[sdiy] VCO builds

[Magnus Danielson]

On 27/08/11 20:25, lanterma at ece.gatech.edu wrote:
>
> On Aug 26, 2011, at 7:19 PM, KA4HJH wrote:
>
>> Take a look at the MG-1 schematics. And don't forget the Oberheim SEM:
>>
>> http://www.crowncity.net/ratcave/Electro/Electro.html
>>
>> Man, it's been ten years since I posted that. I don't even know the
>> password to the site anymore.
>
> That Oberheim SEM VCO is very interesting. I haven't seen another VCO design quite like it. (I had a student try to build that a few years ago, but he didn't get it working, but that's also probably because he started his project at the las minute...)

A detail is that the JFET and PNP buffer amp is powered from +18,5 V, 
which can confuse people for starters. The two-transistor schmitt 
trigger is old-school, but I wonder if it wasn't the best way to get 
some half-decent slew-rate back in the days considering the op-amps 
available then. I can't recall seing the high-frequency tracking 
correction done using the feedback path anywhere else.

The ASM-1 VCO (the ASM-1 is somewhat of a SEM clone) is much more a 
cook-book VCO compared to the SEM, but they do not differ very much.

Cheers,
Magnus