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WIGGLING 'LITE' IN GUEST MODE

Beginner voltage questions
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Beginner voltage questions
Taika-Kim
Hi, I tried searchine the forum, but didn't come up with much.

Hoe does dividing a CV affect the voltage? I had a case few days ago, where having four cables in a multiple caused some problem (like, something not retriggering or something), but removing one restored normal action.. Does the current drop, or does the module just draw more in?

Is it generally safe to plug in other synths' audio outputs to audio (how about CV??) inputs? Like, run the output of my Bombass through my modular's filters and so on.
I have a digital multimeter, but it's slow so I guess it's not accurate enough to determine if the synths output is under 10V...

Are modules meant for audio designed to send out polarized waves, but CV modules deal in positive polarities only? Did I understand correctly some post here? What happens if I run an audio signal into a CV input, does it only regard the positive part of the voltage? If I send a CV to an audio input, do I get a DC offset positive-only voltage?
Mongo1
Wow - that's a lot of interesting questions.
I don't have all the answers, but I'll get the ball rolling:

Quote:
Hoe does dividing a CV affect the voltage? I had a case few days ago, where having four cables in a multiple caused some problem (like, something not retriggering or something), but removing one restored normal action.. Does the current drop, or does the module just draw more in?


Well, the situation you're talking about is called 'fanout'

Any output on a synth or an IC has an inherent output impedance. You can think of the impedance like a resistor in series with the output. If you look at various module schematics you'll actually see a resistor (often between 200-1000 ohms). That impedance limits the amount of current that can be produced by the module.

Every input on a synth also has an impedance. You can think of it as a resistor from the input to ground. It represents the load that module will put on whatever you plug into the input.

So lets say the signal you are using has a low output impedance. It can drive 10 mA of current. You plug it into a module that needs 1 mA to work. That's no problem at all. But if you tried to send that signal to 3 more modules, you're eating 4 of the 10 mA. At some point, the output circuitry can't keep up anymore. The signal voltage starts dropping or becoming distorted.

There are ways to get around this problem. The simplest is to get a buffer module that can take your signal in, and split it into multiple outputs, each with it's own buffer circuitry. I think they have one of those at musicfromouterspace.com

Quote:
Is it generally safe to plug in other synths' audio outputs to audio (how about CV??) inputs? Like, run the output of my Bombass through my modular's filters and so on.
I have a digital multimeter, but it's slow so I guess it's not accurate enough to determine if the synths output is under 10V...


Typically that should be safe. If you hear a bunch of obvious distortion, the you have a problem, but otherwise it should be ok.

Quote:
Are modules meant for audio designed to send out polarized waves, but CV modules deal in positive polarities only? Did I understand correctly some post here? What happens if I run an audio signal into a CV input, does it only regard the positive part of the voltage? If I send a CV to an audio input, do I get a DC offset positive-only voltage?


It sort of depends on the particular equipment, but typically audio signals will go above and below ground (+/- 5V is common), while CVs and triggers are positive. There are definitely cases where you can use an audio signal as a control voltage though. Some modules have special 'ac' inputs for that.
Most audio inputs have a capacitor in the line to block DC voltages, so they won't do very much if you put a CV into them.

I hope that helps.
Gary
e-grad
Taika-Kim wrote:
I had a case few days ago, where having four cables in a multiple caused some problem (like, something not retriggering or something), but removing one restored normal action.. Does the current drop, or does the module just draw more in?


Just to be sure a multiple does not divide voltages but takes one audio signal (or one CV) to several destination. You cannot use a mult for mixing several outputs without asking for trouble.

A multiple used correctly will send one trigger to several trigger inputs without any re-triggering problems. I’d rather suspect a bad contact.

Taika-Kim wrote:
Is it generally safe to plug in other synths' audio outputs to audio (how about CV??) inputs? Like, run the output of my Bombass through my modular's filters and so on.


Modular levels are very hot thus I doubt that you can find any stand alone synth that has a hotter signal out.

Taika-Kim wrote:
Are modules meant for audio designed to send out polarized waves, but CV modules deal in positive polarities only?


