Series power amps using a floating power supply

[rtarbell]

Okay, normally, they say you can NOT put the outputs of two amplifiers in series because both outputs are referenced to ground, and you would be shorting one of the outputs out.
(see attached picture)



==> What if the "top" amplifier had a power supply that was NOT connected to earth ground in any way (it would have a central chassy ground, but the chassy wouldn't be connected to earth)? I think the outputs of the amp would then be floating, and then you could series as many of them as you wanted (conceptually). It would be like bridging an amp, but you could "bridge" the output as many times as you wanted.

==> Would it work?

[Bazukaz]

I was thinking about this.Everything would be OK , but what about input referencing ?

[Tube_Dude]

Originally posted by rtarbell


==> Would it work?

Yes...but you must use a input transformer , otherwise the signal ground from the source will short both grounds together .

But overall is not a good solution, only a conceptual one...

[B Cullingford]

This is of course possible. I think you really need to draw in the power supply as well as the output stage since this is really part of the circuit, you cannot have an output stage without a power source. I think perhaps every variation of power supplies and outputs has been tried, though some are very rare, and difficult to figure out a practical drive circuit.
I think your idea is the same or very similar to a bridged amp with one amp's output grounded, and a common (to both amps) floating power supply. This has been done commercially, I'm pretty sure by Crown for example. The advantage over a bridged amp is that the output to the speaker still has one side grounded (if this is an advantage, it is if your test bench has common grounds for testing power out and you are trying to fix or test the amp).

Sorry I'm not on my computer to draw this out - not too hard to follow I hope. Some where I have a drawing I made of all resonable possible output arrangements, there are not that many. By resonable I mean it does not seem sensible for example to have a bridged amp with one side being SE and the other complimentary, though I guess it would not add that many extra possibilities. Of course then you have to impliment the circuit, bias it and drive it.

Bill

[myhrrhleine]

Amplifiers can be put together serially. It's just not practical.

The problem with stringing together amplifiers is that you increase the power demand from each.
As the voltage goes up, the current demand goes up and you quickly reach a point where things are overloaded and 'blow up'
It's much easier to build an amp for the specific needs or build 2 and bridge them.

[Bazukaz]

Originally posted by myhrrhleine
Amplifiers can be put together serially. It's just not practical.

The problem with stringing together amplifiers is that you increase the power demand from each.
As the voltage goes up, the current demand goes up and you quickly reach a point where things are overloaded and 'blow up'
It's much easier to build an amp for the specific needs or build 2 and bridge them.

How input grounds are connected then ? An input transformer is needed ?

[rtarbell]

In regards to the input for the amps, I was thinking just a simple series DC blocking cap. The input resistor for the input of the floating supply amplifier is normally connected to ground ==> It would now be connected to the output of the grounded amplifier (this is the floating amp's "ground").

I was thinking of this just after I read the grounded bridge paper from Crown. Normally, with a conventional bridge, you can only double the voltage once (one amp for the output signal, the other amp for the inverted output signal). I just figured this method would allow you to repeatedly double the power as much as one wanted (assuming each output stage of each amp could handle all of the current).