Ok, so here is my setup and what I'd like to do.

I have a Digitech RP-1 that is what I use for all my effects. My guitar (Yamaha RGX 121 w/ EMG85 H pickup) goes into that. That all goes out a little Washburn SX10 amp, which only has 1 input, and a clean tone, but its a decent little practice amp and more that loud enough for my little place. I got the guitar for free cause it didn't work (I replaced the volume pot and hooked up the active pickup) RP-1 for free cause it won't give much sound (volume pot was clean, input jack was opened and resoldered by me) and the amp for 20 bucks of kijiji online so my whole "rig" cost me about $32 bucks and a few hours of soldering. What I'd like to do is take a line out signal from my digital USB Tascam mixer playing either songs to play along, or beats and stuff from Cubase into my amp with the guitar. I'd like to add another input jack to my amp. Now the soldering isn't a problem, I'm just curious if I can basically patch in a second 1/4" jack onto the main input. The RP-1 puts out a line signal, my tascam puts out a line signal, so I don't see why adding the two together would create a problem. I'm just curious if it will work as easy as I think it will? I could add in another volume put after the 2nd input, drill a few hole and it should all work, right?
I think it would be just as easy as you think, however, if you double the input, won't you reduce your signal and get a weaker tone? Maybe not an issue. i've never done it myself but it is something to think about
The only thing I can think of is you might have an issue because both inputs are active and there's no isolation between them if you simply wire the second input jack in parallel to the first (in effect you're wiring one output directly to another output). A safer solution might be to place a resistor in series between the 2nd jacks tip and the originals tip. It wouldn't have to be a large value I'd think, probably in the order of 10Kohms.
Another solution for someone who's handy (as you've demonstrated) is to get the schematic diagram for the amp and add the 2nd jack wiring it into the circuit between the pre-amp and buffer/power-amp, creating a true line in.
Moving on.....
Ya, electronics don't worry me in terms or soldering, wiring, adding stuff, I've probably modded and fixed well over 1500 video game consoles. I've just never really done anything with guitars and amps until I started with this guitar, so I was just hoping it would work fairly easy, and for cheap. Guess my other option would be to use my usb mixing board, put the guitar through there, then it will just get mixed with my Cubase output automatically, but one that introduces delay and two always means I have to have to pc up. Most of the time I just want to flick the amp switch and jam, but have the option to add a line-in stream if need, so thats why I'm trying to avoid doing that, because then I have to fire up the computer, turn the mixer on as it only works for mixing and such once it has a USB connection which is a pain, so I'm trying to go the extra line jack in route.
Plug the Monitor/stereo outputs into your amp, usb to computer, and put both guitars into the mixer and it should work, assuming you have a decent mixer. What mixer is it?

EDIT: Could you possibly make or find the wiring diagram? I'm in grade 9 sciene, and this electricity stuf is fresh in my brain.
Last edited by timbit2006 at Feb 25, 2009,
Its a Tascam US-428. Its more of a control surface for computer software and a 4 in, 2 out sound card, all usb. It does let you mix the ports, but its software only.

I can't even find anything about this amp anywhere on the net, so wiring diagrams are gonna be hard to find. Think I'll just take a look at the guts of it, do some wire tracing and see what I can figure out. lol. No better way to find out than to solder a 1/4" jack on it, play the guitar and some tunes from the line and see what happens eh. lol.

That or I should find a cheap line mixer somewhere. That just involves money, which is tight, and I like the DIY approach. We'll see. lol.
Yah, I would say buy another cheap mixer. Check your local on-line listing site for one, There was once a 12 channel mixer for $50 on Castanet(Kelowna website). Or you could get a Behringer Xenyx. Or, If they have them, a signal splitting box.
..I was watching my death.