[sdiy] Diode Matching

Richie Burnett rburnett at richieburnett.co.uk
Sat May 9 18:52:36 CEST 2020


Anyone can make mistakes.  Better spotted now, than later ;-)

-Richie,



-----Original Message----- 
From: Ingo Debus
Sent: Saturday, May 09, 2020 5:36 PM
To: Synth DIY
Subject: Re: [sdiy] Diode Matching


> 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.

Ingo (embarrased)😰


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