I was originally using 2n5551 for the differential pair in the front end of my homebuilt and recently replaced them with the 2sc2705 toshiba 200mhz devices. They have been in over 2 weeks and to my ears atre nothing but positive by comparison, proving to myself that once again while the circuit can be sound different devices can make a substantial "subjective"difference. I wont go into drastic detail aside from the presentation of music is much more effortless/neutral sounding to me. They are also used with a collector current mirror, emitter degeneration resistors and a transistor led current source biased to 4.5ma..I had some comments earlier that i would be better off with low noise semis such as 2sc2240 but the noise is lower than the 2n5551, and i couldnt fine any"genuine" 2240s locally...Which leads me to my biggest issue, counterfeit semis!!!which seem to have hit everything from high power devices to small signal devices, very annoying to have to weed through I feel worse for the poor guys who stick something in that looks more like a 2n3906 marked as a c2240...
Colin
Colin