Hello, I am running Mopidy as a service on a raspberry pi. Sound is currently configured to play through my 3.5mm headphone jack, but I have a pair of old speakers with the black and red bare wires I’d like to play through. Is it possible to configure my Mopidy audio output to play through these speakers strictly through the raspberry pi GPIO? I’m very new with raspberry pi, so understanding I would probably need transistors or some sort of amplifier source for the speaker.
I used something similar to this, for about £10.00 I decided it was a lot easier than messing about with the gpio pins and the problems that seemed to entail. Just plug into headphone socket, attach a power source and speakers and away you go.
you could get yourself a hifiberry AMP module if you have a few coins to throw at the problem.
Otherwise, your best bet is to get some kind of amplifier with a line-in connection. Sound quality from the built-in 3.5mm jack on the Pi is not going to sound great.
You need an amplifier. You can build your own but that’s a project in itself and you’d be better off asking on forums dedicated to that sort of thing.
As already mentioned, cheap-o amps (like this) are an option and I don’t personally think the Pi’s line-out deserves the bad rep it still gets (but maybe I’m just used to the old days when it was really horrible!). Amps connecting via Bluetooth are a bit more fiddly to setup but also another fine option (but wifi and bluetooth at the same time doesn’t work well on Pi Zero models). The HiFiberry MiniAmp and Amp2 (probably overkill) boards connect via the Pi GPIOs, they are nice and compact. Personally I like the Pirate Audio amp board from Pimoroni. Does depend a bit on how big your speakers are.
This seems to be the consensus, and unfortunately kind of what I assumed.
Looks like there are a few other threads I can poke around dealing with audio output configs for the hifiberry, I’ll check those out when it gets in.
Never underestimate the value of total overkill for a project! 
I haven’t looked at the Pirate Audio Amps. I’ll check those out.
edit: those are cute as hell.