Quote Originally Posted by Ianmac View Post
Trying to reduce the reg count !
I already have a dedicated reg supplying only the 6675.
Havent used a LM431 Ill have a look as soon as I get time. What are the advantages of constant current to a Zener over a low noise voltage stabilizer for the Cmos Chip IC302?
Shunt reg vs series regulator. The shunt reg (CCS + zener) kind of splits the line regulation from the load regulation. They are simpler to design and can have excellent properties. I just used it because I had one lying around. I can swap the 317 CCS into a 5V series reg and see it this matters. One point where I think it matters is that the OSC is at a frequency where a pedestrian 317 doesn't operate anymore, but the 431 will.

I'm having difficulty " hearing" the effects of additional tweaks. Any way we can measure the platter rotational accuracy and stability?
Would a 1K tone from a test record into a spectrum analyser help as LF and HF speed variations should show up as sidebands ?
I have ARTA and a pico scope and access to an unmodified Techie
Probably, but I don't think you will get much wiser because it is about the dynamics of the control loop. So if you have a record with pulses or square waves you might be able to learn more. Anyway my main system is stashed away because of the house painter. I'm listening though a headphone (AGK 701) and have no problems identifying changes in the sound as result of the tweaks (that is if the change matters to the sound). I have developed the habit to let everything settle down before judging whether the changes are for the better or worse. Changes that do not work for sound can be identified right away, but for others I take a few days. Lots of tweaks on the 1200 worked but not without adaptations that I made afterwards.