http://www.digikey.com/product-detail/en/AN7523N/AN7523N-ND/440643
Forgive my ignorance. But it looks like this one says it will have a max output of 4W with a 3.5-13v supply. I understand that probably isn't going to give me all 4 watts with a 9v supply, but would it work at all? Maybe produce something in between.
Better give that one a miss. It's obsolete.
The data sheet says that at 9V the output power will be at least 3.2W and typically 4W into an 8Ω load at 10% distortion. But that really means that the supply voltage must be 9V. As I said before, and Dave repeated, a little 9V battery is not up to supplying that much current and its voltage will droop quite badly. So you would never get even 3W from any amplifier powered from a PP3 battery.
Kris mentioned the rechargeable batteries. Either lithium ion or nimh. Would those provide enough umpire alone? Or is he saying to use a package of them together?
Enough umpire? Auto-correct strikes again
You will need a battery, i.e. several cells connected in series, to provide enough voltage. This is because the speaker's impedance limits the amount of power that can be delivered to it, according to the supply voltage of the amplifier.
To deliver 5W (for example) into an 8Ω speaker, you have to apply a voltage of about 6.3V RMS across the speaker. (I'm assuming the speaker is a perfect 8Ω resistive load, which it isn't, but anything else makes the arithmetic impractical.)
6.3V RMS corresponds to about 9V peak or 18V peak-to-peak. A "single-ended" amplifier has a single output stage, and can generate, in principle, a maximum peak-to-peak output voltage equal to its supply voltage (that's assuming the output can swing all the way to both rails, which is never true in practice). So for a single-ended amplifier, you need a supply voltage of at least 18V (more like 22V when you include voltage losses) to deliver 5W into an 8Ω speaker.
The amplifiers you'll be looking at use a trick called "bridge-tied load" ("BTL") where the speaker is connected between the outputs of two separate output stages, which are driven with opposite signals. A BTL amplifier can generate, in principle, a maximum peak-to-peak output voltage equal to twice its supply rails. So a BTL amplifier needs 9V (more like 12V in practice) to deliver 5W into an 8Ω speaker.
So assuming you use a BTL amplifier (which you definitely should), even a 12V supply will only give you a maximum of about 5W into an 8Ω speaker. If you want more power than that, your basic options are (a) use a higher power supply voltage, and/or (b) use a lower speaker impedance.
Right now I'm only getting about a third of a watt out of this oneone. I guess I'll have to play around and see how much power I'd need to make it decent for playing the guitar through. I've read some good things on a tda7052 ic for projects like this. Anyone have experience with it?
I haven't used it.
If you can, try to find a high-efficiency speaker. Modern speakers are normally pitifully inefficient.
Do you just want a practice amp? If so, how about just using headphones? Your neighbours would appreciate it, I'm sure
