[Audino Help] Problems with outputting granular synth audio

Hey everybody, I am currently trying to build an Audino (open source granular synthesizer project), but I am having trouble with the audio output. I am confident my build and code are correct, I think the issue revolves around my connection to the 1/4" jack that I am using. I am currently (for testing purposes) holding the sleeve of the jack to a ground wire and the pin to the PWM output wire. I have this jack attached to my headphones from which I can hear some popping and clicking, so I know that something is happening, but I cannot hear the granular synthesis. Are my headphones (Sony Extra Bass Over Ear Headphones) to large for this output to drive? If so, what should I use instead to hear my output? Do I have to somehow amplify this signal to hear it? Is this maybe a problem of my lack of understanding of the entire project, or maybe the fact that I didn't solder my wires to the output jack? Any help would be very appreciated! The code and schematic can be found on the link provided above!

Are my headphones (Sony Extra Bass Over Ear Headphones) to large for this output to drive?

I don't know if that's the ONLY problem, but you should NOT connect the headphones directly to the Arduino! Those headphones are 24 Ohms... Too low... Don't connect headphones or regular 8-Ohm speakers directly. (A piezo speaker is usually OK.)

The Arduino is rated for 40mA maximum. From [u]Ohm's Law[/u], 5V and 40mA is 125 Ohms minimum.

The easiest solution is to use regular-old powered/active computer speakers. These speakers have a power supply and a power amplifier and an input impedance of 10K Ohms or more.

You can also connect to an audio input on your stereo receiver, but it's a little dangerous to connect "unknown" signals to a high-power amplifier/receiver because you can potentially blow your speakers. (Tweeters are especially vulnerable... A tweeter in a 100W speaker might burn-out with a constant 20W test-tone, and you can even fry a tweeter with a high-frequency signal that you can't hear, or that you can only slightly-hear.)

You also should use a capacitor in series with the Arduino's output to block the Arduino's DC output (or DC biased rectangle waves/pulses) while allowing the AC signal component through. (The required capacitor value depends on the audio frequency and the load impedance.)

You can test your speakers/hardware with [u]tone()[/u].

You my friend, genius, thank you for clarifying. I will try to find some crappy old speakers just to be on the safe side. The capacitor idea is also very smart, being in a microelectronic lab course at my university right now, I should have thought of that myself haha! Cheers!