"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