[sdiy] Simplest stuff to begin with, and a few questions

[Harry Bissell Jr]

yesteryear ?

YESTERYEAR ???!!!

My signal generator STILL uses dual gang
caps.  I was just thinking it might be time
to replace it, as the plug-in electrolytic
caps are prlly no longer available... and 
retrofitting others may be tough. 

It has a maybe 2 octave range... not too useful
for EM use... although I used it in my first band
as a crude theremin (with a fuzzbox)  ;^P

H^) harry



--- Oren Leavitt <oleavitt at ix.netcom.com> wrote:
> With care, you can build a nice audio frequency Wein
> bridge oscillator 
> with a dual gang AM broadcast tuning cap...like the
> old test bench 
> oscillators of yesteryear.
> 
> If you do want to experiment with variable caps
> Ocean State Electronics 
> has a good selection.
> http://www.oselectronics.com
> 
> Of course, there are varactor diodes, too...and they
> are voltage 
> controllable! :)
> 
> Oren
> 
> harrybissell wrote:
> 
> >The reason that FEW people choose variable caps as
> the tuning
> >element is that they are only available in very
> small values, with a
> >very small tuning range.
> >
> >You should consider that... look for those caps you
> want to use
> >before doing the design. Its very easy to design
> something that
> >you find (later) you cannot manufacture...
> >
> >...especially if you use computer simulation
> (spice)
> >
> >H^) harry
> >
> >Robotboy8 at aol.com wrote:
> >
> >  
> >
> >>I noticed you mentioned variable caps in your
> oscillator... most
> >>people try
> >>to avoid this technique for synths.  There's
> nothing wrong with
> >>building an
> >>oscillator this way, but it'll be hard to get
> voltage control of the
> >>rate.
> >>It will probably work fine as an LFO, but you may
> find there are
> >>better
> >>oscillators to use as your main VCOs.
> >>    
> >>
> >
> >I realize this, but I'm not really looking for CV
> at this point - more
> >at something simple enough that I can actually
> finish it, and something
> >with a low enough parts count I could build many of
> them (I'm looking at
> >8, with xfades between each set of two for
> real-time morphing by hand).
> >In other words, at this point I'm mainly just
> trying to see if this
> >proposed oscillator will indeed oscillate.  And if
> all it's good for is
> >an LFO, at least it'll be a working LFO - as
> opposed to the countless
> >unworking audio-frequency oscillators I've started
> and never finished.
> >
> >Basically, it's two transistors turning each other
> on and off.  I'm not
> >sure if the jack is placed in the right place.  I'm
> not sure where to
> >get variable caps.  I'm not sure what value the
> resistors next to the
> >caps should be.  I don't know why there are so many
> damn types of
> >transistor, other than NPN and PNP - and I"m unsure
> if I have those
> >switched around.  All I know is that I need an SPST
> switch to turn it on
> >and off, basically - I know what the components do,
> but not much about
> >the laws surrounding them.  I've tried and I've
> tried to comprehend
> >them, but it's just too much at once as soon as I
> try to do more than
> >one thing with Ohm's law.... but then, I tend to
> think better by doing
> >than staring, so I'm trying to jump in and do
> something I can actually
> >get done.
> >
> >As for the signal levels, you're right but if I
> design all the modules
> >myself they'll all be working at +/-4.5v anyway.
> >
> >Schematics now online:
> >www.geocites.com/tranoschem/oschem.gif
> >
> >
> >  
> >
> 
> -- 
> Oren Leavitt
> oleavitt at ix.netcom.com
> 
> 
>