[sdiy] sh09 cv out drops again

Carlos Portela carlosrochaportela at gmail.com
Wed Jan 14 19:25:57 CET 2015


Couldnt find any problem.

Just changed Q2 by 2n5457. It holds a lot better. maybe 3/4 min per semitone
I test the JFET but was working.
Any idea why's that?

2015-01-14 14:07 GMT+01:00  <rburnett at richieburnett.co.uk>:
>> It has no guard ring on the pcb around LF13741, but datasheet talks
>> about that. It has a cardboard with metal foil connected to ground
>> above this area.
>
>
> Maybe the foil-backed cardboard screening sheet has absorbed moisture and
> become slightly conductive.  You could try putting some polythene sheet
> between the cardboard and the sensitive sample-and-hold area of the PCB.  Or
> temporarily removing the foil/cardboard sheet, and see if the leakage
> problem goes away.  (As far as I know this screening sheet in the SH-09 is
> to stop 50/60Hz electric fields from the mains wiring underneath from
> introducing pitch warble into the expo-converter on the PCB.)
>
> I guess that ideally the PCB would have a guard ring and be coated with
> conformal coating to keep leakage currents in the S&H under control in high
> humidity environments.
>
> -Richie,



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