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Why does modular gear run at 10V instead of line level?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion Goto page 1, 2  Next [all]
Author Why does modular gear run at 10V instead of line level?
chlorinemist
Sorry for the total noob question. I've been googling trying to find an answer to this question and have come up empty.

Why does Eurorack use a nonstandard audio level that requires dedicated preamp and attenuator modules to send normal line level signals in and out? What motivated the engineers to make this unusual design choice?

Thanx!
transistorcat
The short answer is a combination of history (non-euro standards generally have the same ranges), signal to noise (If you have more signal, the noise is less significant), and precision (pitch control signals require a precision that's hard to get at line level voltage swing.
ndkent
Agree. Buchla by the way kept audio and control voltage as separate connections and audio stays audio level.

Moog who served as a template for the vast majority of voltage controlled synths ever built chose to allow control and audio to intermingle for flexibility.

A lot of people love the differentiation of 2 separate paths for Buchla, until they find the lack of both kinds of jacks everywhere.

As to range. Remember that pitch is controlled by voltage. Had one tried to crunch CV for octaves of keys down to a tiny range accurately enough would have cost a fortune. The fairly easy to deal with 1v per octave needs a volt for each octave of pitch.
Graham Hinton
chlorinemist wrote:
Why does Eurorack use a nonstandard audio level that requires dedicated preamp and attenuator modules to send normal line level signals in and out? What motivated the engineers to make this unusual design choice?


The question should really be: why do noobs believe there is such a thing as standard line level? There isn't, there is only a variety of different line reference levels, but the actual signals can be anything within the range of the power rails of the equipment. There is no normal and often there is no real need for dedicated I/O modules.

Historically, before the '70s most audio circuitry was valve or transistor based and operated at "small signal levels". It was more difficult to do DC coupled circuits with large signal levels so this was only done in devices like analogue computers. Then IC operational amplifiers became cheaply available and everything changed. Most synthesizers and mixers use this technology and large DC coupled signals are easy to implement and it makes sense to use higher levels to improve signal to noise ratios and accuracy. Hi-fi and guitar pedals stayed with low level signals even if they use op amps.

ndkent wrote:
Buchla by the way kept audio and control voltage as separate connections and audio stays audio level.


"Audio level" being what was used by 1960s domestic hi-fi tape recorders. Professional tape machines used higher levels even then.
felixer
well, us law says that everything over 50V is lethal and should be taken care of my special measures. so you stay below that (phantom power is 48V for that reason alone). now, i'm sure you heard of signal to noise? there are all sorts of stray electrical currents around. and with all the cellphones it is getting worse. so you want your signal to be on top of everything else. also since a lot of synth/osc are 1V/okt you want a decent range. say 10 oktaves. so what do you get? 10V as a control signal. at least for the keyboard. and while you're at it you might as well make all control voltages 10V. then comes the point where you want to modulate an osc by another osc. so it is handy to have all voltages be 10V. so you can patch anything to anything. can't do that on a buchla. early moog modular doesn't allow that as well.
cornutt
Other control signal standards have certainly been tried. Some Polyfusion gear used 0.1V/octave scaling -- I don't know how well that worked, since I've never seen any user discussion regarding Polyfusion gear, other than a few comments from Steve Pocaro back in the day.

EML proposed and used 1.2V/octave scaling. This makes sense when you realize that it's 0.1V/half step, which eliminates messy math when you are trying to calculate voltages for harmony interval offsets. Kind of a shame this didn't catch on.

I understand that most EMS gear used something in the vicinity of 0.3V/octave. I don't know what the rationale for that particular value was.

