The "Dual Quad 84" amplifier- Now we're playing with POWER...

There was no reason to run separate voltage amps, since there could not be separate feedback loop signals (since the secondaries were paralleled, there's only one feedback signal source).

Perfectly sensible. I was just curious how close to Bogen's method you got. Single voltage amp seems like it would help make sure the drive to the two inverters is the same too, no chance of tube variables becoming one more thing to worry about.

Looks great too.
 
Would it be fair to assume that the power output would be similar to a more conventional PPP design?
 
Would it be fair to assume that the power output would be similar to a more conventional PPP design?

Yes. Power output is primarily dependent on the limitations of the output tubes used, in the end. But, this setup, with these particular output transformers, seems to have power bandwidth in excess of most other designs, especially in the bottom end. It really does seem to not be limited in the bass at all- it's funny, as subjectively, it sometimes seems like less bass than other amps I've had on the bench- but the fact that the speakers are driving almost to the stops, and the bench CD player is skipping, means that there's some serious energy down there. The likely explanation is that there's a lot more FUNDAMENTAL frequency output (20-50Hz) and less distortion harmonics (which makes the bass sound "big", but at a cost of accuracy)...

Regards,
Gordon.
 
Perfectly sensible. I was just curious how close to Bogen's method you got. Single voltage amp seems like it would help make sure the drive to the two inverters is the same too, no chance of tube variables becoming one more thing to worry about.

Looks great too.

Thanks!

With just one voltage amp, it's potentially avoiding not just tube variables- but possible tolerance variations in components and stray capacitance in the feedback loop itself, that with multiple feedback loops, then paralleled, could cause relative phasing errors and other issues. That could turn out to be a real complicated mess- everything from oscillation, to comb filtering, and the like...

Regards,
Gordon.
 
Great looking build, GW. I didn't know this could even be done. But the question running around in my mind is..., could this also be done with mismatched OPTs? Where one would excel at bass output, and the other at HF? Kinda' like running bi-amp, but with one output. Would their be any advantage to this? Or would it be a trainwreck?
 
I think you'd want to build that as separate amps and put yourself a crossover in front of it to end up with a bi-amp configuration. The feedback with two different transformers would never work right.
 
Now that toroidal tranys are becoming more and more popular, someone needs to start making bells for them with mounting feet so they can be mounted vertically on top of the chassis. If there are any I haven't seen them.
There's a photo in post #5 of my CatSkin amplifier thread showing one way to solve this problem. That potting compound isn't cheap, however.
 
I think you'd want to build that as separate amps and put yourself a crossover in front of it to end up with a bi-amp configuration. The feedback with two different transformers would never work right.

Yes- this is actually one of the reasons I decided to separate the two transformer/power tube sets as much as possible, per channel. Even the usually-trivial production tolerances between two ostensibly identical (same make and model) transformers, could cause issues with matching...

Regards,
Gordon.
 
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