QSC USA1300

QSC USA 1300

This is where amplifiers like the preceding Peavey PV-1200 came from. The circuit below is of the QSC USA1300 model. It shows very clearly how this typology works.

Note that the output is actually riding on the positive & negative rails. And also note that their dc offsets are equal and so are their voltage swings. These voltages then pass through a filter bank and when they are summed at the center, their offsets are cancelled. leaving their voltages at 0 reference.

For such a circuit to work, the op-amp supply must be boot-strappped to the power rails. The op-amp alone cannot swing to such a high amplitude.on her own because she is limited by her rails voltages of +-15V. Only with the boot-strap technique is she able to swing so high.

QSC USA1300Fig 1 – QSC USA1300 Amplifier Schematic

Summary

I am not a fan of this typology but that’s only my opinion. This QSC design has been enormously successful for QSC. So much so that other manufacturers try to mimic their design in one way or another.