Any audio signal is bi-polar unless it has a DC off-set. CV are positive or negative but the same CV can change btn positive and negative voltages. Just think of a slowly oscillating LFO which could start a -2.5V and slowly going to +2.5V.

Hope that helps.
daverj
Some good answers already.

Taika-Kim wrote:
Hi, I tried searchine the forum, but didn't come up with much.


Using the search here can sometimes be an art form, depending on what you are searching for. If you use multiple search terms be sure to check the box that All words must be found. Otherwise you get tons more results with just one of the words.

Taika-Kim wrote:

Hoe does dividing a CV affect the voltage? I had a case few days ago, where having four cables in a multiple caused some problem (like, something not retriggering or something), but removing one restored normal action.. Does the current drop, or does the module just draw more in?


As mentioned above, signals can get loaded down when you mult them. In addition, some modules, especially if not well designed, can add a different type of loading known as capacitance, which will cause a fast slope like a gate or trigger to turn into a slower slope and might not cause a trigger anymore.

Taika-Kim wrote:

Is it generally safe to plug in other synths' audio outputs to audio (how about CV??) inputs? Like, run the output of my Bombass through my modular's filters and so on.


Generally yes. Audio outputs of most devices are in the range of about +/-1.5v to +/-2v. Most modulars have audio levels that are several times hotter than that. So it will be safe, but the signal will be low. That means if you go from another synth into a modular filter and back out that typically the signal will be a bit noisy (because signal levels were low compared to what was expected). But it also means that if the filter goes into oscillation or resonance that you could end up outputing a signal that is many times hotter than the original was. If you feed that to some place outside the modular you could end up feeding it a signal that is way too hot.

In general it is best to use modules that convert external audio into the voltages that your modular expects, and then other modules that convert the modular's signal back down to normal audio levels.

Taika-Kim wrote:

I have a digital multimeter, but it's slow so I guess it's not accurate enough to determine if the synths output is under 10V...


A multimeter set to a DC scale can show a fixed DC voltage but won't show an AC voltage (like audio). For slow moving CVs it might be able to see the range of that voltage, if the CV is moving extremely slow. With the multimeter set to an AC scale you might be able to measure a very low frequency audio signal. Most multimeters are filtered so expect AC to be under 100Hz. Plus the reading is going to be in "RMS" voltage, which is different from the peak to peak voltage (RMS is 2.828 times smaller than peak to peak) Certain meters do have special Audio scales. Those can handle higher frequencies, though they often read the voltages in dbU or dbV rather than volts.

Taika-Kim wrote:

Are modules meant for audio designed to send out polarized waves, but CV modules deal in positive polarities only? Did I understand correctly some post here?


Audio signals are AC signals. Sometimes a device might put it out through a capacitor so it is a bipolar signal when patched to the modular (bipolar = postive and negative). Other devices might put out audio directly from circuitry that has a DC voltage added to the AC, assuming that it will be going through a capacitor on the input of the next device.

That is another reason to use an audio input module on a modular. It will have a capacitor on it's input to remove any DC offset. Inputs on modules that are specifically designed for audio inputs usually also have a capacitor on their inputs.

CV signals vary depending on the format of the modular, and the function of the specific module. For example, in Euro modules it is generally safe to plug any signal in the range of +5 to -5 into any input (there are a few exceptions, on poorly designed modules). The CV input, while accepting +/-5 might react to the full range of that signal, or in some cases might react only to +/-2.5 volts. Or in some cases might react only to 0 to +5 volts.

Taika-Kim wrote:

What happens if I run an audio signal into a CV input, does it only regard the positive part of the voltage?


See above. It all depends on what the format of the system is, and what the function of the module is. (plus how strong the audio is)

Taika-Kim wrote:

If I send a CV to an audio input, do I get a DC offset positive-only voltage?


Typically an audio input will remove the DC offset, and will also remove any frequencies below audio. So a slow moving CV will do nothing, while a CV that is in the audio range will make sound.
Taika-Kim
Thanks a LOT everybody, this cleared up things for me a lot!
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