tri lfo with 90deg lag?(blush)

[Haible Juergen]

Well, you asked for triangle waveforms, and not sin / cos waves (;->)

You can get sin and cos directly from a 2pole filter @ self oscillation,
but there is always the problem of amplitude regulation. Make it fast
(even with some clipping, as in the MS-20 filter), and you get non-ideal
waveforms, or make it slow, and changing frequency would possibly
change the relative amplitude of the two outputs until everything is
settled.
No doubt that this works fine for rather fast LFO rates. But have you
checked
at slow rates, too ?

JH.

> -----Original Message-----
> From:	Paul Perry [SMTP:pfperry at melbpc.org.au]
> Sent:	Friday, July 30, 1999 1:45 PM
> To:	synth-diy at mailhost.bpa.nl
> Subject:	tri lfo with 90deg lag?(blush)
> 
> I asked recently for anything on a 90deg  lag sine oscilator
> and as usual got some very good & useful replies..
> 
> 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..
> 
> Boy is my face red! who else would ask the list for a quadrature
> oscillator when he has one running on the bench!! 
> Well I guess this list is educational :-)
> 
> paul perry melbourne australia
> 
> 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..