Re(2): unwanted sync

[Scott Gravenhorst]

I think that the history of the PAiA FatMan oscillators is
poignant here.  Several design changes have been suggested and
all have there merits.

The original solution was to "float" the 555 timer above -v using
a 10 ohm resistor, and then a 100uf cap was placed accross the 
555's actual power terminals.  This was later improved by a mod
that replaced the 10 ohm resistors with LEDs.  Still later another
mod surfaced that replaces the bipolar 555 with a  7555 which is
the CMOS equiv. of the 555.  The first 2 methods sought to suppress
synch by decoupling the VCO system form the supply, like giving each
VCO it's own "mini supply".  The latter method reduces synch by not
doing the nasty TTL totem pole overlap during switching in the 
first place.  I have two fatman synths and I must say that I prefer
the 7555 method.  It works at least as well as the LED method (I
judge it to be superior by ear) and it is a simple drop in replacement.

The upshot here is that in this case, two different approaches are
uncovered, both viable:
1) Decouple the VCOs
2) Reduce or eliminate high current impulse requirments of the supply.

I have not tried the diode method with the 7555 yet.

"danial stocks" <diode at hotmail.com> wrote:
>
>I actually build quite a bit of my stuff with SMD parts.. despite the 
>smallness, I find it can be less time consuming [no to mention less messy!] 
>than drilling all the holes [if only the LM13600 came in a SMD..]

-- Scott Gravenhorst                    | Linux Rex, Linux Vobiscum
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