Variable Band-width Audio Amplifier

Given below is a novel circuit of adjustable band-width audio amplifier suitable for CW / SSB reception for receivers. Resistor R controls the band-pass characteristics of the active filter. C1 determines the low frequency response.

For swichable bandwidth of audio filter, R can be chosen as 4.7K for CW and 1.0K for SSB reception.

For continuously variable bandwidth, use 5K pot in series with 470Ω resistance.

Fig. 2 shows the filter response for R = 4.7K, having peak response at about 750 HZ and insertion loss of 0.54 db suitable fpr CW reception.

Fig. 3 shows the filter response for R = 1K, having a 3-db BW of about 2.7khz and insertion loss of .54db suitable for SSB reception.

Fig. 4 shows the PCB layout for the complete audio amplifier.

                                                                   Fig.1

Audio Filter response curves:

For CW reception

 

 

                                                                                   Fig.2

For SSB reception

                                                                                 Fig.3

                                                                              Fig.4