Just got a new power amp

PS Audio S300 is not fully balanced. "Bridged" output might suggest that, but it isn't a bridge of two amps but 4 Mosfet bridge to flip speaker direction between V+ and GND, since output is single voltage supplied.  Some class D modules, like Hypex, use dual +/- supply and only 2 output Mosfets.  S300 is based on 300AS1 Icepower module, almost identical to 200ASC (in my Rowland 102), but  with stronger output Mosfets.  Both my amps Benchmark AHB2 and Rowland 102  don't have RCA inputs.  

The most important thing is what you can hear.  Some features of XLR, like higher noise rejection or locking connectors with female input side (pins recessed - not exposed) might be very important in a large studio - not so much at home.

PS: Both speaker terminals have about 30V DC (half of supply) on them - do not short  either to GND.

 

@cleeds  It is amplifier with balanced input and not the "Fully Balanced Amplifier".  "Fully Balanced Amplifier" term refers to amplifier consisting of balanced input followed by two separate amplifiers - each driving one terminal of the speaker.

 

@cleeds   I don't see anything in specs showing fully balanced operation.  

Look at page 5, Fig 1  300AS1 datasheet  showing block diagram.  After balanced input, there is only one path (one amplifier).

https://shop.icepoweraudio.com/wp-content/uploads/2023/02/ICEpower300AS1_Datasheet_2_2.pdf

@cleeds   This amplifier has only balanced input.  Circuitry between input and output is not balanced and output is not balanced.  Output is single-ended, with Mosfet bridge to switch "flip" direction of the speaker.

@cleeds   Input stage can be either "balanced" or "true balanced".  "True" refers to inputs that are not referenced to GND, like in instrumentation amp or transformer.
When pre output and amp input are both "true" balanced signal to shield capacitance in cable disappears, since signal is not referenced to GND.  Example of such configuration is output transformer to input transformer.

Amplifier can have balanced inputs or balanced outputs (to increase power), but "Fully Balanced Amplifier" means that balanced input section (instrumentation amp or transformer) is followed by two separate amplifiers, each driving one speaker terminal.  Such configuration helps to improve common mode noise rejection and reduces even harmonics.

That is at least how I understand it.  Other terms like "fully balanced input" are also used, not to mention "rms power".  Most of the time I understand what they mean.
 

@invalid  S300 output is supplied from single supply only.  To achieve net zero output at 50% duty cycle speaker is "flipped" between V+ and GND by bridge of 4 Mosfet transistors.  Some modules achieve it with dual +/- supply and only 2 Mosfets.  To me it is more "bridged" than "balanced", but it doesn't matter, as long as we know what it is.

@cleeds   He talks about benefits of balanced cables and differential inputs.  It has nothing to do with "Fully balanced power amplifier" vs power amplifier with balanced differential inputs.   I will leave it at that.  
 

@atmasphere   "Fully Balanced Amplifier" is in my opinion an amplifier that consists of true balanced input stage, like transformer or instrumentation amp, followed by two amplifiers - each for one leg/phase of the signal.  Speaker is connected between outputs of both amplifiers. 

Icepower 300AS1 module in S300 amplifier has balanced input stage and Mosfet bridge on the output (switching speaker direction), but is not "Fully Balanced", but rather amplifier with balanced input - often called "True Balanced" when done right (no GND reference)

@atmasphere   Fully Balanced, in my opinion, would require two output stages - in your case two Push-Pull stages, which probably wouldn't make much sense.

If we call S300 amplifier "Fully Balanced", then do we call Emotiva XPA-1 "Fully, Fully Balanced"?  

This is design description of Emotiva amp:

"Rather than the two sides of the amp driving two independent channels, the XPA-1 uses the two “channels” of the amp to drive the hot and cold legs of the balanced input signal. The single ended input is copied, and the copy is inverted to feed the two sides of the amp. This is the ultimate expression of balanced drive, with two completely separate halves of the amp used to amplify the inverted and un-inverted legs of the input signal, and then recombined at the output. This completely cancels out any common mode noise that both halves of the input signal see in the amplifier. Bridging a stereo amplifier, as you can do with the XPA-2, does not offer the noise cancellation offered by a fully differential design."

I got this particular amp's name from this article, that talks about challenges of such design:
https://hometheaterhifi.com/technical/technical-reviews/the-fully-balanced-power-amplifier-advantages-and-design-challenges/

IMHO, Fully Balanced configuration (as I call it), doubles the circuitry (cost), with little benefits (other than high output power).  Cancellation of even harmonics is probably not high priority by the most, while small improvement of CMRR is not worth it.  
 

@atmasphere  Perhaps my definition is too restrictive, but IMHO amp with one of speaker terminals at GND is not "Fully Balanced"

Amplifier shown on the first schematic here looks "Fully Balanced" to me

https://www.hifi-amplifiers.com/en/tonewinner-hdcd-player-power-amp-c-90/tonewinner-ad8pa-hiend-pure-class-a-power-amplifier-fully-balanced-output-p-5387.html

Do you agree it is "Fully Balanced"?

@atmasphere   I replaced second "S300" with "such amplifier" to make it general.  To me something that is "Fully Balanced" has all stages, including output stage, balanced.  One criteria of balanced output is lack of GND return current.

@atmasphere   Amplifier in question PS Audio S300 has only balanced input with single ended stages following.  I don’t believe that adding, for instance input transformer, makes any amplifier "Fully Balanced".  In my opinion such amp is an amplifier with true balanced input.

@atmasphere   Tube design is your domain so it is not wise for me to argue, but grounding tap of transformer’s secondary won’t make current return to GND.  Transformer output is balanced, but stage driving primary might be not with one transformer tap returning current to GND.  

I’m sure we can find many exotic configurations that could qualify as Fully Balanced, but PS Audio amp, that started all this, is not.  It is single ended class D amp with differential input stage.  Something should differentiate between this and fully balanced design, like one in the schematic I referred to.   To me it is word "Fully" suggesting, all stages are balanced.

@atmasphere  I agree, "Fully Balanced" design doesn't have to be better - net result is what counts.  There are many imprecise popular or marketing terms in use, why to argue.  I noticed that many great companies still use erroneous "watts RMS" and wonder if it is on purpose.  They likely know it should be just watts or watts average, but that is what most customers think of (product of RMS voltage has to be RMS power) - cannot blame them.