Help me understand how to optimize bass on the Zu Definition Mk IV

Hi Phil, 

Here's some answers to the questions you posed:

-- no cable TV in my sources
-- no balanced / XLR cables
-- preamp is a Cary SLP-98 with integrated tube phono stage, no SUT
-- no ground lift switches on any components
-- no passive components
-- cartridge is a Clearaudio Virtuoso v2 ebony, tonearm is a VPI JMW-9
-- there is a lamp situated above the turntable, which was causing buzz when turned on, but that was mostly eliminated by running a ground to the turntable and then preamp. The lamp is off when listening anyway. No other power supplies near the turntable. 

Interestingly, Sean sent me this response about grounding the sub amps in the Definition (I'm sure he wouldn't mind me posting this): "When I rebuild the amps I float the audio ground, that is one of the benefits of the transformer. Another thing I do is to better float the AC transform, much of the hum you notice is coming from the mechanical singing of the AC transform, the power supply is linear so it’s a big piece of the kit in size and mechanical effect. Things should be much quieter when you get them back." 

David

Well based on that reply, I need to contact Sean about solving my subs hum issues as well.

David, Sean has emailed me to say the solutions he has for you may well suit me too. Great customer service.

That's great, Marc! Maybe this thread will end up solving problems for both of us :) 

By the way, I've also installed Isoacoustics Gaia I's to the Definitions. Can't wait to get the amps back to take them for a test drive! Sean said it was about a week turnaround.