Kaustic Machine's Atari Punk Console: Line Output or Log Pot?
In order to drive a speaker (or headphones) you need to supply quite a bit of current, and the 556 can't do that. If the speaker has its own amplifier - for example, USB or portable speakers - you may be able to connect this circuit directly. That said, headphones are usually not amplified, so you will need to amplify the signal yourself with an op-amp. The typical application circuit for a LM386 will probably accomplish what you need. Just connect your line out to Vin. It even has a 10k potentiometer for volume control! Just be sure to use a logarithmic pot for best results.