The DAC was silent in my system before mods, so there's nothing wrong with the EE DAC. But there is a loop between Gene's DAC and the preamp wethinks. There are probably other ways to fix it, but this was mentioned as the cheap and easy way based on Gene's description of the problem. The hum is gone with a cheat plug, so Sol designed a simple circuit to go between IEC ground pin and chassis that conducts above 1 volt for safety, but does not conduct below that, to stop the hum in mV range. Quiet and safe, and many big name manufacturers use this circuit. Now Gene's DAC is hum proof in any system!