Looks like all the info on this has been lost after Radionecks went down. I even checked Wayback Machine but it didn't archive the thread. So I'm re-posting the design files here for anyone who wants them. Sadly the pages and pages of discussion that showed how the design evolved are probably gone for ever.

Note that the schematic shows 1uF coupling caps, but it was suggested to me by a user over on Radionecks (don't remember who now, sorry) that they should really be 10uF to reduce bass tilt. 1uF gives a response down to <10Hz, but the phase shifts at the low end can become a problem and cause overshoots, and therefore overmodulation. This is especially a problem if you're using a compressor/limiter ahead of the coder, because you'll set your limiter up to limit to +/-75kHz deviation, but the overshoot will mean you're overmodulating still. The 10uF caps put the cut-off frequency way down <1Hz - excessive for audio bandwidth, but means the phase shifts at 20Hz and up aren't so bad.

To be clear, the affected caps are C1, C2, C9, C10 and C27 - these should all be 10uF not 1uF as shown. Increasing C16/C17 to 100uF is probably not a bad idea either. You can also make C19 10uF too - not required, but otherwise its the only 1uF left on the BoM, and increasing it won't hurt.

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Also like I said on the Radionecks thread, I'm working on an SMD version of the coder which hopefully I'll put back up on ebay when done. Might be a while though, I have way too many projects on the go right now.

adding a picture for everyone's viewing pleasure

Here's the demo video I originally posted to Radionecks

@zozo just one of your 1w driver boards into a dummy load

Oh hey Albert didn't realise you'd made it over here too