The present invention relates to apparatus and a method for controlling the tone of sounds produced by electrical musical instruments, and is 5 concerned particularly, although not exclusively, with apparatus and a method for controlling the tone of sounds produced by an electric guitar.

Known circuits for controlling/modifying the tone of sounds produced by an electric guitar generally fall into one of two categories. 10

The first category of circuit is that of the simple capacitor circuit. A capacitor is used to filter off higher frequencies of electrical signals produced by the electric guitar to a greater or lesser extent and to short circuit them to earth. The resulting sound is often rather muffled and unpleasant. This 15 system of tone control has been used since the electric guitar was in its infancy several decades ago, and is still used today.

The second category of circuit is that of the active circuit. Active circuits are able to cut and boost the range of audio frequencies beyond that

20 capable of being produced by the simple capacitor circuits. However, they are subject to several disadvantages. They produce a relatively high level of noise and have an undesirably large circuit failure-rate often requiring the replacement of specialised components such as micro chips. In addition, extensive wiring during production results in relatively high unit costs. i ^"• * ^• * 25 Because of these factors electric guitars employing active circuits for tone control are considered to be both expensive and unreliable.

Accordingly, specific embodiments of the present invention aim to provide a tone control circuit which is simple in construction and which permits a greater selection of tonal variations.

According to a first aspect of the present invention there is provided a method of controlling tone in an electrical musical instrument, wherein said instrument produces an electrical signal having high frequency components and low frequency components which are supplied to an output, characterised in that said high frequency components are supplied to said output in preference to said low frequency components in response to a passive electrical circuit.

Preferably the extent to which said high frequency components are supplied to said output in preference to said low frequency components is manually adjustable.

Said low frequency components may be filtered out from said electrical signal.

Preferably said low frequency components are supplied to ground via an inductive device.

According to a second aspect of the present invention there are provided tone control means for an electrical musical instrument, wherein said instrument produces an electrical signal having high frequency components and low frequency components characterised in that said tone control includes a passive electrical circuit arranged to supply said high frequency components to an output in preference to said low frequency components.

The tone control means may comprise adjustment means to adjust the extent to which said high frequency components are supplied to said output in preference to said low frequency components.

The adjustment means may comprise a first filter to filter said low frequency components to ground.

The first filter may comprise an inductance.

Preferably the first filter comprises at least one capacitance.

There may be provided a second filter to filter said high frequency components to ground.

Preferably the second filter comprises a capacitance.

In a preferred arrangement there is provided at least one variable selector arranged to control the extent to which the first and second filter means filter said low and high frequency components.

The or each variable selector may comprise a potential divider.

In a preferred arrangement there are provided first and second inductances and a first capacitance, the first inductance being electrically connected at one end to earth and being electrically connected at its other end to first ends of both the second inductance and the first capacitance, the second inductance and the first capacitance being electrically connected at their second ends to opposite ends of a first potential divider, a moveable

contact of the first potential divider being arranged to be electrically connected to a source of audio-frequency electrical signals of an electrical musical instrument.

Preferably there is provided a second capacitance, electrically connected at one end to the first inductance and to the first ends of the second inductance and the first capacitance, and being electrically connected at its other end to a second potential divider, which second potential divider is arranged to be electrically connected to a source of audio-frequency electrical signals of an electrical musical instrument.

The first and second potential dividers may be provided by a common potential divider.

Preferably the first and second inductances have a common core.

At least one of the inductances may have a core which core is made from an alloy of aluminium, nickel and cobalt.

The tone control means may be provided in combination with at least one source of audio-frequency electrical signals which comprises a pick-up of an electrical musical instrument.

According to a third aspect of the present invention there is provided a tone control circuit for use with an electrical musical instrument, the tone control circuit comprising first and second capacitors and first and second inductors, in use the first capacitor and the second inductor being arranged to be electrically connected at respective first ends to different contacts of a first

potential divider, and being arranged to be electrically connected together at their second ends, the second capacitor being arranged to be electrically connected at its first end to a second potential divider and being arranged to be electrically connected at its second end to both the first capacitor and second inductor, the common electrical contacts of the first and second capacitors and the second inductor being arranged to be electrically connected to one end of the first inductor, which first inductor is arranged, at its other end, to be electrically connected to earth.

The invention also includes an electrical musical instrument comprising tone control means substantially as herein described with reference to the accompanying drawing.

The invention also includes an electrical musical instrument comprising a tone control circuit substantially as he dm described with reference to the accompanying drawing.

