Dynamic bias in a tape recorder. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment
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Dynamic bias can significantly improve the quality of the recording. As shown in [1], the current of the RF components of the signal is biasing for low and medium frequencies and allows you to reduce the current of the RF bias without degrading the quality of their recording, and the intermodulation distortion is even reduced. In addition, a decrease in the RF bias current contributes to optimizing the recording of the RF components of the signal themselves.
In [2] it is shown that the most optimal in terms of reducing distortion and increasing the recording level of the HF components of the signal is the constancy of the sum of the recording current and the HF bias current. An important advantage [2] is the absence of dynamic distortions in signal processing, since the system is inertialess, but it is quite difficult to implement it in a tape recorder with a low-voltage supply.
The authors tested the system described in [3]. After a little refinement, it showed quite satisfactory results. As can be seen from the diagram (Fig. 1), with the help of resistor R2, the sensitivity threshold of the system is introduced and the capacitances of the capacitors that determine the response time and recovery time are changed.
The response time is determined by the constant R6-R5-C5. Really measured in the original source, it is about 10 ms. While changes in the dynamics of the signal, noticeable by ear, are commensurate with the delay time of the passage of the sound signal between the organs of hearing. To this end, the capacitance of the capacitor C5 was reduced from 0,15 uF to 0,01, while the response time was reduced to 0,5 ms.
The recovery time determines TB=R6C5+R5C4. This time measured in [3] is about 50 ms. Therefore, the value of the resistor R6 is reduced from 27 to 4,7 kOhm.
With the help of resistor R4, a deep DC feedback is introduced, which linearizes the control characteristic of the control channel on transistors VT1, VT2. Capacitor C3 helps to reduce the penetration of RF bias.
The described system was tested in the tape recorder "Belarus M-31 OS" and showed good results.
Literature
- Sukhov N. Adaptive bias or ... again about dynamic. Radio, 1991, N 6,7.
- Aleynov A. Parametric dynamic bias. Radio Yearbook, 1989, pp. 93-116.
See other articles Section Audio equipment.
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