From the published specs, the 70D has virtually no self noise. Certainly not a measurable 14db in stock condition. I find it difficult to believe that it would make much of a difference at all in self noise. In fact, it's certainly plausible that it would have more self noise after the mod (depending on the type of mod). The internal preamp is clean, quiet, and adequate for 95% of all uses.
I've run quite a few of my own comparisons with the quietest preamps known to man, Fred Forssell's SMP500's. (I own four of them plus a Grace 801-
http://www.forsselltech.com/products/2/ ) and while I do get a somewhat better sound overall using the outboard preamps, the difference is negligible to minor. Especially when we are talking about the reduced dynamic range associated with loud concerts. If we are tracking acoustic music in a recording studio, then by all means it will make a larger difference to get your signal much hotter before recording it to the 70D, but without a digital input you are using the internal preamp of the 70D in either case. If you were using a colored preamp, like the Neve stuff...then the outboard would provide a bit of color to the signal. With the type of clean preamps (sax,v3) most tapers would put in front of the 70D, all they are really really doing is providing a louder signal to the built-in Tascam preamp, thus reducing the need for a higher gain setting.
I'm all for modding the units to get a better or sweeter sound, but I think it would be difficult to make them more than a db or two quieter.
I've heard quite a few of JW's mods and I'm just not a fan of ripping apart well designed gear to clean up the signal path just for the sake of a cleaner path. It can easily lose it's musical quality. I once had a 414 B-ULS that JW had "cleaned" up and it just sounded horrible to my ears. I sent it to him for him to check it out and fix what was wrong with it....it came back with a note that said working perfectly, sounds great. No charge for the check up. A few months later, I took it to a studio session where we doing some shootouts on different mics and everyone hated it. Ha! I put it on ebay and clearly stated it was a JW Mod and had just been checked out by JW himself and I also stated I wasn't a fan of the sound in the ad. People went crazy for it, final bid was like $850. The guy that bought it never tried to return it, so to each his own. I guess I'm not a fan of his work, though I do admire his style.
