United States Patent 3812278

A special feature or effect portion of an amplifier for musical instruments has circuitry combinations for generating vibrato, tremolo, fuzz and wah-wah or selective boost. The subject amplifier includes circuitry which permits independent selection of vibrato or tremolo and a combination of the two on an independent basis. Additional circuitry uniquely affects the oscillator therein, switching, vibrato and tremolo modulation, boost or wah-wah production and the fuzz producing means.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
84/706, 984/309
International Classes:
G10H1/02; (IPC1-7): G10H1/04
Field of Search:
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Primary Examiner:
Wilkinson, Richard B.
Assistant Examiner:
Weldon U.
Attorney, Agent or Firm:
Lowe, Kokjer And Kircher
1. In an amplifier for electrical musical instruments having means operably connecting an input, a preamplifier, a special effects circuit, a power supply and an output, the improvement comprising said special effects circuit and having

2. A combination as in claim 1 wherein said tremolo producing means includes an amplifier means, a tremolo switch, and an interconnecting means connecting said switch and said amplifier means for modulating the gain of said amplifier in a controlled fashion, said interconnecting means in said amplifier cooperating to maintain said amplifier output without a net decrease in said amplifier signal when said controlling means is selectively operated to switch on said tremolo producing means for a

3. The combination as in claim 1 including an oscillator, said oscillator having an output interconnected with said vibrato producing means, and

4. The combination as in claim 1 wherein said tremolo and vibrato modifying means includes an oscillator having a phase inverter therein, said inverter interconnected with said vibrato producing means and said tremolo producing means to maintain said substantially 180 degree phase separation

5. The combination as in claim 1 wherein said special effect circuit includes an oscillator, said oscillator having an output interconnected with said vibrato producing means and said tremolo producing means, said oscillator having only one variable element for controlling the center

6. The combination as in claim 5 wherein said variable element is resistive

7. The combination as in claim 5 wherein said oscillator includes an amplifier,

8. The combination as in claim 5 wherein said oscillator circuit includes an inverter having an output therefrom,


Many electric guitar amplifiers (or electric bass amplifiers) have a number of special features such as vibrato, tremolo, reverberation, fuzz, wah-wah or selective boost and a few utilize electrically tuned oscillators. Many of the special functions are controllable by foot switches. This allows the musician to preset, for example, the amount of reverberation and the tone of reverberation that is desirable at a particular portion of the musical rendition. Then at the appropriate time, the activation of a foot switch interjects the amount and tone of reverberation at the critical part of the musicians repertoire. Accordingly, additional special functions or effects are often switched in and out during a performance by activation of a foot switch although it is unusual to utilize all of the special effects or more than one at a time.

Prior art units were generally not capable of independently controlling tremolo and vibrato and many suffered from a lack of modulation. For example, a typical prior art electric guitar amplifier utilized a vibrato oscillator often consisting of a vacuum tube which would operate to modulate a photocell by means of the light from a neon lamp. As a result, a quasi sign wave oscillator which had the capability of performing vibrato production was standard. Even though, vibrato pedals controlled the vibrato oscillator, the controlling was generally limited to off and on and was not utilized as a control of the oscillation rate. Since vibrato may be considered to be a form of phase or frequency modulation and tremolo is generally regarded as amplitude modulation, the above described circuitry was also utilized to produce a combination of both vibrato (or phase shift) as the load on a capacitor would change and to further produce tremolo due to the additional load on the amplifier. This is not necessarily musically unattactive but limits the musician operator in that no independent control existed over both vibrato and tremolo. Further, the depth of modulation was generally not adequate in that most musicians were required to operate the amplifier with the effect knob at maximum in an attempt to achieve enough modulation.

Other amplifiers with special effect techniques such as vibrato circuits utilized a time varying resistance such as a silicon diode as controlled by a low frequency oscillator. Accordingly, to operate on the signal, this circuit was not voltage independent so that the signal to be modulated also resulted in the modulation of the variable element thereby producing intermodulation products and unwanted distortion due to overloaded circuits.

