In message , Stewart
Pinkerton writes
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.

Not staying in Class-A of course :-)
--
Chris Morriss

"Jim Lesurf" wrote in message
...
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 Kraken itself is inside a half-width case, with an external transformer
in a case of its own.

Originally the Kraken was supplied with a single torriodal transformer
inside this case, with room for a second transformer, as a sonic upgrade.
Later models were supplied with the dual transformer PSU as standard. Might
these differences be the cause of the review contradictions?

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.

Sorry about this. Most of the scans and specs are my own, which I try to
list as (still large) JPEGs. Because the site is an "archive", I've tried to
preserve the original source material and make that available, rather then
provide transcripts. To my mind, the originals reviews, brochures and
instruction manuals hold greater authenticity and are more interesting
artefacts.

The large PDFs you refer to are created from scans of the original product
brochures, which I believe are fairly rare. I don't believe that these
contain any further spec. not otherwise listed as text (laid out in tables)
on the product pages themselves. The brochures are curios and as a part of
the sites "archive" function. If spec in a brochure is not viewable as text
on a given product's page, please let me know and I'll update the page in
question.

I could use some OCR software to provide transcripts in parallel, but the
time required to carefully proof and edit these (given the surface quality
of much of the source material) isn't available to me right now, and this
would still be my second choice compared with offering the original
material.

Occassionally, someone is kind enough to create their own scan and send it
to me too. Often these are great, occassionally they aren't.

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. :-/

Really? I'm not aware of any Kraken-related file larger than 4MB -
"kraken_mk2_brochure.pdf". Admittedly this is large, but it is a separate
"download" and not embedded onto any one page. I've just checked and the
entire site is 54MB, so am uncertain which file you are referring to -
please advise.

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

Jim Lesurf 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 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.


Jim, John and Stewart, thanks for the explanations. I may have to hit
the books again, I can't believe how much stuff I have forgotten!

You'll find links to three reviews of the Kraken Integrated (+ lots of
other info) he

http://www.alchemisthifi.info/ranges...pd6_integrated
_amplifier.htm#downloads

There is also info about the separate (and SUPERIOR!) Kraken pre & power
amps.

OK. Many thanks for the above links/info. I will investigate. I may also
take copies (if that is OK) of some items as I collect info on UK audio
for
'historic' and reference purposes.

No worries - the info is there for precisely that function.

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.

This prompts me to see if I can find data on the impedance of the 752s as
that may be relevant here.

They are known to be efficient - 91dB, nominally 8 ohms on paper. I don't
have data beyond that, but they were well-reviewed in their day (mid 90s),
so I'm sure there's plenty of into out there. IIRC HiFi World listed them as
"valve-amp friendly" for their efficiency.

What are you studying at the moment?

I may be misunderstanding what prompted you to ask. However.. :-)

If it was my comment about 'exams',

It was )

then I have this week been writing an
exam paper for an MSc class on 'Terahertz Technology'. I am 'retired'. But
as with many ancient/crumbling ex-academics, I do some teaching, etc, for
'theraputic' purposes. i.e. to give me something useful to do. ;-

That said, I spent an hour this morning chopping down a large tree. This
was probably better for me than writing the exam. :-)

You know you're still a man if you can chop down a tree!

Slainte,

Jim

"Chris Morriss" wrote in message
...
In message , Stewart
Pinkerton writes
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.

Not staying in Class-A of course :-)

The Kraken amp is Class-A, BTW - it just occured to me that most people here
are not familiar with it and I that I haven't mentioned this previously.

"Stewart Pinkerton" wrote in message
...
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" )

Correct - although they're fine as PC speakers.

At one point I was driving them with a three box amp - Kraken pre amp and a
pair of bridged Kraken power amps (claimed 165 watts/ channel Class A) :-O

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.

Well then this is a debate about semantics, which isn't really relevant. At
least I know where you're coming from.

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.

Luckily I'm not seeking a replacement at this time.

On Thu, 25 Nov 2004 21:16:56 +0000, Chris Morriss
wrote:

In message , Stewart
Pinkerton writes
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.

Not staying in Class-A of course :-)

Absolutely not! Often skated over by enthusiastic reviewers, but like
any other 'class A' amplifier, it operates in class A only up to it's
rated output of 50 watts into 8 ohms, i.e. 2.5 amps output current.
Ask for more current, and of course it begins to work in class AB.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Fri, 26 Nov 2004 02:32:02 -0000, "JustMe" wrote:

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

This prompts me to see if I can find data on the impedance of the 752s as
that may be relevant here.

They are known to be efficient - 91dB, nominally 8 ohms on paper. I don't
have data beyond that, but they were well-reviewed in their day (mid 90s),
so I'm sure there's plenty of into out there. IIRC HiFi World listed them as
"valve-amp friendly" for their efficiency.

IMNVHO, the best speaker they made since the original Chartwell-driver
batch of 770s.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Fri, 26 Nov 2004 02:33:51 -0000, "JustMe" wrote:


"Chris Morriss" wrote in message
...
In message , Stewart
Pinkerton writes
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.

Not staying in Class-A of course :-)

The Kraken amp is Class-A, BTW - it just occured to me that most people here
are not familiar with it and I that I haven't mentioned this previously.

Anything that runs *that* hot, had damn well better have lots of bias
by deliberate intent!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...
On Fri, 26 Nov 2004 02:32:02 -0000, "JustMe" wrote:

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

This prompts me to see if I can find data on the impedance of the 752s
as
that may be relevant here.

They are known to be efficient - 91dB, nominally 8 ohms on paper. I don't
have data beyond that, but they were well-reviewed in their day (mid
90s),
so I'm sure there's plenty of into out there. IIRC HiFi World listed them
as
"valve-amp friendly" for their efficiency.

IMNVHO, the best speaker they made since the original Chartwell-driver
batch of 770s.

I haven't heard every speaker that they have ever released, but have heard
most from the last 10 years and many from the years before.
They are - to my ears - the best speakers Mission have made to date.