After a few years from starting the PPA v1 board, I finally had the time to finish off the board and give it a run through. Having forgotten what I was going to do with it, it was hard again, to figure out where I was at, and what I would need to complete it. The photos show the final setup, a real mess. But it works!
Initially I tested it with a TL072 amp, but it didn't work. There was no noise. My mistake is that the TL072 is a dual OPAMP and the board is for single OPAMP. Stupid me... Anyway, plugged a OPA227 in, and she was working like a charm.
Some initial thoughts. The setup is far from ideal, but the music was sourced from iTunes, using lossless AAC. All connectors were temporary, read poor quality connection and cabling. The headphones I used were my Sennheiser HD650.
With the bass boost on, as I put it in by default, the bass is too much for me. Maybe they would be well suited to smaller headphones, but that needs to be confirmed. With the bass boost off, the sound was well balanced, and has a certain 'fullness' and precision/clarity that was missing from my standard Maple Tree Audio EAR+HD tube amp. Mind you, having only used this amp for less then an hour, these comments are by no means definitive. So far, the sound has been very good with the 227, and I hope to test it with OPA627 and AD8610 and may even others. Which I think is the great beauty of the design. Find a single OPAMP and can give it a go.
On the side of noise, there was a low level of floor noise audible. But this could be due to a large number of reasons; dodgy wiring, use of a cheap regulated wall wart, lack of ground of the Alps control (as suggested by Tangentsoft) or maybe just bad wiring. I guess there will be more resolution on this, once everything is correctly wired.
I intend to use this also with my Shure SE210 IEM, and the pending Etymotic ER-4S. But right now, finishing off the case is the highest priority, as well as deciding on the power supply method. At present, using battery power seems to be the option (given I have the battery supply board), but determining a suitable voltage and charging method, that will be another decision in itself. Finally, PPA 2.0C arrived in the mail recently, and given I just soldered PPA1, it might be fine time to put together PPA2 with the diamond buffers.