[sdiy] MS 20 FILTER

[harrybissell]

My only concern is that the 100K might be a little too big to bias the
thing
well.  Maybe the 10uF could be bigger if you can't stand a little more DC
current drain.

The two LEDs should be about 4V... probably good enough !

H^) harry

Tim Escobedo wrote:

> --- synth DIY <bbdsynth at gmail.com> wrote:
>
> > hi! i have this MS 20 filter project to do and i've been have some
> > problems:
> >
> > in this schematic i don't really understand the meaning of the symbol
> > in the
> > output of U1a and U1b.
>
> The LM13600 has two OTAs, hence U1a and U1b.
>
> > "Vr" voltage is the ground voltage?
>
> Yes. Sorta. Running off a single 9V battery, it's necessary to make a
> reference voltage to act kind of like where ground would normally be
> with a bipolar supply. The resistor/LEDs reference is pure hack but
> does work. A regular op amp follower with the non-inverting input
> referenced to 4.5V would probably be a more classy solution.
>
> > between pin 7 and 8 ( and 10 and 9 ) it's a buffer circuit. should i
> > use any
> > specific kind of buffer?
>
> The buffer is built into the chip, at pins 7 and 8 (and 10 and 9).
> Just as shown.
>
> >
> > Lm 136000 datasheet is not available,
>
> The LM13700 will work fine. ISTR JRC still makes their version, the
> NJM13600, along with the NJM13700.
>
> Tim E.
>
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