Advanced recording deck circuit

It is an advanced deck circuit composed of TDA1602A. It includes all the basic functions of a double deck and
uses reliable electronic switches to simplify control. The deck has the following functions: standard playback level (775mV)
output; karaoke recording (mixing, post-dubbing); Fe/Cr02 with automatic recording compensation and automatic bias adjustment; Fe/
CrCb with playback equalization selection; Synchronized high-speed transcription and compensation; automatic squelch circuit. The compensation network is precisely calculated and
fully compliant with NAB standards. The functions of each part of the circuit are introduced as follows: The
    output level of pins 1 and 2 of TDA1602A is 150mV, which can be directly used with the Dolby noise reduction circuit. After line amplification
, a line level of 775mV (O blood) is output to drive the power amplifier circuit. Tantalum electrolytic and non-polar capacitors
(polyester or polypropylene capacitors) can be used.
    3 Pin 4-5.6 is internally used for the external line signal input amplifier, that is, the external recording signal input amplifier b R27. If it is
a feedback resistor, the gain of the amplifier can be adjusted to adapt to different signal sources such as CD players, FM broadcasts, etc., in order to obtain the
best , low distortion tape recording effect. The external Rzs and c stations connected to pin 7 form a differential circuit and serve as an automatic noise suppression circuit
. As can be seen from the figure, this circuit can suppress impact noise regardless of whether card A or card B is playing sound or dual cards are recording simultaneously at high speed. This circuit
is especially indispensable for high-power audio equipment. This feature also enables remote control muting.
    Pin 8 is for A/B card selection and realizes karaoke recording function at the same time. When the base of VTi
is grounded by the karaoke recording switch, VTi is cut off and pin 8 is at high level. At this time, the B card can mix the line input signal and the A card output signal
for recording. The A card can play karaoke tapes or music tapes. If the microphone signal is input from the line input terminal, it can realize duet
recording or soundtrack reading program production. At the same time, this function is combined with the dedicated dual-track (four-track) silencer head
(X24C) to independently record/dubb the left and right channels. You can experience the program production
process and record high-quality Program tape. When card A is playing sound, pin 8 is low level.
    Pin 9 Fe/(r02 has a playback balance selection and an external playback balance low-end frequency adjustment capacitor connected to pin 4039.
The time constant is 120tes and 70rrs.
    Pin 10 is a playback/recording/J Shaanxi recording selection. When playing back, Pin 10 is in the floating state; when recording, pin 10 is 1/2 Vp
level; when fast recording, it is Vp high level, which is provided through VI5. VTz, VT3 and their peripheral resistor network constitute the speed regulation of the two-speed
motor system. The base levels
of VT2 and VL are controlled by the synchronous recording switch. A and B terminals are the speed regulating terminals of the two-speed motor .