tri lfo with 90deg lag?(blush)

[Stewart Pye]

At 09:44 PM 30/07/99 +1000, Paul Perry wrote:
>Today I seemed to remember somethng slightly familiar fron the
>National Semi LM13600 data sheet, an oscillator with 3 OTA
>stages giving 60 deg in each stage.. which made me think if there were 2 
>stages there would be 90 deg difference.. which made me thnk about what 
>my LP filter (clone of the LM13600 Korg MS20 filter) must be doing..
>got out the scope (thanks Barry!) and viola, there it is, when
>it oscillates one of the OTA stages is 90 deg behind the other..
	<SNIP>

>BTW the outputs aren't perfect sine/cos waveforms, but plenty good enough 
>for LFO panning applications. And, putting a fet before the buffer stage
>(thanks JH) should give a nice big range..

I presume the FET buffer would increase range when used as a filter also.
Correct? So, when building a 13600 based filter (AKA MS20) Do you think it
would be a good idea to use a fet before the darlington buffer. Also, does
anyone know if this arrangement would be lower noise than a FET input op
amp, TL072 for example? And ultimately is this (fet+darlington buffer) the
superior arrangement?

Regards,
Stewart