Audio Database


McIntosh MC2125 566,000yen(around the 1980 time)

Stereo power amplifier carrying a power guarding system original with a mac.

If an output wave is electrically compared with an input wave and the wave difference becomes 0.5%, a Limit lamp will light up and a Normal lamp will go out in the circuitry which realized the power guarding system by the wave comparator of the mac original design. Moreover, if a wave difference reaches to 1%, the power guarding circuitry operates, it will prevent amplifier carrying out clipping, and distortion will not be reproduced from a speaker, but a speaker will be protected simultaneously.
An input wave and an output wave are compared by IC differential amplifier, and the wave difference by distortion of an output wave is changed into a voltage. Moreover, this voltage is amplified about 100 times and supplied to a Schmidt trigger circuit through a full wave rectifier circuit. Moreover, this voltage uses a power guarding circuitry, and if it becomes higher than the level which a voltage makes turn on a Limit lamp, it will operate a power guarding circuitry.
The Limit lamp is designed switch on the light also when amplifier overloads, and even if overload status is very short, it is turned on between the grades which can be viewed. In this case, meter displays 200W cuttlefish.
To use a power guarding circuitry, it is necessary to set the power guarding switchpoint of a rear surface panel to Normal. Even if this switchpoint is in the location of out, only the Limit lamp operates.

The output signal of amplifier is supplied to an output-terminal through an output transformer. This transformer is designed match sy copy power termination of every impedance, and even if it uses which output-terminal, the maximum output is obtained to all the signalling frequencies.
Moreover, a transformer eliminates that component and this transformer prevents a corruption of a speaker, when it also has the role which protects a speaker in the case of a malfunction of amplifier, for example, a direct current component mixes in an output.

In order to prevent an output transistor overloading, the output signal is always supervised in the monitor circuitry. This circuitry will become a high impedance if an Output voltage becomes more than a rate. When an output becomes a upper, the signal supplied to an output transistor by the monitor circuitry is restricted, and prevents a corruption of an output transistor.

Two output window meter is carried. If there shall be a tick mark of a watt and a decibel in meter and the thumb of a meter range shall be 0dB or -20dB, the peak value of a signal will be displayed on a decibel tick mark, and if a thumb is set to WATTS, an output will be displayed on a watt tick mark.
The tick mark shows the output of the sinusoidal signal by the average, and the peek of a signal also judges it from this tick mark. For example, the tick mark of 120W shows that the moment peek of a signal is 240W.
Moreover, it is also possible to fix and read meter to a upper by a peek hold facility.

The monolithic transistor differential amplifier with few noises to the input side of a power amplifier part was used, and distortion is removed. An input signal and a feedback signal are supplied to this differential amplifier. The circuitry of the following stage is a voltage amplifying circuit which operates with a Class-A. A driver circuitry and an output circuit adopt a complimentary scheme, carry out the operation near a Class-A, and lessen crossover distortion. To the transition of a temperature, this circuitry is designed so that a moderate bias may always start.
The power transistor serves as AB class operation, and, as for the bias current, the safeness is maintained with the thermistor. The output circuit has adopted the para-push scheme of a single ended, and consists of six reliable complimentary power transistors. For the equilibrium nature Emitter-Follower join, a stability is good, and distortion's has decreased and this circuitry is carrying out B class operation without crossover distortion by adoption of the still more original output bias circuitry.


Rating of a mode
Form Stereo power amplifier
Output power
stereo: 120W+120W
15.5Vrms (at the time of a 2-ohm load intensity)
21.9Vrms (at the time of a 4-ohm load intensity)
31.0Vrms (at the time of an 8-ohm load intensity)
43.8Vrms (at the time of a 16-ohm load intensity)
mono: 240W
15.5Vrms (at the time of a 1-ohm load intensity)
21.9Vrms (at the time of a 2-ohm load intensity)
31.0Vrms (at the time of a 4-ohm load intensity)
43.8Vrms (at the time of an 8-ohm load intensity)
Output load impedance stereo: 2 ohm, 4ohm, 8ohm, 16ohm
mono: 1 ohm, 2ohm, 4ohm, 8ohm
Output-power band 20Hz - 20kHz
THD 0.1% or less (at the time of Outputs 0.25W-120W, 20Hz - 20kHz, and both channel operation)
Cross modulation distortion 0.1% or less (at the time of an Output power)
Frequency characteristic
(at the time of 1W output)
20Hz-20kHz+0 -0.25 dB
10Hz-100kHz+0 -3.0 dB
SN ratio 95dB or more (at the time of an Output power)
Output voltage 25V
Dumping factor stereo: 16 (2ohm), 50 (4ohm), 20 (8ohm), 14 (16ohm)
mono: 16 (1ohm), 50 (2ohm), 20 (4ohm), 14 (8ohm)
Input sensitivity/impedance 0.75V, 2.5V (switching type) / 100kohm
The semiconductor used Silicon transistor: 45 pieces
IC: Eight pieces
Silicon diode: 45 pieces
Supply voltage AC120V, 50Hz/60Hz
Power consumption 50W (at the time of a non-signal)
460W (at the time of a maximum rating output)
Dimensions Main unit: Width 381x height 127x depth of 330.2mm
Front panel: Width 406.4x138.1mm in height
Weight 29.5kg (net)
35.0kg (at the time of an original packaging)