On Wednesday, 3 February 2021 at 01:48:00 UTC, wrote:
gareth magennis is super annoying :
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How can I force this motorboating to happen on my bench, so I can deal with it?
I've not seen it yet.
** FFS !!!
How will you ever know if you have fixed it ?????
Rule one of troubleshooting: " Observe the Fault "
..... Phil
Ok, I think I may have got to the bottom of this.
I found this, which I believe is the issue and its solution.
https://www.gearslutz.com/board/so-m...fications.html
There, it states the mod is a 25pf in series with 100 ohms, which makes much more sense.
I fitted it and, of course, it doesn't drop the level by 12dB.
I did measure things before finding this, and the output inpedence of the circuit is around 360 ohms, in the method described by Mike.
Thanks MIke.
I also tried to measure the low frequency rolloff, which was way below 10 Hz.
Thanks, Phil.
Maybe there never was any "motorboating", this notion came from the customer in his email to the company.
I never found any, despite adding caps on the output like Mike suggested.