The invention also includes an electrical musical instrument employing a method substantially as herein described with reference to the accompanying drawing.

The electrical musical instrument may comprise a guitar.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which:

Figure 1 shows a schematic diagram of a tone control circuit for an electric guitar.

Referring to Figure 1, a pick-up 10 of an electric guitar (not shown) is electrically connected at one end to earth. At its other end, the pick-up 10 is connected to a moveable arm 11a of a main volume potentiometer 11.

The volume potentiometer 11 controls the amplitude level of electrical signals of all frequencies produced in the pick-up 10. Connected to a node 12, between the volume potentiometer 11 and a connection 13 to an amplifier (not shown) is a moveable contact 14a of a first filter potentiometer 14 which is connected to a capacitor 15 and an inductor 16 each of which is connected to an inductor 17 which is, in turn, connected to earth.

In addition, the moveable contact 18a of a second filter potentiometer 18 is connected to the node 12, and one end of the potentiometer 18 is also connected to a capacitor 19. The capacitor 19 is connected to the inductor 17 at the same point as the capacitor 15 and inductor 16.

In use, movement of a string of the electric guitar (not shown) causes disturbances in the magnetic field associated with the pick-up 10. These disturbances manifest themselves as electrical current signals in a range of frequencies in the coil of the pick-up 10 which signals are reduced in amplitude to a greater or lesser degree by the volume potentiometer 11 according to the position of its moveable contact 11a.

The attenuated signal arrives at node 12 and is presented with a route to earth either via potentiometer 18, capacitor 19 and inductor 17 or via potentiometer 14, capacitor 15 and inductor 16 and inductor 17.

The extent to which certain signal components of different frequencies will be filtered to earth depends upon the position of the moveable contacts 18a, 14a of potentiometers 18 and 14 respectively and upon the values of capacitors 19, 15 and of inductors 16, 17.

Referring particularly to potentiometer 14, if the moveable contact 14a is positioned at the inductor extreme frequencies in the lower to middle region of the range will be filtered to ground by the inductors 16 and 17. Alternatively, if the moveable contact 14a of the potentiometer 14 is positioned at the capacitor extreme, frequencies in the upper range will be filtered to ground by capacitor 15 and inductor 17. Since the moveable contact 14a of the potentiometer 14 may be positioned anywhere between these extremes, a compromise may be reached in which different frequencies of an input signal may be filtered off to ground.

In addition to this, the influence of capacitor 19 may be introduced to a greater or lesser extent by the positioning of moveable contact 18a of potentiometer 18. The effect of the capacitor 19 is to filter some higher frequencies to ground and this, combined to a variable extent with the effect of the capacitor 15 and inductors 16 and 17, allows a broad variation in tone of the sound produced from the electrical signal sent to an amplifier (not shown but in use connected to 13).

In a preferred configuration inductor 16 has a winding of 2KΩ and inductor 17 a winding of 1KΩ. They have a common core made from a compound of aluminium, nickel and cobalt. Capacitor 15 preferably has a value of 0.022 mfd, and capacitor 19 of 0.01 mfd.

Since no active circuitry (such as pre-amplifiers) is included in the tone control circuit, there is low noise.

In addition, the simplicity of the circuit means that it is easy to fit to an existing electric guitar.

In use, capacitors 15 and 19 and inductors 16 and 17 are embedded together in an epoxy resin for protection, wires protruding from the epoxy resin for connection to the rest of the circuit.

The simple components used in the circuit mean that the failure rate of the circuit is relatively low.

By using the above described tone control circuit it is possible to produce a broad range of naturally sounding tonal variations . When used with a stratocaster-type guitar the guitar can be made to exhibit the following variations in tone :-

1. The original sound of the guitar. 2. A soft humbucking sound.

3. A hard humbucking sound.

4. Soft mid-ranges like those of an acoustic guitar.

5. High treble sound.

All of the above tonal variations may be achieved by correct positioning of the potentiometers 14 and 18 without the requirement for additional switches etc.

Further advantages of the circuit are that the "sustain" capability of the guitar is increased due to resonance between pick-ups of the guitar and the inductors 16 and 17. In addition, the circuit affects the impedance which the pick-ups present to an amplifier, therefore it is possible to match the impedance of the guitar with that of an amplifier.

It is envisaged that the tone control circuit will be provided both ready installed in a guitar and also in kit form comprising the capacitors 15 and 19 together with the inductors 16 and 17 for easy connection to an existing guitar.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.