Fundamental guitar electronics question

[samuelzero]

Hi folks,

I'm relatively new to working on my guitars' electronics. My experience is limited to swapping pickups, and I'm about to gut, shield, and rewire a cheapo Mexican Jazz Bass for the fun of it.

My question is this: Electricity needs a closed circuit to flow, right? So when you're plugged into an amp, I'm assuming the amp's circuitry becomes part of that loop.

Can someone explain why I don't have 15 watts running back through the coils of my pickups when I crank up my Tiny Terror?

I don't know if there's a simple answer or not, but I appreciate any insight anyone can provide.

samuelzero

[Chuck H]

Electricity needs a closed circuit to flow, right? So when you're plugged into an amp, I'm assuming the amp's circuitry becomes part of that loop.

Can someone explain why I don't have 15 watts running back through the coils of my pickups when I crank up my Tiny Terror?

It simply doesn't work like that. Also, a "closed" circuit doesn't need to have only two ends (in / out). There can be peripheral inputs / outputs that behave relative to the circuitry. I know that probably doesn't make sense now, but remember that we are not just dealing with an electrical circuit, we are dealing with an electronic circuit.

An example would be the way a tube operates. Dual triode tubes act as preamps in your Tiny Terror. A triode is a cathode, a grid and a plate. The cathode is negative and the plate is positive. The plate is carying the high voltage. Electrons are trying to flow from the negative cathode to the positive plate. But the grid gets in the way. The grid is set at an electrical potential so that it only lets electrons pass if signal is applied to it. Signal (from your guitar for example) causes a shift in the electrical potential of the grid allowing electrons to pass from the cathode to the plate. Because the cathode / plate circuit is capable of much more voltage than the guitar signal, small changes at the grid caused by the guitar signal translate to bigger changes at the plate and amplification of the grid signal is achieved. The grid / guitar circuit acts like a valve to adjust the flow of electrons. Just the same way a small effort to turn on and adjust a faucet can allow a great amount of water to flow, depending on the potential of the water pressure. But you, who turned the faucet, in no way got wet or had to carry any water. Your guitar is not part of the output wattage of the amp. It's just turning the spigot.

Chuck

[samuelzero]

It simply doesn't work like that. Also, a "closed" circuit doesn't need to have only two ends (in / out). There can be peripheral inputs / outputs that behave relative to the circuitry. I know that probably doesn't make sense now, but remember that we are not just dealing with an electrical circuit, we are dealing with an electronic circuit.

An example would be the way a tube operates. Dual triode tubes act as preamps in your Tiny Terror. A triode is a cathode, a grid and a plate. The cathode is negative and the plate is positive. The plate is carying the high voltage. Electrons are trying to flow from the negative cathode to the positive plate. But the grid gets in the way. The grid is set at an electrical potential so that it only lets electrons pass if signal is applied to it. Signal (from your guitar for example) causes a shift in the electrical potential of the grid allowing electrons to pass from the cathode to the plate. Because the cathode / plate circuit is capable of much more voltage than the guitar signal, small changes at the grid caused by the guitar signal translate to bigger changes at the plate and amplification of the grid signal is achieved. The grid / guitar circuit acts like a valve to adjust the flow of electrons. Just the same way a small effort to turn on and adjust a faucet can allow a great amount of water to flow, depending on the potential of the water pressure. But you, who turned the faucet, in no way got wet or had to carry any water. Your guitar is not part of the output wattage of the amp. It's just turning the spigot.

Chuck

Thanks for this reply Chuck. This makes sense. I've never quite understood why a tube is called a valve until now.

Good analogy. Thanks again for the info.