[sdiy] AN299 VCO

[Dave Manley]

Michael Bacich wrote:
>
> On Apr 29, 2008, at 10:38 AM, Dave Manley wrote:
>
>> I don't have reference materials at hand, but isn't a very similar 
>> circuit used in one of the later Moog VCOs?  I can dig it out tonight 
>> if there's interest.
>
> Yes, it's the MicroMoog VCO.  It uses at least one of the transistors 
> onboard the 3046 as a "heater", to heat the IC package up to just a 
> little above the typical expected ambient air temperature, making it 
> more immune to air temperature variations.  I'm not sure how it keeps 
> that transistor at a constant temperature, but the complete MicroMoog 
> service manual gives a very detailed circuit operation description.  
> I'm pretty sure that manual is available somewhere out there on the 
> web, but I don't know where.
>
> BTW, it's also the same VCO in the MultiMoog, and quite possibly also 
> in the Moog Rogue, Liberation, Prodigy, and Radio Shack MG-1 synth.  
> Each of those use the 3046 for the VCO core, and none of them utilize 
> Tempco resistors.  They're also amazingly stable -- probably much more 
> than an original MiniMoog VCO.
Hi Michael, I hope you don't mind me forwarding your response to the list.

I took a look, and the Lib, Micro, Multi, Source and Prodigy do use this 
method, and there are some slight differences in the circuits - mainly 
in how the heating transistor is controlled.  The Moog circuit is a bit 
different than AN-299 but the basic concept looks similar - I wonder 
which has precedence?

The combined MicroMoog/MultiMoog service manual gives a well written, 
detailed operational description.

Aaron, do your students do any SPICE analysis?  I'm not knocking the 
bench experience, there's nothing better than hands-on, but some of the 
what-if type questions you've been asking might benefit from 
simulation.  I'm sure you have access to some great tools there  at GA 
Tech, but the Linear Technology LTspice is a free, low learning curve 
tool, integrating schematic capture, simulation, and graphical output 
(you can even output .WAV files and listen to your simulation), with a 
very responsive Yahoo support group.  I wish I had access to such a 
product when I was in school.

-Dave