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Tube Box

that authentic valve sound — using diodes

Published in issue 311, June 2002

The Tube Box lends to a solid state amplifier that characteristic valve sound required by any self-respecting guitarist.Guitar valve (or ‘tube’) amplifiers, as used on stage or in the studio, derive their characteristic sound from the clipping behaviour of the valves when overdriven. Whereas the effect of clipping in a solid state amplifier is very unpleasant (and for many this alone is reason enough not to touch them), it is common to drive valve amplifiers into clipping. But with a disadvantage: if a valve amplifier is to be overdriven, the volume control must be turned all the way up. This does not always go down well with the other band members (or with the neighbours!). With the Tube Box circuit described here, which sits between the guitar and the valve amplifier, this is not necessary. The tiny unit applies the desired distortion to the input signal of the amplifier. The controls on the Tube Box are two potentiometers and two switches, which allow the user to choose from a wide range of possible settings, making the unit suitable for the whole spectrum of guitar music from smooth, warm blues to screaming heavy metal.

Components

Relevant products

Resistors:
R1 = 511kOhm 
R2 = 680kOhm 
R3 = 6kOhm 8
R4 = 15kOhm 
R5 = 1kOhm 2
R6 = 1kOhm 
R7,R8,R10 = 8kOhm 2
R9,R29,R34,R35 = 2kOhm 2
R11 = 1kOhm 8
R12 = 470kOhm 
R13 = 3kOhm 3
R14 = 100Ohm 
R15,R26,R31 = 33kOhm 
R16 = 220kOhm 
R17,R21,R23 = 47kOhm 
R18 = 91kOhm 
R19,R20 = 43kOhm 
R22 = 100kOhm 
R24 = 22kOhm 
R25,R33 = 68kOhm 
R27 = 470Ohm 
R28 = 180kOhm 
R30 = 10kOhm 
R32 = 5kOhm 1
P1,P2 = 100kOhm potentiometer, logarithmic law 
P3= 50kOhm potentiometer, stereo, logarithmic law
Capacitors:
C1,C17,C24,C25,C26 = 100nF
C2,C3,C13,C14 = 47nF
C4,C5,C29,C30 = 10µ F 16V radial
C6 = 33nF
C7,C11 = 470pF
C8 = 1µ F 16V radial
C9 = 1µ F 16V radial
C10 = 2µ F2 16V radial
C12 = 560pF
C15 = 3nF3
C16,C27,C28 = 4nF7
C18 = 100pF
C19 = 39nF
C20 = 22nF
C21 = 220pF
C22 = 22µ F 16V radial
C23,C29,C30 = 10µ F 16V radial
Semiconductors:
D1-D4 = 1N4148
D5,D6 = LED, red
IC1,IC2,IC3 = TL072-CP*
Miscellaneous:
K1,K2 = jack socket, 6.35mm, chassis mount
K3 = solder pin
S1 = rocker switch, 1 x c/o
S2 = rocker switch, 2 x c/o
S3 = pedal switch
Enclosure: Hammond type 1590B*
PCB, order code 010119-1

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