Inside a Technics Amp

[Tenson]

I opened up a Technics amp that seems to use a massive chip for the power amp section. The chips are huge compared to offering from National Semiconductor for example.

It is quite interesting find the chip is actually a plastic cover on a small circuit. Have a look at this

It is made by SVI so it says on the plastic cover. It works really well though, as good as any modern amp in distortion aspects though noise is a little higher than the best I've seen. Anyone ever heard of SVI, not a lot of detail on the web?

I've also seen Technics amps that say 'New Class A'. Is this different than the amp here, is it newer or older etc?

 

[RobHolt]

IIRC 'New Class A' using sliding bias and claims to bring some benefits of Class A with much better efficiency.
Technics have used variations on this theme for the past 30 years.

Interesting circuit though.

The power transistors inside my old Pioneer SA9800 look extra large rather like the 'chip' in the technics. In the case of the Pioneer each amp chip has multiple parallel wired transistors and emitter resistors on one die. Improves power handling (per chip), gives excellent thermal tracking and improves (very) high frequency specs.

 

[felix]

That's a nice discrete hybrid - you are looking at the dies of the output devices! I believe that's an early implementation; later Class-AA lumps I've seen are definitely encapsulated like the Hitachi / STK integrated amp chips.

Yes 'Class AA' is known to be heavily-based on the Dr Sandman 'Class S' approach - I have read it was close enough that Sandman lost a claim for patent infringement

Dr. Sandman's 'Class S' is elegant in a similar way to Quad's current dumping, though not the same. It uses a big dumb Class B amp to drive the load to 'meet' the output of a small-capacity, good Class A amp - like two arms of a bridge amp but doing impedance transformation rather than Quad's feed-forward solution. Neat stuff.