[sdiy] Humans are not Becoming Smaller

[Ian Fritz]

At 12:47 PM 6/2/05, laxt57 at aol.com wrote:

>   Well what I am planning is this. A OTA made with SMD that
>  will fit the footprint of a ca3080. By input I guess I was not
>  asking about the design of the OTA itself, all that is freely
>  available on the web. I guess my question is with the available
>  smd devices 847s,3904 etc do you think this sdiy do able?

Well, that's the question.  I haven't found any good SMD well-matched, 
high-gain transistors.  I've been stocking up on the popular Japanese 
matched pairs, some of which are quite good, but all discontinued.  In my 
most recent discrete OTA I tried a pair of hand-matched ZTX795A's glued 
together, but they didn't work very well.  They had too much LF noise, 
presumably due to temperature fluctuations.

Maybe some of the non-monolithic SDMs could be made to work, I dunno.

Another question is whether it is even a good idea to try to reproduce the 
3080.  The Iabc mirror has always been a pain, requiring a mirror in the 
expo converter.  Why not work with the simpler discrete designs that don't 
have this "feature".

   Ian