California vs. American:
I've had the California for a while now but, after all the good press the American has been getting, I decided to pick one up and give it a try. Here is What I found in a side by side comparison. First I'm using a GK 400RB-III 2X10 (Practice Amp) and bypassing the preamp by going direct into the effects return. This is so I don't color the characteristics of the pedals. I'm using a Fender Jazz Bass with Duncan Quarter Pound pickups and a Gotoh 201B high mass bridge. I also have a fresh set of standard gauge round wounds on it.
California:
Overall the pedal has a darker tone to it which I find preserves the low end really well. It's louder than the American too. Maximum distortion is just over the top on the pedal. But, that's pretty much expected since it's emulating a Boogie guitar amp. I can dial in quite a bit of different tones between the three band EQ and the drive, level and voice settings. There is so much distortion, it can get to the point where it's pretty much unusable if you just crank it. But, if you are somewhat conservative you can get a nice punchy sound that preserves the low end. It feels like there's lots of head room too.
American:
Noticeably brighter than the California. You can get most of the low end back by dealing with the EQ so, not too much of a problem. Overall volume is generally lower than the Cali. Some of the low end is sacrificed a bit when you crank the voice and drive. BUT, that is not necessarily a bad thing since it adds nice clarity to the tone of the distortion. Like the Cali, you can get some nice tone out of this pedal. But, I did not find it to be as punchy and "big" as the Cali when you roll the distortion back.
So, with that said, I tried one more thing. I combined the distortion from the American by neutralizing the EQ and cranking the distortion. Next, I used the EQ from the Cali and got an entirely different tone! This was quite a lot of fun I have to say! If I tweaked the level and voice on the cali it was absolutely crazy!
Summary:
Which one is better? Well, I think both are very usable on Bass, it depends on what your going for. Both have incredible sustain and harmonics ring out clear as a bell. I have to say I liked the tone of the distortion on the American but, found that I wished the EQ was closer to the Cali. I liked the Cali for the punchy sound with the low end intact. The head room was nice too. I can see both ending up on a board depending on what the style of music is. In the end, I don't think you can go wrong with either. And since they are so cheap, why not just grab both?!
I hope this helps, if anyone has questions, fire away.