HEADPHONE HI-FI AMPLIFIER CIRCUIT SCHEMATIC DIAGRAM
This circuit can be used for a headphone amplifier, arose after the purchase of commercial equipment with separate pre and power amplifiers without a headphone output. The intention is to permanently insert the headphone amp between pre and power amps. The gain control being used to pre-set the gain so that the pre-amp's gain control is normally used for setting the listening level.
Its advantages are :
* low output impedance to drive several pairs of phones
* The active gain stage is, almost, perfectly logarithmic and ...
* Independent of the absolute value of the pot
* Excellent channel tracking
* O/P noise reduces with gain reduction.
The first stage is a conventional series feedback circuit using the ubiquitous NE5534, the gain being set by the feedback AOT (adjust on test) resistor to suit individual needs, this stage provides the necessary low impedance output for the variable gain stage. The resistor/ capacitor networks around the input stage may seem a little extravagant, but are necessary to reduce any possible RF pickup especially the 470 pF between the two IC + and - inputs.
