[sdiy] 3046 vco help?

[Dan Snazelle]

These transistor vcos are such fun....

On paper they look like a lot sometimes, but the parts are so compact


I actually built this vco With unmatched discrete transistors (unstead of a3046) just for fun (which allowed me to cut one more transistor)


Drift is not always a bad thing depending on the context

Sent from my iPhone

On Aug 18, 2011, at 5:46 PM, Dave Kendall <davekendall at ntlworld.com> wrote:

> Hi all.
> 
> On Aug 18, 2011, at 20:08, Magnus Danielson wrote:
>> The lower left transistor pair is the expo-pair. The collector on pin 1 pulls current through from the 10 nF capacitor which is then being buffered by the J112 FET which essentially acts like a emitter follower.
>> The output of that is being tossed into the upper pair which acts like a comparator which with the 2N3906 acts like a reset of the sawtooth.Finally, the 2N3904 is the output comparator for the square signal.
>> 
>> There it is. Not too odd setup. The "benefit" of this is the lack of high gain in the feedback path, which can make it warmer due to the inherent trigger jitter, but explaining that can be a bit tricky, but I could go into that if you need me to. Fun thing. Does it sound good?
>> 
>> Cheers,
>> Magnus
> 
> Hi Magnus - going into the detail would be great - thanks -  but like Dan I'm really interested - it seems like such a simple low-parts count dual OSC - 3046's are still available in SOIC last time I looked, and you can still get NOS ones if you look around..
> 
> On Aug 18, 2011, at 22:25, KA4HJH wrote:
> 
>> As I hazily recall the heater took longer to stabilize and a tempco was much simpler. Tom had them in stock, too, so the choice was easy I'm sure I have the entire conversation about it in my email archive--somewhere.
> 
> Terry - I'd be very interested in seeing that conversation if you could dig it out without too much trouble for yourself.... I've got some 1K tempcos (only 3000ppm though) lying around, and a few VCO3D boards...
>> 
>>> Tempcos might be hard to get and cost more...Heater uses much more power, excess heat might make other components drift...(I use tempcos epoxied to dual transistors, usually...)
>>> H^) harry
> 
> A plan might be to use Ian Fritz's transistor matching circuit to get 2 matched trannies and build up a dual tranny/tempco thermally connected epoxy "lump" then... seems like that would help stability....
> 
> Thanks all for the responses.....
> 
> cheers,
> Dave
> 
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