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rellum 29th December 2005 09:55 PM

Simple Killer Amp - Listening impressions
Hello all,

I'm one of the few people here that decided to acquire a Simple Killer Amp.
When I first saw the topology, I was impressed by its simplicity and
specificities. Never saw such a thing, so I ordered a GB150D to test it by
myself. The PCB is nice, well done, compact. I didn't test the mosfets but
the small trannies : well matched. The instructions are clear for a trained
builder. The GB150D can output up to 150W in AB or 50W in class A. I decided
to go for a light class A and built a big dual mono power supply with what I
had on hand. Four 300VA earth screened transformers, two high power bridged
rectifiers, a CRC arrangement wich per rail is composed of 10mF + 1R +
2x22mF low ESR. It's actually oversized because I first made the amps run in
AB mode with 50mA per mosfet to test overall stability. Offset and bias are
stable enough though the trimming principle is incredibly simple. There's no
cap in the signal path and the bootstrap caps are those provided in the kit.
To be able to test it easily and as I don't have a dc coupled preamp on
hand, I replaced the input 1nF polystyrene cap with an 470pf one and added
an 10K ALPS pot. A few other resistor have been downscaled to fit the +-29V
provided by my actual psu. At this time I have no cabinet, everything is on
the floor. When time permits (next year), I will increase the bias (have to
mod some resistors that are actually a safety for not overbiasing) and test
class A performance. From what I can hear now, it will be putted in a
cabinet and not dismantled like many others.

My actual system, a CD14 by Marantz, an AKSA amp, a kt88 cathode coupled
push pull amp and Cabasse Iroise LS given for 92dB/W/m. An easy task and
load for all my amps.

The first thing that impressed me, was the very low residual output noise
with shorted inputs. My 2mV/div Tektronix in diff mode give me a nice 0.6mV
rms noise. I have to put the ear in close contact with my dual concentric
medium/trebble driver to detect something.

The sound is precise, more than my other amps. The bass are tight and very
well damped. No distorsion is audible, totally uncolored on the whole range.
The music flows easily without any agressivity and that's the second thing
that impressed me. It's not usual for me as I most the time listen to tube
amps or hybrids. Overall impression that it's as usual less life-like than a
tube amp but it's so nice and where is the truth ?
I like that amp and will try to get the best from it !

To follow are the listening impressions of Hubert, a friend of mine, who is
way better than me when it comes to put into words what we hear. It's an
experienced speaker builder and he has my AKSA at home too. It's somewhat
different from the usual techno babble we can read on this forum, but will
give you an idea of what you can expect from such a schematic. And of
course, I have no financial interest with the designer of this project.

Happy new year to all,

> Hello Francis,
> Here are my feelings about this new amp we listened yesterday afternoon.
> The stereo was my current system:
> -source: not a true performer but I perfectly know its listening
> characteristics: a Micromega Optic BS using a bitstream DAC, at least the
> "music flow" is preserved in term of fluidity and details remain present.
> -speakers: 1801's Ellis audio, a standed monitor 2-way using a 7" Seas
> magnesium and a 1" Hiquphon tweeter, with a perfect filter (for these
> drivers): not the ultimate performer in bass range but very revealing on
> global bandpass, particularly free of distortions; its relative lack
> in macro-dynamics but only if compared to very good 3-way and...84db
> efficiency...
> IMHO, a real killer amp must be dynamical, revealing, with an extanded
> bandpass from sub-bass to top ends and neutral.
> So, lets go with this one:
> - dynamic: particularly equaly reproduced from sub-bass to top end. Often
> amps have more dynamic in midrange or trebles, this one not; good point.
> a first view I guessed a little lack in this area because of the poor
> efficiency of my 1801's but finaly no.... certainly more "near to the
> than others.
> - details: as with the other solid-state amp I currently use (no no, I
> not write its brand-name but as you know because you are its owner, it is
> well-known and very appreciated kit in the worldwide audioholic community)
> here is THE problem: inner details (micro details) are not on par with my
> tweaked valves-amp Rogers E40a: i.e. the lack of reverberations and
> prolongation of musical notes is obvious, not only in the upper range but
> also in the low-mid. Thus, timbres are affected, but not the musical flow;
> fluidity is preserved even if a few harmonics are "breaked down".
> - frequencies extand: a perfect straight line, allowing to create a right
> image in term of sizes of the instruments and place of recording, in
> relationship with true soundstages; good point.
> - neutrality: the last criterion, for a reason: NEVER HEARD SUCH A
> DISTORTION FREE ELECTRONIC: very, very uncommon: my bad cds aren't so bad,
> they don't become good cds but they are less bad, obviously. NO, my
> aren't harsh sometimes, no the magnesium driver doesn't distord in the
> upper-mid on some cds as I guessed before !!!
> To summarize:
> An almost perfect amp; if the lack of inner details could be avoided, this
> amp would be THE killer for anyone enjoying neutrality but only once
> to a top source and to top speakers at "real" listening level. Others (me
> included) may prefer less accurate electronics, with different listening
> characteristics (notably to compensate less accurate sources and/or
> or to match bad room acoustics or to listen at moderate level), but that's
> another "commonly discutted" issue.
> Thanks again leting me listen to all your electronical buildings, allways
> very instructive.
> Cheers,
> Hubert

dimitri 29th December 2005 11:12 PM

Thank you very much Francis and Hubert
Congratulations, Greg :up:

amplifierguru 29th December 2005 11:19 PM

Well Hi Francis and Hubert,

Welcome to DIY Audio.

Thanks for your honest first impressions of my SKA amplifier and thanks Francis for being one of the very first to 'take a chance' on my first DIY kit offerring.

I hope to hear your further impressions, and, knowing your competence in electronics, any suggestions or tweaks you may come across.

I think it might sound better in a box with neat wiring layout.



mastertech 29th December 2005 11:22 PM

Congratulations Greg :cheers: herve :cuss: hope youre happy:D

AKSA 30th December 2005 03:20 AM

Congratulations, Greg!

Thanks go to Francis and Hubert! :grouphug:

A very good review! :angel:



amplifierguru 30th December 2005 06:34 AM

Thanks Dimitri, Mastertech, and Hugh,

I knew the amp was pretty good but our (wife and I) impressions don't count for much. All kudos go to Francis who has experimented and built himself a creditable amp. I am happy to have facilitated this.

However there a quite a few more who have purchased a pair as a, I suspect, end of year holiday project.

C'mon guys, I can build one in 2 hours to go! Bit longer to get it in a box.



jacco vermeulen 30th December 2005 08:00 AM

Mr Ball,

the SKA can still become DIYaudio component of 2005.
Nice review, congratulations.

Ultima Thule 30th December 2005 12:24 PM

Greg! :up: :)

Thanks also to Francis and Hubert who took the time to verify SKA and write a bit more extended review than normaly seen here on diyAudio, nice reading!

Cheers Michael

amplifierguru 31st December 2005 07:11 PM

Hi jacco,

that would be nice, if deserved.

Hi Michael,

thanks also.

from a small sub-tropical sanctuary island in the Pacific Ocean some 2 hours (30deg) after the international date line -

Happy New Year ALL.


mastertech 31st December 2005 10:54 PM

To summarize:
> An almost perfect amp; if the lack of inner details could be avoided, this
> amp would be THE killer for anyone enjoying neutrality but only once
I f the lack of inner details could be avoided, thats what my friend
jean told me a long time ago, without details and resolution
the amp wont be precise and music will suffer, it all comes down
to the exact implementation of wideband art, all my amp have one
feature in common-"high resolution" thats no neutrality thats


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