Quad balanced amps are not designed to be bridged or paralleled. If they were this would compromise the Quad Balanced design.
Thanks,
Ron-C
Yes I was actually just looking at the diagram for the Autoformer as I slide it out of the cabinet to repair this intermittent meter, the common seems to actually be "common" to the push and the pull amplifiers through the windings in Autoformer, with the common above ground.
So you have two balanced amplifiers driving that one autoformer, one feed is the push amplifier the other being the pull amplifier (Or High Side/Low side, or Negative side and Positive side), or at least thats what it looks like to me, so I can see how bridging a bridged Autoformer amplifier is not going to work, you'd be really messing with impedances and the likes, it just wouldn't work especially with the common tap on the input of the Autoformer.
I think they are for all practical purposes bridged already....ie the speaker ground is floating above chassis ground and each output connection is being driven as a difference signal......
Looking at my MC501, compared to say a MC352, schematic this is quite evident even though these units were before the marketing slogan. The 501 has two drive feeds into the output transformer while the 352 has only 1.
I understand you can't bridge a mono channel amp, however it appears this mono amp does have a new/old transformer design....no longer a autoformer but much more like a tube amp where there is a phase inverter circuit.
After looking at the Autoformer diagram on my MC452, there are two feeds going in, and two coming out, separated by a centre tap which is called Common, this common is not the negative speaker terminal as it is on a traditional amp, but rather there is the Negative amplifier terminals which are the black ones, and the Positive amplifier terminals which are the the red ones, nothing odd there, the thing which is the "gotcha" is the Autoformer winding is common to both channels, and this is where it gets tricky.
Interesting, I thought the MC352 was a "double balanced push pull" design....