There's no question the 660 mods from Doug solved a serious problem with the stock unit.
So far I've read lots of talk here about mods to the 661, but not a lot of talk about the problems that need solving.
I have no doubt Doug does good things. I still want to hear a stock 661 first.
Look at the published specs for the stock 661. A 16 bit SBM-1 has better dynamic range and THD figures. These specs are based on the analog signal path, and prevent the 24 bit AD from receiving a signal that is even just a little better than 16 bit. Since manufacturers have to make a unit that is "all things to all users" essentially, they have to compromise between the needs of different users, and make something that covers as many bases as possible. This leads to a final result that is not optimal.
Doug chooses op amps and input capacitors for his concert mods that are best for high input/low gain applications, the same way as he chooses different ones for low input/high gain applications in the super mod. I am not a blind follower and have never owned a unit modded by Doug, but I have been dealing with the Oade brothers now for almost 20 years and I spent plenty of money at HiFi Sales with 100% satisfaction, and I taped with Doug at a bunch of shows in the early '90s and learned alot about gear from him.
As much as I feel the mod is the way to go, I personally would like to hear a comp of the XLR set to "line in" between the stock and modded unit, just to see what improvement level there is and if it's worth $50, but I know for sure that if I was running mics directly in, I would not even bother with a stock unit, concert mod all the way.
