Nakamichi 620

Stereo Power Amplifier (1977-79)

Description

Nakamichi's Complete Mirror design brings a level of performance to class B amplifiers that was formerly associated only with class A amplifiers.

The 620 is closer to a pure class B amplifier than anything else that has gone before. The first stage of the 620 is a differential amplifier with "current mirror" loading. The final section of the amplifier is a four stage push-pull circuit.

All four stages are full complementary direct coupled, and each stage employs a unique double NPN/PNP combination for the positive and negative halves. This design eliminates the errors inherent in even the most carefully matched pairs of NPN/PNP output devices. These errors, furthermore, are eliminated without the use of bias diodes, bias adjustments and high idle currents.

The 620, in fact, idles at approximately 1/20 the current of conventional class B power amplifiers of comparable output power.

This new approach takes full advantage of class B efficiency with the freedom from switching and crossover distortions that was once thought possible only with class A amplifiers.

Specifications

Power output: 100 watts per channel into 8Ω (stereo)

Frequency response: 5Hz to 100kHz

Total harmonic distortion: 0.005%

Damping factor: 100

Signal to noise ratio: 120dB

Semiconductors: 3 x ICs, 46 x transistors, 41 x diodes

Dimensions: 400 x 189 x 248mm

Weight: 12.5kg

Nakamichi 630

FM Tuner Preamplifier (1977-79)

Specifications

Frequency response: 20Hz to 50kHz

Total harmonic distortion: 0.004%

Input sensitivity: 2mV (MM), 100mV (line)

Signal to noise ratio: 80dB (MM), 100dB (line)

Output: 400mV (line), 1V (Pre out), 5V (Pre out Max)

Dimensions: 400 x 170 x 237mm

Weight: 7kg