Parasound JC
1 Design Elements
by the Parasound JC 1 Design Team
Introduction
Parasound has worked with renowned designer John Curl since
1989. John’s designs are legends dating back to the early 1970s.
These include the Mark Levinson JC-2, Denneson JC-80 preamplifier, Vendetta
phono preamplifier, electronics for The Grateful Dead, and the master
recorders for Wilson Audio and Mobile Fidelity. He has continuously pushed
the boundaries of sound reproduction and has pioneered measurement techniques
which correlate musical accuracy with the materials used in component
parts. We honor John by designating the JC 1’s model number with
his initials.
After a decade of working together, John Curl enlisted Bob
Crump and Carl Thompson to form CTC Builders in 1999. John creates the
electrical designs, Carl engineers the board designs, and Bob chooses
the parts, wires and connectors, and voices the final result.
CTC’s products have earned the utmost respect from
discerning audiophiles and high end magazine reviewers. Owners of the
CTC Blowtorch preamplifier consider it to be without equal.
John Curl on the JC 1 Circuit Design
The JC 1 power amplifier is the culmination of many years
of de-sign and modification of Parasound power amplifiers. The JC 1 design
is based on a complementary dif-ferential J-FET input stage followed by
two stages of selected push-pull MOSFETs, ultimately driving 9 pairs of
the most powerful complementary bipolar power transistors that are available
today. This gives 400 watts into 8 ohms, 800 watts into 4 ohms, and 1200
watts into 2 ohms, without compromise.
In a sense, the JC 1 design started in 1989 with the original
Parasound HCA-2200. This amplifier worked very well, but it was somewhat
limited in power output and features. A number of prototypes and modifications
over the years then evolved into the HCA-3500. This amp is very powerful,
but it lacks some of the JC 1’s refinements, such as much larger
heat sinks, twice the power supply, as well as better connectors, wiring,
and circuit layout. Also, the JC-1’s class A operating region has
been increased to over 25W, so that under normal listening conditions,
the amp is operating entirely in the class A region, only extending to
the class AB region during very loud musical passages, or ‘special
effects’ such as explosions, rocket launches, etc. These refinements
are the key to a high end product that is above and beyond a well-engineered
power amp design. This makes the JC 1 a world-class amplifier that will
compete favorably with any other amplifier presently available at anywhere
near its price range and power level. I am very happy with the listening
and measured results of this new design.
— John Curl
Bob Crump on CTC Builders’ Role in Developing the
JC 1
State of the art audio design requires three things to succeed
where others have failed: the best electrical de-sign, the best layout,
and the best parts. CTC Builders’ skills encompass the best of these
three separate worlds and our results have been amazing down through the
years.
The JC 1 project arose out of the modifications CTC performed
on the Parasound HCA-3500 between 1999 and 2001. Taking things a step
at a time, various changes to the circuit design and parts yielded an
absolutely wonderful amplifier we called the CTC BBQ. The BBQ was exhibited
at the 2001 International Consumer Electronics Show and it turned heads.
In 2001 Parasound commissioned CTC to de-velop a no-compromise mono am-plifier
comparable to the BBQ and the result is the JC 1.
The JC 1 breaks new ground in parts quality, as there is
nothing in high end audio that approaches the quality of parts we chose
– reflect-ing many years of our continuing parts research and evaluation.
The JC 1 also breaks new ground for circuit boards which
allows such attributes as focus, speed and imme-diacy to shine through
due to the highly unusual, very tight layouts Carl designed. Some of the
outstanding high performance parts are as follows:
-
Vampire Direct gold-plated OFC RCA jacks
-
Neutrik XLR connectors
-
Reliable RT DC bypass and Zobel capacitors
-
Superior Electric binding posts
-
Vampire continuous cast copper signal and DC wiring
-
Nichicon Great Supply raw DC capacitors (132,000uF
in the high current supply)
-
Nichicon Muse DC and local by-pass capacitors
-
Harris hyperfast soft recovery diodes for all bridge
rectifiers
-
Sanken output transistors - the most powerful complementary
transistors available
The JC 1 delivers 25w in class A allowing most amplification
to be contained within the class A mode except for large bass transients.
The unit uses separate power supplies for the input/driver section allowing
the JC 1 to be totally immune to fluctuations in the AC line voltage.
We did the best we could with the electrical design, layout and parts
selection/voicing and we’re confident the JC 1 will surpasses virtually
every other amplifier on the market regardless of price.
— Bob Crump
Carl Thompson on the JC 1 Layout
The real challenge in the JC 1 project was to take John’s
subtle and elegant circuits, Bob’s well-considered parts selections,
and implement everything in an uncompromised, cost-effective manner, without
the performance sacrifices usually associated with other than astronomically
priced equipment. Circuit functions were divided between four separate,
carefully oriented circuit boards (and associated wiring) to minimize
un-wanted circuit interactions. Overall, system signal flow was developed
in concert with the board layout with special emphasis on overall system
grounding. Boards underwent many layout iterations both to optimize manufacturability
and performance. The final main board can handle double the very, very
substantial current of which the JC 1 is capable. This required very wide
matched circuit paths in 2 oz. copper on both sides of the board for critical
nodes.
The JC 1 is very difficult to stress so that audible strain
due to layout-generated resistance will be vanish-ingly small. Part of
the reason for such a beefy layout is the huge power supply that required
fitting four very large filter capacitors plus the separate input stage
power supply on the main circuit board. The separate dedicated input board
is thus more immune to power supply noise and from circuit noise in the
separate auto turn on control board. The JC 1 input board mounts directly
on the back panel for minimum input and input select wiring length. The
layout is absolutely symmetrical with the minimum possible signal path.
Here too, there’s an emphasis on minimum resistance to reduce unwanted
circuit interactions.
