[sdiy] Diode Matching

mskala at ansuz.sooke.bc.ca mskala at ansuz.sooke.bc.ca
Sat May 9 15:37:16 CEST 2020

On Sat, 9 May 2020, Ingo Debus wrote:
> 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

Some resistors are made with the resistive element in a coiled shape; it's
typically a coating on the surface of a cylinder, with a helical groove to
increase the resistance.  Resistors designed that way will have a little
bit of inductance and sensitivity to external magnetic fields.  So if
there's a strong 50Hz magnetic field in your location, such a resistor
might end up with an induced 50Hz voltage; and a less inductive resistor
would see less of that.  That could be a reason for one of them to hum and
the other not, at the same resistance value.

Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before tribes.

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