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

[Oren Leavitt]

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