PIONEER SPEC 4 POWER AMPLIFIER

Dynamic 150 + 150 Watts Power Output, Generous High-power Design

The Spec-4 employs DC construction which excludes capacitors from the NFB circuits and uses a dual transistor differential amplifier with a current mirror circuit in the 1st stage. This provides a stable operation and also high gain over a wide frequency range. The pre-driver stage is a class A amplifier circuit with a regulated current circuit for the load. This makes for high-gain amplification with superior linearity.Furthermore, there is an overdrive limiter and power limiter circuit which is designed to protect the power transistors and make for added reliability.The power stage employs a 3-stage Darlington pure complementary parallel SEPP circuit.The SPEC-4 delivers Continuous Power Output of 150 watts per channel, min. RMS, at 8 ohms from 20 Hertz to 20,000 Hertz with no more than 0.01% total harmonic distortion.

Completely Independent and Perfectly Stable Left / Right Power Supplies

The mighty power supplies are completely separated for the left and right channels. Also, each channel is provided with two 22,000uF large-capacity electrolytic capacitors and large transistors with a superior regulation. They achieve outstanding channel separation and a clear, powerful reproduced sound, in addition to the wide frequency response. There is a built-in surge killer circuit to suppress inrush currents from the power transformers and high currents which charge the electrolytic capacitors. This circuit ensures that none of the parts are affected by these adverse currents.

Protective Circuits Composed of Fast-response Relays and Electronic Circuits

Each channel is protected by a DC and over current detection relay circuit. In the event of the speaker terminal shorting due to poor connections or when DC current is generated in the output, the output circuit is immediately disengaged and the speakers and transistors are safeguarded against any possible damage. The protective circuits also function as muting circuits when the power switch is turned on and off.

Peak Level Meters with Outstanding Waveform Response

This power amplifier incorporates logarithmic compression peak meters with a wide scale (-40 -+3dB). With 8-ohm speakers, they allow the output to be read out from 0.01W to 300W. Moreover, the meters feature a fast response for peak signal indication. In addition to the peak output reading, it is easy to interpret the dynamic margin with respect to the SPEC-4’s clipping level.

Input Level Controls with dB Calibration

The SPEC-4 is equipped with input level controls with direct readout attenuation values (-dB). These can be used to continuously adjust the input levels for each channel in accordance with the rated output voltage of the preamplifier. In this way, the SPEC-4 can perform the proper gain control according to the preamplifier’s output level. The preamplifier will thus be used in the condition possible for the best S-N ratio and distortion characteristics.

Stylishly Professional Front Panel Design

Just as you would expect from a sophisticated system, the SPEC-4’s front panel is professionally designed with the large level meters in the center. Also. The front panel’s dimensions allow the model to be mounted in an EIA standard rack, just like real professional-use amplifiers.

SPECIFICATIONS

ICs………………………………........................................2

Transistors………………………………...........................61

Diodes……………………………….................................62

Power Amplifier

Circuitry………………………………Current mirror loaded differential Amplifier

3 stage darlington parallel push-pull

Direct-coupled OCL. (DC amplifier construction)

Continuous Power Output of 150 watts * per channel, min. RMS, at 8 ohms from 20 Hertz to 20,000 Hertz with no more than 0.01% total harmonic distortion, or 180 watts per channel at 4 ohms from 20 Hertz to 20,000 Hertz with no more than 0.03% total harmonic distortion.

Total Harmonic Distortion (20 Hertz to 20,000 Hertz, 8 ohms)

Continuous rated power output………………………………................................0.01%

75 watts per channel power output……………………………….......................... 0.01%

1 watt per channel power output……………………………….............................0.01%

Intermodulation Distortion (50 Hertz to 7,000 Hertz = 4:1, 8 ohms)

Continuous rated power output………………………………................................0.01%

75 watts per channel power output……………………………….........................0.005%

1 watt per channel power output………………………………........................... 0.005%

Frequency Response………………………………...............5 Hertz to 100 kHertz +0/1 dB

Input (Sensitivity / impedance)……………………………............................1V/50k ohms

Output

Speaker……………………………….................................................4 ohms to 16 ohms

Damping Factor (20 Hertz to 20,000 Hertz, 8 ohms……………………………….........100

Hum and Noise (IHF, short circuited, A network………………………………........11 5dB

Miscellaneous

Power Requirements………………………………...................................AC 120V 60 Hertz

Power Consumption………………………………..........................................760 watts (UL)

Dimensions………………………………..............................480(W) x 187(H) x 445 (D)mm 18-7/8 x 7-3/8 x 17-7/16 in

Mcintosh MC 250 Power Amplifier

Technical Description A two stage preamplifier with three transistors in each channel increases the input voltage 16 dB. There are 13 transistors in each power amplifier section. The two stage preamplifier is fed to a pair of matched transistors arranged as an emitter coupled amplifier with two inputs and one output. The signal from the preamplifier section connects to one of these inputs. Both AC and DC negative feedback are applied to the other input. This large quantity of feedback is used to reduce noise and distortion. The signal is then fed to a voltage amplifier. The voltage amplifier is followed by two driver transistors. The output section is arranged as a series pushpull amplifier. The power transistors used in the output section of your MC 250 are selected for their high power dissipation capability, wide frequency response, and large "safe operating area." In addition, each power transistor is given four separate tests before it is put in your MC 250. This additional testing makes sure your MC 250 will deliver its rated power from 20 Hz to 20,000 Hz with low distortion and complete reliability.

The power transistors are mounted on oversized anodized heat sinks. The heat sinks assure that under normal operation the transistors will operate at a low temperature. If temperatures increase due to a shorted speaker, or restricted ventilation, an automatic temperature sensing device turns off the MC 250. The device operates automatically at a preset temperature. The MC 250 will turn on again when the temperature has returned to normal limits. This additional feature gives your MC 250 complete reliability under the most extreme operating conditions. The output stages are matched to the load by the Mclntosh autoformer. The Mclntosh autoformer is carefully wound using Mclntosh trifilar winding and interleaving techniques. Trifilar winding and interleaving gives the autoformers exceptional bandwidth. The autoformers properly match the power transistors to 4, 8, and 16 ohm loads at all audio frequencies. The use of the Mclntosh designed trifilar autoformer makes the Mclntosh solid state amplifiers the only amplifiers that deliver FULL POWER AT ALL SPEAKER IMPEDANCES. You have not been power penalized for your choice of loudspeakers when using the Mclntosh MC 250. Another of the advantages of the autoformers is the 25 volt output for a constant voltage distribution system. With the MC 250 several sets of speakers can be operated independently throughout your home.



To further insure reliability a special power output SENTRY MONITORING CIRCUIT prevents failure of the power output transistors due to excessive mismatch of the output. When your MC 250 operates normally the SENTRY MONITORING CIRCUIT has no effect on signals passing through the power amplifier. If the power dissipation should rise above normal operation, the SENTRY MONITORING CIRCUIT restricts the drive to the output transistors. The SENTRY MONITORING CIRCUIT acts instantaneously for any input signal or load combination. This arrangement assures complete circuit reliability. Only Mclntosh gives you this degree of protection. There are three separate power supply sections, One positive and one negative high current supply is used for the output stages. The other positive supply is used for the driving amplifier stages. All supplies are full wave and use silicon rectifiers. Adequate filtering is used to assure an absolute minimum of hum. The power output stage filter capacitors have very high capacity, which allows full power output below 20 Hz. The power transformer is generous in size and runs cool, even under heavy use.