Mad Scientist IC’s

So in another thread, I described having issues with audible speaker hum when I connected my Jolida dac directly to my NuForce STA-200 amp via a pair of Schroeder-Dueland IC’s.  Lots of discussion regarding the high gain of the NuForce and the output impedance of the dac.  A few weeks ago, I purchased a pair of Mad Scientist HAC+ IC’s from MrTriode (who btw is a great guy to deal with), which after proper break-in, replaced the Schroeder-Dueland IC’s. First off, they sound amazingly detailed and three dimensional in my system.  Second, the hum disappeared altogether.  Going back to the Schroeder IC’s reproduced the hum.  So I’m curious— the Mad Scientist’s use carbon fiber; the Dueland’s, tinned copper.  What difference in the materials used eliminated the hum?
Of all the many things it could be you assume its this one in particular. Why?
Speakers hum with the Schroeder- Dueland IC’s; they don’t hum with the Mad Scientist IC’s.  No other changes to the system.  
It's obviously the different RCA plugs used by each; it couldn't be anything else.....................
@renisnceman - WRT the hum
1. is the hum a 50/60 Hz mains hum? or is it higher or lower in frequency
2. is the hum a constant level?
3. or does it get louder as the volume is increased?
4. what speaker cables are you using?

Which model Jolida DAC do you have?

I see the STA200 is a power amp
- so I assume you are controlling the volume via the DAC - correct?

The microphonic effect - e.g. The cable from my turntable suffers a microphonic effect.
- i.e. I can hear sound if I tap the cable with my fingernail
- does this happen in your case?
- this can cause hum if in close proximity to other cables

Is the cable in question near a power cable or a component power supply?

One last thing to try - using a piece of wire, touch one end to the neutral side of the RCA socket the cable is plugged into and the other end to a "common ground point"
- does the hum go away?
- if yes, it may be because of the grounding design of the attached components and the geometry of one of the cables highlights this anomaly

Also, Cables can cause issues within attached components and sometimes it is another cable (e.g. speaker cables) in the system that causes the problem
- answers to all questions above will help get to the "root cause" of this problem

Regards - Steve

@williewonka the dac is the Jolida dsd non- bluetooth version connected to a Bluesound Node 2 via a Nordost Silver Shadow digital cable with bnc-rca adapters.  Speaker cables are diy silver over copper ribbon 10 AWG with cable lifters.  The hum is not the typical 50/60 Hz- higher in frequency and it increases as the volume control increases on the dac.  Power cables for the dac and Node are Cullen and Transparent for the amp.  Thing is, without changing anything, except for switching back and forth between the Dueland-Schroeder IC’s and the Mad Scientist IC’s, the Mad Scientist are dead quiet and the Schroeder’s hum.  Tapping the Schroeder’s doesn’t add to the hum, but moving them around tends to alter it. The good thing is the MS sound better, but I’m curious as to why they’re silent. At this point it’s more an intellectual exercise, but I wonder if the carbon fiber for the signal conductor in the MS cables has something to do with it.