Owner's Manual

Parasound A 23+ Design Overview

Circuit Designed by John Curl

Parasound design consultant John Curl has been a legend among audiophiles and electronic engineers

for decades. He pioneered measurements to correlate musical accuracy with the materials used in parts,

worked with world-class touring companies, has designed highly coveted audio classics, including the original

Mark Levinson JC-2, Denneson JC-80, Vendetta Phono Preamplifier, and CTC Blowtorch preamplifiers;

master recorders for Wilson Audio and Mobile Fidelity; and the mixing consoles used in live concerts by The

Grateful Dead and the Montreux Jazz Festival in Switzerland.

As our featured amplifier designer since 1990, he has created many products that have earned

Parasound worldwide acclaim, including the Parasound Halo JC 1, JC 2 and JC 2 BP, JC 3, JC 3+ and JC 3

Jr. and JC 5. John is particularly proud of what he and Parasound have accomplished together: “The circuits I

design for Parasound are extremely sophisticated and are typical of products that are far more expensive. I

can’t think of any other audio products that offer nearly as much bang for the buck.”

Parts Selection

Every part within the A 23+ is carefully chosen for its accuracy and reliability. Metal film resistors with 1%

tolerance are selected for their precision and because their values don’t drift as they heat up during operation.

Polypropylene and mica capacitors are used extensively for their superior linearity and low dielectric

absorption. Semiconductors are selected for superior performance in their specific roles in the circuit. Gold

has the best conductivity and corrosion resistance of any metal, so we use high quality gold-plated input

connectors and speaker terminals. The double-sided circuit boards are FR4 glass epoxy for long-term

durability. The chassis is made of heavy gauge steel to safely house the internal circuitry. This attention to

detail when selecting parts makes the difference between a very good amplifier and an outstanding amplifier.

The Power Supply

The heart of the power supply is a 1.3 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 23+ 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 B+ and B- supply rails use high-speed rectifier diodes and four 6,800uF electrolytic filter

capacitors (8 total), 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 23+ 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 A 23+ 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 23+ is in full operation.