darTZeel Audio NHB-108 - Manual (Page 21)

darTZeel NHB-108 model one Audiophile's technical manual Page 21 of 28
7. Power supplies
7.1. From mains to loudspeakers
More and more, audio manufacturers are
insisting on the quality of the power sup-
plies. They are quite right!
After all, the electric energy fed to your
loudspeakers comes from the power sup-
ply and nowhere else.
The audio circuit itself is really just a sort
of regulator for this energy.
The better the quality of the source en-
ergy, the easier the task of modulating it
into sound waves.
This modulation is truly the audio signal
you listen to. It is this same signal that
will deliver the energy supply to your
loudspeakers, which in turn will excite
the air molecules to vibration, producing
that magical feeling we audiophiles call
"music".
In your darTZeel NHB-108 model one, the
power supplies are not really standard
ones. The amplifier is a true dual mono.
We apologize about stressing the word
"true", but much too often this descrip-
tion is abused.
The darTZeel NHB-108 model one has 2
fully independent power supplies, one for
each channel. The two channels are fully
insulated from each other. The crosstalk
figure speaks for itself, at more than
90dB separation across the entire audio
spectrum.
Toroidal transformers, each of 300VA,
are wound on 450VA cores. Magnetic
fields are thus reduced to the point that
no core saturation can occur, ensuring
clear power output under any dynamic
conditions, without induced hysteresis
distortion.
Cores are grain oriented, and primaries
are electrostatically shielded from the
secondaries, keeping RFI away. The en-
tire units are impregnated in epoxy
resin, eliminating possible winding vibra-
tion.
As seen above, the transformers are also
suspended. Their residual mechanical
noise is so low that even in very quiet
listening rooms, you will not be disturbed
anymore.
Immediately after the rectifier bridges,
the DC sources are filtered by 6 paral-
leled, 22mF, capacitors for each rail,
totaling a whopping storage energy of
230 joules per channel. Not so bad for a
100 watter…
The copper bus bars, CNC machined in
5mm-thick blocks, connect the filtering
capacitors' leads together, creating as it
were a low impedance power supply “on
the spot”. The output transistors are lo-
cated only a few centimeters away from
the power supply: hence no problem in
case of high current demand.
Our power supplies are filtered only,
avoiding any dynamic limitation for
which regulated supplies are often re-
sponsible. Fully regulated supplies have
very low output impedance through high
feedback regulation (NFB everywhere!).
When huge dynamic changes arise, the
NFB is in a state of overflow and the
output impedance suddenly increases
dramatically, causing dynamic compres-
sion. Does this remind you of some-
thing?
7.2. Voltage or current?
For purity reasons invoked earlier, the
output stages of darTZeel NHB-108 model
one only have a single bipolar pair of
output transistors.
The vast majority of amplifiers of over
50wpc use paralleled transistors, from 3
to 24(!) – or even more – pairs. The
purpose of this parallelism is to obtain a
greater output current, as required by
low impedance loudspeakers.
This method is much cheaper than the
solution used in the darTZeel NHB-108
model one, power transistors being much
less expensive than in the past.
But parallelism has numerous draw-
backs, as follows:
- The need to match components for
even heat spreading.
- The signal path is divided into multi-
ple parallel paths, leading to TD
(Temporal Distortion) by degradation
of propagation time delay uniformity,
each path not being of the very same
length.
- Much longer mean path length, con-
siderably increasing the output im-