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Parasitic circuits?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Parasitic circuits?
hirnlego
Hi!

I had a few IC laying around and was wondering if and how they could be driven just using the rectified output of a VCO (or a self-oscillating filter, or an EG).
So I tried and came up with 3/4 really simple circuits (one is a sequencer), that I think are neither active nor passive, more parasitic, as they draw juice from others. As expected their behaviour is a bit erratic and the output is always kind of distorted and fuzzy, but in the end I like the result and every one has its character.

I think that, even if they suck from others (in my case eurorack modules), these circuits are not harmful, but as I'm a novice with a novice's knowledge of electronic I have a few novice's questions:

- is correct the assumption that they're parasitic?
- are they safe in terms of damaging the modules they draw from?
- what should I take care of, if I should, for protecting them?
- are there any resources online for this kind of projects?

If interested here is a video of Aphid, one of these parasites:

https://www.youtube.com/watch?v=Uncnxj1nJq4

Thanks!
mskala
This is the same thing as what most people in the modular-synth world call "passive," but since that word really means something else, "parasitic" is probably a better term.

There should be no danger of damaging the module that's supplying the power - what you're doing is no worse than short-circuiting the output and modules need to be protected against that already.
hirnlego
Thanks, I thought so.

Are there any particular or interesting examples of using ICs in "passive" circuits? At the moment I'm trying to replicate active circuits (like a 4017 sequencer or a 4046 oscillator) and obviously the results couldn't be far from the active versions (not that I bother or expected otherwise). I'm looking for other applications than the classic ones (LPG, filters, ring modulation, multiples, attenuation, ...).
guest
there are a lot of devices powered from MIDI data, which have a lot in common. these tend to use microcontrollers. if you want to do purely analog circuits, there are extremely low power, rail to rail opamps that would work well. and the LM13700 can work down to a few volts as well, so you could build filters and such, as long as you keep total power consumption under a few milliamps, and you can expect a +/-5V signal of relatively high frequency at the input. you wont be able to chain them, though, as they will progressively loose power along the chain.
hirnlego
Thanks!

Yes, I'd like to do only analog circuits, I'll investigate some op-amps. I'm looking for minimizing current consumption and voltage requirement, is that correct?

At the moment I'm powering the circuits by rectifying the audio signal using a bridge rectifier (like this one: http://www.mouser.es/ProductDetail/Rectron/RB151/?qs=sGAEpiMZZMtQ8nqTK tFS%2fNgL6ac11fJuU%252bDPn1NW8uM%3d) with a 10n cap for smoothing (the cap may vary depending on the application).
Is this the correct way to maximize and stabilize the powering signal?
windspirit
You are going to have difficulty converting ac power to dc power from a vco and providing enough current or voltage stability tonpower an IC. If I were you Ibwould look into using transistors and optocouplers and just using CV inputs to power the circuit. This is basically how my 0HP modules work.
guest
one way to do it would be:

1. take all inputs, and connect them via 2 diodes to your powersupply rails. one diode for the positive rail, one diode for the negative rail. this way the largest of your input voltages becomes your rail. you can use shottkey diodes if you want to get the most out of those inputs. then put 100uF or larger caps on the powersupply rails. you will want something large here to hold the voltage while the input signal dips negative. but, if you go too large, the capacitor will never charge up due to the output impedance of the driving module. so something between 100uF and 470uF should be fine.

2. use either low power transistor circuits, or use low power opamps to do signal processing. the TL062 would be an easy place to start, but it draws 200uA per amplifier, so you couldnt use too many of them before you pull your powersupply rails down. the OPA2170 is 110uA, MAX44248 is 90uA, and ADA4096 is 60uA. there are even lower ones (down to 700nA!!) but frequency response or powersupply rail limits really begin to degrade.

3. use high value resistors to limit current flow through circuit elements. this will increase noise, but you dont have much choice.
hirnlego
Thanks for the ideas!
I'm not sure how to implement the first one as I don't have a negative rail, just the ground. Are they the same in my context?
Anyway, just putting a 220uF cap as suggested is already stabilizing the voltage.
guest
depending upon your circuit, you will need a negative rail. for example, if you want the ouput of your circuit to be able to generate negative voltages. typical audio waveforms will go +/-5V. to make the negative rail, you just replicate what you did for the positive rail, but with the capacitor and diode reversed.
guest
here is an example of a vca:

whoop_john
hirnlego wrote:
Hi!

I had a few IC laying around and was wondering if and how they could be driven just using the rectified output of a VCO (or a self-oscillating filter, or an EG).
So I tried and came up with 3/4 really simple circuits (one is a sequencer), that I think are neither active nor passive, more parasitic, as they draw juice from others. As expected their behaviour is a bit erratic and the output is always kind of distorted and fuzzy, but in the end I like the result and every one has its character.

I think that, even if they suck from others (in my case eurorack modules), these circuits are not harmful, but as I'm a novice with a novice's knowledge of electronic I have a few novice's questions:

- is correct the assumption that they're parasitic?
- are they safe in terms of damaging the modules they draw from?
- what should I take care of, if I should, for protecting them?
- are there any resources online for this kind of projects?

If interested here is a video of Aphid, one of these parasites:

https://www.youtube.com/watch?v=Uncnxj1nJq4

Thanks!


