JC-120 tone disalbed?

[onthegreenline]

Thanks again for helping me out with my Chorus issue - after replacing all the old 250K pots in my original JC-120 with 500K pots, I have a clean, quiet amp. I noticed last night, however, something strange - my volume and treble controls on both channels work perfectly, but the mid and bass are acting up. The mid seems to control the mid -and- bass - turning it to zero reduces the tone to only the highest frequencies, turning it to 10 creates a big, fat tone, like you'd expect with the bass set to 5. The bass control does nothing at all on either channel! I feel like I'm missing out on the bottom end... I was assured by a roland tech that swapping out the pots for higher values won't cause any odd behavior, as they recommend 1MB pots as replacements. Any ideas? I've checked all connections again, everything looks pristine...

edit - "DISABLED" - haven't had coffee yet...

[52 Bill]

...The mid seems to control the mid -and- bass - turning it to zero reduces the tone to only the highest frequencies, turning it to 10 creates a big, fat tone, like you'd expect with the bass set to 5. The bass control does nothing at all on either channel! I feel like I'm missing out on the bottom end...

Without looking at the schematic, the first thing that I'd suspect is the pot value change. In many designs, the values are interactive and changing one value will shift the range of operation of the other controls.

...I feel like I'm missing out on the bottom end...

Have you changed or checked the speaker phasing? This will effect the chorus as well as the bottom end of the amp.

[onthegreenline]

hmm... phasing doesn't make a difference. I'm wondering if in fact my amp was all original - every single pot. with the exception of the distortion was a 250KV pot, so I replaced them all with 500KB and expected things to go smoothly. Looking at the schematics for what I believe to be my amp (the '79 with huge rocker switch for chorus/vibrato) it looks like the Volume was 100KB, treble was 50KB, Middle was 5KB and the Bass was 100KA. Can someone verify this is correct?