Abstract
An 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.
Published Version
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