Analog Discovery 2 THD Measurement

[simonra]

Hi,
I've been using an Analog Discovery 2 to test an amplifier; when I test THD the maximum reading I can get is -70dB. I realised that the THD spec for the waveform generator in the unit was -70dB so I bought one of victor's 1kHz signal generators. I still get a -70dB THD (testing just the signal generator) while others report -120dB, does anyone know if this is a limitation of the analog discovery?
Thanks,
Simon.

 

[BaffleChallenged]

You can try averaging, I use it with good result.
In the spectrum window, click channel option on the right hand side.
for channel1 sample mode, change decimate to averaging.
do the same for channel 2.
You can also try to change the trace1 and trace 2 type from sample to something else, but for me averaging did the trick.

 

[simonra]

Thanks for the reply, that gets me down to -76dB but nowhere near what other people measure for the signal generator. Obviously it may be my test setup, but do you know how low I should be able to measure with the Analog Discovery 2?

 

[BaffleChallenged]

if you use minimum hold continuous as trace1 type, it should get you close to -120db, but it takes more than 100 samples to acheive that. Why do you need to get that low?

 

[simonra]

Good question!.. I probably don't need to I guess. I started out trying to test the THD of a chip amp I built recently and it always produces the same result as the signal source - I was trying to find a signal source that out performed the amp so that I could come up with a THD figure. I guess I could just stop and say it's good enough, it certainly sounds fine. Also I'm currently working on an RIAA stage and wanted to make sure I was getting as little distortion from that as possible. Plus I'm new to all this and just feeling my way around.