ASM-1 VCO

Paul Maddox Paul.Maddox at unilever.com
Mon Nov 1 16:21:32 CET 1999


Steve/Jorgen,

   As a sudden thought, why not use TWO 2n3819's 
in parrellel(sp?).... half the RDS on Value..

   Paul

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-----Original Message-----
From:	jorgen.bergfors at idg.se [SMTP:jorgen.bergfors at idg.se]
Sent:	Monday, November 01, 1999 12:06 PM
To:	s.grainger at staffs.ac.uk; synth-diy at mailhost.bpa.nl
Subject:	Re: ASM-1 VCO

Yes, it is probably the FET. The 2N3819 might not be ideal. You should use the
2N4391, if you can find it. Most FETs don't discharge the capacitor fully in
the time given. You can increase the time by increasing the 18p cap. But that
makes the saw ramp less steep, which is a problem for saw to triangle
converters.

/Jorgen





MIME:s.grainger at staffs.ac.uk on 99-11-01 12:59:08
To:  synth-diy at mailhost.bpa.nl @ SMTP cc:  (bcc: Jorgen Bergfors/IDGSE)
Subject: ASM-1 VCO 

Dear All,

 In amoment of madness had a go at the ASM-1 VCO at the weekend.

 It works fine except for the amplitude of the sawtooth which instead
 of being 0 to +5V is up at +2.5V to +5V (peak to peak) ie. it has
 a large DC offset.

 I suspect this might be caused by the ON resistance of the JFET
 (Rds (ON)) for which I am using a 2N3819, causing the integrator
 capacitor to not discharge completely.

 Any comments on this problem - given that this is the UK and  JFETs seem as
rare as hen's teeth !

 Regards

 Steve Grainger









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