[sdiy] Who apart from me things the whole MIDI board needs replacing ?

Mike Bryant mbryant at futurehorizons.com
Thu Jan 27 12:03:56 CET 2022


About 20 years actually :-)   But they don't seem to want to make anything that helps EMI obligatory for some reason so it's just 'recommended'.


-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Roman Sowa
Sent: 27 January 2022 11:00
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Who apart from me things the whole MIDI board needs replacing ?

100nF between cable shield (pin 2) and device GND is now in MIDI DIN hardware specs, I guess for 8 years or so. Can't recall a word "obligatory" in there, but it probably is.

Roman

W dniu 2022-01-26 o 16:30, rburnett at richieburnett.co.uk pisze:
> That's a good point.
> 
> Often you can solve problems like this by connecting the shield to 
> ground via a 100nF capacitor and 1Meg resistor in parallel (at one or 
> both ends.)  The impedance of the parallel combination is low for 
> high-frequency signals (and most noise that has come through the air 
> before coupling onto your cable is high-frequency in nature,) and 
> conversely the impedance is nice and high for low-frequency signals 
> (like 50Hz "hum" currents due to earth loops,) so not much current 
> flows at these low frequencies.  The 1Meg resistor prevents static 
> build up across the 100nF capacitor, so it at least tries to keep them 
> with the same DC potential if one of the bits of kit is "floating" 
> relative to the other.
> 
> -Richie,
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