[sdiy] 566 , was Re: Midwest Analog Product Books

[john mahoney]

----- Original Message ----- 
From: "Roy J. Tellason" <rtellason at blazenet.net>


> On Sunday 26 September 2004 08:05 pm, john mahoney wrote:
> > I bought Thomas Henry's 566 book because I ended up with some of
those
> > oft-maligned chips in some grab bags. (Not 556, not 565, but the
> > obsolete 566 VCO/Function Generator.)
>
> Speaking of which,  I got one of those chips too,  in a similar
situation -- 
> in a bag of miscellaneous parts.  What's it good for?

Short answer: a sound effects box like the old Paia Gnome. Runners up:
a VCO or *maybe* a VC-LFO.

It sort of depends on whether you are using it the according to the
datasheet or with Thomas Henry's tricks. The specs say: 10-to-1
frequency range; inverted, linear voltage response; square and
triangle waves with strange peak-to-peak levels.

With TH's tips you can get this: 1000:1 freq range; temperature
compensated, 1V/octave response; hard sync; suboctave square wave;
square, pulse, triangle, sine, and quadrature square wave outputs at
standard synth levels. You can choose to have a ramp instead of tri
(and sine).

However, while TH reveals how to do all this he writes that "if ultra
precision is your goal... there are more effective ways of designing
an exponential VCO for synth work."

The quadrature outputs made me think "Great for an LFO!"
Unfortunately, though, the triangle wave doesn't hold together at
frequencies below 80 Hertz. I'm not sure how low the square waves can
go, although TH's books shows 10Hz with a -6V input. If it'll go even
lower then it may be useful as an LFO.

One person on the Synth-DIY list said he'd built a 566-based VCO and
it was pretty good, much better than the naysayers were, um,
naysaying. ;-P

But for me? My crystal ball shows a few sound effects gadgets in my
future.
--
john