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
