Best Stereo Upgrade Value


A question for you audiophiles...

What "upgrade/change" has singularly given you the biggest (not incremental) improvement to your stereo system?  Upgraded amp, pre-amp, tubes, room correction unit, subs, connectors, cables, speakers, streamer, stylus, speaker placement, acoustic panels, etc.?

bheyamoto

 Just added a Rel Carbon Special sub. Just wow. So much controlled power. Like an AMG v8. Massive overall performance upgrade in my system. 

Given that I have excellent speakers, the amp (integrated) probably made the most difference but the DAC then continued the changes further. I spent twice as much on the DAC as the amp.  I think in most systems the DAC is a fertile ground for improvment.

Jerry