The subject invention includes a preamplifier with a SELECTONE feature (discussed in bulletin entitled "Kasino Amplifiers" published by Kustom Electronics, Inc., of Chanute, Kansas in December of 1970) and a second preamplifier without the selectone feature. Both preamplifiers have an input to terminal strips located on the special effect printed circuit board which includes circuit components for the production of fuzz and selective boost or wah-wah and the above mentioned tremolo and vibrato production. A conventional power supply and power amplifier operate in conjunction with the preamps and the special effects circuitry to appropriately power the above for sound and music production. The input to the special effects circuitry from the preamp boards (generally from the preamp II) with a summing amplifier thereon is first delivered to the vibrato modulator. A tremolo modulator is connected to the output of the vibrato modulator and a unique oscillator and tremolo vibrato switch (electrical switch) effectively operates in accordance with the activation of foot pedals to independently or collectively control the operation of either the vibrato or tremolo modulator. Foot switch control is also provided to operate the unique boost or wah-wah circuit and the fuzz circuit.

An object of my invention is to provide a unique amplifier for an electric guitar or electric bass or similarly related electrically operated musical instrument.

Another object of my invention is to provide a unique circuit for generating vibrato or tremolo. It is a feature of the invention that this circuit is economically produced and easily incorportated into portable musical equipment, more particularly electric guitars, bass and certain vocal effects.

Another object of my invention is to provide a uniquely constructed circuit for use with electrical musical instruments that permits independent selection of vibrato or tremolo or a combination of the two on an independent basis.

Another object of the invention is to provide a unique circuit of the character described above that permits independent control over vibrato and tremolo and in addition has sufficient depth of modulation for proper utilization thereof.

A further object of my invention is to provide a uniquely constructed vibrato modulator for electrical musical instruments which is oscillator and switch controlled by a unique tremolo and vibrato switching circuit.

A still further object of the invention is to provide a unique circuit for use with electrical musical instruments which provides a means for enhancing the special effect portion of same. It is a feature of the invention that the circuitry permits sufficient depth of modulation so that the special effect portion of the amplifier circuit will not have to be operated at a maximum.

A still further object of the invention is to provide a uniquely constructed electric musical instrument amplifier including a vibrato oscillator that is voltage independent. It is a feature of the invention that intermodulation by-products are reduced as is the tendency to overload the circuit so that unwanted distortion is virtually eliminated.

A further object of the invention is to provide in an amplifier circuit for an electrical musical instrument, an improved tremolo circuit that does not require the amplifier gain to be adjusted if the operator and/or musician switches on the tremolo effect circuit portion in order to maintain the same equivalent loudness as existed prior to the tremolo switching.

Another object of the invention is to provide a circuit for electric musical instruments that causes sound passing through an associated vibrato modulator to be phase shifted at a rate controlled by an oscillator circuit utilized therwith so that the phase shift appears as frequency modulation to a listener.

Another object of the invention is to provide a circuit of the character described immediately above which generates the maximum aesthetic effect to the listener by independently controlling associated vibrato and tremolo modulators. It is a feature of the invention that the vibrato and tremolo modulation voltages are 180° out of phase in an oscillator circuit and that the out of phase relationship between the voltage applied to the vibrato modulator and the voltage applied to the tremolo modulator can be adjusted to approximate the sound of a rotating speaker which is otherwise known as a LESLIE effect. (LESLIE is a registered trademark owned by the Hammond Organ Company.)

A further object of the invention is to provide a unique oscillator circuit for electric musical instruments that has extremely low distortion and is controlled by a single resistive element.

A still further object of the invention is to provide a unique circuit for electrical musical instruments that is capable of economically producing a very low distortion sine wave at frequencies other than a fixed frequency.

A further object of the invention is to provide the circuit of the character described above, said circuit having a center frequency controlled by a single variable element to further insure the economic production of a low distortion sine wave.

Another object of the invention is to provide a unique amplifier for electric musical instruments that have unique selective boost or wah-wah producing circuitry therein.

Another object of my invention is to provide a circuit of the character described immediately above that utilizes a fairly high Q resonance at a lower frequency which degenerates into a low Q resonance at a higher frequency. It is a feature of the invention that this frequency and associated action is controlled by a single variable element and that same can be easily placed in a foot pedal or separate control that is remote from the amplifier.

Another object of the invention is to provide a unique musical circuit for utilization in electric guitars or bass which is capable of producing a sound similar to a wah made by the human voice. This circuit has an important feature in that a tunable low pass resonator may be used if the resonator's "Q" decreases as the boost frequency increases.

A still further object of the invention is to provide a unique fuzz circuit operable to produce both symmetrical distortion and asymmetrical distortion in the sound emanating from the amplifier circuit associated therewith.

Another object of the invention is to provide a uniquely constructed tremolo and/or vibrato controlling means which is utilizable to independently control the vibrato modulator or tremolo modulator or any combined use thereof.

Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.


