made everything OPA2134's and the sound is incredible. Its the sound I've been looking for 

curiosity won't leave me alone so I continued tweaking  xP It's a 100% opamp design and the only opamp is the NJM4558. So I replaced all 5 opamps with sockets and popped in NE5532's. Wow the sound is more clearer and the hiss at high volumes went away. For sh*ts and giggles I popped in some LM4562's and it was a noisy mess. more than likely they were oscillating. I was wondering are there more modern chips I can replace the NE5532's with? I was going to try some NJM2068's next but its old like the 4558

I think I'll leave it as is. don't wanna push my luck. swapping those caps for 22nf really improved the bass

Thanks for the info. The rest of the circuit goes to an equalizer with the lowest pot being 63 Hz so thats probably why they made the cutoff at 67 Hz. I replaced C1 & C2 with 22nf and there was indeed more bass coming through the speaker. So you're saying I can replace C1 with a jumper and keep C2 at 22nf? Here is the rest of the circuit before the equalizer

I just fixed a bass amp I got cheap in a garage sale. I'm trying to see what tweaks I can do. Can somebody explain what C1 & C2 are doing as the input signal is going to the first opamp stage? The value .01uF looks low for a bass signal. Is this some kind of high pass filter? I looked at other bass amp designs and they have a much larger cap like 2.2uF going to the first opamp stage