Τhank you very much for the answers.I have finished an amplifier with mosfet IRFP9240 and IRFP240 and I want to see what it does on the oscilloscope.Τhe black box in the photo is a preamplifier.
I am using probe of the oscilloscope and it is set correctly.The load test 4ohm.Τhe Sine wave looks good until 11khz.
What I want is to learn good oscilloscope and to fix the circuit I have as best as possible
I am concerned about the spikes I saw in the square pulse
Sorry my english is not very good
I first check the signal of the generator on the oscilloscope and then on the amplifier. I understand that the square is a difficult wave but I put the same wave on other amplifiers built and I see it right.
NOTE. Τhe amplifier works very well in the ear. the offset is less than 10mv, the quiescent current is 50ma with a continuous 45-0-45 volt power supply.two mosfets on each side
there is no noise in the speakers.
Well done on providing photos and describing your situation.
Too often people looking at audio amplifiers only think about the frequency domain. With amplifiers some behaviour is best described in the time domain.
The classic example is trying to describe and measure "transient intermodulation distortion" (TID), since the numbers are a function of frequency and amplitude. It is much better and easier to think in terms of "slew rate".
So, have a look at the
edge of the response to a square wave input. The period/frequency is not particularly important.
Characterise the "overshoot" visible in the traces. If it looks like half of a sine wave, what would be the period of the sine wave (and hence frequency)? Alternatively, if your scope supports it, show a single cycle on the display and get the scope to transform it into the frequency domain (i.e. do an FFT!).
Make sure the load and amplitude are representative of a real system.