Too much distortion

[lky]

I finished construction of a clone of AB763 circuit fender and I the following problem: when I play a E bass string (and only with this string) I have too much distortion.
This is the sample:

http://www.italianhost.org/public/files/VORC0023.MP3

The amplifier is extremely quiet with no noise or hum.
The problem seems to reduce slightly using the low input.
Nell'ampli I teke off the first channel and the tremolo.

There may be a problem on the filters capacitors after the choke?

Or

I change the value of res. on the cathode of the first and second stage of amplification from 1k5/820 to 2k7 for both (I also change caps with 0.68 uF value?), that is raising tension on the cathode to 3.8 V and doing less current flow (about 0.5 mA of 1.8 mA instead).