[sdiy] ElectroNotes substitutions

[Oren Leavitt]

alfred.pear at gmail.com wrote:
> Hi -
> 
> I've been reviewing the ElectroNotes C.V. applications and wanted to
> ask people about what they substitute the AD821 matched transistors
> with. I'm specifically looking at the VCF Option 1, and it seems to
> serve the purpose of a buffer, so I'm thinking about just using an Op
> Amp instead... However, there are two separate terminal ouputs used
> that are directed to two different OTAs.
> Can I use a single op-amp ouput for the same effect?
> 
> Perhaps more efficiently: Does anyone know of any modernized versions
> of these schematics, with more readily available materials?
> 
> Thanks,
> Alfred
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Hi Alfred,

As for the AD821 transistors, they serve as a two-output current source 
to drive each of the CA3080s.
There are a few modern matched PNP transistor alternatives out there you 
can use. One is the MAT03 (which is a bit expensive).
In a pinch, you can use two 2N3906s in place of the AD821 to test the 
filter and get it working.

Best of luck with the filter!
- Oren (Trying to get into some SDIY after a two year hiatus)