TECHNOLOGY

It took over 10 years of dedicated research in which time
we explored the world of quality amplification. Our goal
was to reach the absolute limits of excellence. In order to
achieve this, one has to evaluate and experience every
available technology in amplification circuits and
components. Our experience to true live music gave us
the opportunity to have a reference. Combined with our
background in electronics and sound engineering we were
able to explore what is possible in high quality reproduction.

There are two schools of how an audio signal can be
amplified depending on the active components used:
Solid State and Vacuum Tubes.

We came to the conclusion that the real dilemma
is not Solid State versus Vacuum Tubes but
Single-ended amplification versus Push-Pull amplification.


PUSH PULL

In Push-Pull class A or class AB two (or bank of parallel)
active components are used, where one sinks current and
the other sources current.In class AB operation the
problem is that crossover distortion produces a cold and
harsh sound. In class A operation most of the times
the two halves are not the same components (PNP with
NPN transistor or P-channel with N-channel mosfet). In quasi-complementary topology where two same
components are used in the two halves, the problem arises
from the different topology e.g. One half NPN transistor
common emitter, the other half common collector. To
minimize distortion various topologies have been used
with different types of feedback. e.g. voltage feedback,
current feedback, nested feedback/error correction, leading
down a one way root to lifeless music. Even when there
are two same halves in a Class A pentode or a triode P-P
amplifier the sound is not as convincingly natural. This
happens because one half acts somewhat as an "active"
current source to the other half and thus loading each other
producing a mechanical sound. An additional problem
is the phase-splliter stage. There is no way it can be done
in a consistent manner with active devices. The conclusion
is that P-P is not the way forward for reaching the best.


SINGLE-ENDED

In Single-Ended amplification only one (or bank of parallel)
active component is used. This demands operation in
Class A, where current flows independently of the audio
signal. Generally single-ended amplifiers are low wattage
tube amplifiers. They provide musical involvement when
realized properly. Most commonly used big output tubes
are 211,845 and 833. The drawback is that in order to
achieve maximum available power they have to be driven
in class A2 (Grid starts to draw current from the previous
stage). The result is a difficult and awkward load for the
driver stage that starts loosing its consistency. E.g. 211 in
pure class A delivers about 12 watts, after this and up to
25-30 watts starts to draw up to 30-50mA. The load that the
driver stage sees is not constant during the full sinewave.
Paralleling multiple tubes, also, is not a solution. Each tube
loads the others in a strange way due to differences
between each other. This causes a harsh and edgy sound.
Also the measured distortion contains more odd
harmonics (3th,5th,7th). Another issue that needs to be
considered is the output impedance. Without feedback this
is normally more than 1,5-2 ohms. The amplifier will alter
its frequency response in loudspeakers with big dips
and peaks in their impedance curve changing the tonal
accuracy of the loudspeaker.


Here are some of our views regarding design solutions:

-feedback: all types that are returning from the output of
one stage to a previous one, destroy the musical
experience. Feedback is trying to correct something that
has already happened. The more you include to the
feedback loop the worse the circuit sounds. In general it is
the most unnatural technique used in designing amplifiers.

-followers: Circuit topology meaning emitter follower or
cathode follower or source follower. It is a topology that
provides gain nearly times one. This is a 100% feedback
topology. Cold sound and flat image. Instruments
don't float in space.

-symmetrical: one half sees the other as a load.
Theoretically it is a not a contributing load since it is too
high, but it compresses and distorts the images' depth.
Also symmetrical topologies lead to clinical sound.

-balanced (or bridged): Meaning two amplifiers working
in antiphase. For us, meaning that two amplifiers are
in series with the signal. Double the trouble. This
topology is supposed to cancel second order harmonic
distortion. It does however nothing for 3rd,5th,7th etc.

-differential amplifier: The majority of solid-state
amplifiers use at the input a differential amplifier
as a first stage. Usually the feedback is returned to one
leg or some times both legs are used as plus and
minus inputs. We think that always one leg
operates as a follower driving the other half.

-very low output impedance: We hear usually that
an amplifier has very good driving capabilities because it
provides very low output impedance. Although it is good
to have low enough output impedance in order not to
alter frequency response of the loudspeakers, lower
output imp. means more feedback in one or another way,
regardless of circuit topology. Some claim a no-feedback
design with 0,1 ohm output impedance. This most
probably means there is an emitter (or source) follower
at the output: 100% feedback.


THE SOLUTION

Single-ended amplification provides something that no
P-P could ever provide. It is closer to the "real thing",
music flows in a way that happens only in live
unamplified performances. By incorporating a unique
single-ended mosfet output stage we achieved on having
all the virtues of a big single-ended triode output stage
without having its drawbacks. We manage to have more
power and drive with transparency, musical involvement
and above all with music flowing naturally. With only
two gain stages, tube input with tube rectification
and mosfet output, without using overall feedback we
achieved on having output power more than 100 watts,
enough gain, and sufficient output impedance. The result
is an amplifier that produces music in its true natural scale,
but above all it brings you as close as possible to the
music event, to feel the music rather than hear it, to be
touched and overwhelmed by the deeper feeling, with music
emerging and not only sounding in a clear undistorted way.