Passive possibilities?

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Trilloquist
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Passive possibilities?

Post by Trilloquist » Wed Feb 12, 2020 11:32 am

With a Moog DFAM as a starting point (vco, vcf, lfo, eg, vca), what sort of modest explorations could be available with passive modules? I'm still learning about the mechanics of it all, but as I understand it, passive modules dont require power. So the case itself, at least in this context, is just a box with rails?
Not that I want it to stay that way, just curious what sort of functions are provided by passive modules, if the main synth duties are covered by other semi modular gear? Is it possible to have a very limited but technically functioning rack without power and still expand on the DFAM?

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Yes Powder
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Re: Passive possibilities?

Post by Yes Powder » Wed Feb 12, 2020 12:10 pm

Off the top of my head, here's what you can get from passive modules:
Ring Modulation
Low-Pass Gates
Logic (though no N- functions since those would require voltage output when receiving nothing)
Passive filtering/EQ
Attenuators
Whatever the hell the Razmasynth Super Warp Generator is

There was someone in another thread about passive modules who mentioned once seeing a bass oscillator that was entirely powered by a gate signal, but I can't seem to find anything about it.

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Pelsea
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Re: Passive possibilities?

Post by Pelsea » Wed Feb 12, 2020 12:20 pm

Well, clearly not voltage control. However, attenuation, mixing, and even filtering can be done with passive circuits. Some of these are quite interesting, such as the ring modulator. The gotcha is everything you do reduces the signal by 3 dB or more, so you probably have to add an amplifier at the end. This increases noise compared to the active versions of the circuits. Also, some passive operations require transformers, which are big and heavy.
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Arneb
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Re: Passive possibilities?

Post by Arneb » Wed Feb 12, 2020 12:42 pm

Yes Powder wrote:
Wed Feb 12, 2020 12:10 pm
Off the top of my head, here's what you can get from passive modules:
Ring Modulation
Low-Pass Gates
Logic (though no N- functions since those would require voltage output when receiving nothing)
Passive filtering/EQ
Attenuators
Whatever the hell the Razmasynth Super Warp Generator is

There was someone in another thread about passive modules who mentioned once seeing a bass oscillator that was entirely powered by a gate signal, but I can't seem to find anything about it.
That plus:
- Slew limiting
- Mixing
- Apparently there are also transformer-based passive gainers around

KSS
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Re: Passive possibilities?

Post by KSS » Wed Feb 12, 2020 8:23 pm

Pelsea wrote:
Wed Feb 12, 2020 12:20 pm
Well, clearly not voltage control.
'Vactrol' VCFs and VCAs arecan be passive.

Would be more fair to say optoisolators. Then the older lamp/LDR style 'Vactrols' remove the possbility of using the diode in the LED type as reason to cry foul at calling a vactrol passive. 8-)

theB94
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Re: Passive possibilities?

Post by theB94 » Wed Feb 12, 2020 11:41 pm

This is my little passive setup. Deciding on whether to get a vactrol lpg or a mixer for the last slot. Its a helpful and fun little box.
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