discrete simple SODFA amp - questions

[the_manta]

Hi,
it's my first time with Class-D.
This schematic is from 1983 and was originally posted by Elektor.

I built that amplifier and have some problems. First, it doesn't sound bad. Really detailed and powerful. Bandwidth is good, too

Problem is the huge amount of noise and the output ripple. Is it normal that there is like 10Vpp ripple ? [output_ripple.jpg]

The signal from the OP-amp output is clean [drive_signal.jpg]

But at the output it shows some ringing. Where does that come from and how can I prevent this ? Does this cause the noise ? When i touch some pins of the CMOS inverter with the oscilloscope probe, the noise is suddenly reduced. This doesn't happen always. The noise is reduced when I reduce the supply voltage [low_supply.jpg ; signal_1.jpg ; signal_1.jpg]

Since this is a published circuit, it must have worked...kind of.

Are there similar SODFA circuits out there with better results and Mosfets ?

[luka]

well c5 and c7 are pretty small, now unless you have high freq. 10vpp is/could be normal for that freq