Circuit-bending a Funky Furby #4: audio jack

As I mentioned in the last post, I found some sound bends on the Funky Furby I’m circuit-bending.

The next step was to add an audio jack so I could play the Furby’s sound through a mini amp.

This is only the second project I’ve ever added an audio output to, so I’m still kind of fumbling my way through.

To cut a long story short, through a combination of peering at Alfonso‘s innards and section 7 of this circuit bending faq, I arrived at the following:

Wiring of the audio jack, including a 10 ohm resistor between points a and c

I’m using a 3.5mm enclosed chassis mount jack socket from RS, (part number 106-874), which has quite an open structure, so it’s pretty easy to see which bit is which.

Basically the two bottom connectors are the signals, and the one coming off the side is the ground.

Here’s a diagram of the wiring and how it connects up to the circuitboard and the speaker:

Diagram showing the wiring arrangement I ended up with for the audio jack

It’s ever so slightly different from what’s described on the oscillateur faq page, since I’m connecting c to b, rather than c to the ground of the speaker. I did try that, but got no sound.

The other thing I’m finding is that I still get sound from the Furby’s speaker when I plug the amp in. This doesn’t happen when the resistor is omitted, but the sound quality isn’t so nice, so I think I’ll put up with that.

I’m still not really convinced I’m doing this right, but I’ve not yet found any other combination of wiring that works. Maybe I’ve got my positive and negative terminals on the speaker mixed up?

If anyone can point me in the direction of a solution then I’d be most grateful, because this is something that’s going to keep coming up and I’d quite like to learn how to do it properly!

Update!
I had wrongly identified which were the positive and negative terminals on the speaker. After changing that starting point, the audio jack now works as expected with the following wiring:

Correct (I think!) wiring for the audio jack. Without an amp plugged in, the Furby's internal speaker is used. When the amp is plugged in, the internal speaker cuts out.