maybe this is stupid but how is it a signal and voltage travel together

[hesamadman]

What I mean is, you strum a note on a guitar, the signal travels through the circuit blah blah blah and then out of the speaker.At the same time a power source powers the speaker through the same connection. I'd like to understand how this works? Any input or suggested reading?

[Steve Conner]

"Signal" is just EE jargon for a particular kind of voltage. One that varies with time in a way that represents some sort of information we are interested in.

So, the signal and the voltage travel together because they're the same thing.

[hesamadman]

"Signal" is just EE jargon for a particular kind of voltage. One that varies with time in a way that represents some sort of information we are interested in.

So, the signal and the voltage travel together because they're the same thing.

So as the small voltage that's plucked from a guitar string gets i ncreased in the power amp, is it safe to say the frequency does not change?

[Dave H]

So as the small voltage that's plucked from a guitar string gets i ncreased in the power amp, is it safe to say the frequency does not change?

The frequency is the same. The small guitar voltage controls the ‘valve’ (power amp) which lets power from the power supply through to the speaker.

[soundmasterg]

The tubes are powered by DC voltage which comes from the power transformer. It starts as an AC voltage and this is converted to DC with diodes, and RC circuits (resistor and capacitor) and/or inductors filter the noisy AC ripple out of the DC so that the tubes won't amplify noise and hum.

The signal is an AC voltage that is generated by your guitar. This AC voltage goes into the grid of the tubes in most cases and because of how vacuum tubes work, a small signal at the grid controls a large, amplified signal that usually comes out the plate. This signal starts out small, gets amplified, goes through a tone stack and gets attenuated, gets amplified again and again, goes through a phase inverter to split the phase for each power tube, gets amplified a lot by the power tubes, (which supply a lot of current which is what gives power gain) and goes out to the speaker through the output transformer. At each stage the sound of your AC guitar signal is modified and shaped and extra harmonics are introduced or taken away. The AC signal rides on top of the DC supply voltage and capacitors are used to block the DC from interfering where it shouldn't so that only the AC signal passes from stage to stage.

Hope that is basic enough for you to get an idea of how it works....

Greg

[rjb]

The tubes are powered by DC voltage which comes from the power transformer...
Hope that is basic enough for you to get an idea of how it works....

But, but, but... I have a solid state amp.

[R.G.]

Then it's all because your amp is possessed by Maxwell's Demon in solid form.

[Steve Conner]

The Three-Legged Fiend, even.

In an attempt to summarise SoundmasterG's post: an amplifier is a device for making a small signal bigger by fashioning an enlarged copy of it out of electricity drawn from the wall socket. In hi-fi amps the emphasis is on making an accurate copy. Guitar amps are designed to alter ("distort") the signal somewhat to make it sound more exciting.

[DrGonz78]

Not a long thread (Yet) but to all that ask this same question, which should be all beginners or intermediates, should read twice or more. Nothing is stupid about this thread at all. Starting at a source then tracing the signal through the amp is what we want to achieve - output. Whether it is a tube or solid state amp. I am happy with the answers already given which these guys are way beyond me. I just want to add to the OP that guitar pickups are transducers of a Sine Wave (AC signal voltage) that is passed through to the preamp of a guitar amplifier. Just remember that Sine waves are what we ultimately hear and not DC waves. Cuz if your hearing DC waves then you have a not so natural sounding wave signal. Often times a solid state amp will clip a sine wave and that is ultimately why a Solid State amp will get the reputation of having a harsh sound. Then again tube distortion is clipping the waveform just the same, although the signal has harmonic values that cannot be achieved in a solid state domain. Thus we say a tube distortion is much more natural and warm sounding than a solid state distortion effect. The battle between even and odd order harmonics begins.

[blearyeyes]

The strings move back and forth through the magnetic field of the pickup generating a small fluctuating voltage in the coil inside. How frequently it moves back and forth is frequency. You now have an analogous signal the represents the vibrating guitar which will also contain overtones or harmonics which are multiples of your fundamental frequency which is the basic speed of the strings vibration. Harmonics are what create the timbre or tone of the instrument which is how we can tell the difference between a trumpet and guitar playing the same note. That signal goes into a pre amp that raises the voltage or amplitude of the signal from a tiny fluctuating representation of your guitar to a line level. You also can raise or lower ranges of frequencies using circuits that use phase cancelation and addition to change the "tone" and timbre of the signal. This has the same fundemental frequencies of the vibrating strings even though it is modified with EQ. This line level signal goes to the power amplifier stage and its voltage is increased again to speaker level. This signal is run into the coils of the speaker which generates a magnetic field that represents what you played. That fluctuating magnetic field reacts with the fixed magnet in the speaker to push or pull the speaker back and forth in a fashion that represents your guitar playing. This is the reverse of your guitars pickup. Sound pressure waves are created that travel through the air to your ear which translates the frequencies into a signal that your brain analyzes and recognizes as a guitar because of the tone or timbre and frequency content traveling through the air.

