Using a Mac with guitar amp speakers.

I really must preface this post with the caveat that I'm knackered, so take what I say with a pinch of salt (brain functioning somewhere around 60% right now).....

I think for it to work you'd need some kind of speaker system amplifier or preamp between the mac and the amp. You can get passive speakers (i.e. they don't need their own power supply) that you can hook up to computers, but they tend to be pretty small and weak, in my experience. You can also get better passive speakers but, I believe (i.e. I'm not 100% on this) that they need a certain amount of preamp power from e.g. a mixer between the computer and the speakers (they're used in e.g. home recording, so there's a good chance the user will have a mixer or similar system to hoook the speakers up to).

I've only ever used active speakers with my Mac, and I've never tried hooking my guitar amp up to my Mac, so I really can't say with any certainty it'd work, but it sounds plausible.

That said, there are a bunch of folk on here who know tones more about this than me, so I'd wait for them to reply. Shouldn't take long.

Thanks for the info! I usually use these speakers called Creature Speakers that work quite well and sound great, but they need to be plugged into the wall. I would think that the amp needs it's own power source...

actually, since the signal from a guitar going into an amp is fairly low anyway......it seems pretty plausible that you could connect the headphone output on the mac into the guitar jack input on your amp provided you have a 1/8 to 1/4 adapter. It shouldn't be harmful to your computer (unless there's some freak major electrical fault which coincides with your using it this way). If it was harfmul for your computer, then its likely it would be harmful to your guitar and, since this isn't the case (or we wouldn't have guitar amps, lol), it could work.

I've no idea what it would sound like, though. you might have to do a fair bit of fiddling with the EQ on the amp to get a decent sound out of it.

in the long run, however, I wouldn't want to deal with the hooking up and unplugging of all my gear every time I wanted to use it in a different setting (e.g. unhooking the amp from the Mac so you can play guitar through the amp). I'd just invest in some decent computer speakers or budget home recording speakers/monitors.

That's the thing though, I really really dislike the amp and would want to use GarageBand all the time.

Not familiar at all with the Line6 amps. Does it have a line in jack? If so you could hook the PowerBook up directly. What you want to use is a 1/8" stereo male to 1/4" stereo/mono (depending on the amp but likely mono) male cable or 1/8" stereo male to 1/8" stereo/mono male cable with a 1/8" female to 1/4" male adapter (mono to mono if your cable does the stereo to mono conversion or stereo to mono if the cable doesn't).

I have done this with pretty much the exact same Mac laptop to my Roland Cube 30 amp which does have a line in. You could go through the instrument input but you will need to turn the volume down on either the Mac side or the amp side and you might not be able to get it low enough - line level is higher than instrument level and it may just be too loud.

I wouldn't do this. The problem will be with impedence. The amp will be expecting a high impedence input. The mac will be sending a relativeily low impedence signal. This is like adding an extra load to the line out. Think of it as hooking up an 8 ohm speaker to a 4 ohm output. You would need a reverse D.I. box to make this work without any issues.

I wouldn't do this. The problem will be with impedence. The amp will be expecting a high impedence input. The mac will be sending a relativeily low impedence signal. This is like adding an extra load to the line out. Think of it as hooking up an 8 ohm speaker to a 4 ohm output. You would need a reverse D.I. box to make this work without any issues.

Only in the case of hooking the Mac PowerBook to the amp's instrument input. It will still "work" but you will get a higher volume that may not be able to be turned down enough, more noise, and perhaps a change of tone. Doing this for temporary practice use (e.g. having the Mac output a backing track) should be fine. It won't be the greatest audio but if it's all you can do then it will work.

However, the better choice, as I noted, would be to hook the PowerBook's headphone / line-out jack to the amps line-in jack. That's just what I did with my Roland Cube 30. You may not have a "line-in" on many amps but you may have an effect send and return. The effect return is essentially a line-in. As I look up the specs on the Spider Valve it says that it's got a pre-amp out (effect send) and a power amp in (effect return) as 1/4" jacks. So, just get yourself a 1/8" stereo to 1/8" stereo cable and get a 1/8" stereo to 1/4" mono adapter.