audio-talk

Nick wrote: ↑Sun Jan 17, 2021 6:48 pm All I will point out is I would not look at sine waves, I would meeasure a frequency sweep if it can do that or a number of spot frequencys if not. And I would look at a FFT of the sine wave, if you can see distortion its up close to 1%

Thanks Nick. I know the frequency generator will do a sweep but I haven't figured out how to make the scope app draw a results graph. Will look at that tomorrow.

OK, I learned a couple more functions of my AD2 today.

Firstly the frequency sweep, which I set to go from 10Hz to 100kHz, 2V amplitude. I ran the same test with offset set to 2mV, 0mV and -2mV. These settings corresponded to multimeter readings of 0.3mV, -1.7mV and -3.6mV obtained before the frequency tests began, suggesting the AD2 has 1.7mV offset of its own. You could see the value changing on the multimeter as it was adjusted in software. I don't know if this remained stable through the frequency sweep, but the range I selected should mean the tests were run with a minimum of 2mV of offset.

The graphs show no visible difference in frequency response or phase shift: Yellow line is input, blue line is output:





Similar with FFT readings - 500Hz test signal at 5 volts amplitude:

Looks good. I would use more cycles for the FFT if you can, also it may have the option for a log x axis which would be more informative.

The AD2 looks like a '" 'andy bit o' kit " as my Grandpa used to say.
BTW, I remembered this paper:
https://www.sowter.co.uk/pdf/GAVS.pdf
which answers my question about magnetising mumetal - 'It should be stressed that Mumetal does not easily acquire unidirectional magnetization under normal operating conditions'

And I guess it would be simple to demagnetise with an AC source and slowly reducing the amplitude.

Yes, Mr Sowter says to use either AC or continuously reversing DC

I know what he means, but continuously reversing DC sounds like AC to me.....

Max N wrote: ↑Mon Jan 18, 2021 6:45 pm The AD2 looks like a '" 'andy bit o' kit " as my Grandpa used to say.

It really is, I've been very impressed with it. Some hackaday write-ups have complained that it's not all that accurate into the Mhz region because of the poor quality test leads etc, but for our purposes it seems absolutely fine, and when you're doing this in a cramped flat it's far easier to pull out a small USB powered device and attach a few clip leads than dragging out a whole oscilloscope and frequency generator. It does have a downside that the scope connections don't have an AC coupling option, so measuring things "in circuit" that have HT applied could be problematic.

Thermionic Idler wrote: ↑Mon Jan 18, 2021 11:36 pm It does have a downside that the scope connections don't have an AC coupling option, so measuring things "in circuit" that have HT applied could be problematic.

I found my USB scope to have very low voltage rating so can't measure much with anything HT on it but it is quite old now.