parts for Adjustable ccs cascode

[tomst]

I've just fitted a Opa627 to a rotel cd player. i want to try it in class A. From what Iv'e read i believe the best way to do this is use a Jfet cascode. I would like to be able to adjust the current going through the cassocde so i can better match the cascode for each side and also try different bias currents to see which sound best to me. From what i"ve read the absolute max bias this opamp will take is 10mA and minimum 2.5mA. To achieve this presume i will need what looks like the picture shown. The only problem is i don't know the maths to get the right Parts.
R1 500 Ohm about 250mW (this balances out the capacitance of the jfets)
Q2 Jfet with higher Idss than Q1
Q1 Jfet with idss of 13mA (something with a low Vgs no more than 8 max)
Rs 1K ohm (there needs to be enough to get it down to 2ma and up to 10ma

I have got this from various sources on the internet but the info was mostly for head phone amps.
Thanks
Tom

 

[Gopher]

Have you seen this:

http://tangentsoft.net/audio/opamp-bias.html

What more info do you need?

 

[tomst]

Have i got the parts and values right?