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Borborygmi · Jul 9, 2002, 09:31 PM

Has anyone come up with a way to enable both the regular headphone jack and amplified mini-jack simultaneously? I have a set of Apple Pro speakers running off the amplified jack, and want to add a subwoofer to the other (normal) jack. Problem is, only one seems to work at a time. Any suggestions appreciated.

P.S. Don't want to buy an iSub... I already have a nice subwoofer to use.

Carl Norum · Jul 10, 2002, 09:55 AM

This job is probably just 30 seconds of soldering. Or get a Y-cable for the one jack you are using. If the amplified jack overdrives whatever else you plug in, you can always just attenuate the signal...

atarirat · Jul 10, 2002, 10:51 AM

So, who makes a Y-adaptor that accepts a mini plug & the Apple Pro speakers plug?

The speakers that came with my LCD iMac sound fine in the office, but I'd like to wire the living room as well.

Carl Norum · Jul 10, 2002, 12:30 PM

Oh - I didn't know the plugs were different. Come to think of it though, I thought the Apple Pro Speakers were PWM to the speakers, not analog.... in that case you're screwed.

Borborygmi · Jul 11, 2002, 02:03 PM

Er..... I don't know what this means (PWM).... how does the headphone jack know to cut out sound when something is plugged into the powered jack? Let's start there..... is there something I can cut/snip/bypass/solder/yank out? Can we get some schematics for this?

Carl Norum · Jul 11, 2002, 03:27 PM

PWM = Pulse-width modulation. Instead of the signal being a continuously varying voltage (analog), it is represented with 2 discrete voltage levels (high & low, 0 & 1, whatever you want to call them). In the analog world, quiet spots have low voltage levels, and in PWM they have short pulse lengths. Conversely, loud signals in analog-land are high(er) voltage, and in PWM they have long pulse lengths. You could try putting a smallish capacitor from the tip to the sleeve of the pro speaker connection and another between the ring and the sleeve (I think it has three connections, right?). The signal you get across the cap might be ok. It would be a miracle, though.

I will have to percolate on this for a while.... I have an iMac at home with pro speakers, so I'll look at what's coming out there. I just need to "borrow" a scope from school.

Evangellydonut · Jul 11, 2002, 06:09 PM

they let u "borrow" scopes that easily? afterall, those things are a few thousand to tens of thousand of dollars...especially the logic analyzers...which i'd love to have to play with

i'm thinking of some way to do 4.1 audio decoder over USB...any ideas? ^_^; (TI has the chips, but i'm not sure 'bout feasibility 'n such)

Mac Zealot · Jul 11, 2002, 10:04 PM

Formac makes an external device that pro speakers can plug into and I believe other things may at the same time as well, but altering the g4's sound card would take major soldering because the sound you are talking about is controlled by a unit that has 3 modes:

mode 1: internal speaker, which is mono/digital
mode 2: external speakers, stereo/digital depending on output
mode 3: external speakers, 2 channel stereo to the analog jack

i don't think there is any way but in the actual controller itself to modify how this works, and how I generate this is not from any technical knowledge but because if you switch your output, the g4 actually puases the sound output to 'switch modes' if you pay a lot of attention <img border="0" title="" alt="[Wink]" src="wink.gif" />

Carl Norum · Jul 16, 2002, 12:07 PM

It turns out that there are a bunch of chips that are made just for driving two different outputs like these. My lab partner was using one from National. There's a way to make the chip drive both of its outputs... but it might overheat, depending on how they are implemented in the circuit.

So maybe you can do some hardware hacking to make it all come together, but it might be a giant pain in the ass.

Evangellydonut · Jul 16, 2002, 03:47 PM

<blockquote>quote:<hr />Originally posted by Carl Norum:
It turns out that there are a bunch of chips that are made just for driving two different outputs like these. My lab partner was using one from National. There's a way to make the chip drive both of its outputs... but it might overheat, depending on how they are implemented in the circuit.

So maybe you can do some hardware hacking to make it all come together, but it might be a giant pain in the ass.<hr /></blockquote>Finding the pin-out of the current DAC might not be too hard, but modifying it will be close to impossible. Given how thin the current PCB traces are, and how small the components are, it'll be extremely hard to removie PCB traces and do point-to-point soldering and not short anything around it. The risks involved and the expertese necessary is not worth it...I'd rather use the time and effort, and some extra $ to build a better sound system instead!

Carl Norum · Jul 16, 2002, 05:12 PM

<blockquote>quote:<hr />Originally posted by Evangellydonut:
I'd rather use the time and effort, and some extra $ to build a better sound system instead!<hr /></blockquote>Hear hear! My thoughts exactly.

lebannen · Jul 17, 2002, 06:00 PM

Returning to the original question, I'm pretty sure it can be done in software. I can't remember the name, but there's a pro-level mp3 DJ package for mac os 9 and X which lets you output to the output jack as per normal AND do premixing etc on the headphone jacks. If you can do that kind of control, would it be possible to write something that enabled both sets as standard for all output?