AbstractAn electrical musical instrument amplifier is disclosed in which a signal which has been provided by an instrument to a second one of two different preamplifiers for amplification therein is passed to one of the inputs of a summing amplifier together with the output of the first preamplifier, the output of the summing amplifier being coupled through a tube driven power amplifier to
a loudspeaker system. The amplified signal from the second preamplifier is applied to a second input of the summing amplifier via a circuit arranged as a voltage divider and having a variable resistance provided by a field effect transistor driven by an oscillator. The modulation provided by the field effect transistor and associated oscillator can be adjusted to provide total phase reversal as
well as amplitude modulation when combined with the signal at the output of the second preamplifier, to provide a tremolo or vibrato effect. Improved reverberation control is provided by a control common to the volume controls of both a delayed reverberation signal from the second preamplifier and the combined signal which results when the instrument signal from the second preamplifier is combined with the delayed reverberation signal. The power amplifier can be operated in a distortion mode to achieve desirable harmonics without overloading the voice coils in an attached speaker system through use of a power supply which applies reduced voltages to the power amplifier whenever the gain of the power amplifier is adjusted to a high setting while at the same time regulating the voltage applied to the first and second preamplifiers to keep such voltage constant.ClaimsWhat is claimed is:
1. An amplifier for an electrical musical instrument comprising:
a summing circuit having inverting and non-inverting inputs;
a first preamplifier capable of receiving a signal from an electrical musical instrument and having an output coupled to one of the inputs of the summing circuit;
a
second preamplifier capable of receiving a signal from an electrical musical instrument and having an output coupled to said one of the inputs of the summing circuit;
a first circuit path coupling the output of the second preamplifier to the other one of the inputs of the summing circuit, the first circuit path including a fixed resistance;
a second circuit path coupled to the first circuit path between the fixed resistance and said other one of the inputs of the summing circuit, the second circuit path including a variable resistance; and
an oscillator coupled to vary the resistance of the variable resistance in the second circuit path.
2. The invention defined in claim 1, wherein the variable resistance comprises a field effect transistor having source and drain terminals coupled in the second circuit and a gaate terminal coupled to the oscillator.
3. The invention defined in claim 2, further including an adjustable resistance coupled in parallel with the field effect transistor.
4. An amplifier for electrical musical instruments comprising:
amplifier means for amplifying a signal from an electrical musical
instrument to provide a loudspeaker drive signal, the amplifier means comprising a plurality of controllably conductive power amplifying devices and having a variable gain;
control means for varying the gain of the amplifier means; and
power supply means coupled to said amplifier means for supplying a plurality of signals to the controllably conductive power amplifying devices to establish operating parameters for
the controllably conductive power amplifying devices, said powersupply means being adjustable between a first setting which provides the loudspeaker drive signal with normal power when the gain of the amplifier means is in a first range and a second setting which reduces the values of the plurality of signals tochange the operating parameters of the controllably conductive power amplifying devices and the
