Extended-play-circuit
A single operational amplifier, one of four included in the widely used LM324, is functioning within a variable pulse-width, free-running square wave oscillator circuit. Its output drives two transistors that manage the on/off cycle of the tape-drive motor. The oscillator's positive feedback path is crucial for the effective operation of the variable on/off timing signal. The configuration includes two diodes and a pulse-width potentiometer (R8), which allows for the adjustment of the on and off times without impacting the oscillator's operating frequency. One diode permits only the discharge current to flow through it and its corresponding section of R8, while the other diode and its associated portion of R8 determine the charge time for the timing capacitor (C3). The precise control of the recorder's speed relies on the accurate on/off timing provided by the oscillator. Additionally, a simple voltage regulator circuit (Q1, R3, and D4) is incorporated. To connect the speed control to most cassette recorders, one can easily access the recorder and disconnect either of the motor's power leads; it is generally advisable to disconnect the ground or common side. This can then be linked to the control circuit using a length of small, shielded cable. Some recorders may feature a remote input jack that allows for remote operation of the recorder. Before modifying a recorder with a remote jack, it is recommended to first connect the circuit to the external remote input.
The circuit employs a single op-amp in the LM324 package to create a square wave oscillator, which is essential for controlling the operation of the tape-drive motor in a cassette recorder. The oscillator's design utilizes positive feedback to maintain a stable oscillation frequency while allowing for variable pulse widths. The two diodes in the circuit serve distinct functions: one diode enables the discharge of the timing capacitor (C3) during the off period, while the second diode is responsible for the charging phase, thereby defining the duration of the on state. The pulse-width potentiometer (R8) is strategically placed to adjust the timing without altering the frequency of oscillation, ensuring that the motor operates smoothly and efficiently.
The voltage regulator circuit, consisting of Q1, R3, and D4, stabilizes the voltage supplied to the motor, which is critical for consistent performance. This design ensures that fluctuations in power supply do not adversely affect the operation of the motor, which could lead to variations in playback speed. When integrating this circuit with a cassette recorder, it is vital to ensure that the connections are secure and that the correct leads are used to prevent damage to the recorder.
For recorders equipped with a remote input jack, the integration process can be simplified by connecting the control circuit directly to this input, allowing for remote operation without the need for invasive modifications. This feature enhances user convenience and provides flexibility in operation, making it an advantageous addition to modern cassette recorders. Overall, this circuit design exemplifies an effective approach to motor control in audio equipment, leveraging the capabilities of the LM324 op-amp in a practical application.A single op amp-one of four contained in the popular LM324-is operating in a variable pulsewidth, free-running squarewave oscillator circuit, with its timed output driving two transistors that control the on/ off cycle of the tape-drive motor. The Dscillator" s positive feedback path holds the secret to the successful operation of the variable on/ off timing signal.
The two diodes and pulsewidth potentiometer R8 allows the setting of the on and off time, without affecting the oscillator"s operating frequency. One diode allows only the discharge current to flow through it and the section of R8 that it"s connected to. The other diode, and its portion of R8, sets the charge time for the timing capacitor, C3. Since the recorder"s speed is controlled by the precise off/on timing of the oscillator, a simple voltage-regulator circuit (Ql, R3, and D4) is included.
Connecting the speed control to most cassette recorders is a simple matter of digging into the recorder and disconnecting either of the· motor"s power leads, the ground or common side might be best, and connecting the recorder through a length of small, shielded ci!ble to the control circuit. In some recorders, a remote input jack is furnished to remotely tum on and off the recorder. Before going in and modifying a recorder with a remote jack, try connecting the circuit to the external remote input.
🔗 External reference
The circuit employs a single op-amp in the LM324 package to create a square wave oscillator, which is essential for controlling the operation of the tape-drive motor in a cassette recorder. The oscillator's design utilizes positive feedback to maintain a stable oscillation frequency while allowing for variable pulse widths. The two diodes in the circuit serve distinct functions: one diode enables the discharge of the timing capacitor (C3) during the off period, while the second diode is responsible for the charging phase, thereby defining the duration of the on state. The pulse-width potentiometer (R8) is strategically placed to adjust the timing without altering the frequency of oscillation, ensuring that the motor operates smoothly and efficiently.
The voltage regulator circuit, consisting of Q1, R3, and D4, stabilizes the voltage supplied to the motor, which is critical for consistent performance. This design ensures that fluctuations in power supply do not adversely affect the operation of the motor, which could lead to variations in playback speed. When integrating this circuit with a cassette recorder, it is vital to ensure that the connections are secure and that the correct leads are used to prevent damage to the recorder.
For recorders equipped with a remote input jack, the integration process can be simplified by connecting the control circuit directly to this input, allowing for remote operation without the need for invasive modifications. This feature enhances user convenience and provides flexibility in operation, making it an advantageous addition to modern cassette recorders. Overall, this circuit design exemplifies an effective approach to motor control in audio equipment, leveraging the capabilities of the LM324 op-amp in a practical application.A single op amp-one of four contained in the popular LM324-is operating in a variable pulsewidth, free-running squarewave oscillator circuit, with its timed output driving two transistors that control the on/ off cycle of the tape-drive motor. The Dscillator" s positive feedback path holds the secret to the successful operation of the variable on/ off timing signal.
The two diodes and pulsewidth potentiometer R8 allows the setting of the on and off time, without affecting the oscillator"s operating frequency. One diode allows only the discharge current to flow through it and the section of R8 that it"s connected to. The other diode, and its portion of R8, sets the charge time for the timing capacitor, C3. Since the recorder"s speed is controlled by the precise off/on timing of the oscillator, a simple voltage-regulator circuit (Ql, R3, and D4) is included.
Connecting the speed control to most cassette recorders is a simple matter of digging into the recorder and disconnecting either of the· motor"s power leads, the ground or common side might be best, and connecting the recorder through a length of small, shielded ci!ble to the control circuit. In some recorders, a remote input jack is furnished to remotely tum on and off the recorder. Before going in and modifying a recorder with a remote jack, try connecting the circuit to the external remote input.
🔗 External reference