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Beginner Questions About Guitar Wiring And The Science Behind It


Cordeduroi
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Hello all! Since I am a new member and this is my first post, allow me to give some background on myself before I dive into my "beginner questions". (Feel free to skip this paragraph if you don't care. B)) I've been an acoustic player for well over 10 years (Taylors, mostly) and have only started playing electric guitar for about a year now. Right now I have a late-model (2008, I think) Gibson Melody Maker. This guitar has the single coil bridge pickup + 1 volume + 1 tone. Verrrry basic! I eventually got curious and took off the pick guard to look at the internals. That sparked the urge to learn as much as I can about guitar wiring and make some mods to my guitar. The Melody Maker seems like an excellent candidate for trying out different guitar mods (even moreso than a Strat, IMO) because everything is housed right under the pick guard, making it very easy to mount new pickups and pots, with plenty of room for wiring. I am also not concerned with this guitar's resell value as I plan to hang onto it no matter what. So having said all that, I've been researching wiring techniques, pickup types, pots, shielding, etc for months. I've been reading websites, forums, YouTube, etc. And now I find myself pretty knowledgeable in some areas but lacking the foundational basics. And I'm not sure how/where to get that basic engineering/electrical knowledge.

These are the kinds of questions that I have rattling around in my head: ( :D )

(1) When you plug a passive pickup into a guitar amp, does the amplifier send power into the guitar's circuit? Or is it just a one-way signal flow from the guitar to the amp?

(2) What kind of power is flowing inside a guitar circuit between the pickups, pots and output jack? There must be some level of low-wattage electricity. Is the electricity generated by the magnetics in the pickup? Is there still power flowing in the guitar's circuit even when the guitar is not plugged in (assuming it's a complete circuit)?

(3) What is a "line-level" signal? (4) Is there a scientific specification for line-level sound? (5) Is the signal coming out of the guitar before amplification considered line-level? (6) How do you know when you're dealing with a line-level signal or an amplified signal? If in doubt, can you use a voltmeter or something?

(7) What does an amplifier actually do to the signal to make it louder? (I have a vague understanding of amps, volts, wattage, ohms.) Does it simply increase the wattage, leaving everything else the same?

(8) Why is it that you never hear about amps or volts when dealing with guitars or amplifiers? You only hear about X wattage @ X ohms. Does an electrical audio signal not use amps/volts? (9) Is an electric audio signal AC or DC?

(10) Is an audio signal considered analog any time that there is a real, electrical current flowing? (For example, the output directly from the guitar.)

(11) When I look at the internals of an amp, the wiring consists of little, thin wires and circuit boards up until the actual amplification. After amplification, I begin to see thick, beefier wires. What is the difference between pre-amp and post-amp wiring? Just a larger gauge/thickness of wire? (12) Why is a larger wire necessary after amplification? (13) How do you know what type of wire you need? Is there only pre-amp and post-amp wire types? (14) Why is only copper wire used in guitars/amps?

(15) What happens if you accidentally touch the live wires inside of a guitar while it is plugged into an amp? Will it zap you? (16) If you temporarily short the circuit inside a guitar, can you ruin some of the electronics? (17) What about post-amplification wires? I have an amp that outputs 120 watts @ 8 ohms. Is that enough to zap you if you accidentally touch the live wire? (18) Can you ruin the amp if you temporarily short circuit the wires?

I've listed all of these questions not necessarily expecting an answer on each one, but rather to give examples of the kinds of questions that I have. I would like to discuss these questions in this thread if anyone is willing. But I'd also be happy to have you suggest ways that I can learn these audio basics on my own (books, websites) B). If you know these engineering-type questions, how did you originally learn this stuff?

Please help a guy out who is new at this stuff! It will be much-appreciated! I plan to continue participating in these forums on a regular basis. I also plan to post pictures/descriptions on my website of the mods that I work on. I will keep those links in my signature so anyone can check out my latest projects.

Thanks! :D

Edited by Cordeduroi
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(1) When you plug a passive pickup into a guitar amp, does the amplifier send power into the guitar's circuit?

