Application circuit of HA12058

The application of HA12058 is shown in Figure 5-5. In the circuit, pin 7 is the Dolby level test point. This circuit is strictly stipulated
as 580mV. It is mainly used for testing during adjustment. The practical circuit can be designed according to the test circuit. Generally
, no changes are required except for the transfer switch.
    The actual noise reduction effect of the circuit is closely related to the level of the input recording and playback signals. If the input recording and playback level does not meet
the requirements the performance of the circuit may deteriorate, and the noise reduction effect may not even be achieved, so adjust the input signal. Level is very
important. When adjusting this circuit, it needs to be connected to the output of the balanced amplifier stage of the cassette recorder or the output of the recording amplifier. Before
adjusting the Dolby level, you should first check that the equalizer amplifier, recording amplifier, bias oscillator and other circuits of the recording socket are all
in normal working condition, and then adjust the Dolby level. Due to the input and output linear amplifier of
HA12058 The voltage gain is about 25dB. The amplified Dolby level input from pin 1 or 4 is 580mV. 25dB is approximately equal to
17.8 times, so the input level of pin 1 or 4 is about 32mV to meet the requirements.
    When playing back, put the recording and playback switch in the playback state, put an OdB benchmark test signal (frequency is
315 ground, magnetic level is 250nwb.rn) in the tape box, and adjust the playback balance level of the recorder's playback circuit. Adjust the gain and trimmer resistor so that
the level of pin 7 of the integrated circuit is 580mV. Fix the trimmer resistor and the playback adjustment is completed.
    When recording, put the record and playback switch in the recording state, input a 1mV.315Hz signal from the microphone socket,
adjust the gain adjustment trimming resistor of the recording loop of the equalizing amplifier, so that the level of pin 7 of the circuit is 580mV, and
the trimming is fixed. resistor, and then adjust the input signal of the recording amplifier or the gain of this stage so that the tape in the cassette can be recorded to
200nwb/rr, then the adjustment of the recording Dolby level is also completed.
    The R and C components related to the time constant in the circuit are R7, Lu, Rz”C12, C13, R19, c27 and RJ8.Li.
These components should use metal film resistors with an error of <1% and capacitors with an error of <5%. Among them, polyester capacitors should be used for C13.
Li has a large inductance, so it can use a structure with a densely wound core and a magnetic ring shield. The inductance is 36mH.