Don't we call this phantom powered? Potencia fantasma?
hirnlego
guest wrote:
here is an example of a vca:



The up and down arrows are common connections to the positive and negative rails (as in all the up arrows are connected together and so are the down arrows)?
hirnlego
whoop_john wrote:
hirnlego wrote:
Hi!

I had a few IC laying around and was wondering if and how they could be driven just using the rectified output of a VCO (or a self-oscillating filter, or an EG).
So I tried and came up with 3/4 really simple circuits (one is a sequencer), that I think are neither active nor passive, more parasitic, as they draw juice from others. As expected their behaviour is a bit erratic and the output is always kind of distorted and fuzzy, but in the end I like the result and every one has its character.

I think that, even if they suck from others (in my case eurorack modules), these circuits are not harmful, but as I'm a novice with a novice's knowledge of electronic I have a few novice's questions:

- is correct the assumption that they're parasitic?
- are they safe in terms of damaging the modules they draw from?
- what should I take care of, if I should, for protecting them?
- are there any resources online for this kind of projects?

If interested here is a video of Aphid, one of these parasites:

https://www.youtube.com/watch?v=Uncnxj1nJq4

Thanks!


Don't we call this phantom powered? Potencia fantasma?


Do we call it so? I didn't think about phantom powering, isn't it just used for powering microphones? I don't know of (and cannot find references to) any other audio applications, do you have a suggestion?

Thanks!
whoop_john
hirnlego wrote:
whoop_john wrote:
hirnlego wrote:
Hi!

I had a few IC laying around and was wondering if and how they could be driven just using the rectified output of a VCO (or a self-oscillating filter, or an EG).
So I tried and came up with 3/4 really simple circuits (one is a sequencer), that I think are neither active nor passive, more parasitic, as they draw juice from others. As expected their behaviour is a bit erratic and the output is always kind of distorted and fuzzy, but in the end I like the result and every one has its character.

I think that, even if they suck from others (in my case eurorack modules), these circuits are not harmful, but as I'm a novice with a novice's knowledge of electronic I have a few novice's questions:

- is correct the assumption that they're parasitic?
- are they safe in terms of damaging the modules they draw from?
- what should I take care of, if I should, for protecting them?
- are there any resources online for this kind of projects?

If interested here is a video of Aphid, one of these parasites:

https://www.youtube.com/watch?v=Uncnxj1nJq4

Thanks!


Don't we call this phantom powered? Potencia fantasma?


Do we call it so? I didn't think about phantom powering, isn't it just used for powering microphones? I don't know of (and cannot find references to) any other audio applications, do you have a suggestion?

Thanks!


I once had a small MIDI recorder and playback device that took its power from the MIDI data stream and as I remember this was described as phantom powered. I think it is a better term to use rather than parasitic, which already has an accepted different meaning in electronics:

"In a semiconductor device, a parasitic structure is a portion of the device that resembles in structure some other, simpler semiconductor device, and causes the device to enter an unintended mode of operation when subjected to conditions outside of its normal range"

Parasitic beads are used to suppress high frequency parasitic oscillation, they are often used on the power input to synth modules. This is another use of the word parasitic.

I am unsure whether you are using the intermittent power from some source to deliberately distort the sound from another module, or you are attempting to smooth and store the power for conventional power supply purposes.
Grumble
Quote:
I once had a small MIDI recorder and playback device that took its power from the MIDI data stream

This is possible since the "no data" condition is about a 10mA current, suitable to power small circuits.
hirnlego
whoop_john wrote:

I am unsure whether you are using the intermittent power from some source to deliberately distort the sound from another module, or you are attempting to smooth and store the power for conventional power supply purposes.


I guess I'm interested in understanding how to accomplish the latter, but just to see how far I can go with this approach (and my knowledge).

My objective here is building unconventional tools for my music using components that I already have, that don't require batteries or a power inlet and don't waste space in my rack. I'm not interested neither in quality nor precision.

For example: I just finished a ridiculously simple and compact 8 step cv sequencer with just a 4017, 8 pots, 8 diodes, 4 jacks, a rectifier and a cap. I give it power with a VCO, a clock with an EG and plug the output to the V/OCT input of another VCO. That's it. No pitch precision whatsoever, but it can give musical results nontheless and it just hangs from the rack. That's what I'm after!
guest
hirnlego wrote:
The up and down arrows are common connections to the positive and negative rails (as in all the up arrows are connected together and so are the down arrows)?


yes. generally in a schematic, any time there is the same symbol on a line, it means the lines are connected. sometimes its circles, squares, or just a horizontal line. there are even differences such as a filled in triangle is a different voltage than an outlined triangle.


phantom powered is probably the right term here, as its used a fair bit in audio circuits, but there is also a whole class of circuits under the parasitic power / energy harvesting umbrella, although this may just be academic research related.
mskala
I think phantom power nearly always means a DC offset added to the signal voltage to provide power for a microphone in particular. It's something that you have to add on purpose, and usually added at the signal-receiving end of the connection. That seems a lot different from a circuit designed to receive an AC signal with no significant DC offset and also harvest power, not deliberately added, from the signal voltage itself.
hirnlego
guest wrote:

yes. generally in a schematic, any time there is the same symbol on a line, it means the lines are connected. sometimes its circles, squares, or just a horizontal line. there are even differences such as a filled in triangle is a different voltage than an outlined triangle.


Great, I'll try it!
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