[sdiy] Diode Matching
igg.debus at gmail.com
Sat May 9 18:36:01 CEST 2020
> Am 09.05.2020 um 13:09 schrieb Ingo Debus <igg.debus at gmail.com>:
> 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.
Boy, I do feel stupid now. I often do goofy things, but this is a highlight.
These aren’t 470 k resistors, these are 470 ohms resistors. I had labelled the belt with 470 k after I had bought them and put them into the wrong bin. This is the small variant (0204 I think), so I can hardly see the color rings without a magnifier. Hopefully I haven’t used them in too many projects.
This DMM has huge digits, but the k and the M letter is rather small. When switching from 560 k to 470 ohms, I didn’t notice the small letter switched from M to k.
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