Magenta ACRH-1, User Manual

ACRH-1 Hybrid integrated audio amplifier

It is well known that a good preamplifier is the heart of an
audio system.  With this in mind, Margules Audio has
undertaken the task of developing an integrated amplifier that
blends an extraordinary tube preamplifier with an excellent
solid-state power amplifier

,

 thus allowing the end user the

ability to upgrade and/or customize his system based on the
preamplifier.

For example:  perhaps the owner of an ACRH-1 wants to
upgrade the system so he buys a tube amplifier.  In this case
the internal power amplifiers of the ACRH-1 can be used with
an add-on component from Magenta such as an active
crossover to power a subwoofer.  Or to power another pair of
loudspeakers controlled remotely by an external controller.  Or
a quad power unit that, when connected, will convert the unit
from 75W/channel to 220W/channel.

Also, with an external processor, the ACRH-1 may be used to
power a pair of surround speakers.

Description:

Preamplifier section

Tube Preamplifier

The preamplifier unit is based on two dual triodes (12AU7) per
side that act as unity gain buffers coupling

the source and the

power amplifier.  The circuit is based on the knowledge and
experience acquired in developing the highly acclaimed
Margules SF220r.

Regulated Power

The power supply of the preamplifier is fully regulated. Good
regulation reduces the loss of signal integrity that occurs when
the signal itself shifts the preamplifier's operating point. The
filament supply is DC (not AC) for minimum hum. It, too, is
regulated.

Remote-Control Operation

The remote operation is unusually versatile. Besides input,
volume, on and off, you can also switch the AC power to
associated equipment drawing up to 20 amperes (2500 watts).
All input switching is through electromechanical relays. The
audio signal never passes through a semiconductor device.

Amplifier section

DC coupling

The topology of the power amplifier is designed in such a way
that all coupling is direct thus avoiding interstage capacitors that,
in most cases, result in higher distortion.

All discrete bipolar transistors

The power amplifier does not utilize any integrated circuits.

Variable Bias

The output stage is designed with a variable bias.  This optimizes
the operating point of the semiconductors to avoid the typical
overheating in Class A operation and reduce the Class B
distortion.

The ACRH-1's innovative design is complemented with precision
metal-film resistors and a silver coated PC board.