In the accompanying drawing, which forms a part of the specification and is to be read in conjunction therewith and in which like reference numerals are employed to indicate like parts in the various views:

FIG. 1 is a block diagram of an amplifier for an electric guitar or a bass unit utilizing the special effects circuitry with the improvements therein;

FIG. 2 is a schematic diagram of the special effects portion of an electric guitar or amplifier showing the unique circuit portions; and

FIG. 3 is a circuit diagram of an idealized resonator concept used in the boost or wah-wah portion of the special effect circuitry.

The block diagram shown in FIG. 1 diagrammatically represents an electric guitar or base amplifier and utilizes therein two separate preamplifiers 10 and 11. These two preamps (10 and 11) are generally not used by an instrumentalists at the same time however, both preamps (and the associated unit) are usable by two different instrumentalists simultaneously even though the two may have distinctive sounds. In this situation, it becomes a matter of preference of the particular musician as to which preamp sound is preferable for a particular rendition since the preamps have radically different frequency responses. In any event, there is a summing amplifier 15 electrically located between the preamp 10 and preamp 11 so that the signal from either or both is then delivered to the appropriate input terminal strip on special effects amplifier circuitry which is schematically shown in FIG 2. This special effects circuit (12) receives power from power supply 13 and has an output through power amplifier 14 to either a tape recorder or suitable speakers. In both cases, the power supply and power amplifier are of a conventional design.

Turning now to the special effects circuitry shown in FIG. 2, the summing amplifier 15 has an output which is delivered to the terminal strip 16 and from thence to the input of inverter 17 in the vibrato modulator circuit portion. The signal flow (after being inverted in inverter 17) is delivered to the follower amplifier 18 and from thence to the tremolo modulator (identified in part by the integrated circuit 19) through the follower amplifier 20 and out through the effect control designated as R-43 and located on the boost or wah-wah circuit portion. The signal then from the above mentioned effect control is delivered to the follower 21 and on to a final amplifier which is diagrammatically represented by the "output" terminal on terminal strip 22.

The integrated circuit elements 17, 18, 20 and 21 (along with later discussed IC (integrated circuit) elements 23 and 26) are conventional operational amplifiers, however, tremolo modulator IC 19 (and later discussed IC elements 24 and 25) is a transconductance amplifier which has an output current proportional to the input voltage. Additionally, the transconductance is a function of the bias current on the pin identified by numeral 5 thereon. As will be shown, if R-72 (the tremolo control) is set at a minimum value, then the bias current flowing from ground through R-73 and R-76 to pin 5 on modulator IC 19 would cause modulator 19 to have unity gain between the output of the follower amplifier 18 (pin 1) and the output of the tremolo modulator 19 (pin 6). In the operation of the tremolo modulator, there is a voltage divider comprising the resistors R-18 and R-19 followed by the gain of the tremolo modulator 19. Accordingly, current developed within modulator IC 19 flows across the resistor R-27 which effects the generation of an output voltage proportional to the bias current and transconductance. This output voltage is eventually delivered to the input (pin 3) of the follower amplifier 20. As suggested, the gain across the transconductance amplifier tremolo modulator 19 is unity when the variable resistance R-72 is set at a minimum.

The tremolo-vibrato electronic switch is operably connected to a foot switch as shown on the terminal strip 22 and includes the transistors Q-5, Q-6 and Q-7. If the tremolo-vibrato foot switch is activated the transistors Q-5 and Q-7 will be turned on through the foot switch control transistor Q-6 and an approximate 20 volt peak-to-peak sine wave will appear at the upper portion of the manually adjustable variable resistor R-72. This sine wave appears on the output of the oscillator circuit (which will be discussed in more detail) schematically designated as the output pin 7 on amplifier 23. Therefore, if the tremolo control (R-72) is set above the minimum value mentioned above, then the alternating voltage (having a value of between 0 and (+)9 or (-)9 volts) will be present on the center arm of the variable resistor R-72. This alternating voltage will modulate the bias current going into pin 5 of tremolo modulator 19 and will modulate the gain of this transconductor amplifier in an up and down sine wave fashion. For example, if the adjustable resistor R-72 is set a maximum (at the peak of the 20 volt sine wave) the gain of the tremolo modulator amplifier 19 will be twice that of the quiescent state at the negative portion of the cycle, the gain of modulator 19 will approach 0. It should be pointed out that this is extremely desirable since most prior art tremolo circuits utilize a passive element so that when the tremolo effect was in operation, a net decrease in volume occurred. The volume decrease resulted since the maximum level was generally that of the peak of the sine wave so that the average value was halfway between 0 and peak value. This required the amplifier gain to be readjusted to produce the same equivalent loudness if the operator were to switch on the tremolo effect. Further information concerning transconductance amplifiers may be seen in the publication entitled RCA Application Note (Linear Integrated Circuits) ICAN-6668, printed September, 1971 under the authorship of H. A. Wittlinger.

