I try to measure the output from my circuit board. Therefore i am using an Agilent MSOX 2004A and a MATLAB programm. The thing is that I sill have a lot of switching frequencies remaining in the outputsignal. I read the document "SLOA068A Guidelines for Measuring Audio Power Amplifier Performance" and tried the RC filter on Page 8 in Figure 5, but that only set the amplifier in HiZ mode, as long as i connected the ground of the am to the ground of the RC Lowpass.
Whats funny is, that this RC filter worked just fine for my TPA3129 board, but doesnt for my TAS5806MD board.
How do i correctly lowpass the switching frequencies in order to measure the output?