what happens inside a line level convertor and how can i build one?
“line level converter” is a bit of an ambiguous term, but usually it refers to a device that can convert a speaker output signal to a balance line level signal.
“Passive” ones are basically specially designed transformers with appropriate (may be adjustable) load circuits on the inputs.
“Active” versions replace the transformer with a solid state balanced line driver (such as this: http://sound.westhost.com/project51.htm)
For low power systems (for example connecting a portable CD player headphone out to a computer sound card input) it may be sufficient to use a simple resistor divider.
It is particularly important that the load impedance (the input resistance) of the converter is suitable for the amplifier that you are using or at best the sound quality will be poor and at worst you could blow up the amplifier, the converter, or both.
If possible I would recommend not using one. It’s much better if you can do all of your signal routing at line level.
What kind of signal do you want to convert to line level?
want to convert from mic level to line level. and maybe from line level to speaker level.
i am doing a project to make a sound powered generator or at least make plans for one. i figure that microphones convert sound into electricity but it needs to be amplified to be useful. so i want to amplify it as much as i can and run a generator on it.
You need a mic preamp. If you want to build one there should be a lot of electronic circuits available on the web just search for mic preamp.
Check this thread too: https://forum.audacityteam.org/t/ssm2019-monolithic-pre-amp-chip/13341/1
The datasheet for that chip (SSM2019) has a few examples of some simple designs.
And here’s where you run into the Law of Conservation of Energy.
This law basically says that you can never get more energy out of a system than you put into it. The sound energy you are going to put in to your system will be tiny. For example, if you hold a sheet of paper in front of you and speak or sing close to it, there will be barely enough energy to move the paper. So that’s the sound energy going into your system. The rest of the energy going in is the electricity that is powering your amplifier, and this is the energy that will run the motor you will need to run your generator. You can use the sound power to control when the generator starts and stops, and maybe control the speed, but the bulk of the power is going to come from the socket in the wall.
Sorry, but you can’t break the laws of physics.
(But don’t let that stop you from building the project - you’ll learn a lot from it).
POL
That’s called a “microphone pre-amp”.
That’s a “power amplifier”.
As Irish pointed out, these are not “passive” devices but need to be powered.
(unfortunate in a way, otherwise we could could have perpetual motion and end the worlds energy crisis.)
There are certainly Line to Mic adapters which is relatively easy to do. Line or high level audio is relatively controlled and well behaved and it’s easy to reduce the level to something a microphone system can handle. Many people make them.
http://store.shure.com/store/shure/en_US/pd/productID.104210800
Going back up to high level is a lot harder. No two people talk or sing into a microphone at the same level. That’s why Microphone Amplifiers (Mic Amps, Mic-Pres) all have a knob for adjustment, volume meters, and overload flashers.
The closest anybody ever gets to an adjustment-free mic to line adapter is the USB microphones. People post on the forum all the time about the sound level being wrong on those.
Koz