No.

(2) What kind of power is flowing inside a guitar circuit between the pickups, pots and output jack?

Very little.

Is the electricity generated by the magnetics in the pickup?

As a reaction to the vibrating strings.

Is there still power flowing in the guitar's circuit even when the guitar is not plugged in (assuming it's a complete circuit)?

Yes, if you strike the strings, it's dissipated internally as microscopic levels of heat.

(3) What is a "line-level" signal?

Whatever your equipment manufacturer says it is, there's no universal standard.

(4) Is there a scientific specification for line-level sound?

No, see (4), above.

(5) Is the signal coming out of the guitar before amplification considered line-level?

For most audio gear, it's a little lower than Line Level (but far higher than Mic Level!)

(6) How do you know when you're dealing with a line-level signal or an amplified signal?

A "line-level signal" is a good match to the expected input of the equipment...

Not too much (which leads to distortion) or too little (where it'll get lost in background noise).

If in doubt, can you use a voltmeter or something?

Input level meters on each piece of equipment are usual.

(7) What does an amplifier actually do to the signal to make it louder?

Takes your 0.5 volt, high-impedance guitar signal and amplifies it through gain stages.

(8) Why is it that you never hear about amps or volts when dealing with guitars or amplifiers? You only hear about X wattage @ X ohms.

Because that's the information you need to have to select the correct loudspeakers.

(9) Is an electric audio signal AC or DC?

AC

(10) Is an audio signal considered analog any time that there is a real, electrical current flowing? (For example, the output directly from the guitar.)

Yes. It would only be digital when converted to a bit-stream for processing.

(11) When I look at the internals of an amp, the wiring consists of little, thin wires and circuit boards up until the actual amplification. After amplification, I begin to see thick, beefier wires. What is the difference between pre-amp and post-amp wiring? Just a larger gauge/thickness of wire?

Thicker wires carry heavier currents without overheating.

In the POWER stage of your amp, there are heavier currents.

(12) Why is a larger wire necessary after amplification?

See (11).

(13) How do you know what type of wire you need? Is there only pre-amp and post-amp wire types?

You can use the heaviest gauge wire throughout if you want.

It makes economic sense to use thinner wire when you can get away with it.

Early in the signal chain, where the signals are weak, SHIELDED CABLE is used to prevent electrical interference.

(14) Why is only copper wire used in guitars/amps?

It's a good-conductivity, relatively cheap wire.

No need for gold...

(15) What happens if you accidentally touch the live wires inside of a guitar while it is plugged into an amp? Will it zap you?

Only if your amplifier is faulty and leaking high voltages up your guitar cable.

(16) If you temporarily short the circuit inside a guitar, can you ruin some of the electronics?

Not with only a magnetic pickup and passive electronics (pots and capacitors).

You may ruin onboard active electronics by careless handling (but it's not likely).

(17) What about post-amplification wires? I have an amp that outputs 120 watts @ 8 ohms. Is that enough to zap you if you accidentally touch the live wire?

120w at 8 ohms means a signal voltage of approximately 31 volts AC...

No, that will not result in a lethal current passing through your body.

(18) Can you ruin the amp if you temporarily short circuit the wires?

You can ruin a Valve Amp if you run it without a speaker connected.

Most amps can recover from running into a short circuit for a short time.

You can't damage your guitar amp by shorting-out the guitar cable.

how did you originally learn this stuff?

Like you- asking questions, reading, experimenting...

Edited by elmo7sharp9
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(1) When you plug a passive pickup into a guitar amp, does the amplifier send power into the guitar's circuit? Or is it just a one-way signal flow from the guitar to the amp? no

(2) What kind of power is flowing inside a guitar circuit between the pickups, pots and output jack? There must be some level of low-wattage electricity. Is the electricity generated by the magnetics in the pickup? Is there still power flowing in the guitar's circuit even when the guitar is not plugged in (assuming it's a complete circuit)? the strings vibration over the pickups creates the power, the amp boosts that so you can hear it.

