Whenever you go negative with, say your 101, you will be stressing which material is there to protect. It may resist a lot of times, but perhaps not forever.
Sorry, but there's no technical reason to believe this.
It's all up to how something is designed and which parts are used.
Protection can be designed in to limit voltages and the parts won't wear out.
Bad design is bad design tho.
If something is designed poorly, parts
can fail whether it's positive or negative.
Generally speaking, one shouldn't exceed the voltage that a device itself is running on.
Since most synths use opamps powered by +15 and -15, inputting a voltage higher than 15 (or actually a bit lower usually) can cause problems.
But most opamps are protected for things like this.
They simply can't amplify a signal greater than they're supplied with.
And many opamps are protected on their outputs.
Even the ancient 741 opamp can have it's output shorted all day and not care.
CV inputs usually don't add any protection for inputs.
If one was to, say, add a diode to protect against negative voltages, it would also rectify audio waveforms with very audible results.
Designers usually expect control voltages to hit 10 volts max because that's 10 octaves and covers the normal hearing range.
But many circuits can handle more voltage, while other circuits can't handle negative voltages well at all.
Again, it's all up to the design, parts chosen, etc.
I think it's safe to say that it's rare for most modular gear to generate signals hot enough to do any damage to other modules of the same type.
This is kind of an inherent design thing: the same power supply generating voltages is the same one processing those voltages.
Therefore, a synth usually can't generate a voltage hotter than it can handle.
One might well distort something to shreds, but it likely won't do any real damage unless very poorly designed.
Of course, plugging an audio amp's speaker output into a pedal or modular will usually deliver
way more voltage than expected and *can* fry things quite quickly.
Fwiw, not all synths expect negative voltages. Strange things can happen, but usually not damaging.
One might get an opamp "locked up" for example, where it stays at a voltage and won't change unless powered down again.
Also, sometimes people feed in voltages so high, their vcos
are playing, but they're at a frequency higher than normal human hearing.
That's common to see on synths that don't limit things to defined musical ranges (like modulars, for example.)
The vco is working fine, but the player's ears or tweeters aren't. (and after about 50 years of age, expect your high end hearing to diminish.)
One thing not defined well is gate voltages.
Most are positive and 15 volts or under, but there's no standard as to the minimum voltage required for gating.
Stranger, many envelope generators will derive their maximum attack and sustain levels from their input gate voltage.
So a low gate voltage may produce a low envelope output voltage and vice-versa.
Many Arps are like this. Moogs, not so much.
It's a cool thing too because controlled correctly, one can achieve voltage controlled envs to some degree- very good for velocity sensitivity for example.
Few envs will trigger given negative voltages (unless they're expecting an S-trig perhaps.)
Fwiw, it's possible to mod many sequencers that puts out -5 to +5 into one that outputs 0 to 10 volts instead.
With some designs, it's as easy as adding just one resistor.
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