Could a SE/30 Stereo Speaker Mod Be Possible?

[MeTheMac]

Hi,
I recently bought two 4Ohm 5W speakers and a 5W+5W Stereo speaker amplifier to drive them. I had then planned to plug it into the speaker header on the SE/30 motherboard once I get my motherboard back.

However, while louder sound is cool, mono is still boring. I know there is a way to modify Color Classics with stereo speakers, and I was wondering if there would be any way to do a similar mod on the motherboard of an SE/30.

I've heard the headphone jack on the SE/30 is stereo, so it should be possible to wire it up to the headphone jack. However, this would most likely remove the external headphone jack functionality. There must be somewhere on the motherboard that generates stereo audio, I would think?

Any ideas are appreciated! Thanks for all the help!

 

[Nycturne]

I'd start by looking at the schematics so you can work back from the jack and see where it gets the signals and pick a spot to pull the signal from. That said, I still think you probably want to pull from the stereo jack or very close to it. The catch is that the circuit appears to be setup to sum the two signals as part of the speaker op-amp to produce the stereo signal, and cutting out the internal speaker happens because the signal passes through the stereo jack. If a plug is in the jack, then it cuts off the signal to R1 and R2, which seems to shut off the op-amp. That assumes I'm reading the schematic properly.

So my take would be to tap into the outputs of the speaker jack that are fed into the mono speaker circuit. They should be right next to R1/R2 on the bottom of the board. From there, you can get your line level signals, and have the signal be cut when someone plugs in external speakers. And you want the ground line as well, so this seems the simplest.

Assuming that works, you could even remove R1/R2 to completely cut the mono circuit out of the loop, but that is probably overkill?

 

[MeTheMac]

Hmm... interesting.
So plugging in a headphone jack would disable the internal speakers if wired up in this way? if so, then it would almost work perfectly.

--

Probably not worth the time and effot it to would take to go through and remove the components lol but it makes sense.

 

[Nycturne]

Hmm... interesting.
So plugging in a headphone jack would disable the internal speakers if wired up in this way? if so, then it would almost work perfectly.

Yes. The speaker jack has 5 lines: Ground, Right (In), Left (In), Right (Out) and Left (Out). So the jack is also similar to a switch. No plug? Signal passes from the inputs to the outputs. Plug inserted? The outputs are disconnected/floating and the plug receives the signal.

Basically, by tapping into the line levels coming out of the jack, you get the stereo signal before it gets summed and amplified into the mono signal for the internal speaker.

 

[MeTheMac]

Huh, never thought about it like that. My only concern would be removing the motherboard from the computer, but I could probably use some little connect wires 1 or 2 pin connectors and wire them up like that. I will let everybody know how it goes once I have a chance and get my motherboard back!