Harry Bissell 3 phase VCO

[StephenGiles]

http://www.edn.com/article/CA6298270.html

[DougH]

Very nice, and simple too!

Could be used for stereo modulation, but what to do with the 3rd output??? Use it for panning maybe?

[StephenGiles]

Make a fourth and use quadrature for who knows what!

[puretube]

There once was a simpler version, too.
Haven`t tried both, yet...
(iirc, both had been posted here in the past).
("leading" people on other fora meanwhile are still wondering how to turn those inv*rterz into VCRs...). 

[SeanCostello]

Seems similar to the 3-phase LFO used in the Korg Polysix for the ensemble section. There were 2 of these LFOs, one for the slow (~0.7 Hz) oscillator, another for the fast (~7 Hz) oscillator, based around a single 4069. The slow and fast outputs for a given phase were summed, and used to modulate the length of a BBD, as follows:

0 degrees slow + 0 degrees fast -> BBD1
120 degrees slow + 120 degrees fast -> BBD2
240 degrees slow + 240 degrees fast -> BBD3

This produces the classic "string ensemble" sound, as heard in the Solina, ARP String Ensemble, Moog Opus 3, Crumar Performer, et al.

Sean Costello

[DougH]

There once was a simpler version, too.

That's the original circuit referenced in the article from which this claims to be an improvement on.

Thanks for the link. For some reason the reference link on the article page is not working.

[slacker]

Nice, even if you don't use the different phases for anything it looks like a pretty simple way to make a sine wave VCO/LFO.

[puretube]

Seems similar to the 3-phase LFO used in the Korg Polysix for the ensemble section. There were 2 of these LFOs, one for the slow (~0.7 Hz) oscillator, another for the fast (~7 Hz) oscillator, based around a single 4069. The slow and fast outputs for a given phase were summed, and used to modulate the length of a BBD, as follows:

0 degrees slow + 0 degrees fast -> BBD1
120 degrees slow + 120 degrees fast -> BBD2
240 degrees slow + 240 degrees fast -> BBD3

This produces the classic "string ensemble" sound, as heard in the Solina, ARP String Ensemble, Moog Opus 3, Crumar Performer, et al.

Sean Costello

Yep: ~10 years ago, I was lucky to find the last TCA590 BBDs to repair an old Salina (or was it crumar?) stringy-thingy...
(and still enjoy that band`s keyboarder using it live in P-Funk concerts).

[slacker]

I've just breadboarded the simpler version of this if anyone's interested. It makes a nice simple audio oscillator using the stock components and increasing the size of the 100n caps to 100u gives frequencies that look like they'd be good for an LFO. I haven't tried to do anything useful with it but on the scope it looks like it's a decent sine wave even at very slow speeds.
If I get time I'll build the newer version and hook it up to a VCF or something to see how it behaves as an LFO.

[puretube]

Make a fourth and use quadrature for who knows what!

...: add another (inverting) shift-stage, plus an extra inverter!

[stm]

Make a fourth and use quadrature for who knows what!

...: add another (inverting) shift-stage, plus an extra inverter!

Another way is adding just a fourth stage that adds ouputs 0º and 120º with proper gains in order to obtain 90º.  For instance, use a 180k feedback resistor, a 300k resistor connected to Output 0º and a 150k resistor to output 120º.  As you can see, the two outputs are combined in a 1:2 ratio and some additional gain ( 2/sqrt(3) ) is added to normalize gain.

[StephenGiles]

Thanks Sebastian, how is your winter down there?

[stm]

Thanks Sebastian, how is your winter down there?

Hi Stephen. Winter has been relatively benign this season, not too cold (always above 0ºC) and not too much rain. Pollution is a big issue during winter here, as smog tends to remain low instead of dispersing in the atmosphere.

Cheers.

[StephenGiles]

Thanks Sebastian, how is your winter down there?

Hi Stephen. Winter has been relatively benign this season, not too cold (always above 0ºC) and not too much rain. Pollution is a big issue during winter here, as smog tends to remain low instead of dispersing in the atmosphere.

Cheers.

We found the polution in Buenos Aires bad too. It has been hot and very humid here in the south of England - like walking through dulce de leche!