It's half way to being correct - I was thinking of a two transistor current source. You can find the schematic on this page, its (b) in fig 9.24 (scroll down). Its using two NPN transistors, BC846B work well but its not very critical on transistor type. R1 will be 220ohm and R2, 47k when fed from a 15V supply (i.e. the 0V rail).
https://www.edn.com/Home/PrintView?contentItemId=4015906
https://www.edn.com/Home/PrintView?contentItemId=4015906
I've used two jfets which works well (jfet cascode) - this is where I read this years ago - Tangentsoft Biasing Op-Amps into Class A It's somewhat easier to follow than the edn page, although the latter is more comprehensive.
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To get back to the topic of the AD1865 board in the original post, I bought one a while back and finally had the chance to compare it apples to apples with my Subbu DAC. Used optical in from a CD player as transport, dual mono Aikido pre and an AlephJ amp to speakers. The only thing I did was to bridge the output caps which was an improvement. I am very surprised how nice it sounds, I was expecting for it to be spanked by the Subbu, but that wasn't the case. It sounds warmer than the Subbu, but very musical with good punchy base and nice mids. Piano sounds good, you could say the highs are a bit splashy and boosted, the Subbu seems to have more realistic highs and a cleaner sound. All in all worth the money and an easy way to throw together a cheap and cheerful DAC. I'll throw it into a box and give it to my son as a present. Next up is the ESS 9038k2m board with the crazy long thread, I will try a few of the more easy mods and see where that takes it.
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