ELECTRICAL NOISE REDUCTION SWITCH

In place of the normal mechanical noise reduction onoff

switch the circuit below is often used to permit electrical NR

control When using this circuit the following points should

be noted

1 Signal boost is reduced by increasing DC voltage on Pin

14 (see curve) A voltage of approximately 3V is adequate

to achieve NR OFF

2 Supply current may be significantly increased by high pin

14 forced voltages Values for V and R should thus be

chosen such that pin 14 voltage is 3V – 4V

3 When electrical NR switching is used signal level is

slightly affected by the minimum value of the internal vari-

able impedance (At 10 kHz – 10 dB a residual boost of

approximately 04 dB remains) This is not the case for

mechanical NR switching

TLH7876 – 10

Note 1

Where not otherwise specified component tolerances are g10%

(Encode 10 kHz)

Signal Boost vs Pin 14 Control Voltage

(VS e 12V) (Encode 10 kHz)

Supply Current vs Pin 14 Control Voltage

TLH7876 – 11

5