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1) Connect the both speaker '-' binding posts to the PCB ground at the GND eyelet. You can connect both '-' posts together and then run one wire to GND. Note: The Darlings are usually floating and will benefit. A Chubby Clementine with no feedback will need it, but the ones built with feedback (like the ULtra) should already have this connection.
2) Run a wire from the GND eyelet to a chassis screw, such as a transformer bolt. Secure it with a star washer or a crimp eyelet connector.

These mods will drop the noise floor into the dirt. I'll update the connection documents.

Shannon

Hi Shannon
Do any of these mods apply to the ultra?
Regards
Mike

The ULtra already has #1 done, due to the feedback connections. Go ahead and do #2. The difference is very small and possibly inaudible, but was noticeable as I experimented with adding a headphone jack to my Clementines. My headphones are rated at 106dB at 1mW, so they really expose everything. My headphone post is forthcoming.

Shannon

Hi Shannon
I just finished doing mod 2 on my ultra....connecting the board earth to chassis ....definitely eliminates the last of the residual hum....now dead quiet through my big old vintage speakers between tracks so I would say well worth the effort....even for non headphone users....
Regards
Mike

Excellent! Thanks for the update.

Shannon