, although I have only heard one or two valve amps
in such a context, so haven't the range of reference as I do with SS amps.

You might say that one man's "nonlinearity" is another man's "sweet".

Indeed, but if seeking a repacement, it's helpful to know *why* the
one you like, sounds the way it does.

What are you studying at the moment?

He's a lecturer in electronics and physics at St Andrews University.
He's not filling in the exam paper, he's creating it.............

I misinterpreted his statement.

Yes, he knows what he's talking about.

That is clear from Jim's posts. He also engages with interest, enthusiasm
and without condescension - I'm sure he's a very good teacher.


--

Stewart Pinkerton | Music is Art - Audio is Engineering

Every amp in one
 

In article , Stewart
Pinkerton
wrote:

And Jim's research did indeed lead staright to what's wrong with the
Kraken - appalling current delivery! Into 4 ohms, it can only put out
the voltage equivalent of 18 watts into 8 ohms. You just *know* that's
going to be audible on peaks...........

OTOH, the effects decribed would be not unlike one of the classic
nonlinearities of valve amps, so that may be why you like it.

Well, the reports that I've now read from the URL that 'JustMe' gave seem
to contradict the HFW review in some respects, so the situation is not
entirely clear.

One 'nice' thing from my POV is that one of the other reviews comments to
the effect that the Kraken is designed to 'soft clip' so my guess on that
may be correct.

There are also - apparently - at least two versions of the Kraken, and
their behaviours may differ. One review (HFC) comments that the version
under test delivers more current (5.5A) than a previous version. They also
say they got a dynamic power of 90W into 4 Ohms.

The review in HFW (Sept 92) said the power was 50W/8Ohms but just
36W/4Ohms. However NK commented that this was distortion limited, so the
actual available power may be higher.

Taking the HFW values literally implies limits of 20Vrms (2.5Arms) into
8Ohms and 12Vrms (3Arms) into 4 Ohms if I calculate correctly.

The claimed 90W into 4 Ohms in the HFC review implies (assuming they mean
short-burst mean power) 18.9Vrms (4.7Arms). The 4.7Arms for a sinewave
implies a peak current of 6.7A which is above the 5.5A value they quote.

Taken at face value, the results seem inconsistent in detail, but make me
suspect two things:

1) That the amp and PSU can deliver higher currents and voltages for short
bursts than for sustained delivery.

2) That the o/p impedance may be 'high' - i.e. above 0.1 Ohms.

One report says the distortion level and frequency response alter as the
amp warms up. This may mean it is a low feedback design, which seems
consistent with (2).

Hence I suspect that this amp may be one that at times measures less well
with continuous sinewaves than it actually performs on music. Can't be sure
though, for the usual reasons - i.e. the reviews may simply contain errors
of fact, and certainly omit details that would tell us more.

BTW Afraid I found the website awkward to use. e.g. Data in large (6MB in
one case) PDFs that are essentially large bitmaps scans of the pages. Not a
very efficient way to provide a few pictures and some lines of text.
Interesting data, but I wish it had been provided as simple HTML, etc.
Took ages to download on my old dial-up connection. Then involved
manipulating 35MB+ bitmaps to read/print. :-/

He's a lecturer in electronics and physics at St Andrews University.
He's not filling in the exam paper, he's creating it.............

Yes, he knows what he's talking about.

My wife might disagree. Depends upon whether I'm agreeing with her, or
not... :-)

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

Every amp in one
 

In article , Tat Chan
wrote:

Excuse me for jumping in, but going back to Jim's finding that,
"although measured to deliver 50W into 8 Ohm loads, this fell to 36W
into 4 Ohm loads", wouldn't this mean the amp was improperly specced or
designed? I am under the impression that most amps would deliver more
power (not necessarily double) into a 4 Ohm load than an 8 Ohm load.

I think others have already explained this apparent puzzle in detail. But,
to confirm, yes, the problem may be that the amp in question cannot deliver
sustained (or peak) currents high enough to allow the power to double.

What is not clear from the reviews/reports I have seen on the Kraken is how
much this occurs with real musical waveforms as opposed to continuous
sinewaves... How much it may 'matter' depends on info we don't have, and
the choice of loudspeakers, music, etc...

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

Every amp in one
 

In article , Tat Chan
wrote:
Jim Lesurf wrote:



The second was that, although measured to deliver 50W into 8 Ohm
loads, this fell to 36W into 4 Ohm loads.

So I take it the current the amp delivers can change with the load?
(apologies if this seems elementary, I haven't done these calculations
in a while!)

The higher resistance loads may mean the amp voltage limits before the
maximum current it can deliver is required. This is almost unavoidable at
some point. Just that Krell and some others put this point well below 4
Ohms, and others do not. :-)

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

Every amp in one
 

In article , Tat Chan wrote:
Thus the Kraken could
be considered to be perfectly well designed to provide 18 Watts
into a nominally 6 Ohm loudspeaker (i.e. one with an impedance of 4
Ohms minimum).

so a speaker with a nominal impedance of 6 Ohm has as its minumum
impedance, 4 Ohms? I thought it could go below that at certain frequencies.

I thought not, BICBW.

[1] Some amplifiers exceed this. The older Krells, for example, continue
doubling output power down to to 2 Ohms or even lower.

So the newer Krells might not do this? Cost cutting reasons, or they
don't make them like they used to?

I have only seen the specs for KSA-80s and other Krells of that vintage,
and this is what I recall, so I cannot say anything for more modern Krell
amplifiers. SP says the doubling goes down to 1 Ohm with the KSA-50.

--
John Phillips