Stompbox electric basics...

[ggduff]

I have an effects pedal kit that I intend to build for the first time. I am taking my time learning about each component before I even think about getting started. I don't wanna get zapped and I don't wanna zap nothin. I made my first circuit on a breadboard the other day - a resistor, an LED and a battery... It reminded me of creating a 'hello world' program whenever I learn a new computer language. 

So, I have a very basic, big picture question. Three of them actually. But first let me see if I understand things correctly so far...

The magnets in the pickups of the guitar trigger a very small amount of voltage and current when the strings move across them. So this current goes through the cable and into the pedal I plan to build. Let's say it is a fuzz or distortion pedal. At some place(s) in the circuit there is some type of transistor or op-amp that combines the voltage and current from a larger power supply such as a 9v battery, so therefore the signal going forward, leaving the transistor or op-amp is now carrying more voltage and current. Am I correct on this?

If so, here is what I would like to understand:

1. What is the range of voltage and current that is likely to travel from guitar pickups through a cable to the input of a pedal?
2. What is the range of voltage and current that should travel through the effects circuit in a typical fuzz pedal?
3. What is the range of voltage and current that should leave the output of a typical fuzz pedal? How much is too much?

The 3rd question is the one that is most on my mind.

Thanks in advance for helping a newbie out.

[PRR]

> I don't wanna get zapped

9V battery through skin will NOT zap you.

Quality "9V" power supplies are also safe.

> a resistor, an LED and a battery

Good.

I suppose you noticed it matters which-way the battery and LED go? That the resistor which-way does not matter? The resistor value 1K 10K 100 ohms does make a difference?

> The magnets in the pickups

There's a wire involved, actually many-many turns of wire because you don't get much voltage from one turn.

Here's an old experiment. Find 50 feet of thin wire, a nail, a strong magnet, and a sensitive volt-meter. Wind all the wire on the nail, bare both ends, connect the meter. Wave the magnet near the nail. The meter will twitch. (This worked great on sensitive old mechanical meters; some DMMs may get goofy, though I have seen a significant response from a car ABS system which is also coil and magnet.)

If you put the magnet on an axle and spin it, you get a steady back/forth voltage (slow DC twitch; if fast use the AC function). This is how all generators work.

You also get twitches if you stick the magnet to the nail and wave another chunk of iron in the area, although not-as-much because of more air in the path. This is how a pickup (magnet and coil) detects the (iron) string flapping near it.

Signal voltages in guitar-chains are less than a Volt (very momentary few-V peaks).

Zap? Touch both ends of a 1.5V battery with your fingers. Nothing. Touch both terminals of a 9V battery. Nothing? Soak your fingers then touch 9V. Maybe something? Get VERY sweaty and lean on a 12V car battery unexpectedly.... you may be surprised at the odd tingle, but hardly zapped. You can lick a 9V battery. If very fresh, it "zaps" a few nerves, like a sip of too-too-hot coffee; you'll be fine. With experience you can tell fresh 9V from weak old 7V battery by tongue. (However do not open your chest and put 9V directly across your heart, it will go nuts.) (Also do NOT let your cat chew on 9V wires.... somehow they are more sensitive and can be seriously mouth-burned.) (Cows can be spooked by 3V tingles.... if they have to cross a small electric-leak to reach food or water, they won't fatten/milk well.)

[Perrow]

Licking 9v batteries is defined standard testing procedure for toy store workers, well, maybe not, but definitely the de facto standard.

Caution, opening your chest and applying 9v to it might scare off friends AND babes.

[stevie1556]

Also, the reason why people can survive a lightening strike (20,000+ volts!) is that voltage is rarely a killer, it's the current, or amps that will cause it. Thankfully, most guitar pedals are low power, generally 9 volts, but you get some at 18 volts, but they are still low current.

[Kesh]

1. What is the range of voltage and current that is likely to travel from guitar pickups through a cable to the input of a pedal?
For the sustained part of the note this could be 10s or 100s of millivolts. For the peak when plucked, a volt or more.
Current depends on what it is driving, that is the impedance (resistance) of what it is plugged into, and its internal impedance. Ohms law etc. Typically in microamps or less.

2. What is the range of voltage and current that should travel through the effects circuit in a typical fuzz pedal?
You generally drive the transistor or op-amp to clipping, which occurs at a bit less than whatever you are powering it with. So a 9V powered pedal may give about 7V peak to peak.
Current depends on the circuit, transistors are often set up to pass about a milliamp or so. Op amps in a pedal may drain, say, 1mA with no signal, up to 10mA+ with signal. Depends on which op amp.

