Owner's Manual

14
The Power Supply
The heart of the power supply is a 1.5 kVA toroid power transformer, chosen for its
efficiency, low hum field, and high power rating. Encapsulating this massive power
transformer in an epoxy-filled steel canister assures ultra-quiet performance.
The A 52+ power transformer employs multiple independent secondary windings so that
each amplifier channel has its own power supply, assuring more than ample DC voltage at all
times and under all conditions. It also reduces inter-channel crosstalk that can blur the sound
and impair the correct sense of where instruments, dialogue and effects are positioned.
Each channel’s +/- 80 Vdc B+ and B- supply rails use high-speed rectifier diodes and
two Rubycon custom-made 10,000uF electrolytic filter capacitors, chosen for their low
Equivalent Series Resistance (ESR), dielectric absorption and resistance to high temperature.
In addition, these filter capacitors are bypassed with smaller polypropylene capacitors to
reduce AC ripple in the DC supply and to further eliminate noise and interference that is
generated in AC power lines from computers and other appliances in the home.
Relay-Bypassed Soft Start Circuit
When the A 52+ is first turned on, there is a significant amount of in-rush current
required to charge the enormous power supply capacitors. In order to slow down and
suppress this in-rush current and to prevent nuisance tripping of a household circuit breaker,
we employ a NTC (negative temperature coefficient) thermistor. A thermistor cuts the in-rush
current by approximately 50%. In a few seconds as it heats up to its operating temperature it
it’s essentially a jumper wire with zero ohms resistance. However, the A 52+ goes one step
further for this circuit. After the NTC resistor has done its job of suppressing in-rush current a
relay with gold contacts automatically activates to jump across it to completely bypass it. This
extra step insures that the thermistor does not restrict any current whatsoever when the A 52+
is in full operation.
Audio Circuit Path Topology
Parasound’s circuit topology is a hybrid of carefully chosen discrete transistors that
result in superior performance at each stage. We use JFETs (Junction Field Effect
Transistors) for the input voltage amplifier stage; MOSFETs (Metal Oxide Field Effect
Transistors) for the drivers of a second voltage amplifier stage and bipolar transistors for the
current amplifier output stage. Discrete transistors are more sonically accurate than integrated
circuits commonly used by other brands.
Complementary Configuration
Each stage of amplification has transistors fed by the positive DC power supply and
complementary transistors fed by the negative DC power supply. Thus, half of the devices
amplify the positive half of the musical waveform while the other half of the devices amplify
the negative half. This complementary topology is inherently linear, which reduces distortion
and improves sonic accuracy.
The Input Stage
The A 52+’s input stage uses matched pairs of discrete JFETs arranged in a differential
configuration. JFETs are ideal for the input stage because their inherently high impedance is
unaffected by the impedance of source components. (Ordinary bi-polar transistors are low
impedance devices) Differential configuration provides superior noise reduction. These
precision input JFETs are also cascaded to produce the current necessary to drive the
MOSFET drivers in the following stage.