According the DS it is a current driven output stage with idle current of 20-30mA (Class-A region).
NAKAMICHI 620 SERVICE MANUAL Pdf Download | ManualsLib
NAKAMICHI 620 SERVICE MANUAL Pdf Download | ManualsLib
Most amplifiers work in class B, that means having an optimized bias for the lowest crossover distortion.
I suggest you read this Douglas Self's book :
The Audio Power Amplifier Design Handbook
The output impedance of the VAS is not so high and the input impedance of the followers are not so low that we can speak of current driven.
The output stage looks a bit like a "diamond" (NPN loaded by CCS + PNP) and (PNP loaded by a CCS + NPN) as introduced by Audio Research first solid state amplifiers, I think, but here with more devices.
For a bit less distortion, the emitter resistors of Q017 and Q018 should not be connected to the output rail.
Annoying discussion, A or A / B or B or C or...
There are technicians who claim that real class-B does not exist because the transistor characteristics do not allow for a clear classification. Consider infinitesimal calculus.
Ultimately, the vast majority of so-called class B amplifiers are either class AB with a very low quiescent current, or they are class C constructions such as B. current dumping.
There are technicians who claim that real class-B does not exist because the transistor characteristics do not allow for a clear classification. Consider infinitesimal calculus.
Ultimately, the vast majority of so-called class B amplifiers are either class AB with a very low quiescent current, or they are class C constructions such as B. current dumping.
This is different from what I've heard. I've heard that most SS power amplifiers are class AB. Class B is produced in a very small number. Nakamichi 620 may be one of them.
Many people say there is much distortion produced by Class B, but I'm interested to this class after I've heard the Nak 620 and want to listen to other class B amps.
not commercial but my diy class-b, current driven outputs, distortion 0.00x, good harmonics profile
Low distortion current driven Class-B output stage
measurements
Low distortion current driven Class-B output stage
Low distortion current driven Class-B output stage
measurements
Low distortion current driven Class-B output stage
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It depends on what exactly you mean by AB and B. Some people use AB to describe a stage just biased into 50% conduction, based on the fallacy that class B means unbiased. Others use it to describe a stage with 180 degrees conduction angle. I am in the latter camp, along with Douglas Self and every RF engineer on the planet. And, apparently, Nakamichi.
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