The vibrato modulator (on the special effects circuit shown in FIG. 2) is also controlled by the oscillator mentioned above and is switched by the tremolo-vibrato switching circuits. This circuit comprises a gyrator which, in active filter terms, is a circuit which translates a capacitor an inductor. In this particular circuit, capacitor C-1 is translated to appear as an inductor between the input on terminal strip 16 and input pin 3 on follower amplifier 18. Additionally, the gyrator circuit consists of the transconductance amplifiers 24 and 25 (similar in design to amplifier 19) and resistors R-1, R-2, R-3, R-4, R-8, R-9 and the above mentioned capacitor C-1.

To further illustrate the utilization of the follower amplifier inverter 18 and its association with the vibrato modulator, a conventional pure phase shift circuit such as an operational amplifier inverter circuit should be considered. For instance, such a circuit is comprised of an operational inverter (having essentially a unity gain) with the output seeing resistance R, and an inductor L connecting the output back to the input of the operational amplifier inverter. Analysis of this circuit shows that at extremely low frequencies, E-in (voltage input) is equal to E-out (voltage output between R and L) because of the low impedence of the inductor L. Also, at extremely high frequencies, E-out will equal E-in as the inductor will become extremely high in reactance compared to resistance R and the net path will be through the inverter and resistor R to E-out. Since E-out sees a high impedence load, no current is assumed to flow through the output terminal

In a similar manner, follower amplifier 18 is effectively utilized. That is, amplifier 18 follows the vibrato modulator circuit with a very high impedance follower. It is therefore important to note that the output of such a circuit has constant amplitude with respect to frequency and has a phase shift of 180° at high frequencies and a 0 phase shift at low frequencies. The frequency of transition between 0° and 180° is dependent upon the value of j omega L and R. L now is actually a synthetic inductor generated by the transconductance amplifiers 24 and 25 in conjunction with capacitor C-1. Therefore, the effective value of this inductor is modulated by the bias current which is, in turn, controlled by the vibrato manual control R-58. The frequency of "crossover" will move up and down between some low point of around 200 cycles and some upper point of around 3,000 cycles. The effect of this on the music emanating therefrom is at a frequency in the order of 1,000 cycles will be alternately unshifted and then shifted 180° as the vibrator modulator moves from one side to the other. This phase shift will take place in an oscillatory fashion as the modulator is in fact the oscillator with the resultant effect that any sound passing through the vibrato modulator will be phase shifted at a rate controlled by the oscillator circuit. It has been shown that phase shift can be assumed to be a version of frequency shift or frequency modulation under certain conditions so that the effect on the listener is to approximate frequency modulation.

It has been suggested above that the subject invention has particular utility since the vibrato and tremolo condition are independently controllable. However, by utilization of an oscillator circuit that maintains 180° phase separation additional benefits are obtainable. For example, the oscillator circuit includes the integrated circuit 23 which performs the function of a phase inverter with unity gain (similar to inverter 17) so that the voltage on the tremolo potentiometer (R-72) reaches a maximum at a 180° out of phase condition from that of the voltage associated with the vibrato effect in the oscillator circuitry. It has been found, that such a phase condition produces a much more effective combined effect than if both vibrato and tremolo took place "in phase" rather than by the above mentioned "out of phase" relationship. Stated another way, the out of phase relationship between the voltage applied to the vibrato modulator and the voltage applied to the tremolo modulator generates the maximum aesthetic effect to the listener and approximates sounds which are similar to what is sometimes referred to as the Leslie effect (a rotating speaker effect).

The tremolo-vibrato switch (which was described above) is again activated by a ground on pin number 10 of the terminal strip which is usually accomplished by the deactivation (or controlled) of a tremolo-vibrato footswitch. This ground condition will turn on transistor Q-6 which, through the diode CR-6, turns off the field effect transistors Q-5 and Q-7 thereby eliminating the vibrato modulation from the variable resistor R-72. At the same time, the bias current to the transconductance amplifier 24 and 25 is removed or shunted to a -12 volt value by means of diode CR-5 through the now turned on transistor Q-6. In this manner, Q-6 operates to turn off both vibrato and tremolo effect conditions.