I’ve only occasionally said of the design of very highly
refined equipment that it starts to “glow” after a certain point.
It’s when you just know that there are virtually no unquestioned
design elements and there is a deceptive simplicity and wholeness to the
overall package that is apparent to the practiced eye. The JC 1 glows.
— Carl Thompson
Parasound JC 1 Design Overview
The Power Supply
The heart of the power supply is a 10 ampere (continuous!)
toroid 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.
To create the high voltage B+ and B- supply rails for the
output stage, we use high-speed, fast-recovery rectifier diodes and four
enormous 33,000 uF Nichicon electrolytic filter capacitors, chosen for
their low Equivalent Series Resistance (ESR) and dielectric absorption.
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 JC 1 is first turned on, there is a significant
amount of in-rush current required to charge the enormous power supply
capacitors. In order to suppress this in-rush current and to prevent nuisance
tripping of circuit breakers, we employ NTC (negative temperature coefficient)
resistors. These resistors cut the in-rush current by approximately 50%.
Once they heat up, they essentially become a jumper with zero ohms resistance.
However, the JC 1 goes one step further for this circuit. After the NTC
resistors have done their job of suppressing in-rush current a gold contact
relay automatically is activated to jump across the NTC resistors to completely
bypass them. This extra step insures that the resistors do not restrict
any current whatsoever to the power supply once the JC 1 is in full operation.
Complementary Configuration
Each stage of amplification uses NPN transistors fed by
the positive DC power supply and complementary PNP transistors fed by
the negative DC power supply. Thus, half the devices amplify the positive
half of the musical waveform while the others amplify the negative half.
This complementary topology is inher-ently linear, which reduces distortion
and improves sonic accuracy.
The Input Stage
The JC 1’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. Differential configuration provides superior
noise reduction. These precision input JFETs are also cascoded 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 complementary matched pairs of MOSFETs selected for their tube-like
sonic qualities. MOSFETs tend to generate less odd-order harmonic distortion
than bipolar transistors. This is important because odd-order distortion
sounds unnatural and fa-tiguing 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 amplifiers.
The B+ and B- power for our input and driver stages cannot
sag under load because it is supplied by inde-pendent transformer secondary
windings with independent rectification, filtering, and voltage regulation.
This preserves soundstage width and depth even when the JC 1 output stage
is drawing enormous amounts of current.
The Output Stage
The amplifier’s sonic character-istics are established
by its input and driver stages. Now, the sole job of its output stage
is to deliver the enormous amounts of 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. The JC 1’s output stage employs nine pairs
of high current (15-ampere) 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 1.
Class A/AB Operation
Pure class A operation provides the purest sound. However,
an amplifier operating entirely in class A opera-tion would be enormous,
highly inefficient, and generate far too much heat. Class AB combines
some of the advantages of Class A with the efficiency of Class B operation.
It is a compromise that reduces the heat generated in pure class A operation
and the oddorder harmonic distortion created in class B. In class AB,
the driver and out-put stages are always turned on, which provides a nominal
amount of pure class A operation.
At higher power levels, when the musical waveform swings
from positive to negative and vice versa, each bank of transistors is
allowed to rest momentarily. This resting, or quiescent time, makes it
possible to deliver high amounts of power without overheating. It also
makes it possible to use passive cooling and avoid fans, whose noise can
be heard over the music. The JC 1 input and driver stages are 100% pure
Class A while its output stage provides up to 25 watts of pure Class A
-- more than amplifiers selling for three or four times its price. The
result is less fatiguing, more natural sound at a refreshing price.
Total Protection
DC Servo
Direct Current (DC) burns out speakers. Therefore, every
power amplifier must have some way to insure that DC from its power supply
never reaches its + or - speaker terminals. Most amplifiers simply use
trim controls to reduce their DC offset or capacitors to block DC. Unfortunately,
trim controls can allow DC offset to increase over time, and even the
most expensive capacitors in the audio signal path will “veil”
sonic clarity and attenuate bass response.
Parasound power amplifiers incorporate ingenious and fast-acting
DC servo circuits, completely eliminating the need for coupling and blocking
capacitors. The JC 1 is direct-coupled from its input jack to its speaker
terminals. This advanced circuitry never needs adjustment or maintenance.
It operates outside the audio signal path to keep the DC offset at the
output of the JC 1 at a constant 0.00 Vdc. The results are startling clarity,
freedom from listening fatigue, and formidable bass response.
Relay Protection
The JC 1 has a high-quality protection relay with gold-plated
contacts for long-term reliability. This relay functions to protect either
the amplifier, the speaker, or both. When the JC 1 is first powered on,
the relay remains open for three seconds as the positive and negative
power supplies stabilize and reach equilibrium. This prevents annoying
popping or other transient noises. Relay protection also prevents speaker
damage in case of a catastrophic amplifier failure. Any amplifier that
doesn’t use relay protection for its speaker outputs compromises
the safety of the am-plifier and your speakers.
Over-Current Protection
Specialized current-sensing transis-tors are connected to
the output stage of the JC 1 to constantly monitor the current flow through
the output transistors. If the current drawn by this stage exceeds a predetermined
safe level due to a load impedance below 1 ohm or a short circuit at the
speaker terminals, the output relay will open immediately to prevent the
output transistors or other parts from failing.
Fuse Protection
The JC 1 has a separate fuse for its positive and negative
DC voltage rails. These fuses provide backup protection in case the over-current
protection does not work in time, or if an internal part fails. In the
event of a part failure, these fuses halt operation to minimize damage
to additional parts.
Chassis
The JC 1 chassis is heavy gauge aluminum. Aluminum is non-magnetic
and cannot be energized by high voltage and current flow, thereby removing
a potential cause of “smearing” or other audible in-trusion.
Parasound JC 1 Specifications
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