LM13600 vs LM13700N

[tomg]

> > > Having a tidy up the other day I stumbled across a tube of 24 x
> LM13700N.
> > > Lucky me! Is the LM13700N a drop in replacement for the LM13600N in
VCO
> > > applications?
> > 
> > You'll need to place a FET before the darlington buffer to raise its
> input
> > impedance (higher than in the 13600, but not enough). Or you can use an
> > opamp follower at the OTA output, bypassing the darlington.
> > 
> > Edu
> 
> I think it's probably ok. I'm going to try it later to see.
> 
> -tg

I tied and Edu is correct the vco works but will not scale. If you change
the 470 ohm to 510 you can get about 3 octaves. Replacing the darlington
with opamps or fet followers fixes it. This is too bad but probably means
3080s and fets would also work.

BTW as long as I had the scope and a tri vco out I looked at the descret
ota sine converters output and it's only shaping half the wave.
-tg