Some early synths used "linear", that is, V/Hz scaling. I don't know what standards were used; I've seen reference to 1000 Hz/octave somewhere. A lot of modular VCOs have a linear input, for doing "proper" FM. I should do some experimenting with one of my Q106's to see exactly what the linear input scales to.
pricklyrobot
felixer wrote:
well, us law says that everything over 50V is lethal

50V is just the threshold for needing an Electrician’s license to work on something. It’s not really a good indicator of lethality/potential for injury.
morgulbee
As I was researching audio mixers last night, I saw mention of "consumer line level" and "pro line level". So even when you talk about line level, there isn't just one line level.
felixer
pricklyrobot wrote:
felixer wrote:
well, us law says that everything over 50V is lethal

50V is just the threshold for needing an Electrician’s license to work on something. It’s not really a good indicator of lethality/potential for injury.

ofcourse it isn't. but that is the law in us. fact is that at about 50V your muscles start contracting and you can't let go of anything. so unless you do some trick or have a buddy to tear you loose, you'l be hanging there for ever ...
cornutt
pricklyrobot wrote:
felixer wrote:
well, us law says that everything over 50V is lethal

50V is just the threshold for needing an Electrician’s license to work on something. It’s not really a good indicator of lethality/potential for injury.


Well, it's more than just the license. It's the point at where you have to start using power wiring and UL/CSA listed devices -- Romex, plugs and receptacles, switches, etc., and you have to conform with accepted methods for power wiring.
Rex Coil 7
cornutt wrote:
pricklyrobot wrote:
felixer wrote:
well, us law says that everything over 50V is lethal

50V is just the threshold for needing an Electrician’s license to work on something. It’s not really a good indicator of lethality/potential for injury.


Well, it's more than just the license. It's the point at where you have to start using power wiring and UL/CSA listed devices -- Romex, plugs and receptacles, switches, etc., and you have to conform with accepted methods for power wiring.
Yea ... because I was going to say that pretty much any arc welder (SMAW) has at least 72 ocv ("Open Circuit Voltage"). Your better arc welders actually have 80 ocv, such as Miller Electric. Higher ocv is needed to help get the arc started more easily, especially when using a welding rod that is partially used because the "flux" on the outside of the welding rod melts and forms a boundary on the tip of the rod. When re-striking the arc the higher ocv helps to establish the arc through that melted "seal" on the tip of the rod. Higher ocv also helps when the metal being welded has crap/rust/paint on it's surface. Some oil/natural gas pipeline jobs spec out anywhere from 72 ocv (for welding machines made by Lincoln Electric) to 80 ocv (welding machines made by Miller Electric).

If I recall, OSHA says 100 ocv is lethal, but that only applies to 60HZ power. TIG welding machines use a "high frequency generator" to circumvent that specification by using 1MHZ at 3K OCV, which is not lethal.

hmmm..... hmmm.....
mskala
The 48V telephone DC voltage is probably also relevant. I'm sure it predated electrician licensing in the modern form of that, and it'd make sense that when making those rules they might want to have the rules not apply to existing telephone systems.
Graham Hinton
felixer wrote:
phantom power is 48V for that reason alone


That's just supposition. P48 is defined as 48V +/-4V through two resistors that limit the current to 14ma if both sides are shorted to 0V. It may make a frog's leg twitch, but it won't kill you and it predated all these modern regulations.

Quote:
fact is that at about 50V your muscles start contracting and you can't let go of anything.


Where are you getting your "facts" from? Anybody can Google the real facts and see that you are barking up the wrong tree.
sduck
felixer wrote:
us law says that everything over 50V is lethal and should be taken care of my special measures.


What? Who said what? What law? Lethal? License what? Do you actually know what you're talking about?

You don't need a license in the US to work on anything above 50v. I have several licensed electrician friends, and that has nothing to do with how the licensing works. I routinely work on 120 and 240 volt circuits with no license. Knowledge is the key. Knowledge and a few dollars will get you a license.
Rex Coil 7
sduck wrote:
felixer wrote:
us law says that everything over 50V is lethal and should be taken care of my special measures.


What? Who said what? What law? Lethal? License what? Do you actually know what you're talking about?

You don't need a license in the US to work on anything above 50v. I have several licensed electrician friends, and that has nothing to do with how the licensing works. I routinely work on 120 and 240 volt circuits with no license. Knowledge is the key. Knowledge and a few dollars will get you a license.
Agreed ... I don't know where this whole 50v bullshit is coming from but it's way off the mark. I worked on power equipment and did plasma cutter installations that ran on 460v 3 phase for over fifteen years. No license required.

