[sdiy] Diode Matching

Didier Leplae didierleplae at yahoo.com
Fri May 8 22:39:02 CEST 2020


 I had been meaning to send an update on this, btw. I got a better DMM and the results do seem to make more sense, although it is still a bit confusing ie, if I measure some diodes and come back to measure the same diodes a bit later, the results are a bit inconsistent. So, it seems having a good DMM is critical and I think it is probably best to match diodes that were tested closely together in time. 
I also think think that these 4148 silicone diodes which are from the same batch are very closely matched to begin with, so, not sure how much it matters. 
I certainly get the argument that matching may not be necessary, but good to know how to do it if you want to, I think.
    On Friday, May 8, 2020, 03:06:24 PM EDT, Ingo Debus <igg.debus at gmail.com> wrote:  
 
 
> Am 11.04.2020 um 01:12 schrieb Didier Leplae via Synth-diy <synth-diy at synth-diy.org>:
> 
> Incidentally, if I change the multimeter to read another diode, the reading stays at the elevated reading, 365mV. So that suggests to me that the meter is what's heating up, or causing the change, rather than the diode.

While we’re on the subject, there’s a funny thing I observed on my DMM measuring resistors. When I connect a 560 kOhms resistor the DMM shows something like 0.565 MOhms. It drifts a little, but not much. Now, when I grab one of the test lead, just the isolation, without making contact to the wire, the value changes drastically. When I grab the other lead, the values changes into the other direction. Seems like a mains hum probrem to me.
On the other hand, with a 470 kOhms resistor the displayed value is rock stable. 

Funny, eh? That’s an old battery operated Voltcraft multimeter, not a very expensive one.

Ingo
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