LM13600 vs LM13700N

[tomg]

----------
> From: Jezz Brookes <jbrookes at bluebear.freeserve.co.uk>
> To: tomg <vco at mindspring.com>
> Subject: Re: LM13600 vs LM13700N
> Date: Tuesday, February 23, 1999 7:21 AM
> 
> >>>> 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.
> 
> 
> >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.
> 
> 
> Thanks! Now I need to work out how to do a FET follower (any help
> appreciated!) Or if I was going to go for an op-amp follower, should I be
> looking for a high impedance input (FET?) op-amp?
> 
> Jezz.

I answer public 'cause I attached the fix..

-tg
-------------- next part --------------
A non-text attachment was scrubbed...
Name: vco5c.gif
Type: application/octet-stream
Size: 5428 bytes
Desc: vco5c.gif (GIF File)
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/19990223/fd0f009b/attachment.obj>