Re: DUOr interference from headphone outputs #eladduo #fdm-duor #duor

Klaus Brosche, DK3QN

The 'Boucherot' filter is also known as the 'Zobel' filter in HiFi amp output stages.

Klaus, DK3QN

Am 24.09.2020 um 22:49 schrieb Klaus Brosche:

As you wrote, you are loading the output with 4.7 ohms in series with cap. Which results, as your
indications say,  in an LPF at minus 3dB @ 50KHz.

I have currently no way of verifying that. I don't have my Ham Radio Laptop at hand right now
with the simulation software. It is just my guess.
So, maybe I'm wrong. In such case: forgive me ;-)

Klaus, DK3QN

Am 24.09.2020 um 22:36 schrieb Ad Dieleman:
I don't think that the interference comes from spurious switching signals from a class D amplifier: the 2.4 MHz signals disappears completely when loading the output with a low enough resistance, i.e. no high-frequency filtering at all. The filter I applied also doesn't really filter out HF signals, it just loads the output with 4.7 ohm for frequencies over roughly 50 kHz, this being the 3 dB cutoff point. So I still think that the output stage is oscillating under certain circumstances, be it a class D amplifier or something else.

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