Your guitar sound is represented by fluctuating voltage.

The amplifier makes your little pickups fluctuating voltage output strong enough to push speakers around.

[Rick Erickson]

Probably just rehashing what has already been said here, but:
The electrons from the guitar (signal) never reach the speaker. The guitar signal is used to control a series of "valve's" (not necessarily tubes) that in effect replicate and amplify the original signal, by means of the power supply, and send the resulting new signal to the speaker. No amplifier made can do this perfectly, so we typically measure an amp's ability to convert a small signal to a large signal (amplification) in terms of harmonic distortion and signal to noise ratio - that is: how many artifacts, or "extra" signals are added to the original signal during the amplification process. The size of the power supply in effect controls how much power `can be delivered to the speaker. The signal from the guitar pickup(s) is sent to ground after it reaches the first stage of an amplifier. Everything after that is a replica of that original signal.

[blearyeyes]

Interesting.

Just like the vibrations from the guitar never really reach the speakers. An analog representation is sent to the amp.

So the input coming from the guitar is sent to ground after it is used to control whatever is going to output a higher gain version of the fluctuating voltage?

Is the preamp output sent to ground after being used to control the output tubes or ICs as well?

[J M Fahey]

So the input coming from the guitar is sent to ground after it is used to control whatever is going to output a higher gain version of the fluctuating voltage?

Is the preamp output sent to ground after being used to control the output tubes or ICs as well?

Yes, of course.

Although to be more precise, rather than "to ground" what you need is a return path for the electrons, literally.

That's why you need 2 wires for everything.

Using the metallic chassis as return path and calling it "ground" is just to simplify the concept and layout, but that's what it actually is.

[eschertron]

Interesting.

Just like the vibrations from the guitar never really reach the speakers.

..and just like at my house, the vibrations from my wife's voice never reach my ears


but to be clear, the 'vibrations' i.e. the signal from the guitar absolutely DOES pass all the way to the speakers and beyond. As Juan explains, the ELECTRONS make theire circuits inside each portion on the signal path - guitar to input tube grid, tube 1 plate (the first stage of amplification) to the next grid, etc. etc., the power tube to the OT, the OT secondaries to the speaker voice coil - where the sound is TRANSDUCED back into acoustic wave energy and the sound travels to the listener's ears. All part of the same signal (distorted as it is by the time it reaches the listener) but consisting inside tha amp of several current loops. I'm just learning the amplifier theory myself, but it seems to me that it is when the individual current loops inside the amp 'mingle' by way of poor grounding (the return path that Juan mentions) then the amp is susceptible to hum.

[blearyeyes]

..and just like at my house, the vibrations from my wife's voice never reach my ears


but to be clear, the 'vibrations' i.e. the signal from the guitar absolutely DOES pass all the way to the speakers and beyond. As Juan explains, the ELECTRONS make theire circuits inside each portion on the signal path - guitar to input tube grid, tube 1 plate (the first stage of amplification) to the next grid, etc. etc., the power tube to the OT, the OT secondaries to the speaker voice coil - where the sound is TRANSDUCED back into acoustic wave energy and the sound travels to the listener's ears. All part of the same signal (distorted as it is by the time it reaches the listener) but consisting inside tha amp of several current loops. I'm just learning the amplifier theory myself, but it seems to me that it is when the individual current loops inside the amp 'mingle' by way of poor grounding (the return path that Juan mentions) then the amp is susceptible to hum.

I get what you're saying. But what I meant was what starts as acoustic vibrations of string and wood is transduced into electrons. At that point the acoustic energy is no longer used. It dissipates into the air. So it never makes it to the speakers. It's analog representation travels on down the chain and is eventually recreated by a speaker, back into acoustic energy. But the original acoustic energy is physically gone.


It's crazy. Humans have harnessed electrons and use them to make music.