Class A headphone amplifier mini.
The amplifier is assembled according to the scheme of Lehmann Audio Black Cube, but unlike the original, the trace of the tracks is reduced more than 3 times, which can not positively affect the operation of the device. Also, unlike the original, separation capacitors at the input are not used, but instead a quality non-polar electrolytic capacitor is included for the reference "0" in the NHS circuit in the OP. There are several options available:

Transistors.
- Output BD140 / BD139 Philips transistors, loaded in gray body with copper legs.
- The output transistors BD140 / BD139 (Fairchild Semiconductor) are in the past ON, and even earlier MOTOROLLA
- Output transistors BD140 / BD139 (ST)
- driver transistors BC546 / BC556 Philips, loaded with silver muzzle
- driver transistors BC546 / BC556 (Fairchild Semiconductor) they are in the past «ON», and even earlier «MOTOROLLA»
- driver transistors BC546 / BC556 (China)

Resistors
Metal film resistors Vishay DALE
Metal film resistors Vishay Beyschlag mbb0207
Metal Film Resistors China

It is recommended to use in conjunction with the headset protection module

The amplifier module is equipped with an op amp
NE5532 or TL072 to choose from.
For an additional charge it may include:
LME49860
OPA2134
The supply voltage is variable 2x13 ... 16V
There are toroidal transformers to power this amplifier.