Parasound Halo JC 5, Owner'S Manual

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15
Relay-Bypassed Soft Start Circuit
When the JC 5 is first turned on, there is a significant amount of in-rush current required to charge the
enormous power supply capacitors. We employ a NTC (negative temperature coefficient) thermistor order to
slow down and suppress this in-rush current and to prevent nuisance tripping of a household circuit breaker.
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 JC 5 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 JC 5 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 JC 5’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.
The Driver Stage
The driver stage provides critical amplification for which we employ a complementary matched pair of
MOSFETs selected for their tube-like sonic qualities. MOSFETs tend to generate less odd-order higher
harmonic distortion than bipolar transistors. This is important because odd-order distortion sounds unnatural
and fatiguing to the human ear, whereas even-order distortion is less offensive because it is consonant, rather
than dissonant. Our MOSFET driver stage prevents the harshness and brittle sound so often found in other
solid state amplifiers.
The Output Stage
The amplifier’s sonic characteristics are established by its input and driver stages. Now, the sole job of its
output stage is to deliver the enormous current and voltage from its power supply to the speakers. Bipolar
output transistors are better than MOSFETS in the output stage because of their higher safe operating area
(SOA) and inherent ruggedness. Each channel’s output stage employs six pairs of high current (15-amp)
bipolar transistors to insure long-term reliability, even with continuous high power operation and challenging
speaker loads. Lightning-fast (60
MHz) transistors respond instantly to complex demands in the musical
signal, virtually eliminating distortions that occur with “slower” transistors. Slew rate limiting and Transient
Intermodulation Distortion (TIM) are simply not an issue in the JC 5.