14
design negative feedback circuits so they contribute
to the extremely low distortion performance expected
from a McIntosh amplifier. The typical McIntosh
owner would never accept the approximately 100
times higher distortion of many non-feedback designs.
Double Balanced Push-Pull design is used from in-
put to output. Each half of the amplifier contains com-
plimentary balanced circuitry. The resulting double
balanced configuration cancels even order distortion.
Refer to figure 14.
All transistors are selected to have nearly constant
current gain over the entire current range they must
cover. Output transistors in particular, have matched
uniform current gain, high current bandwidth product
and large active region safe operating
area. These Power Transistors are the
very latest in semiconductor technology
and incorporate a new design known as
ThermalTrak™. Refer to figure 15. This
allows for the instantaneous and accu-
rate monitoring of the Power Transistor
Temperature. The MC1.25KW Power
Output Circuitry has a specially designed
bias circuit to take full advantage of the
ThermalTrak™ Power Transistors and thus precisely
controls the power amplifier operation over a wide
range of music conditions with the benefits of lower
distortion and cooler operation. Precision metal film
resistors and low dielectric absorption film capacitors
are used in all critical circuit locations.
The output signals of the two balanced circuits are
coupled together in the unique McIntosh MC1.25KW
Output Autoformer. It provides low distortion power
transfer at frequencies from below 20Hz to well
beyond 20,000Hz with optimum impedance points of
two ohms, four ohms and eight ohms. The unequaled
Technical Description
McIntosh Laboratory, the company who introduced
the world’s first amplifier that could be called “High
Fidelity”, has done it again. The McIntosh engineering
staff has created a power amplifier without compro-
mise, using the most advanced McIntosh circuit design
concepts. Refer to figure 13.
A continuous average power output rating of 1,200
watts and with an output current of 200 amperes,
makes this one of the most advanced and most power-
ful amplifier McIntosh has ever manufactured. The
distortion limits for the MC1.25KW are no more
than 0.005% at rated power output for all frequencies
from 20Hz to 20,000Hz. Typical
performance at mid frequen-
cies is less than 0.002%. The
true distortion readings on the
MC1.25KW are so low, it takes
special measuring techniques
to make accurate readings. The
MC1.25KW can deliver the best
possible performance from any
type of high quality loudspeaker
system.
Creating an amplifier with
this level of performance did not
come easily. Many months of de-
sign, testing and measuring were
required. Extensive controlled
listening tests, the ultimate form
of measuring, were made before
the final design was accepted.
Design Philosophy
The design philosophy incorpo-
rated in the MC1.25KW involved
several different techniques, all
based on sound scientific logic.
Every stage of voltage or cur-
rent amplification must be as
linear as possible prior to the use
of negative feedback. McIntosh
engineers know how to properly
Figure 15
Figure 13
