Triangle VCO with adjustable symmetry?

Regebro · Joined: Sep 12, 2004 Posts: 61

I'm thinking about making a VCO, and I'd like it to have a triangle-saw VCO, ie a triangle with adjustable up/down symmetry. Does anybody know of any proven circuitry that does that? Analog electronics was always my weak point in engineering school so I'd like to avoid trying to figure this out myself. Smile

Best idea I have so far is adapting Thomas Henry's XR-VCO since the XR2206 seems to be able to do this (I'm not 100% sure though). But it seems like it should be possible to be made simpler.

Grumble · Posted: Wed Mar 15, 2017 2:52 am Post subject:

You could do it like this: http://tinyurl.com/hg96gtz
But the frequency will shift when the potmeter value changes, this can be minimised by using schottky diodes (lowest Vknee possible)

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Regebro · Joined: Sep 12, 2004 Posts: 61

Nice site, that will come in handy. Thanks for the idea, will investigate.

Regebro · Joined: Sep 12, 2004 Posts: 61

After much ado about all this I came up with this: http://tinyurl.com/lmsmtvm which takes your idea but has nice linear slopes.

I wonder if I'll be able to compensate for the frequency shift. Hm, I just got an idea, maybe I can control it as a phase locked loop...?

Anyway, I investigated the XR2206 wave shaping stuff it it doesn't do what I want at all, so that idea is out.

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blue hell · Posted: Fri Mar 17, 2017 11:49 am Post subject:

Wasn't there some FET trick to make low voltage drop diodes? I forgot how tho.

The problem with a PLL is that it needs some periods to settle - which will be slow or an LFO.

Grumble · Posted: Fri Mar 17, 2017 1:28 pm Post subject:

yes

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Regebro · Joined: Sep 12, 2004 Posts: 61