(5) Is the signal coming out of the guitar before amplification considered line-level? no

(11) When I look at the internals of an amp, the wiring consists of little, thin wires and circuit boards up until the actual amplification. After amplification, I begin to see thick, beefier wires. What is the difference between pre-amp and post-amp wiring? Just a larger gauge/thickness of wire?

(12) Why is a larger wire necessary after amplification?

(13) How do you know what type of wire you need? Is there only pre-amp and post-amp wire types? you can use any, just make sure its thick enough for the amount of voltage going through it, or it will be like fuse wire.

(14) Why is only copper wire used in guitars/amps? its not, aluminium, silver wire can be used

(15) What happens if you accidentally touch the live wires inside of a guitar while it is plugged into an amp? Will it zap you? no

(16) If you temporarily short the circuit inside a guitar, can you ruin some of the electronics? no, thats how kill switches work

(17) What about post-amplification wires? I have an amp that outputs 120 watts @ 8 ohms. Is that enough to zap you if you accidentally touch the live wire? speakers can give you a shock if they are high voltage, ive not had one from a guitar amp.

(18) Can you ruin the amp if you temporarily short circuit the wires? very possible if you mess with the internals.

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i dont mean to be condecending but if you are really interested in this i think you should do some reading on electronics in general.

btw i would never short or unload the output of one of my amps they are made to be hooked to a speaker load at all times and it can do some damage to them if not.

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Thank you all for your most thorough answers! I really appreciate it.

One more questions about the use of potentiometers: I understand that higher rating pots allow a wider frequency range towards the higher end to pass through. But if you are using multiple pots of different ratings in your circuit, is the audio signal result always going to be reduced to the lowest-rated pot? For example, if I have a circuit of 3 pots: 1M + 250K + 1M ... does the use of the 250K pot in the circuit automatically nullify the 'benefit' of the 1M pots by reducing the entire audio signal output down to 250K?

(14) Why is only copper wire used in guitars/amps? its not, aluminium, silver wire can be used

Samba Pa Ti, does that mean that aluminium or other metal foil besides copper can be used for shielding purposes inside the guitar housing? Or is copper still the best metal for this job even with its high cost?

i dont mean to be condecending but if you are really interested in this i think you should do some reading on electronics in general.

Tim37, I agree, and as I stated in my original post, I have been actively researching these topics for a few months. The questions I had in my original post were specific issues that were still plaguing me after doing a significant amount of study on my own.

If anyone can suggest a good book or other resource on audio signal engineering that will help me boost my knowledge level, I'd appreciate it. I definitely want to learn more about this stuff. Thanks all!

:D

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One more questions about the use of potentiometers: I understand that higher rating pots allow a wider frequency range towards the higher end to pass through. But if you are using multiple pots of different ratings in your circuit, is the audio signal result always going to be reduced to the lowest-rated pot? For example, if I have a circuit of 3 pots: 1M + 250K + 1M ... does the use of the 250K pot in the circuit automatically nullify the 'benefit' of the 1M pots by reducing the entire audio signal output down to 250K?

It depends entirely on the circuit design.

For example a tone control circuit in an amplifier could use both pot values along with a variety of capacitors and resistors to give a suitable tone adjustment. There is no 'benefit' of using 1M or 250K or whatever. It depends entirely on the ear of the listener and what the designer is trying to achieve.

Potentiometers are purely resistive components ie they do not have a frequency dependent component (not at audio frequencies at least) In order to use them as a tone control, as in a guitar, they have to be coupled with a suitable capacitor to form a variable filter. Capacitors have an impedance determined by their value X = 1/(2 * pi * f) ie the higher the frequency (f) the lower the impedance.

Keith

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(14) Why is only copper wire used in guitars/amps? its not, aluminium, silver wire can be used

Samba Pa Ti, does that mean that aluminium or other metal foil besides copper can be used for shielding purposes inside the guitar housing? Or is copper still the best metal for this job even with its high cost?

alluminium works fine and is used in loads of guitars, if you have the budget put copper in, another good way is shielding paint but id only buy that if i was shielding a lot of guitars.