The subject oscillator is also important in that it has extremely low distortion and is controlled by a single resistive element R-61. This resistive element (R-61) will control the oscillator (in conjunction with the capacitors and resistors indicated in FIG. 2) from a frequency of approximately 3 cycles per second to approximately 18 cycles per second and will produce an oscillatory sine wave of approximately one-fourth percent distortion or less. The oscillator circuitry includes an integrated circuit 26 in conjunction with the resistor capacitor combination R-59, C-29, C-32, R-65 and R-61, R-62, forming a band pass filter having a gain determined by R-65 and R-59 with center frequency determined primarily by R-61. This band pass filter is followed by the inverter 23 (and resistors R-66 and R-69) having unity gain at 180° phase shift thereby providing a net phase shift of 360° with a positive feed back at the center frequency of the band pass filter. This effects an oscillating condition as the positive feed back and loop gain (of slightly greater than unity) will generate ever increasing oscillations.

The steady state amplitude of the oscillator is determined by the clipper circuit comprised of the diodes CR-1 and CR-2, CR-3 and CR-4 and the associated resistors connected to same (R-67, R-68 and R-63, R-64). As mentioned above, the output of the phase inverter 23 is a sine wave having very low distortion, and when presented to the above described clipper network, a symmetrically clipped sine wave results at resistor R-65. The clipped sine wave, when passed through the filter circuit (including IC-26) will be regenerated into a sine wave again since the filter circuit will only pass a fundamental component of the symmetrically clipped wave. A very low distortion sine wave is thereby economically produced at more than a fixed frequency. Further, there is no requirement of tandem potentiometers or other complicated and expensive limiting mechanisms. Quite the contrary, the above described circuit requires a limiting mechanism which is controlled, rather than allowing the signal amplitude to build up until an uncontrolled limiting occurred by deliberately clipping the amplifier signal in a way that will produce a minimum distortion, the purety of the recreated wave form is optimized with an economy of parts and elements. Therefore, utilization of a single variable element (resistor R-61) such as that described above enables an economical low frequency sine wave oscillatory signal to be generated having a very low distortion and with the center frequency controlled by the single variable element.

The selective boost or wah-wah circuit is shown in the upper right hand portion of FIG. 2 and is cooperatingly utilized with the above described circuit for several purposes including the emulating the "wah" sound as if it were produced by a human voice. This circuit is characterized by a fairly high Q resonance at a lower frequency which degenerates into a low Q resonance at a higher frequency. As will be seen, it is very desirable to also have this frequency and action controlled by a single variable element which may be conveniently placed in a separate control (such as a foot pedal) remote from the amplifier circuit. Likewise, it is desirable to have a minimum of circuitry external to the amplifier and, in terms of hum and other possible unwanted sounds, it is desirable that the above mentioned variable element be a variable resistor rather than a potentiometer and that at least one terminal of the subject variable resistor be connected to ground.

A pass band resonator or buffered resonator has been described in an article by Philip R. Geffe in the May, 1970 IEE SPECTRUM beginning at page 63 entitled "Toward high stability in active filters." The circuit shown on page 66 in the Geffee article was intended as a band pass resonator or Q-invariant resonator but it has been discovered that the low pass section of the resonator could be brought out and caused to serve as a tunable low pass filter whose Q would decrease as the boost frequency is increased thereby becoming an extremely valuable tool in the production of the wah sound.

An idealized buffered resonator is shown in FIG. 3 and is similar to that shown in FIG. 6 of the above mentioned Geffee IEEE article. This idealized resonator is, in principal, incorporated in the boost or wah-wah circuit as will now be described. For example, a comparison between FIGS. 2 and 3 indicate that the capacitors C-18 and C-20 are equivalent to capacitors C-1A and C-2A respectively. Resistor R-35 in combination with resistor R-36 forms an equivalent to the resistor R-1A in FIG. 3. The selective boost switch S-2 and any one of the selectable resistors (R-44 through R-49) in series with the resistance of the boost pedal to ground form the R-2A value in the FIG. 3.

Finally, transistors Q-2 and Q-3 along with IC-28 correspond to amplifiers A-1 and A-2, with the voltage output from A-1 (terminal X) forming the wah voltage. The switch (transistor Q-4) allows the wah-wah effect to be switched in and out with the remote foot switch. For example, if the boost switch is off, Q-4 becomes an open circuit. In this condition, the output of the follower 20 is transferred to the input of the IC (follower) 21 without regard to the setting on the effect control, variable resistor R-43. If Q-4 (the field effect transistor) is turned off the position of the manually adjustable variable resistor R-43 (the effect control) is not important as it is simply a small resistance in series with extremely high input impedance of the follower 21 and associated resistance R-51. When the boost is on, Q-4 becomes short-circuited between the output of the low pass filter section beginning at the collector of transistor Q-3. The output of this low pass section is connected to the input of the IC follower 21 with the output being variable depending upon the setting of the effect control R-43.

