Mac MA-5100 - Is this a capacitor coupled design?

[mjarve]

Attached is a scan of the schematic of a Mac MA-5100 right-channel amplifier. A friend and I are having a discussion of whether it is a CC design, or DC design. He says it must be capacitor coupled, as all quasi-complementary power amps are CC. I say it is not, as there is no sign of an output cap, and I also point to the h/k x30 series receivers (save the early 330’s and 230’s), not to mention the Peavey CS-800 as evidence that quasi-complementary does not mean capacitor coupled.

He backs up his claim by saying: “Trust me. This was designed before Bart Locanthi's groundbreaking "T circuit" based SA-600. It does not use balanced NPN/PNP devices in the output. They were not even available when the unit was designed!!!”

So who is right? There is pride on the line here!

Click image for larger view...

An externally hosted image should be here but it was not working when we last tested it.

 

[jaycee]

He is talking rubbish. It is a DC coupled design with a quasi-complimentary output stage. Capacitor coupled designs are typically non-symmetric power supply based. I've never seen an amp yet that has symmetric supplies and is capacitively coupled, quasi complimentary or not. If he wants proof tell him to look at http://www.ampslab.com/c200qc.htm, or the Cyrus One amp schematic http://www.tcaas.btinternet.co.uk/cyrus1pwr.gif.

What does Bart Locanthi's T-circuit have to do with anything ? This is simply a way to improve the linearity and crossover distortion in the output stage, it has nothing to do with how it functions.

 

[anatech]

Hi mjarve,
It's direct coupled, no capacitors. Simply put, if you feed DC in, you get DC out (no servo circuit to cancel DC). The output transistor configuration has zero to do with it.
-Chris

 

[mjarve]

That's what I thought.

That is about what I thought. Neither of us are experts, but I know what I know, and that is a direct coupled amp.

On the matter of the pre-amp section, he is right, but I never contested that.