[sdiy] MAD 1108 VCF6

harrybissell at wowway.com harrybissell at wowway.com
Wed Sep 12 16:54:14 CEST 2007


LOL you are both lucky...

The VCF6 has a layout that, even with the MAD1108...
does not correctly take advantage of the matching.
Horizontal paies of diodes need to be in the SAME
package, not one package lest, one right.  Could have worked...
but the PCB is wrong.

If the devices are not matched, there may be excessive DC
offset shift in the output. This was SO the case for me.

The capacitor in the feedback circuit should be like 200uF
(I think its 10uF now). This will limit the frequency over which it
will resonate.

There can be some ultrasonic oscillation at high freqs... I added
a small cap in series with one of the resistors in the feedback
circuit to cure this. I forget but I could take a look if anyone
wants to know

H^) harry


On Tue, 11 Sep 2007 18:57:54 -0400, Dave Magnuson wrote
> Hi Gino,
> 
> I built an EFM VCF6 with unmatched 1N914 and it sounds pretty good 
> to me....
> 
> Maybe I just got lucky?
> 
> Dave
> 
> ----- Original Message ----- 
> From: "gino wong" <wonggster at gmail.com>
> To: "SDIY" <synth-diy at dropmix.xs4all.nl>
> Sent: Tuesday, September 11, 2007 12:10 PM
> Subject: [sdiy] MAD 1108 VCF6
> 
> > My other EFM VCF6 is missing a crucial part.
> > Anybody have a single MAD1108 they can part with.  I gave away all but
> > the four i needed and  our cleaning lady vacuumed one up.  She is a
> > sweet Polish Lady (no English)  and I was not about to have her dig
> > for it and she takes our vacuum bags and dog hair away when she
> > finishes.  I would never be anything but pleasant to her.
> >
> > As an alternative.  What about switched arrays of different diode
> > configurations, maybe some matching, maybe some not.
> >
> > The standard module with the trimmer mod is brilliant.  I don't know
> > if the above makes any sense at all/
> > _______________________________________________
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> 
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Harry Bissell & Nora Abdullah 4eva




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