If 50v were lethal there would be one hell of a lot of welders falling dead on the job every 24 hours. As I mentioned previously there is a LOT of welding equipment that produces at least 80 OCV. So if the operator leaned his elbow on the workbench while holding the stinger in one hand, while the ground clamp is bolted to the workbench, there's 80 volts running through his body. Totally not twitching .. totally not unable to let go of the stinger ... totally not dead.

I probably burned over two thousand pounds of welding rod, TIG rod, and MIG wire over the course of ten+ years. Not even a tickle ... not once.

Too many people around here that get their education from the University of "Everybody Knows That".

meh
wackelpeter
It's the current that's lethal… a small spark from static discharge when you pull off your Shirt can have several Kvolts and it isn't lethal also here in Germany for the old ISDN telephone standard the voltage getting in to the Uk0 socket of the terminal Adapter where it would be changed to the S0 bus was 90V... i used to check this often by touching it and "feel" if it's there.

On the other Hand if you have an accumulator like say 12V/24Ah you can nicely make bigger metal strips glow with it because it can deliver a lot of current, but touching both ends (+ and -) doesn't harm you because 12V and some Megaohms (the average body resistance) according to ohms law doesn'T deliver much current...

Also DC voltage at higher Levels is also more likely to contract your muscles so that you're stuck on the object as the same voltage in AC.

Also there is the high voltage area where you better Keep some distance to the object because without even touching it and when you come to lcose this can cause an electric rollover (is that the correct term?) that is likely supposed to kill you, because high voltage source able to drive a big load of current makes your body and air resistance negligible in it's urge to drive it'S load down to earth and settle the different load/Electric potential between both Sources...
dubonaire
wackelpeter wrote:

Also DC voltage at higher Levels is also more likely to contract your muscles so that you're stuck on the object as the same voltage in AC.


Partly true, both contract your muscles but because AC goes through zero you have an opportunity to pull away, which is exactly what does happen except at very high levels. I've had a couple of 240V shocks and fortunately the pathway was less dangerous. I've also had a 100V DC shock and it was a really strange and disconcerting experience. My arm muscles just kept on tightening and I didn't realise what was happening at first.

For what it's worth AC is most dangerous when it passes in a direction in your body closest to a nerve pathway in the heart from a node called the Bundle of His to the point of the apex of the fascicular branches. Unfortunately 50-60Hz frequency is very efficient for electricity transmission, but is coincidentally the most likely to stop the correct rhythm of heart contractions.
wackelpeter
dubonaire wrote:
wackelpeter wrote:

Also DC voltage at higher Levels is also more likely to contract your muscles so that you're stuck on the object as the same voltage in AC.


Partly true, both contract your muscles but because AC goes through zero you have an opportunity to pull away, which is exactly what does happen except at very high levels. I've had a couple of 240V shocks and fortunately the pathway was less dangerous. I've also had a 100V DC shock and it was a really strange and disconcerting experience. My arm muscles just kept on tightening and I didn't realise what was happening at first.

For what it's worth AC is most dangerous when it passes in a direction in your body closest to a nerve pathway in the heart from a node called the Bundle of His to the point of the apex of the fascicular branches. Unfortunately 50-60Hz frequency is very efficient for electricity transmission, but is coincidentally the most likely to stop the correct rhythm of heart contractions.