The field effect transistor Q-13 serves to disable the gain of integrated circuit inverter 28 when boost is switched out as some dynamic overloading conditions may take place. Otherwise, an extremely high voltage at the collector of Q-3 would short across the source to drain of transistor Q-4 even when Q-4 was turned off. Accordingly, it is necessary to insure that the integrated circuit amplifier 28 is operated at low gain during the time the boost is not in effect.

When the wah-wah pedal is not in the depressed position, the circuit therein has a resistance of approximately 25 kohms. When the pedal is pushed all the way in the resistance approximates 0. With the selective boost switch S-2 in the number 6 position (contacting a circuit having a resistance R-49 therein the boost pedal will have maximum effect and the wah-wah will operate between its maximum and minimum frequency strains. As the selective boost switch S-2 is turned down toward position number 1, the variable pedal has less and less effect thereby permitting the degree of effect to be chosen by the operator.

The fuzz circuit is shown in the lower right hand portion of FIG. 2 and pertains to a device for deliberately generating distortion of an existing sound. The distortion in the subject amplifier circuit is generated by a clipping action via diodes CR-10 and CR-11. Referring again to FIG. 1, the signal flow comes into a preamp No. 2 (11) and is amplified and delivered to pin 2 of the terminal strip 29 (in FIG 2). This pin 2 interconnects with the junction of transistors Q-8, Q-9 and the capacitor C-36. If the fuzz effect has been switched off, Q-8 and Q-9 will be conducting and the signal will go through these two field effect transistors and out pin 1 back to preamp 11. However, if the fuzz effect is turned on by the operator, transistors Q-8 and Q-9 will not be conducting and, due to the reverse bias on the drain of the transistors 8 and 9, if the switch S-3 is in the off position, the foot switch line will be a minus voltage condition (actually -12 volts) turning on diodes CR-8 and CR-9 and back-biasing transistors Q-8 and Q-9. If the fuzz is turned off, switch S-3 will ground the foot switch line and allow the gates of the field effect transistors to be at the same potential as their drains. This condition will result in the turning on of the above mentioned transistors. If the fuzz is turned on, the signal, instead of going through the fuzz circuit immediately back to the preamplifier will instead go through capacitor C-36 and resistor R-80 and out the effect potentiometer R-81. This will then drive the base of the transistor Q-11 to a varying degree depending upon the manual setting of the resistance R-81.

Transistor Q-11 which is driven from the output terminal of resistance R-84 may be thought of as a high gain amplifier which is easily overloaded and deliberately arranged to be overloaded under certain conditions. If driven with a strong signal, the amplifier will overload and conduct base current, thereby changing the charge on capacitor C-38 and throwing the amplifier circuit out of symmetry. In addition, diode CR-10 and 11 will severely clip the signal, by a shunt to ground, if a positive or negative voltage of approximately three-tenths of a volt is exceeded. The clipped output wave form is amplified by the transistor follower Q-12 and is presented to level potentiometer R-95 and from thence through resistors R-94, R-93 and capacitor C-44 back to the preamplifier via the terminal strip 29. The degree of fuzz is determined by the position of the effect control (R-81) and the volume of fuzz is independently controlled by the level control (R-95). Accordingly, a guitar player may want to go from the accompanyment type playing to a lead position wherein an increase in volume will be demanded. By having independnet level control on fuzz, the volume of the amplifier can be set to be different than when it is played normally with fuzz off.

In addition to the unique way in which the fuzz circuit is switched in and out of the overall amplifier, both symmetrical distortion and asymmetrical distortion are achievable. The diodes CR-10 and CR-11 operate to clip the signal symmetrically, however, as the effect control (R-81) is increased towards a maximum, a point will be reached where transistor Q-11 saturates on part of the cycle and the base of Q-11 goes into high conduction thereby charging capacitor C-38. The resultant charge on capacitor C-38 will asymmetrically bias the amplifier so that the output of amplifier Q-11 is a rectangular wave form having other than a 50 percent duty cycle. This will result in certain other types of intermodulation products having a different sound than those resulting from symmetrical clipping.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.