Q: I wonder if there could be a sonic comparison
posted between this unusual design amp and some recognised reference
amps, AKSA etc. I presume some people have now built a variant of this
design and feedback on sonics would be helpful for others thinking of
embarking on this path.
A: "Recognised reference
amps" you’re kidding I presume?
If you manage to identify a reliable example of what constitutes the
perfect amplifier, let alone any typical group of listeners who would
agree with your choice when applied to a real-world listening
environment, I’d like to hear about it?
If somehow you were able to make the amplifier ‘disappear’ you would
still hear anomalies attributable to the rest of the system, and
probably more clearly than if the amplifier was adding its own signature
to the performance.
Susan’s design which she has based on the concept of “wire with gain” no
matter how well carried out, will still leave room for an argument along
the lines of “what sort of wire?”
From a (relatively brief) listening experience, and from some
preliminary experiments of my own using the Zeus output configuration,
it is my opinion that her design has some interesting features which set
it apart from the usual configurations.
1: It uses transformer coupling to the speaker and hence gives an extra
degree of autonomy to both components. When transformer coupling is also
applied to the input side (as in conjunction with the line stage) this
gives some additional freedom from ground loop generated noise and
distortion and can also remove the need for an input capacitor.
2: By use of a very low impedance solid state output devices on the
primary of the transformer, back EMF from the voice coil can be absorbed
and rendered relatively harmless to the integrity of the sonic picture.
3: By optimising conditions to achieve very low levels of generated
distortion in a circuit with adequately wide frequency response there is
no need to introduce negative feedback into the equation. NFB can be a
highly effective destroyer of imaging and soundstage accuracy, due to
its unavoidable effect on phase response when applied to even well
If you are rash enough to attempt to apply NFB across ANY coupling
transformer you will further compound the problems. Fortunately for the
NFB brigade most composite systems are already so deficient in the phase
domain that gross NFB generated phase errors are able to slip by largely
As predicted by theory, initial auditioning of the Zeus power amplifier
reveals a smooth surefooted presentation that is free of grain and
artefacts of the type that induce listener fatigue.
It was not possible to focus on anything in particular that would
identify the presence of the amplifier which suggests wide frequency
response and good transient ability. This makes comparison with other
amplifiers in other systems somewhat difficult. Even very highly rated
amplifiers can and do interact with the connected source and load and
hence sound ‘different’ in different systems. It is likely from what I
have observed so far that the Zeus will be largely free of this variable
but its presence no doubt will reveal the strengths and weaknesses of
other components in the system, making it somewhat unwise to predict
If you are looking for a competent reliable and easy to construct power
amplifier, and one that will readily reveal any shortcomings in other
parts of the system, thus allowing you to make and assess intelligent
upgrades, a Zeus offers a lot of performance for relatively little money
and effort. Being such an elegantly straightforward ‘easy to get on
with’ circuit, it would take a high degree of constructor incompetence
to damage. It also has the major advantage that even under the most
catastrophic of DIY failures, your input stage and speakers are
One thing you can be pretty sure it will not do is colour (rose or
otherwise) the sound to complement less able components in the system.
Some complex speaker systems might prefer a higher damping factor but
most should be ok. I’d guess that this promises to be an amplifier
eminently suited to single driver configurations where its excellent
phase coherence can be fully appreciated.
K. Williams -
(Note: references to negative feedback, i.e.
NFB, are referring to external loop negative feedback, not the
follower internal negative feedback):
A friend and I were lucky enough just over a week ago to
get to audition Susan's Zeus amplifier along with the rest of her system
and I have to say we were pretty impressed with what we heard ...
Susan explained that the system did not have any esoteric, hi end,
expensive components - just stuff that she happened to have at the time
when she built the system.
Of course, it is always difficult to know what is contributing what in
an unfamiliar system but the overall sound cannot be better that the
weakest link and overall sound was VERY good.
Over the last 5 years or so I have listened to quite a few home systems
of different friends. Many DIY, some bought. I have also auditioned some
very expensive stuff at dealers and attended a couple of hi-fi shows.
Susan's system seemed to combine good balance of detail, clarity and
dynamics along with a lovely fluidity that made it really easy to listen
to. I regard this combination as very rare. The sound was also quite big
I have heard beautiful sounding systems that sounded somewhat
compressed. I have heard very detailed systems that sound somehow too
analytical or dry or rough. Then there are systems that sound nice and
soft but lack detail.
For me, Susan's system had a special combination of fluidity, detail and
dynamics that I regard as the best I have heard to date. ( not bad
considering some of the systems mentioned above cost £50,000+ ).
I will be ordering my transformers soon and I am really looking forward
to hearing a Zeus amp in my system ( although realistically I think it
will be mid January before this is realised ).
Mikelm - 7th December 2004 - (Reproduced with permission.)
Audiophonics reviews published between 1992 and 1996.
To Be Added.
First Audiophonics advertisement mentioning the Zeus