303 clone filter and VCO not reproducable

[Heiko van der Linden]

HI
as you will know you must use the matched transistors in the difference amplifier
and the current source. These double-transistors are still available. And I used
not matched transistors in the diode ladder. I got resonance up to oscillatio by
putting a variable resistor in series with the two 2k2 resistors of the current
source : With this you get a higher voltage going into the output transistor.
I also made the filter without the matched transistors for the current source and
the current source and it also worked reasonably.

I still have a few problems and maybe you know the answers : The vco doesn't always
start at once and then blows out q27 (that's th transistor in the transistor made
thyrisitor) Do you know how to cure this.
And do you know a website where there's resources about building diode
ladderfilters

Martin Czech wrote:

> > I'm sorry but I cloned it this weekend and got a great working vco and vcf. I
> > even made a mod to the filter so i can work up the resonance all the way to
> > oscillation.
> > A tip for the cloners watch q27 you're sure to blow it up afew times
> >
> Could you please be more specific about that ?
> What did you use as transistors ?
> The original japanese types?
> Did you match only the 4 dual transistors in the ladder?
>
> m.c.


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