CXA1878Q
5. High frequency calibration
The CXA1878Q allows the high frequency response of the recording equalizer to be finely adjusted with a DC
voltage.
Therefore, the recording level in high frequencies (peak) can be varied by approximately ±4dB simply by
applying DC voltages of 0 to 5V (for dual power supply) to the GP CAL pin (Pin 32). The table below shows
3
the input range of control voltages with the power supplies used.
Output level
Down (Vdown)
DGND to 2.5V
Typ.
2.5V
Up (Vup)
4
GP CAL pin voltage
2.5V to VCC
3
4
Although the above range of voltages can be input to the control pin, the controllable input voltage range is
as follows.
2.5V < Vup ≤ 5.0V
DGND ≤ Vdown < 2.5V
Control voltages for this IC are referenced to the DGND pin (Pin 30).
Also note that when not using this high frequency calibration function, simply leave the GP CAL pin (Pin 32)
open, so that the voltage of the GP CAL pin is matched to the internal reference voltage (2.5V), with the
high frequency equalizer amplifier characteristics set for the standard gain.
Gain
[dB]
GP CAL
REC CAL
REC CAL
GP CAL
GP CAL
REC CAL
REC CAL
REC CAL
REC CAL
Frequency [Hz]
Fig. 3. Conceptual diagram of the recording level/high frequency calibration functions
6. Meter circuit
The CXA1878Q has a built-in full-wave rectifier circuit for the level meter. Therefore, a DC voltage can be
obtained by attaching time constants to the METER 1 and 2 output pins. The output voltage is set to 1.6V
(+1.1dBv) during reference input. (for an external time constant of 56kΩ, 33µF)
The MT C pin detects only the AC component. The low frequency cut-off is determined with the capacitor
connected to this pin and the 14kΩ internal resistor. (Approximately 10Hz for 1µF)
7. Recording volume control circuit
The CXA1878Q adjusts the size of the recording signal with a built-in control circuit. Therefore, the gain can be
controlled by applying the voltage between DVCC and DGND to the REC VOL pin (Pin 28).
(A 0dB signal is output when voltage of 2.0V is applied.)
– 27 –
SONY [ SONY CORPORATION ]
