Sorry I am not sure where this should go but my project is to have some leds that’s state is tied to what a amplifier/speaker is doing
So I am planning to hook an Arduino volt meter or amp meter to the speaker or amp. then with programming tie the led’ state to feedback from the sensor.
So my question is does a speaker or amp draw a different amount of volts or current based on if its on but not playing anything vs playing music ?
Hi,
It sounds like you are trying to make a VU meter.
arduino vu meter
Tom... 
So my question is does a speaker or amp draw a different amount of volts or current based on if its on but not playing anything vs playing music ?
The current varies based on how much energy is going to the speaker.
Most good amplifiers have a well regulated power supply that holds the voltage rock-solid.
Measuring current isn't easy or practical. If you've got a "regular" stereo amplifier with a built-in power supply you'd have to open it up to measure voltage and modify it to measure current.
It's very common to read the [u]line level[/u] audio signal (voltage) into the amplifier (or a headphone signal which is very close to line level, depending on volume).
Or you can read the signal out of the amp to the speaker. But, if it's more than a couple of watts you'll need a [u]voltage divider[/u], plus it's a good idea to add an over voltage [u]protection circuit[/u].
In either case you need to protect the Arduino from the negative half of the audio signal with a [u]bias circuit[/u].
thank you I'm googling the things you have suggested the real goal is just to have some leds flash when the thing is playing and go off when the amp is on but not playing I was planning to build my own amp will be one that runs off a 5v power supply so I can run it off a usb cable from my laptop.
You could use one of these on the audio input:-
This is what I did with two of these chips although not on an Arduino:-
and more conventionally
But you can easily use LEDs.