Low-distortion Audio-range Oscillator

[Elvee]

Thanks, that's very interesting. However, the coil doesn't seem to use a magnetic core, which would explain the ideal linearity. The shielding is quite substantial, logically. The capacitors are the excellent Rifa extended foil PS

 

[JensH]

Is that black material ferrite? It looks a lot like a plastic bobbin. If so, it would "just" be an air coil in a metal box, which would be good for distortion and noise.

 

[JensH]

A quick calculation shows that it should be possible to do with an air coil.
I used this https://coil32.net/online-calculators/multilayer-coil-calculator.html
and approximate dimensions estimated from the pictures.

 

[mediatechnology]

A quick check of some 10K resistors on hand- I had to go up to 30V to get out of the noise floor. The HD3 residual on 2 Dale 1/4W and a Vishay S102 were the same at around -168. I did not want to go to 100V before doing some calculations to make sure I don't fry the resistors. Basically nothing to see here.
WRT CLT-1 some pictures and the schematic for the low pass filter.

May I send you some of the 10K CMF-55 from 2023 and "RN" CMF-55 from 1984?