Harman Kardon 75+ receiver - how is this not cap coupled

[leesonic]

I've been looking at a Harman Kardon 75+ receiver for sale locally. I need another project like another hole in the head, but it looks so cool with the joystick control on the right. Looking at the schematics though, I'm puzzled. How can this this not have a capacitor coupled output? It has two NPN output transistors (2SD332M) per channel, and plus and minus supply rails. But the NPN on the negative supply rail, is that going to work as if it were a PNP?

I know other cap coupled receivers such as the Pioneer SX-626, they use a single rail supply for the power amp, with the two output transistors amplifying the waveform with a DC offset, and then the output capacitor blocking the DC component. But this H/K? The power amp / power supply part of the schematic is shown below.

Maybe I'm too tired to understand it, I've been awake since 4am....

Lee.

 

[blhagstrom]

Quasi complementary amp system.
The drivers are complementary, not the outputs.

Cool units.
I had one for years with a wood case.
Semi modular so recapping is fairly easy.
Excellent old school build.

 

[Goldie99]

I think the quasi complementary amp topology dates back to the early silicon days, when the NPN devices were more reliable than the early PNP's , so it was better to just use 2X NPN, with either a single power rail + gnd, and a coupling cap on the output to remove the 'offset', or split power rails as here, and no need for a coupling cap on the output.

.... probably a bit before your time Lee

 

[ConradH]

Not as elegant as full complimentary outputs, but they work just fine and that circuit looks decent. I'd far rather have that than STK modules, a non-diff front end or even cap coupling.

 

[sregor]

I think you are guilty of over thinking it. Until the late 70's - all HK amps had quasi complimentary direct coupled. Look at 630, 430, 930, citation 12 (and many others) and you see same topology. Only the 330's and a few other early models are cap coupled. My 2 cents...

 

[leesonic]

It's all academic now anyway, since the receiver sold, or is no longer on Craigslist. Lately, I've adopted the attitude where I wait and wait, and if it hasn't sold when the time comes round that I have time to get it, I do. Like the DCM KX212 speakers that someone had brush painted white. They're still for sale...

Lee.

 

[Zeromort]

Very good sounding unit

 

[markoh]

Has anyone tried to compare it with hk730? Are schematics the same?

 

[Lavane]

This must be similar to some of the Realistic designs. I had a Realistic integrated from '75 that at first, I thought was cap coupled when I saw a main filter cap and then two of what I thought at first were coupling caps and seeing all four output transistors were the same. But I saw it wasn't cap coupled at all when I looked over the schematic. One realistic receiver sitting in my garage uses transformers for drivers. I thought it strange since it was built in the mid 70's.