Concept
My first try was a circuit with an op-amp and BD139 / BD140 as current booster (I often saw so a kind of headphone amplifier on ebay). But this amplifier, in combination with my Audio Technica headphone, was definitively too loud also with the lowest recommended gain. I looked for a circuit with an op-amp only and found it here.
Hardware
The first op-amp in this circuit acts as voltage and the second one as current amplifier. The headphone amplifier has separate voltage regulators for a better decoupling from the rest of the preamplifier power supply. The volume potentiometer is mounted on the front panel (ALPS, RK27112, 100kOhms, logarithmic characteristic). I added also a plop-noise protection with a simple relay circuit.
The whole KiCad-project (including Gerber-files) can be found here. Remark: it was made under Linux with KiCad-version 4.0.7 using this additional libaries. The bill of material (bom) as semicolon separated text file contains some comments about part dimensioning / quality.
License
Please keep in mind: all content on this page is licensed under the terms of the GPLv3.
falk.richter*at*yandex.com
Last update: December 20, 2019