Those QSC's are masterpieces of very economic PA amp design. Their "grounded" output stage is brilliant in this regard, all collectors tied to GND/earth on the heatsink, making isolation unneccessary (don't know if they actually did it, though). It took my quite a while to figure out how these amps worked when I first saw a schematic, this is not the textbooks 
In some of their bigger amps they used centertapped transfomers (and ommited this hum trim circuit), and those had DC-coupled frontends, which this one has not, for that specific reason.
- Klaus
In some of their bigger amps they used centertapped transfomers (and ommited this hum trim circuit), and those had DC-coupled frontends, which this one has not, for that specific reason.
- Klaus
I only have experience from headphone amplifiers, but I've found active virtual ground channel to sound better than passive (relying on capacitor quality). I've never used fancy capacitors though, just Panasonic FM, Sanyo WX and such.
My experience is that the active ground channel must have a very low output impedance to sound good, otherwise it sounds thin and a bit out of phase. The quality of the ground channel affects the sound as much as left/right channels. After opamp rolling in headphone amps this is quite obvious.
The sound of an amplifier with active ground channel should be about the same as a balanced amp, shouln't it?
My experience is that the active ground channel must have a very low output impedance to sound good, otherwise it sounds thin and a bit out of phase. The quality of the ground channel affects the sound as much as left/right channels. After opamp rolling in headphone amps this is quite obvious.
The sound of an amplifier with active ground channel should be about the same as a balanced amp, shouln't it?
virtual earth
Klaus gave a good account and this should have ended the thread.
We read subsequent comments regarding this topic, the most ridiculous would be from those citing a background in electronics.
I don't understand what virtual earth has to do with China,
maybe an excuse for anything that is not understood must be a cheap trick from China.
How does earth relate to equipment in Skylab, or is this point called "space". Lets change its name to "virtual earth" then this concept should be clear to every space cadet.
Klaus gave a good account and this should have ended the thread.
We read subsequent comments regarding this topic, the most ridiculous would be from those citing a background in electronics.
I don't understand what virtual earth has to do with China,
maybe an excuse for anything that is not understood must be a cheap trick from China.How does earth relate to equipment in Skylab, or is this point called "space". Lets change its name to "virtual earth" then this concept should be clear to every space cadet.
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