This is a preamplifier circuit for bass guitar. This circuit is suitable you join with the power amplifier 60 W. preamplifier is working on the frequency range 50Hz to 20KHz-0.5dB,-1.5dB @ 40Hz,-3.5dB @ 30Hz.

for the bass control as follows:
Fully clockwise = +13.7 dB @ 100Hz,-23dB @ 10KHz
Center position = -4.5dB @ 100Hz
Fully counterclockwise = -12.5dB @ 100Hz, +0.7 dB @ 1KHz and 10KHz

Part :
P1 = 10K   Linear Potentiometer
P2 = 10K   Log. Potentiometer
R1,R2 = 68K
R3 = 680K
R4 = 220K
R5 = 33K
R6 = 2K2
R7 = 5K6
R8,R18 = 330R
R9 = 47K
R10 = 18K
R11 = 4K7
R12 = 1K
R13 = 1K5
R14,R15,R16 = 100K
R17 = 10K
C1,C4,C8,C9,C10 = 10µF
C2 = 47µF
C3 = 47pF
C5 = 220nF
C6 = 470nF
C7 = 100nF
C11 = 220µF
Q1,Q3 = BC546
Q2 = BC556
J1,J2 = 6.3mm. Mono Jack sockets
SW1 = SPST Switch