Hi Tony, no problem ask away...
To be honest when I first bought this DAC I didn't know about the output transformer upgrade. When I discovered the Diyaudio thread, I took heed and made the decision to try transformers to see what all the fuss was about. If I didn't like them, I could always sell them on. Well, I'm so glad I did because they sound brilliant.
Essentially the main purpose of an interstage audio transformer is to isolate the DC and couple the signal, with minimal loss. Valve amps and top flight mixing desks (primarily what the UTC A-20's were designed for) use this principle.
Here is an excerpt from the web explaining 1:1 output transformers:
"A unity transformer allows an audio signal to pass unmodified from the primary to the secondary while blocking DC voltage and radio frequency interference (RFI). Also, since the primary and secondary are insulated from each other, a unity transformer will electrically isolate different pieces of equipment. This can solve hum problems by isolating ("lifting") the grounds of different devices"
I guess it is a cleaner, simpler circuit than the dual op-amp circuit on the DAC. Although the DAC is well designed, some feel that op-amps are a compromise, considering production costs etc.
The Burson op-amps you linked to are supposed to be very, very good. However, as Martin Clark pointed out in a thread recently, there is no reason why a properly implemented IC op-amp should be any worse. It is a case of finding the right one for the circuit and ensuring the circuit is optimised for the op-amp. (For the same money you could get a nice pair of quality output transformers)
If you are really keen to try a discreete op-amp then these are loads cheaper and seem highly recommended. The 'Sun' dual model especially:
http://www.audiocominternational.co...ucts_id=134&osCsid=03sqdp5v1c4b1r8n8nh157tq31.
The LED's are part of the regulator circuit. So best to leave them in. I have removed one and have replaced it with a blue LED attached to flying leads to allow it to be inserted in the front panel as an 'On' indicator. The rest won't be seen if in a case.
As for the selector switch, you only have to move one jumper so a single pole switch will work. Hook the pole to the center pin and the switch positions to the outer pins. You could also use a SPDT toggle switch.
Hope this helps. I am no expert but have recieved loads of help so am glad to pass on the info.
Rich