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will 9vDC harm a guitar pickup?

Hey all;

Will 9vDC damage a guitar pickup? I have a piezo pickup in my electric guitar, as well as 2 magnetics. The piezo provides acoustic sound and connects to my pedalboard on the ring of a TRS phone plug. I'd like to put a buffer amp inside the guitar and phantom power it from my pedalboard by putting 9vDC on the ring of the pedalboard input jack. However, if I do this, the tip of the plug (which will be connected to my magnetic pickups) will come in contact with the 9v as it pushes past the ring connector on the jack. Could this cause harm to my pickups? Also, if I were to connect a normal (i.e., 2 conductor) plug to the input, for use with another guitar, the 9vDC would be shorted to ground. I know that the 78xx series of regulators have short circuit protection, but would it withstand being shorted to ground for an extended period of time?

Thanks

Reply to
tempus fugit
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A little clarification please. You can't just put 9 volts somewhere, it has to be 9 volts with respect to another point. Where is the other point? If your pickup also shares these two points you may do damage to the device. I'm not sure what you want to do with the regulator, but no, I will not 'like' to be shorted that's why its protected against it. It will shut off. Tom

Reply to
Tom Biasi

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The 9v would be with respect to ground - the same ground that the pickups would be connected to. When you say 'do damage to the device' which device are you referring to? The pickup or the buffer amp?

Thanks

Reply to
tempus fugit

Huh?

The very notion of "phantom power" means superimposing DC power along a line that is used to carry an audio signal. By its very definition, it takes both signals into effect.

You couple your pickup to the line with a suitable value coupling capacitor, which means the pickup will never see DC. Then at the other and, there is another coupling capacitor before the signal hits the preamp, so it will only see the audio signal, no DC.

Then, the audio line can be at any DC voltage, the audio signal will never notice. You couple the DC in at the preamp side with a resistor of suitable value (you'll want it to be a reasonably high value resistor so it doesn't load down the audio circuit, which of course is why there is a limit on how much power you can draw from this, since the larger value resistor will become a larger part of the circuit the more power is pulled through it), and then at the guitar end, you have another resistor to pull the power off the audio line.

Michael

Reply to
Michael Black

"tempus fugit"

** No.

The piezo device has near infinite DC resistance while the magnetic ones will have about 5 to 10 kohms - making the heat dissipation miniscule.

..... Phil

Reply to
Phil Allison

Normally a volume-control potentiometer exists between the pickup and the guitar's jack socket and one of the possible wiring arrangements has the wiper connected to the tip and one end of the track connected to the sleeve of the guitar's jack socket. In that case, a possible danger is applying 9 volts to the end of the pot track if the guitar volume is turned down when the 3-pole jack plug on the other end of the cable is inserted into the box providing the power.

There's also scope for some loud bangs if the output of the buffer amp is capacitively coupled (and the guitar's volume is turned up) - on the way in to the power box, the tip of the jack plug sees 9 volts, then it's connected to the input of a high-gain amplifier. You might need to post a warning on the front of your amp to keep its volume down when connecting!

There are better ways to do this. Since the jack wiring will be non-standard, you could consider putting power on the tip and audio on the ring. And surely the power could be supplied through a resistor to limit the maximum current.

Chris

Reply to
christofire

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