Stupid argument

[SpiderVenom]

Got into an argument with a guy yesterday about amps.

Now, my belief is that it's an input only device (in terms of plugging the guitar in). That is, pickups generate a signal and send it to the amp. The end. He reckons the amp sends power back, as well... or something like that.

Who's right?

 

[Artie]

Re: Stupid argument

The amp doesn't send power back to the guitar . . . unless its broke.

The amp does have an input impedance, however, and that can have a very slight affect on the guitars sound.

 

[tone4days]

Re: Stupid argument

well, at least you know the arguement is stupid

the guitar generates an AC signal that is fed into the amp ... period

since every circuit requires a 'round trip' in order to work, it might be put forth by someone trying to make a very silly and useless arguement that the signal reverses direction every half cycle (frequency dependent, natch) ... but this is not the same as the amp changing from a device receiving a signal to one generating a signal

t4d

 

[jdm61]

Re: Stupid argument

Techinically, a guitar cannot generate an AC signal unless it is being fed something......now the signal may take the form of voltage or current no matter how miniscule.....i have no clue, but SOME kind of signal must be travlelng up that cable in onder to get those coils a poppin....lol For those of you that are old enough to remember records, think about how many wires went to your turntable cartridge.........4, when you only need 2 to output a stereo signal. Likewise, why are pickups grounded?

 

[tone4days]

Re: Stupid argument

Techinically, a guitar cannot generate an AC signal unless it is being fed something......now the signal may take the form of voltage or current no matter how miniscule.....i have no clue, but SOME kind of signal must be travlelng up that cable in onder to get those coils a poppin....lol

jdm61's post is completely incorrect

the pickup generates the signal ... the vibrating guitar string creates a disturbance in the electromagnetic field that is created by the pickup JUST FROM BEING THERE (it is not fed anything) ... this disturbance is transduced (i.e. 'picked up') into a current in the coil which flows out the guitar to the amp

pickups are grounded to reduce EM noise picked up from the environment ... i would imagine that there is a safety measure there in case any malfunction in the chain sends a DC bias back up the chain

as for the four wires on the turntable cartridge, you answer your own question .. you need two wires per side to capture the stereo AC signal from the stylus ...

 

[Artie]

Re: Stupid argument

I gotta back-up T4D here. The signal that comes from a guitar is absolutely AC. The current reverses direction at the frequency of the strings vibrating.

And yup . . . all my turntables had 4 wires coming out of them. Left+ground, and right+ground.

 

[tone4days]

Re: Stupid argument

yeah, it's pretty straightforward ... faraday's law in action

Faraday's law tells us that a changing magnetic flux will induce an emf in a coil ... in the case of a guitar, the guitar string changes the magnetic flux caused by the presence of the magnets in the pickup ... 'emf' is an acronym for electromotive force which most people just call voltage .. the voltage gets created in the coil of wire wrapped around the bobbin

 

[SpiderVenom]

Re: Stupid argument

Yay!

I tried my hardest to tell him that all that happened was strings vibrate, disturb a magnetic field, and create a signal in the coil which is fed to the amp. But no, he was convinced the amp sends power back somehow.

I'll be showing him this thread, and then gloating for a while. Thanks guys

 

[greendy123]

Re: Stupid argument

yeah, it's pretty straightforward ... faraday's law in action

Faraday's law tells us that a changing magnetic flux will induce an emf in a coil ... in the case of a guitar, the guitar string changes the magnetic flux caused by the presence of the magnets in the pickup ... 'emf' is an acronym for electromotive force which most people just call voltage .. the voltage gets created in the coil of wire wrapped around the bobbin

You just reminded how much physics class sucks, but that was one good thing I learned in there.

 

[aleclee]

Exception to the rule

Exception to the rule

The Vetta can power a Variax using a VDI cable but somehow I doubt this is what the guy was talking about.