HI,got this bass amp from someone.The amp had this distortion and crackle sound when play..The note could still be heard but die quickly!
Need someone to direct the problem is cause by the power supply, power stage or the preamp.
Could kind soul here help me to solve the problem.Below is the schematic for the amp.

http://www.tremolo.pl/Firmowe/LANEY/RBW200.pdf

Found this hybrid preamp that run on 12v dc.Was think of building this for my DIY guitar amp project.
http://www.sugardas.lt/~igoramps/grass_preamp.htm
Sound clean on the sound clip for me.Was thinking to change the tone section to marshall tone stack.
The power amp section will be LM3886.
1.Was wondering,the cap c3 &c8 still needed, if i replace the tone section to marshall tone stack?
2.Should i add a gain between the tube?

Any help?