The working principle of the audio amplifier is where the signal from the microphone is amplified by the recording amplifier block Bias oscillator, high frequency produces frequency voltage for premagnetization of the tape, so that the recording process is free from defects (distortion), then from the air gap of the recording head comes out a magnetic field that is in tune with the signal from the microphone. On the recording tape there are magnetic fields (zones) due to induction from the recording head, during recording the tape moves regularly through the air gap of the recording head. A tape that already contains a magnetic record if it moves regularly at the same speed as the recording time, then by the magnetic zones it is induced voltage on the reproduction head. This signal is amplified by the reproduction circuit and by the Loudspeaker, converted into mechanical vibrations (oscillators), Erase is a high frequency generator to erase the tape from the deepest magnetic recording.
Recorder Amplifier
There are 3 functions where the change of functions is carried out with the function switches, the functions are as follows:
1. Record Amplifier
As a recording amplifier is usually divided into 2, where the front amplifier becomes the input signal amplifier, while the final amplifier becomes the oscillator, because when recording frequencies above 300hz there is a lot of shrinkage so that this is a loss, so there needs to be a boost (to strengthen certain frequencies in order to obtain an average output voltage level for a certain frequency). Boost is a kind of additional amplifier for certain frequencies in the context above for frequencies 5kHz to 20kHz.
Response correction occurs during the recording process and is often referred to as "Pre-Emphasis" and at the time of reproduction it is called "Post-Emphasis".
The final amplifier is used as an oscillator during recording, this is discussed further in the high frequency bias section.
2. Reproductive Enhancer
As a reproduction amplifier, there is no need for a treble boost. Because this boost will cause noise amplification from the tape or the amplifier itself. In this reproduction amplifier, a boost is normally performed, for bass usually between 200Hz to 20kHz and this is usually done by a recording amplifier. This will cause the recording of the network frequency, resulting in wasted recording, besides that it will also cause excessive loading on the tape so that distortion occurs.
Amplifiers -- amplifiers designed for vinyl recording can usually be used for tape recorders provided a correction network is added to compensate for the needs or requirements needed for magnetic recording "correction" / equalization (equal = same), this is done with various methods by various manufacturers, the following is the basic circuit:
Recorder Amplifier Analysis at points A, B, C and D