This example describes the memory enhancer , is actually a kind of "anti- disturbances reading device " , it first user's voice through the microphone into electrical signals, via multi-level audio amplification , the final will be amplified through the headphones the sound signal Play out , so that users can hear my pronunciation , focus , and thus enhance memory play a supporting role .
Circuit works
The retention of circuit from the microphone ( microphone ) BM, 3 audio amplifier and headphones etc. , as shown in Figure 9-76 .
No. l -class audio amplifier circuit by the transistors Vl and resistors Rl-R3, capacitor Cl, C2 composition; the first two audio amplifier circuit by the transistor V2 and resistors R4, R5, capacitors C2, C5 composition; the first three audio amplifier By the transistor V3, V4, resistors R7-R9, potentiometer RP and other components.
BM voice signals converted into electric signal by the microphone , via capacitor Cl coupled to Vl of the base (b pole) by Vl buffer amplified signal from the V1 of the collector (c pole ) output by the capacitor C2 coupled to the V2 's Base , V2 audio signal amplified by the C5 and RP1 added to the base of V3 by V3 and V4 complex amplified to drive headphones BE given resonant voice .
RP 's resistance adjustment can change the playback volume of the size of the headset .
Components Selection
Rl-R5, R7-R9 are selected 1/8W carbon film resistors ; R6 use 1/4W carbon film resistors .
RP chosen small potentiometer with switch .
Cl-C5 are chosen value of 1OV voltage aluminum electrolytic capacitors .
3AX3l Vl-V3 are selected Germanium PNP type transistor ; V4 use 3AX81 type Germanium PNP transistor .
BM electret microphone selection cassette .
BE can be linked together using two 8O ear , stereo headset can also be ordinary headphones the left and right channel series before use.
Operating Current Adjustment
Circuit installation is complete, at all levels should be adjusted to enlarge the work of the current collector tube . First in the collector loop string Vl people ammeter , and then adjust the resistor R7, to Vl of the collector current of 0.4-0.6mA.
V2 loop in the string of one collector ammeter , adjust the resistance R4 so that V2 of the collector current of 0.6-0.8mA.
Disconnect the headset with the circuit , in V3, V4 of the collector and the ammeter connected in series between the negative power supply , the adjustment of R7 's resistance , the composite tube (V3 and V4) of the collector operating current 2.4-3mA.