Analog Discovery 2 problem

[WayneW]

My device is new to me and I have not been able to get it to work.

It repeatedly displays the error "Over 25% distortion"

All leads are correct. I have tried 3 amps to test. Waveforms and the Audio Analyzer Suite each do the same thing

Getting a bit desperate

Some screen shots are attached including the setup. I keep getting the error "Over 35% distortion" despite trying several amps to test

[tggzzz]

By "3 amps" I guess you mean "3 amplifiers" not "3 Amperes"; the latter would be entertaining.

Why have you drawn a yellow arrow?

If you connect the AD AWG output to the AD scope input, what does the AD indicate.

I don't see any connection to either of the amplifier inputs.

What happens if you don't connect the probe shields to the black terminals?

One of the blue traces (not sure what it is meant to be) looks like a clipped sine wave.

A 1V input signal may be too high; what happens if you reduce it?

[newbrain]

Another thing to check, hinted by tggzzz here:

What happens if you don't connect the probe shields to the black terminals?

Are those class D amps?
Very often, the negative speaker terminals are not ground but one of the outputs of a bridge configuration, and shorting them together (through the probes' GNDs) will affect the result - chances are that it might also damage the amplifiers.

[tggzzz]

For the OP: do not disconnect the scope from the mains earth. If you do that then all parts of the scope and PC will at the same voltage as the scope shield.

[WayneW]

Hello

I am pretty electronics illiterate. I have been testing various amps. The yellow arrow is to show the USB power cable
I set the tests up according to Skunkie Designs who I follow on Youtube
I used this video (the setup starts at about 10 minutes)


Wayne

[Fungus]

As noted here, the most likely problem is that the load impedance is too low.

https://forum.digilent.com/topic/31182-help-with-analog-discovery-2/

[egonotto]

Hello,

some of the pictures are not even yours, but from the video.

I have the impression that you have just overdriven the input of the amplifier. Either you turn down the volume or you select a lower output level of the Analog Discovery.

Best regards
egonotto

[WayneW]

Thank you for the advice.
You are correct regarding the photos. Some are screen shots from Skunkie's video that I took to show the Diligent forum what I was doing.
Unfortunately that was never answered as the link shows

I have used the speaker output of the amps jus as Skunkie did.
The amp does not have a volume control
So now I really do not know what to do

[tggzzz]

So now I really do not know what to do

Start by working out what you expect to be able measure, simple numerical input and output voltages. Then check each item works on its own. Then gradually connect them together and verify measurements correspond to predictions.

Does the AD work? Connect the AWG outputs to the scope inputs.

Does the amplifier work? Use it in a normal audio amplifier configuration.

What is the amplifier maximum power output, into what resistance? Use that to calculate the maximum output voltage, RMS. Compare that with the amplifier peak-peak output voltage you previously measured. (Remember for a sine wave, V_pp = 2.8V_rms). Was the amplifier clipping?

Connect the AWG outputs to the amplifier input, and listen to the output. Does the volume sound sensible and undistorted? Measure the output voltage (RMS) with a voltmeter, not the AD. Compare that with the voltage calculated above. Make sure the measured voltage is much lower than the maximum voltage. If not, reduce the AWG output voltage.

Connect the scope probe inner to an amplifier output, but do not connect the probe shield to anything. What does the scope show? A sine wave, or a clipped sine wave etc.

Finally, only when all that looks right, do a distortion measurement.

[WayneW]

Thank you tggzzz

I appreciate your advice