What I noticed is that I have a lot of noise, both hum on 50hz and pink noise when going straight to output transformer without any series load. My output transformers are 10k:10k edcor. If I strap 100R to primary then the noise drops. I tried lower values like 22r and 47r but they don't work in my case.
Are you sure it's pink noise you're getting, not white?
The (optional) series resistor has nothing to do with noise, it's there to prevent the output stage from oscillating (when this happens, it sounds like tuning an old radio). Your 100R might be large enough for dropping the audio signal as well as the noise, so you won't improve anything there.
The circuit itself
is very noisy by today's standards. It's much noisier than my 1176 for example for similar in / out and compression levels, but it's still workable. From my simulations most of the noise comes from the inherent high impedance of the Zener pairs, so there's no way to lower it - but this noise is WHITE, not pink!
You shouldn't be getting 50Hz hum, however. Try shorting the input and see if it goes away. Going un-balanced into the unit can pick up noise like this but you may also have a ground loop somewhere. My units do not hum at all.
These are the noise plots of both the 1176 (purple) and one of my Zeners (white). Input signal on both is an 800Hz sine wave at 0 dBu with 4dB of compression, output levels adjusted to be the same going back into the audio interface. The spikes at 50, 100 and 150 Hz are from the 1176.
