Huge thanks to gilshultz for helping me get my 2-speaker systerm working. Here's my functioning schematic (I ended up removing potentiometers to simplify wiring):
Now, I would like to add two more speakers, and considerable volume. I have some parts lying around but I would really like to know what you fellas think about the optimal way to add two speakers and volume. I can buy more parts if needed. I'm using two 40mm 5W max 4oHm speakers and would like to add two of the same. The stereo amp is only pushing 3W max to each channel, and I know they can handle a lot more juice.
Any advice is welcome as I'm only one post away from a complete noob to the game.
I do not think you will get a lot more out of that amp. What you have is 2.5W Output at 10% THD (Total Harmonic Distortion) with a 2 ohm Load and 5V Power Supply at Class-D Mode 3.3W Output at 10% THD with a 4 ohm Load and 5V Power Supply. The one below is rated at 40 Watts. Be careful when adding speakers, you do not want the impedance to go below the amp rating.
Replace the stereo amp with one that can deliver the power you need, and has outputs for the four speakers you want to connect.
The DAC outputs of the DF Player should be line level, thus can be fed into just about any amplifier. That includes home stereo systems, PA systems, etc.
Thanks! But do you think I could just use a two-channel relay with two stereo amplifiers, instead? I need to run everything on 18650 cells, along with LEDs, so maybe I'm okay with the power being delivered to these speakers. But I'd still like to add two. Cheers!
Doubling the power is only 3dB louder which is noticeable but not a dramatic increase.
I'm going to hit you with some formulas...
I assume you know Ohm's Law (Current = Voltage/Resistance).
The basic power calculation is Wattage = Voltage x Current.
With AC (including audio), that's the RMS voltage. (1)
Of course, all of the power has to come from the power supply so for example, with 5V and 1A, the maximum you can get is 5 Watts.
From those two formulas you can derive Power (Watts) = Voltage squared / Resistance, which is handy for audio.
RMS is 0.707 x peak. With a 5V supply and a "regular" single-ended amplifier, you can get 5V peak-to-peak = 2.5V peak = 5V peak = 1.77V RMS which is 0.78W into a 4-Ohm speaker. (That's best case assuming no voltage loss through the amplifier.)
The DF player has bridge amplifier to drive the speaker terminals with opposite voltages (no ground connection the speaker). That gives you 10V peak-to-peak from a 5V supply or around 3W into a 4-Ohm speaker.
...High-power car stereo amplifiers have voltage-boosting power supplies built-into them so you aren't limited by the 12V. (This requires the amplifier to "suck" more current from the alternator/battery, but car batteries can provide LOTS of current.)
(1) Here in the U.S. we have 120VAC (RMS) at the wall outlet. That's 168V peak or 336V peak-to-peak. If you have a regular-old 100W incandescent light bulb, It will consume 100W with 120VAC RMS or with 120VDC and it will be the same brightness.
