Audio output to a car amplifier?

Just working out the feasibility of playing an audio output through a car amplifier. Is it as simple as connecting the output pin to the amp or do I need some bits inbetween?


Does this have anything to do with Arduino?

Yea sorry audio being played from arduino sd card based different tracks being played based on the value of a potentiometer

An Arduino doesn't have an analog output (at least not the basic models). What is the goal of your project?

It’s for playing the sound of a helicopter engine based on the position of the throttle, so at low throttle it’ll play the sound of a helicopter engine at low throttle same for mid throttle and full throttle (it’s a very large static model) it needs to be fairly loud so was gonna use a car audio system (amp and speakers)

So you just want to change the volume, based off the position of the throttle?

No change tracks based on pot value eg 0 - 50 track 1 51- 100 track 2. I've seen people just plug a speaker into the breadboard but I need it to be loud

It should work.

It would be a good idea to put a capacitor in series (~ 0.1 to 1uF) to block the DC component*, although the amplifier probably already has one internally. And, the 5V peak-to-peak signal will be a little "hot" fore a line-level signal so you may want to add a pot as a [u]volume control[/u].

No change tracks based on pot value eg 0 - 50 track 1 51- 100 track 2.

Does that mean you are using an audio shield?

I've seen people just plug a speaker into the breadboard but I need it to be loud

The minimum load on an Arduino output pin is 125 Ohms (based on the maximum current spec). So if you connect an 8-Ohm speaker you need a series resistor and that will knock the volume way-way down. If you are using an audio shield there are some that can drive a speaker (at low/moderate volume).

  • The Arduino output switches between 0 and +5V,which makes a square wave biased at 2.5V. Normal audio is AC. A series capacitor will block the DC, giving you a signal that switches/swings between -2.5 and +2.5V, and it will rest at zero when the Arduino is static at 0 or 5V.

A car amplifier should be just like any other audio amplifier, use a capacitor to remove any DC component, send 0.4 to
1V rms signal via an RCA jack (probably want a mono->stereo splitter cable). Its common for audio equipment to have 47k input impedance or so, no problem to drive at all.

Car amplifiers quite often have the ability to take as high as 4 or 5v on the input, but this is very much amplifier dependent.


If you’re using phono plugs for line level hook up, I’d still put at least a 100 ohm resistor in series with any arduino output. Phono plugs are very easily shorted to GND by design, and the outputs may not survive that.

If you are using an audio board this will probably be taken care of by the board.

Would I need to use an audio shield or can I get away with just an sd card?

Since the Arduino doesn't have a digital-to-analog converter I strongly recommend an audio shield. (There is a TMRpcm library for "simulating" analog output but an audio shield will make programming a LOT easier and you'll probably get better sound quality.)

The audio shield basically does all of the "work"... The Arduno simply has to send a few control-commands and the audio shield does everything else... It reads the file from the SDcard, in the case of an MP3 shield it compresses the MP3, it has a built-in sample-rate clock, a built-in DAC, and it may have a digital volume control.

And yeah... An audio shield will put-out a standard [u]line-level[/u] (or headphone-level*) signal so it will work with a car amp, or your home stereo, or into the audio inputs of your TV, etc.

  • A headphone-output has about the same voltage as line-level depending on how loud you are listening. The main difference is that a headphone output is capable of driving lower impedance loads, and a headphone output always has a volume control. So you can use a headphone-output into a line-input, but you can't plug headphones into a line-output.

Can I just use a dac?
either breakout board or breadboard one (trying to keep costs down cause the main part of the project is quite pricey lol)

P.s really appreciate the help guys!

Can I just use a dac?

Sure, if you think you can handle the programming (and the wiring).

The audio shield is probably a 1 day project. The DAC might take a couple of weeks or more depending on your skill & experience.