[sdiy] Diode Matching

Ben Stuyts ben at stuyts.nl
Sat May 9 13:26:57 CEST 2020



> On 9 May 2020, at 13:09, Ingo Debus <igg.debus at gmail.com> wrote:
> 
> Sorry, this is getting OT, but I really got curious. So I hooked my scope across the resistor, in parallel with the DMM. With the 560 k resistor, the scope showed some heavy 50 Hz hum. With the 470 k resistor there’s absolutely no hum. Then I grabbed some other 470 k resistors of a different type: voila, the hum as well as the instable reading of the DMM is back again! When I use 470 k resistors of the same type than the first one, from the same belt (is belt the correct term here?), there’s no hum, and the display is stable within one digit.
> I also tried resistors from the first type with a different value (301 k) and they do hum.

Just to make sure you’re not chasing ghosts here: have you measured those resistors with your DMM to make sure they are actually the correct value?

Ben





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