Some time ago I started a thread here to design a power supply. I will order the pcb's somwhere next week and do some prototyping. However a power supply needs something to power. I made it primarily to be used with an unbalanced to balanced line driver board. I have also made a design of that board and I'd like to hear your thoughts on it. It isn't exactly headphone related as it will be used to send an unbalanced signal out of a mixing console to some powered dynacord monitors. The length of the cable is about 20m. Right now it is used with an unbalanced cable but there is quite a bit of hum, hiss and cellphone noise.
The circuit consists of an OPA227 at unity gain driving a THAT 1646. The OPA227 can be replaced with the OPA627, but only for small channel counts or by those with slightly to much money. the connector is an amphenol ACJS-MHD double trs. I couldn't find an eagle library for it so I made one myself.
It's a bit hard to see but the trace to pin 12 on the connector isn't connected to the ground plane