Technical Description - McIntosh C28 Owner's Manual

Technical Description

Basically, each channel of your C 28 consists of
four main parts: low level amplifier, high level ampli-
fier, active filters and headphone amplifier. Common
regulated power supplies furnish power to both chan-
nels.
LOW LEVEL AMPLIFIER
Each channel of the low level amplifier is a four
transistor differential amplifier input circuit. Pre-
cise equalization is maintained by the use of negative
feedback and appropriate components specially de-
signed for low noise. Particular attention has been
exercised in the use of transistors having exceptional
low noise characteristics. The differential amplifier
stage is the basis for the high open-loop gain of this
portion of the circuit. With a higher open-loop gain
there is ample negative feedback available under all
equalization conditions to ensure an extremely low
level of harmonic distortion. Because equalization
has been designed for minimum error the response
from both tape and records is accurate.
One of the important features of this section is the
use of set level potentiometers in the phono circuit.
The gam of the phono preamplifier stages can be
adjusted from 32 dB to 42 dB to correspond to the
sensitivity of your phono cartridge.
The phono set level controls in your C 28 are de-
signed into the negative feedback loop. They are not
potentiometers at the input or output of the low level
amplifier. This important design consideration allows
the gam to be reduced from 42 dB to 32 dB without
adversely affecting the noise level. Because the con-
trol is in the feedback loop the level of noise and
distortion is reduced 10 dB but the maximum input
voltage that this section can handle is increased by
10 dB. With 42 dB of gain in the phono section the
maximum input voltage that the low level amplifier
can accept without overloading is 150 mV at 1000 Hz.
When the gam is reduced to 32 dB this section can
accept over 0.5 volt without overloading at 1000 Hz.
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