How to choose a transitor?

How do you choose (and use) a transistor to make led lights blink to music? I am making a speaker system and thought it would be cool to add a led light system. Also where would i add the transistor, to the audio in line? or to the output line (its a 12w output)? i have looked around a bit but still cannot figure out how to connect and use a transistor... HELP! :)

Thanks :)

A transistor is an amplifier: In a bipolar transistor it will take a small change in current in the base, and amplifies it to a larger current in the collector/emitter. One of the critical properties is called BETA or Hfe, which is the current gain of the transistor.

In a FET, the VOLTAGE on the GATE has a similar effect, this leads to a VOLTAGE controlling a CURRENT, which leads to the key property of a FET being described as the Transconductace, since it has the dimensions of current/voltage.

Take the time to study how transistor action really works. Most works simplify it too much.

Re-design6 years ago
Google "color organ schematic" . Get some experience before you try to design you own stuff.

Designing stuff has enough heartbreaks even if you know what you're doing. If it doesn't work you don't know if it's the design, construction error, parts choice or a bad part.
astroboy907 (author)  Re-design6 years ago
usually when i design it its fine. For my projects (mostly just order then solder stuff) i can find what part of the circuit or what part is not functioning properly. Also i usually have the developers circuit design also. If i build my own thing (circuit, design, and parts list) then it would be a lot harder, but i am not into electronics that much to do anything major yet.
a transistor is one of the "major" electronic components that i do not know how to use, i have tried to learn before but i am having a hard time getting it
i do have an idea, but i am not sure what someone more knowledged than me would say about it. I am thinking that a transistor is sort of like a voltage regulator type thing, where a signal is input onto one side of it, and if it passes a threshold value, a different power source is connected to ground, thus completing the circuit (unlike a voltage regulator, where the voltage/current would then be let through to the other "side" of the circuit, instead of an entire different supply) is this *semi* correct?

i am thinking of building it like music led light box (on instructables). also saw a project on the side bar that looks like it might contain an answer. looking at it now. Thx
You are correct basically in how a basic transistor works -- how each invdividul one works is different, hence the different flavours.

They do have a curve of how conductive they are based on the amount of voltage applied to the base. *Correct me if I'm wrong. This makes some seem to jump on a various levels, others have more pronounced semi-conductive behaviour, more linear, where a little voltage on the base makes a little conductivity, lots makes lots, better for analog circuits.

You choose your transistor based on a) polarity required, b) power consumption, c) that curve. Know your inputs and how much power you need to burn through (how many leds will be turning on and how much signal voltage you have). Can I be specific? no.