[sdiy] "spiral" waveforms and scope XY mode

[Oren Leavitt]

I've found XY mode handy for adjusting the 1V/oct tracking of VC filters.
Works great with state variable and low pass filters.
Connect the saw output of a calibrated VCO to the scope Y input, and to the input of the filter being tested.
Connect the VCF output to the scope X input.
Connect a common CV source to the 1V/Oct CV inputs of the VCO and VCF.

Turn everything on and set the VCO to about a 100Hz or so.
Set the VCF frequency a few octaves above that of the VCO.
Turn up the resonance just enough so that you see a shapeon the scope with a damped sine wave in it.
Now sweep the common CV up and down or use a triangle LFO.
If the filter is not tracking, the number of humps in the shape will compress and expand as the CV is swept.

Simply adjust the filter's 1V/Oct trim up or down in the filter until see minimal changing of the shape you see on the scope as the CV is swept.

Oren


-----Original Message-----
From: Scott Stites <scottnoanh at peoplepc.com>
Sent: Apr 7, 2004 8:42 AM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] "spiral" waveforms


Actually, I use the function on a regular basis at work - mostly for tuning frequency reference oscillators to the house standard - 10MHz into X, 10 MHz into Y, make the purty picture stop spinning.  Could be done with just a horizontal display, but it's funner....=0)

If one really investigates it though, Lissajous patterns are a great tool for observing phase relationships, etc.

Cheers,
Scott




-----Original Message-----
From: Harry Bissell Jr <harrybissell at prodigy.net>
Sent: Apr 7, 2004 9:48 AM
To: "Byron G. Jacquot" <thescum at surfree.com>, synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] "spiral" waveforms

 "Byron G. Jacquot" wrote:

> Am I the only person who knocks the scope into X-Y
> mode form time to 
> time, just to see what pops up?

Yes... you are  :^P

H^) harry


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