This is the circuit for oscillator that is used for the audio. This circuit is based on op amp TL064 for control the circuit. There are only two control pots (RV1 and RV2) and two DPDT switches. The output level pot includes an on-off switch and is of logarithmic taper to allow easier setting at low (i.e. milli volt) levels. This pot is directly coupled to A4's output to minimize response errors, provided that the load impedance is constant or quite high compared to the output impedance provided by Mini oscillator. This is the figure of the circuit.
The frequency sweep control (RV1A/B) has a range of about 24:1 and in combination with the High-Low range switch having a 18:1 ratio, the audio band is covered (with the exception of the lowest octave) in two overlapping ranges. The possibility of a single sweep of the audio band without the range switch was tried out and later dropped in preference to the present design. The square/sine wave switch works by disconnecting the negative feedback around A4 allowing the op-amp to run "open loop". In this condition it is overdriven by the oscillator stage causing its output to saturate at the positive and negative supply voltages producing a squared waveform. The additional four diode network which is switched across the output of A4 and voltage limits the output level in square wave mode to match the sine wave level and at the same time regulates against variations in the battery voltage.
The actual operating level of Miniosc is limited by the use of a single nine volt battery. The discharge curves for various types show a voltage variation of from 9.5 volts down to 6.3 volts is to be expected from "fresh" to "flat". The miniosc operates as specified over this range with a maximum output level of 1.27 volts RMS sine and 1.45 volts square. The battery drain in sine wave mode is a miniscule 1.7mA increasing to about 4.7mA in square wave mode. This very low drain is mainly the result of using the Texas Instruments TL064 low power quad FET op-amp which is ideally suited to the design.
The frequency sweep control (RV1A/B) has a range of about 24:1 and in combination with the High-Low range switch having a 18:1 ratio, the audio band is covered (with the exception of the lowest octave) in two overlapping ranges. The possibility of a single sweep of the audio band without the range switch was tried out and later dropped in preference to the present design. The square/sine wave switch works by disconnecting the negative feedback around A4 allowing the op-amp to run "open loop". In this condition it is overdriven by the oscillator stage causing its output to saturate at the positive and negative supply voltages producing a squared waveform. The additional four diode network which is switched across the output of A4 and voltage limits the output level in square wave mode to match the sine wave level and at the same time regulates against variations in the battery voltage.
The actual operating level of Miniosc is limited by the use of a single nine volt battery. The discharge curves for various types show a voltage variation of from 9.5 volts down to 6.3 volts is to be expected from "fresh" to "flat". The miniosc operates as specified over this range with a maximum output level of 1.27 volts RMS sine and 1.45 volts square. The battery drain in sine wave mode is a miniscule 1.7mA increasing to about 4.7mA in square wave mode. This very low drain is mainly the result of using the Texas Instruments TL064 low power quad FET op-amp which is ideally suited to the design.
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