If in the past, there were many headphones with impedances of 600 ohms, we saw many diagrams with a single NE5532. Nowadays, we find more 32 ohms and there a simple AOP is not enough. It is necessary to attack in current and to have recourse to transistors of outputs. The basis of my circuit remains the same but allows you to choose the final stage. We can therefore create pairs of NPN / PNP Style BC337 & 327, BC550 & 560, ...

The Texas BUF634 also does the same function and is available in DIP & SOIC.

Very simple, the assembly is powered by +/- 12V and the gain is calculated with the following formula: G = 1+ (RCR / RP). Personally, I have RCR = 15K & RP = 3K3

Small thoughts around headphone amps:
There are 2 things to consider, gain and volume. Often times, I find that in some commercial mixers, the gain is sometimes pushed quite hard and the only way to get a proper level is to lower the input volume but in this case the signal to noise ratio of listening is less good. For my part, I set my input volume to 70% and adjust RCR for comfort. I am in the 12 to 15 dB range.

What to create can be your duo or multi-headphones system. It can also be used as a stereo line booster.
At its simplest, you insert a volume potentiometer before the module but nothing prevents you from placing a matrix to add Talk Back returns.

With a footprint of 34mm, it can easily be placed vertically in 1U (44mm) format