Well this went rather uneventfully. I bought it because I have found soldering the pin headers onto maker modules very therapeutic, so wanted something with a bit more meat.
It took me about 45 minutes to solder it together and surprisingly to me I was soldering things faster than my 25W Weller could keep up with and I had to pause to let it heat back up. This is a surprise because as a teenager I couldn't solder to save my life, but now soldering pin headers and ICs seems easy.
On, "1 thousand", in with the solder, wait till it flows around and into the hole, off. Next.
Also slightly disappointed that it worked first time. I gave it 15V from the bench PSU, audio from my Burr Brown headphone DAC amp passthrough and connected my old Sennheiser phones (I'm not stupid enough to connect my £300 Audio Techniq to something I built!).
Do you have a schematic for the 47 headphone amplifier? Searching for it using Google, gives a variety of different circuits, many of which require a dual power supply.
It has some odd artefacts which add a kind of wooden, compared to the Burr Brown/Head Box amp, potentially clipping/square wave under tone, but I'm just being picky. It has enough gain to "pop" the Sennheisers so that's a plus over the Head box amp which is nanny state limited.
Do either of those amplifiers have tone control?
If not, then both amplifiers should sound the same. If either amplifier is affecting the sound, then it's either not designed/built properly or it's being overdriven. Another possibility is cognitive bias: you might believe there's a difference, because you built the one amplifier and not the other, they look different, the price or branding and therefore perceive a difference, when there isn't any.
Fortunately, it's very easy to determine this, with the help of a signal generator, an oscilloscope, some audio connectors and cables. Set both amplifiers to the same gain. Firstly connect one amplifier (doesn't matter which one) to your preferred music source and set the volume a comfortable listening level. Remove the music source and replace it with a 1kHz sine wave from the signal generator (don't put the headphones on when you do this). Look at the output using an oscilloscope and adjust the signal generator's level, until the 'scope shows a 500mV peak to peak sine wave. Swap the amplifier, keep the 'scope and signal generator settings the same and adjust the volume control on the other amplifier, until the 'scope shows a 500mV peak to peak sine wave. If the sine wave appears distorted, then the amplifier is bad.
Now you have both amplifiers set to exactly the same gain, you can see if one really sounds different from the other. Connect each amplifier to a set of input/output extension cables, of the same length, type and colour (they must look identical). Hide the amplifiers in a box. Make it so you don't know which input/output is connected to which amplifier. Now you can try swapping the input and your headphones between the two amplifier, without knowing, which is which. Can you hear any difference? Try tracing the cables back, to see which amplifier you're using. Repeat the test a few times. You might be surprised at how little difference there really is.
I've encountered my own cognitive bias, when testing audio amplifiers before, which is why I rely on my test equipment, more than my ears.