what makes an amp Amp?

[newperson]

Hi,

I have been messing around with a Ruby amp and stuck it in the guitar effect line as an effect.  I got several people telling me not to do this because of voltage.  So I got to measuring voltage of things.  With loud strumming and maxed out guitar signal I read DC .13 and AC 1.2 volts with the ruby.  So I picked up the next loudest thing which happens to be the Crash Sync.  It measures DC .15 and AC 2.8 volts.  This is with the same maxed out volume on effect and guitar strumming hard.  So the numbers are higher than the Ruby.  I plug the output of the Crash Sync into a speaker and can only get the smallest amount of sound from the speaker.

So my question is: What makes one an amp and the other not?  The non-amp effect reads higher numbers on my meter, so why does it not power a speaker?  What am I leaving out?  I am betting it has something to do with Ohm's law?

-Paul.

[Sir H C]

You have to have a load connected.  The amplifier doesn't just do voltage amplification it does current amplification.  It can put 1 volt into an 8 ohm load, while the pedal output will be destroyed or squashed out by such a small load.

[twabelljr]

It has to do with current. my EMG active pickups and tone controls put out .85volts max, but only 920 micro-amps.
Measure the amperage of the Ruby, then the pedal. Tell us the diff.

[R.G.]

Both the previous responders are correct. It's a power thing.

Power is the product of voltage and current. Something may have a lot of voltage and very little power, or a little voltage and a lot of power. You only measured voltage with your meter.

Consider an analogy. Mechanical power is force times speed, speed being like voltage, force like current. I shoot a pingpong ball at you  at 50 feet per second. It bounces off, and you're unhurt. I shoot a brick at you at 50fps, and break your rib. Or consider another analogy. I have here two vehicles. One is a Harley Davidson Sportster, which I can get up to over 100 mph. The second is a Caterpiller D9 bulldozer that can barely do 3mph. One is very speedy, but it's ill suited for moving things around. The other is quite slow, but I can move almost anything with it.

Another thing you are missing is that we commonly delete the qualifiers "voltage", "current" and "power" from the term "amplifier". A voltage amp makes bigger voltages from smalller ones. A power amp makes bigger power from smaller ones. To move speakers you need a power amp, not a voltage amp.

[twabelljr]

This might mean something: According to the datasheets a LM386 dissipates 1.25 watts, whereas a RC4558 dissipates a nominal 90 milliwatts.

[Herr Masel]

So deadly electrical shocks are caused by high current, not high voltage? Or both?

[twabelljr]

deadly electrical shocks are caused by high current

Exactly

[R.G.]

So deadly electrical shocks are caused by high current, not high voltage? Or both?

That's like saying "What kind of bicycle does a fish prefer?"

Things vary in terms of what electricity does to them, and in what location. The details matter.

A 10kV electrical arc may not damage a computer with a solidly grounded metal shell at all. 20V at under 10ma in the wrong place inside will kill it dead.

Likewise with humans. Microamperes through your heart muscle will stop the heart, but people can and have survived lightning strokes.

In general, dry human skin is similar to a 20K resistor. Wet and/or sweaty human skin is much lower resistance.
Something like 20ma at 60Hz will cause ventricular fibrillation in most human hearts, and death results if someone does not kick-start the heart with a few hundred volts of DC by way of defibrillating the heart and resynchronizing it. That's 20ma through the chest. The same 20ma is quite painful through a leg, or leg to leg, but doesn't do anything to the heart. Leg to arm, it may stop the heart. Across the temples, it may or may not have any lasting effect.

The voltage, frequency, and current of an electrical stimulation to a human body all matter.

If the voltage is enough to put a dangerous (over a few milliamperes) amount of current through the human chest, that's a dangerous voltage. If the skin is dry, it may be 60-70V. If the skin is wet, 35V may do. If the current is limited to under a few milliamperes, the voltage doesn't matter. If the voltage is DC, it tends to clamp everything in one position, which does not tend to start ventricular fibrillation. It may be used to resynchronize a struggling heart. If the frequency is 50-60Hz, it tends to cause ventricular fibrillation much more readily than either DC or higher frequencies. Quite high frequencies are largely carried in the skin, not the internal organs, and so may be moderately harmless until the power is such that the skin is cooked by heating.

Voltages as low as a few volts may kill if they get through cuts in the skin. You can burn a finger off by getting your gold ring across a source of a few volts but high current - like a car battery.

Details matter.

[newperson]

How do I Measure the amperage of the Ruby and the effect? 
-p.

[Herr Masel]

Wow thanks that was very interesting. Explains some well-known but not so well-known facts.