TUBE SOUND FUZZDeflnltlon: Recreates the types ot distortion normallyassociated with tubes, but with a solid-state design torlow current consumption, compactness, and reliability.

Figore 5-137 1

The Tube Sound Fuzz mounted in a small box foronstage use.

BackgroundMusicians in general, and guitarists in particular, preferthe sound of lube amps to the sound of conventionaltransistor amps. However, tubes have certain disadvan-tages (fragility, sensitivity to mechanical vibration andshock, need for high-voltage power supplies, high currentconsumption, and change in sound as they age ),' there-Jare, transistor amps are often used where reliable oper-ation is paramount.

Luckily, however, there is a memberofthe transistorfamily called the field effect transistor (FET) that hap-pens to distort in very much the same mann er as atube.This fuzz takes advantage ofthe FET's distortion charac-teristics to yield a tube-type distortion sound.

Level of Difficulty: Beginner to intermediate

Features. Low.level or line-level operation. Low noise compared with conventional fuzzes. Rhythmjlead switch gives law levels of distortion

for playing chords, and high levels of distortion forplaying lead lines.

Contruction Tips. This project uses CM as ICs; be sure to reread the

instructions on handing CMaS ICs inc1uded in the "Con-struction Tips" section ofProject No. 15.

. Plug the IC into its socket after a11 wiring is com-p1ete but before you app1y power to the unit.

. Separate input and output leads by at 1east l cm(1/2").

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. ShieId the input Iead. If the wires connecting toSI and R5 exceed 7.2 cm (3"), use shieIded cabIe forthese algo.

. Even thOUgh sections ICIC-ICl F appear to haveno influence on the operation of the circuit, be SUTe towiTe them up exactly as shown. Leave the outputs ofthese sections unconnected.

. Keep all wiring as short and direct as possibIe.

Modifications. De-emphasized low-frequency response: Reduce

the value of C4 to O.O5slF or even O.O2slF. This givesyou nice, biting le ad lines for guitar without having thehass strings muddy things up too much when you hitthem.

. De-emphasized high-frequency response: Increasethe value of C2. A value of 50pF starts rolling orf thehigh frequencies at approximately 4000Hz.

. Less intense fuzz effect: Une-level signals mayproduce too fuzzy a sound for som e tastes. In this case,increase R3 to 220k or even 470k.

In Case of DifficuIty

. Excessive current consumption (eats batteries):Same 4049s draw moce current than others. If you havea couple fo 4049s around, tfY plugging in different chips(tum orf power while changing chips!!) and reading thecurrent consumption willi a meter (see Project No. 19).Choose the chip willi the 10west current consumption.

. Oscillations or squeals: Check lead layout. Checkthat C6 is correctly polarized. Increase the value of C2to 20 or 3OpF.

Using the Tube Sound Fuzz

This fuzz works best willi line levels; however, it willalso work very well willi low-Ievel inputs. Willi SI inthe rhythm position, R5 compensates for differences ininput signallevels.

. Plug your instrument into JI and patch J2 to youramp. Although most people associate fuzzes willi guitars,this unit also works well willi electric pianos and otherkeyboards.

. Willi SI in the rhythm position, vary R5's position.You should obtain more intense fuzz effects as you tumthis control clockwise. Try playing some "chunky,"R&B types of riffs; adjust R5 until you get that old tubeamp type of sound.

. To increase the fuzz beyond the options offeredby R5, change SI to the lead position.

. By tuming R7 up fulI, you can probably overloadthe input of your amp and thereby create additionaldistortion.

. To increase the intensity of the fuzz still further,patch a compressor (Project No. 8) between your instru-ment and the fuzz input.

Figure 5-138Artwork for the foil side of the circuit board,shown 1 to 1.

..e 8m-

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"

*Since this unit doesn't hard clip, these figures representwhere distortion starts increasing rapidly. If you observea sine wave going through the fuzz and slowly tum upthe level of the sine wave, it will become increasing³ydistorted. With very large input levels, the output wave.form is a square wave with gently rounded comers.

SpecificationsCurrent consumption: t7mA (depends on the individual

4049)Maximum input before clipping, SI in lead position*:

15mVMaximum input before clipping, SI in rhythm position,

R5=0*: 150mV

Figure 5-139Component /ayout for the lube sauna fuzz.

C2 C3

nl~

IC1C1

C:=)

~ ~

~~+- I

csO. I .

MNCD".~~8m

-R1- C4

O~6 eo + c; I A B C

How it WorksICI is a 4049 hex CM OS inverter/buffer that was never really intended foraudio use. It's a digital IC (the type used in computers), and is generallygrouped willi Iots of other digital ICs to impIement same type of digitalfunction (microcomputer, industrial control, and so on). But as it so hap-pens, each inverter of the IC may be modified to run as a linear (audio) IC,and because these inverters ale based on FET circuitry, distorting themgives a tube-type distortion sound.

The input couples through R3 and C4 into the first stage of the fuzz,IC 1 A. This basically amplifies the input signal a lot, and may or may notadd same distortion, depending on the setting of SI/RS. However, even ifthis stage doesn't add distortion, the greatly amplified signal level willoverload the second stage (ICIB) and cause distortion in that stage. CI andC2 are designed to discourage oscillation in the first and second stages,respectively; C2 also helps cut out same of the superhigh frequenciesgenerated by the fuzz. Mter leaving the second stage, the output signalcouples through CS into output control R7.

How a musician reacts to a fuzz is highly subjective, perhaps mOle sothan willi any other type of effect. Nonetheless, this fuzz has pleased hard-to-please musicians . . . it distorts in a very smooth manner, doesn't soundgritty or harsh, and is very quiet (I measured the noise spec in the leadposition as -S8dB, which is pretty remarkable for a fuzz device!). Oneprominent manufacturer has even based the design of one of its productsaround this circuit; 1 hope you enjoy it as much as other people have, andthat you fmd it as useful as 1 have.

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