Are there any technical reasons not to use the classic 4-20mA industrial current loop standard for powering the onboard electronics in a guitar, and delivering the audio signal?
Current loop industrial sensors have existed for decades, yet I can find little information about their use with analog signals that extend beyond the vocal frequency range.
Cable wise you could just use a standard microphone twisted pair cable with a TRS 1/4" jack on either end.
Current loop industrial sensors have existed for decades, yet I can find little information about their use with analog signals that extend beyond the vocal frequency range.
Cable wise you could just use a standard microphone twisted pair cable with a TRS 1/4" jack on either end.
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I can't see any reason why it could not be made to work. A current can carry an analogue signal just as well as a voltage. You just have to remember to invert all your thinking. For example, you need high source impedance and low load impedance and a cable with not too much inductance.
You piqued my curiosity and I read something about them.
Very interesting idea, and extremely clever/useful for their original intended application: process monitoring and data transmitting.
They claim very low sensitivity to noise and interference, which is clear to understand doing a little Math: 24V supply and 20 mA current translate to 1200 ohm equivalent impedance, and being sensitive to current only and not at all to voltage makes it "comparable" to a balanced Audio line (which IS sensitive to voltage interference but cancels it if well adjusted).
So a Current Loop system seems to be an alternative way to transmite Data/Signal reliably, over long distances and with minimal or no interference.
So far it looks very good.
Now to perceived disadvantages (not an expert by any means, but long experience in Audio and Analog design) :
a) you need a 24V 20mA capable source.
No big deal, since it would be situated at the Amplifier end, the Guitar end being powered by the loop itself.
b) now the crux of the question: haven´t read 20mA loop general specs, nor device datasheets (yet, I found them VERY interesting so I will) BUT have already read warnings that they are "not well adapted to Serial Data transmission" and they are "slow".
So that seems to imply they have trouble even handling Telephone Audio (250 to 2500 Hz) which is able to transmit "serial data" (think of an old style Telephone Modem) which makes me fear they won´t be able to properly handle a Guitar signal, which should have *at least* 5 to 7 kHz bandwidth.
That said, I have designed and built "similar" 2 wire preamp powered Microphone heads, which I use for remote audio pickup around my Home and Shop, for security purposes, go figure.
At will I can listen to Audio/conversations anywhere around my Home, in remote rooms 4 floors away, etc, with very simple 2 wire connections.
So I guess you can build a similar dedicated system, even if not strictly an Industrial 20mA Loop nor using its dedicated ICs and Hardware.
Or you can build a Phantom Powered preamp inside your Guitar, which would be the mainstream Audio approved solution 🙂
Very interesting idea, and extremely clever/useful for their original intended application: process monitoring and data transmitting.
They claim very low sensitivity to noise and interference, which is clear to understand doing a little Math: 24V supply and 20 mA current translate to 1200 ohm equivalent impedance, and being sensitive to current only and not at all to voltage makes it "comparable" to a balanced Audio line (which IS sensitive to voltage interference but cancels it if well adjusted).
So a Current Loop system seems to be an alternative way to transmite Data/Signal reliably, over long distances and with minimal or no interference.
So far it looks very good.
Now to perceived disadvantages (not an expert by any means, but long experience in Audio and Analog design) :
a) you need a 24V 20mA capable source.
No big deal, since it would be situated at the Amplifier end, the Guitar end being powered by the loop itself.
b) now the crux of the question: haven´t read 20mA loop general specs, nor device datasheets (yet, I found them VERY interesting so I will) BUT have already read warnings that they are "not well adapted to Serial Data transmission" and they are "slow".
So that seems to imply they have trouble even handling Telephone Audio (250 to 2500 Hz) which is able to transmit "serial data" (think of an old style Telephone Modem) which makes me fear they won´t be able to properly handle a Guitar signal, which should have *at least* 5 to 7 kHz bandwidth.
That said, I have designed and built "similar" 2 wire preamp powered Microphone heads, which I use for remote audio pickup around my Home and Shop, for security purposes, go figure.
At will I can listen to Audio/conversations anywhere around my Home, in remote rooms 4 floors away, etc, with very simple 2 wire connections.
So I guess you can build a similar dedicated system, even if not strictly an Industrial 20mA Loop nor using its dedicated ICs and Hardware.
Or you can build a Phantom Powered preamp inside your Guitar, which would be the mainstream Audio approved solution 🙂
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$1 electret mikes are "current loop", though not near 20mA.
Phantom mikes run power and signal together, but signal is normally handled low-Z and extracted differentially.
I used a self-made stereo powered interface for decades. (It might still be in use.) Invented for suspended spaced-pair microphones. However I also ran a pair 10 feet apart and 150 feet from the recording closet, and much of that in clear speaker line.
Line capacitance is important. As the scheme started recording to good cassette and lines could be long I picked ~~500r as a line termination. Various versions had amplifier output impedance from 47r to >1K, all seemed to have good treble. 470r into 10,000pFd is 35KHz. (One worst-case bench-test with "zero" impedance killed a transistor; also you want "some" impedance into RF, so I always had a plain series resistor in the amp.)
Phantom mikes run power and signal together, but signal is normally handled low-Z and extracted differentially.
I used a self-made stereo powered interface for decades. (It might still be in use.) Invented for suspended spaced-pair microphones. However I also ran a pair 10 feet apart and 150 feet from the recording closet, and much of that in clear speaker line.
Line capacitance is important. As the scheme started recording to good cassette and lines could be long I picked ~~500r as a line termination. Various versions had amplifier output impedance from 47r to >1K, all seemed to have good treble. 470r into 10,000pFd is 35KHz. (One worst-case bench-test with "zero" impedance killed a transistor; also you want "some" impedance into RF, so I always had a plain series resistor in the amp.)
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