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alluminium works fine and is used in loads of guitars, if you have the budget put copper in, another good way is shielding paint but id only buy that if i was shielding a lot of guitars.

Awesome, I didn't know you could just use aluminum. I've seen the shielding paint for around $60 a pint. And I've found copper foil as an industrial supply for about $0.50 per foot, but it's not sold in small quantities so it would be an order of $40 up to $100. :D I'm trying to keep this as a relatively cheap hobby for now so I think I will use aluminum. Especially since I can always go back and re-do it with copper or paint later.

Anyway, your answer sparked another question: Is it equally beneficial to shield the inside of a speaker or amp cabinet with paint or metal foil? (It would have to be a very secure fit to prevent rattling, right?) And if you were re-wiring a speaker cabinet, would it still be beneficial to use shielded wire?

Just as a side thought, I bought some 22 AWG shielded wire for experimentation purposes (going to practice soldering, etc) and it is almost impossible to strip! The outer black casing slides off very easily, taking the shielding with it. And the inner clear plastic hangs on like grim death, stretching and bouncing back. I've completely cut through and/or crushed more wire than I've successfully stripped. B) Next time I will buy the shielded vintage push-back cable for sure! It has to be worth the extra $$. (See? I'm learning things already. :D )

Edited by Cordeduroi
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Potentiometers are purely resistive components ie they do not have a frequency dependent component (not at audio frequencies at least) In order to use them as a tone control, as in a guitar, they have to be coupled with a suitable capacitor to form a variable filter. Capacitors have an impedance determined by their value X = 1/(2 * pi * f) ie the higher the frequency (f) the lower the impedance.

Keith, thanks for your explanation. A light bulb came on when I read your reply. I've seen the use of capacitors such as orange drops in wiring diagrams, but they seem to be wired to be 'always on'. I eventually learned what these capacitors do at the technical level. I even researched tone bleed issues, etc.

But I did not understand the capacitors' function in tone control. If I now understand correctly, every potentiometer is nothing more than a volume control in itself. (Or to be more specific, a blender of 2 possible signals, one being full volume and the other being nothing.) But when you add a capacitor to one 'end' of a pot, you're basically adjusting the volume of that capacitor's specific impedance against the total/complete audio signal.

(P.S. This is really fun stuff now that I'm starting to understand it!)

Do the EQ knobs on an amp or stomp box work the same way? Just a chain of pots of various values with different sized capacitors attached to them?

Is the use of capacitors the only known way to alter the EQ of an analog audio signal? Or are there other wiring methods that will achieving the same result?

Edited by Cordeduroi
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But I did not understand the capacitors' function in tone control. If I now understand correctly, every potentiometer is nothing more than a volume control in itself. (Or to be more specific, a blender of 2 possible signals, one being full volume and the other being nothing.) But when you add a capacitor to one 'end' of a pot, you're basically adjusting the volume of that capacitor's specific impedance against the total/complete audio signal.

Well sort of. There is only 1 signal though. In a potentiometer for a volume control it is applied across the resistance of the track with one end being at ground, usually. The wiper moves across the track and forms a potential divider which taps off the output depending on what the ratio of the two parts is. This will vary from 0:R to R:0 and all possible ratios in between where R is the value of the pot.

A tone control is a variable resistance in series with a capacitor such that the total impedance is R + X where R is the resistance value and X is the impedance determined as I explained above. So changing the R will determine which frequencies get passed through.

Do the EQ knobs on an amp or stomp box work the same way? Just a chain of pots of various values with different sized capacitors attached to them?

Yes

Is the use of capacitors the only known way to alter the EQ of an analog audio signal? Or are there other wiring methods that will achieving the same result?

No capacitors are not the only way. You can use an inductor as well. Inductors are the inverse of capacitors ie X = 2 * pi * F * L the impedance increases with frequency Capacitors X = 1/(2*pi* F* C) (I forgot the C above) However inductors are usually formed by coils of wire which can and do pick up noise induction from around them so are generally avoided as far as possible.

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