3. What is the range of voltage and current that should leave the output of a typical fuzz pedal? How much is too much?
Voltage as 2 above as the typical max voltage. Usually on a pedal there is a volume control last thing, which is a voltage divider. So you could turn it back down to just typical guitar voltage levels if you want, as per answer 1. Current depends on what it is driving, that is, the impedance of what it is plugged into afterwards. but very low mA or uA range. Too much is a signal that drives the next stage into clipping, assuming you don't want that. If you are following a fuzz pedal with, say, a digital reverb, you don't want the ugly digital clipping, though almost all gear can cope with max pedal signal. If you are however following a fuzz with a tube amp, you definitely do want to drive it too hard.

[Mark Hammer]

I have an effects pedal kit that I intend to build for the first time. I am taking my time learning about each component before I even think about getting started. I don't wanna get zapped and I don't wanna zap nothin. I made my first circuit on a breadboard the other day - a resistor, an LED and a battery... It reminded me of creating a 'hello world' program whenever I learn a new computer language. 

So, I have a very basic, big picture question. Three of them actually. But first let me see if I understand things correctly so far...

The magnets in the pickups of the guitar trigger a very small amount of voltage and current when the strings move across them. So this current goes through the cable and into the pedal I plan to build. Let's say it is a fuzz or distortion pedal. At some place(s) in the circuit there is some type of transistor or op-amp that combines the voltage and current from a larger power supply such as a 9v battery, so therefore the signal going forward, leaving the transistor or op-amp is now carrying more voltage and current. Am I correct on this?

If so, here is what I would like to understand:

1. What is the range of voltage and current that is likely to travel from guitar pickups through a cable to the input of a pedal?
2. What is the range of voltage and current that should travel through the effects circuit in a typical fuzz pedal?
3. What is the range of voltage and current that should leave the output of a typical fuzz pedal? How much is too much?

The 3rd question is the one that is most on my mind.

Thanks in advance for helping a newbie out.

A couple of ideas to ponder....

1) The pickup desn't really "trigger" anything, but rather produces a voltage/current when the deformation of the magnetic field, produced by the strings moving back and forth (and up and down, etc.) within that field is sensed by the coil.

2)  Kesh is correct about the approximate voltage that will show up on your meter.  Do keep in mind that, because the string is moving around, and not in any consistent way, the output will vary considerably across the lifespan of any picked/plucked note.  Depending on the pickup strength, how it is height adjusted, how many strings are strummed and which strings are strummed (heavier wound ones deform the magnetic field mroe), you'll get different initial voltages. 

3) Think of the loudspeaker as a big bucket, and the succession of devices, whether transistor or chip (which is a bunch of transistors internally) between the guitar and loudspeakers as a series of people telling the next person in line to open a door and let water in...only those people cannot speak to each other.  All they can do is open a door and let water through.  The amount of water they let through tells the next person they need to open their door.  Each door opening l;ets progressively more and more water through, until the last few doors  let large amounts of water in...because the loudspeakers provide a very big bucket that needs a lot of water to fill it.  Your power supply is the water source feeding all these doors to be opened.  It should be able to supply enough water for all their needs.  Which is why the power amplifier requires large power supplies, and devices earlier in the signal path only need a battery.

[ggduff]

These answers are great - I have a much better understanding now - thank you...

So if I understand correctly, if I'm running my guitar into a fuzz pedal I will have probably no more than a volt and a tiny amount of current coming from typical pickups, but leaving the fuzz pedal I may have up to 6 or 7 volts and a current of somewhere less than a quarter watt? I'm assuming this is on the very high end of things and clipping would likely occur, but I don't have to worry about any damage to the next pedal in the chain with this small of a current - and that I'm really only concerned about how it sounds?

[PRR]

> a current of somewhere less than a quarter watt?

Hit the textbooks. Current does not come in Watts.

> leaving the fuzz pedal I may have up to 6 or 7 volts and a current of somewhere less than a quarter watt?

No way. True, it IS possible to suck 0.05W even 0.1W from some opamp chips.... but pedal output circuits generally have added resistance, and next-pedal input circuit is invariably a high impedance, over 20K, usually over 200K.

3V rms in 50,000 ohms is 0.000,2 Watts.

> I don't have to worry about any damage to the next pedal in the chain

Can you imagine Hendrix or Matthews or any of the Youngs standing there "hmmm, 1.23V into 47K is, uh, uh, carry the eight, shift the decimal...."?

Guitarists hook-up stuff randomly. Mostly it does not blow-up. The signal ports are mostly too weak to do real harm. "Most" stuff can even accept being connected to speaker lines (20+V), though that's risky/stupid.

One thing that *can* cause rapid part-death is reverse power polarity.