[KurtW]

I recently have put in a low current FET cascode current sources into my Porta Corda. I used a 2N5457 with a 2N5486 and a 100 ohm resistor to give me around 1.2mA. The layout of the Porta-Corda is such that it is easier to put in than it was in the Corda HA-1. Unlike the standard Corda, the Porta Corda wasn't biased into Class A operation. The biggest fault I had found with the Porta Corda was a little harshness in the treble and I think this mod has help a lot in this regard. The only downside is about 16% higher standby current, a worthwhile trade off IMO.

 

[tangent]

Did you bias all four chips, or just the output pair?

 

[KurtW]

I put the current sources on only the input pair. I typically use low impedance headphones which would have required a much higher bias current to keep it in class A, and I didn't think that was worth the extra battery drain (although I didn't try it).