yep that's what i meant, therefore i wrote being stuck on the object… i had several contacts with the life wire of AC mains in my life and got thankfully fie away every time... only once i fell from a ladder, but that was onyl due to my shock and in was only 1,5 meter up on the ladder… needed some power for my Access Control unit and had a Junction box in the ceiling… was working with it under power as i couldn't find the fuse for it and accidentally touched the life wire with my Hand and my arm leaning on the metal Frame of this suspended ceiling i had the current flowing from my Hand through my arm into the metal… yeah thatwas very unpleasant but in this case also a bit of good fortune… anyway i wasn'T fast enough to recognize it and so half stumbled and half i fell from the ladder losing my balance because of the surprise, making a lot of noise and shortly after all the doors on the Floor were open and People Looking at me, myself trying to act as if Nothing happened… smile
chachi
long ago i had a friend whose dad worked for the san jose science and tech museum, and they grew up with all these “toys” of bygone ages. one was a machine that was meant to use electricity to cure you of whatever ails, it had two large pieces of brass connected to electrical generation and you would hold these handles while a little brass slide was pulled out to increase the voltage. kids being kids, the two brothers were trying to see how much voltage they could take one day and my friend’s brother musta been pissed at something cause he pulled the slide all the way out and tossed it across the room, leaving his brother unable to ungrip the paddles and put the slide back in. apparently my friend was trying to pick it up with his teeth to get it back in.
felixer
obviously voltage isn't everything. what makes something deadly is the current that goes thru your body. esp from one hand to the other as it goes thru the heart. i've had shocks from a 7KV/800W neon psu. not very nice and to be avoided. but i survived ... now let's move on to a nicer subject ...
cornutt
never mind, dup
cornutt
mskala wrote:
The 48V telephone DC voltage is probably also relevant. I'm sure it predated electrician licensing in the modern form of that, and it'd make sense that when making those rules they might want to have the rules not apply to existing telephone systems.


It's my understanding that it was a result of the batteries used. Kind of fun story: A long time ago, I worked on a video switching system for Pacific Bell. Part of the spec was that it had to run off of 48V DC, because that was what they had in the switching office. We puzzled over how to test it, since we didn't have a power supply that could run at 48V and supply enough current. The answer was four car batteries on a pallet, wired in series. To charge this mess, they rigged up something with an old transformer, a couple of power diodes, and a clothes dryer heating element as a current limiting resistor. All of this was mounted on the pallet using the old ceramic knobs that they used to use for knob-and-tube circuits. I was always afraid that the heating element was going to ignite the hydrogen from the batteries. They kept a fan blowing on it when it was charging. It was mad-scientist as hell, but it worked.
slow_riot
The electrostatic speakers I use are biased internally at around 7kV (albiet at low currents). If you wanna meet up with your alien buddies the shell of your spaceship will likely be biased at a higher voltage even than 7kV. Working with electricity is a part of our world now.

My oscillator modules output at +/-10V. Offset voltage/current, crossover distortion are all lower; signal to noise is higher.
mskala
cornutt wrote:
mskala wrote:
The 48V telephone DC voltage is probably also relevant. I'm sure it predated electrician licensing in the modern form of that, and it'd make sense that when making those rules they might want to have the rules not apply to existing telephone systems.


It's my understanding that it was a result of the batteries used. Kind of fun story: A long time ago, I worked on a video switching system for Pacific Bell. Part of the spec was that it had to run off of 48V DC, because that was what they had in the switching office.


Yes. Telephone central offices always used to have big banks of batteries supplying 48VDC for the whole works - which was one reason the phones could stay up even during a failure of the regular power grid.
pricklyrobot
Rex Coil 7 wrote:
sduck wrote:
felixer wrote:
us law says that everything over 50V is lethal and should be taken care of my special measures.


What? Who said what? What law? Lethal? License what? Do you actually know what you're talking about?

You don't need a license in the US to work on anything above 50v. I have several licensed electrician friends, and that has nothing to do with how the licensing works. I routinely work on 120 and 240 volt circuits with no license. Knowledge is the key. Knowledge and a few dollars will get you a license.
Agreed ... I don't know where this whole 50v bullshit is coming from but it's way off the mark

50V is the cutoff when you’re talking about building/repairing the power delivery system (installing wire, receptacles, tying into the utility’s supply).
Which is why I need an Electrical License to do my job, but the guys who run the Data/Fire Alarm/AV cables don’t.
This obviously doesn’t apply to equipment connected to the power delivery system (which is probably more relevant to this thread). You don’t need an Electrical License simply to work on ‘equipment that uses electricity’ regardless of the voltage.
My initial comment was just a speculative attempt to clarify what I thought Felixer might have been trying to get at. hmmm.....
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