When using 2 probes in the time domain (like an oscilloscope) I think it’s quite a lot of work to get this working. I succeeded only partially. On one channel I could get a nice full screen sinewave, but the other signal (in opposite phase) was barely visible because this signal was much weaker.
I couldn’t find a way to increase the view on the second channel. And to limit the view to just one sinewave is still a lot of work, for some part with trial and error.
So I’m interested how other users use 2 channels so scope different signals.
If you really need to see two signals with quite different amplitudes on the trace at the same time, you could use scope probes with switchable x1/x10 functions to bring the two traces closer. Set one to x1 and the larger amplitude to x10.
Most audio testing we want both (L/R) channels to be virtually identical in level and the internal range/attenuator controls are ganged so they change together.
It sounds like you wanted functionality like a 2ch 'scope/DSO with individual V/Div controls for each channel.
In this case I have to see both the input AND the output. And the amplifier has a lot of gain. I use the probes like you suggested, but the difference in signal strenght is still way too high.
So yes, I need to find a (better) way to use the QA403 as a 2 channel scope with independent settings for each channel.
What exactly are you trying to see with the probes? Usually any non-sinusoidal behavior is so low-level that it’s not visible on a scope which is why we use the frequency domain and logarithmic values to ‘see’ signals that are 100dB down from the fundamental.
I’m not entirely sure what you mean by ‘see what the phase does’ in a time domain display.
If you want to measure the gain (amp/phase) of an amplifier by frequency you could use the QA40xPlot Gain chart which in one chart shows gain and phase vs frequency. I’m pretty sure that the factory app has a way to do that also but I’m not very familiar with the templating on it.
Why you don’t use Phonalyser? In it you can apply different vertical resolution for both channel not only from fixed values, but also manually entered.
In my test work, I find it very useful to operate QA403 in frequency domain and monitor input and output signals simultaneously with a Rigol 4 channel oscilloscope. Yes, it is an added expense but I find this approach very useful. Cost for a scope suitable for audio frequency analysis is very reasonable.
Hi, Phonalyser works great. I can monitor the waveform of 2 channels (input and output). And I can see the FFT at the same time. This software is super and saves buying an additonal oscilloscope!
Note: I could see now that for lower frequencies the phase is nearly perfect between input and output. Around and above 10 kHz. I can see a little phase shift, as expected. I’m glad it can be measured this way.
