As you have probably seen, @thebiglebowski has his M7 Silver preamp back following Covid lockdown
It has a 220V mains transformer, and after considering a few options I decided to go for an external step-down isolating transformer
The linestage and phono were both rather noisy, so to help address this I created a star earth for the psu, another for the phono, a third for the linestage and a star of stars at the chassis connection. It was also necessary to add bypass caps to the heaters on the phono input valves, and sort out the earth continuity between the different chassis panels.
The circuit was brought back as closely as possible to the original circuit using 2 x 6072A in the line stage, and 3 x 6072A in the phono stage. The linestage had 25 dB gain, but the MM phono only had about 20 dB of gain. To increase the MM gain I added Black Gate bypass caps to the cascode input stage and common cathode second stage, bringing it up to about 44 dB, or just about right for an MM phono stage. Finally, the riaa eq wasn’t that accurate, so a couple of resistor tweaks were installed using some old Shinkoh tantalum films to match the rest of the amp.
At the end it was nice and quiet, and sounded like a lovely musical M7 Silver preamp.