Digital vol. adjustment circuit for audio amplifier - has photoresistor as vol. adjuster in input circuit of inverting operational amplifier

摘要

The amplifier is controlled via a D/A converter. In the input circuit of an inverting operational amplifier (OP2) is incorporated a photoresistor (PH) as adjusting element for the vol. setting. It is fitted in the effective range of at least one light emitting elementm (LED). Pref. the current for the LEDs is generated by a digital, current controlled current source, forming simultaneously the D/A converter. The digital current control may be carried out by current summation at the current source input. The circuit may contain an EPROM for correction values for the characteristic of an opto-coupler. -ADVANTAGE - No cracking noise and distortion of output signal.