06
Simple amplifier stage configuration
The cascode bootstrap circuitry in the
PMA-SA1 achieves ideal characteristics at the
power amplification stage and ensures stable
operation. This solution simplifies the configuration
of the power amplification stage and allows the
amplifier to reproduce music with total purity. The
stable operation and drive capabilities of the
UHC-MOS also help eliminate sources of resistance
that degrade the quality of the musical signal. This
produces a circuit configuration in which the output
stage, equipped with powerful drive capabilities, is
directly connected to the speakers.
All-stage balanced amplifier
configuration, to protect clarity of
musical signals
The PMA-SA1 has achieved a balance among
all stages. Since a balanced configuration makes it
possible to keep internal voltage at a low level,
superior devices for low voltage can also be used.
Furthermore, since noise and interference between
circuits can be suppressed and output current to the
speakers is completely separated from the ground
circuit, the speakers are driven purely by the output
stage, giving the PMA-SA1 superior drive capabili-
ties. The resulting sound features a truly realistic
spatial expression and the music is full of life.
Inverted ∑ Balance Circuit, realising
a balanced amplifier for high sound
quality
The PMA-SA1 is endowed with an Inverted ∑
Balance Circuit that supports both balanced and
unbalanced input. This design does not require
separate conversion circuits in the preceding stage
but allows the signal to be input directly to the
power stage in a balanced configuration. Along
with the UHC-MOS of the output stage, this circuit
adheres to the principle of "simple and straight" to
ensure a beautiful, transparent sound.
High-grade volume control
The PMA-SA1 has a 50mm-diameter volume
control for ultimate audio performance. Low-distortion
carbon ink and a multiple-contact, gold-plated wire
brush have been used to ensure faithful music
playback and enable highly precise volume control
with maximum attenuation of -120 dB. Superior
sound quality and channel separation are
achieved through the use of a machined copper
case that shuts out the unwanted influences of
external vibration or noise.
Aluminum transformer case and
capacitor holder
Since the transformer is the largest source of vibra-
tion inside an amplifier, the transformer has been
placed into a highly vibration-resistant sand-cast case.
Also, since the capacitors are particularly sensitive to
the effects of vibration, they have been secured inside
sand-cast holders. These efforts to totally protect the
audio signal from the adverse effects of vibration
ensure that the playback sound is perfectly clean.
Robust power supply for each section
In the PMA-SA1's power unit, the output stage
requiring large current and the voltage amplifica-
tion stage requiring stability are completely isolated
from the transformer coil stage. A large-capacity
electrode capacitor utilising low-impedance
electrode foil and high-quality-sound capacitors of
different frequencies have been combined for use
in rectification. In addition, low-loss, low-noise,
high-speed Schottky barrier diodes have been
used for the rectifier elements. These features
ensure a sufficiently clean, powerful current supply.
The control system including relays has also been
isolated from the transformer coils to eliminate
adverse influences on sound quality.
Input
Conventional System
New Inverted ∑ Balance Circuit
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A1
A1
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Input
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