IC's and Humm

I hooked up another amplifier that I added to my system. My preamp has two pair of outputs. Before my system is dead quiet. The new amplifier runs quiet as I tried it running my main speakers. But when I try it with a secondary small speakers I get humm....so I tried switching the IC's from my monoblocks(NBS) to this stereo amp which was connected using some ($100) Monster IC's. The NBS are dead quiet and the Monsters produce a low audible hum. When using the monsters the humm also increases slightly when I turn the lights on. I think the problem is that I have run out of dedicated ports for this amp....so I use a nearby regular port. Sorry for the long description but I'm wondering is it just the IC or should I have a couple more dedicated ports installed. I run 2 pairs of monoblocks,preamp,dac,transport....and to get it dead quiet is like a combination to a safe....it must have a certain layout or I get humm and my tube amps are realy finicky about it.
As an experiment, I'd suggest putting the entire stereo system, including both sets of power amps, on the same dedicated port (assuming it has sufficient current capability).

I'm thinking that there could be voltage offsets between the ac safety ground and/or neutral of each of the dedicated ports and those of the other dedicated ports, as well as between them and the ac safety ground and/or neutral of the regular port. Those offsets would then appear between the chassis of the various components, since they are connected to ac safety ground, and also to a small but possibly significant extent are coupled to ac neutral due to leakage paths. That in turn would cause small ac currents to flow in the shields of the interconnects that connect those components, in common with signal returns which also flow through those shields.

That could account for both the hum and the sensitivity to which interconnect is used, since the shield resistance (and consequently the amount of unwanted current flow) would be different between the two sets of cables.

And the current drawn by the lights when they are turned on could very well be increasing the voltage offset between the regular port and the dedicated ports.

Use of multiple dedicated ac ports for different parts of the same audio system, while having potential advantages that are well documented, has this kind of potential downside as well.

Hope that helps,
-- Al
Al...thanks for the input...I was pretty pround that installed 4 dedicated ports and having it dead quiet with all this equipment. I haven't the guts to put all 4 mono blocks on the same circuit....with the better shielded cable...A+... but with the Monster...humm. Another observation is that one VAC 140 will pickup humm if paired with another amp on the same port. So for now it goes solo...which leaves me with a unused receptcle....The Vac's have 3 different ground setting.....AF is used right now...but I have yet to experiment. I think I will contact my electrician...step back and then go foward. I have a general idea of what your explaining but this kinda of thing is frustrating.....thanks.
Another observation is that one VAC 140 will pickup humm if paired with another amp on the same port.

Perhaps, along the lines of what I was suggesting, that is because with the two amps each drawing substantial current from the same port, the voltage offset between that port and the port that the preamp is on is increased. Causing increased ac current flow in the shields of the interconnects between preamp and power amps. Again, your problem might be too many dedicated ports for the interconnected components, not too few.

-- Al
If possible, try using balanced interconnects between your amp and preamp. I had a similar problem where my front speakers had no hum and my rear surrounds constantly had hum/buzz. Once I connected the xlr/balanced cables, the problem was completely eradicated.

Al....interesting...it's late...will continue

Aaron....RCA'a only...
If possible, try using balanced interconnects between your amp and preamp.

Yes, if the cause of the problem is along the lines I described, a balanced interface (if your components support that) would most likely resolve it.

That is because with a balanced interface the power amp responds to the difference between the + and - signal inputs, and extraneous ground currents in the cable are ignored (unless they are so severe that they overwhelm the balanced operation, or what is more properly referred to as the common mode rejection capability).

If your components can't run balanced, again I would suggest that you try connecting everything, or at least preamp, power amps, and analog source components, to the same ac port. If that solves the problem, then see what you can move to separate ports without re-introducing the problem.

-- Al
You may experience a "ground" differential problem using different AC circuits.It is also possible that this may arise from the quality of grounding in the two cables.Had you tried "floating" the earth-ground on the humming culprit?
My preamp and amps do not support a balanced mode....just single ended....I tried a while ago running my preamp and dac on the same line with a conditioner....the sound was degraded. NBS advises their PC's direct to port.

Al....I will try running my subwoofer mono blocks thru one port and see what happens.....I plan to upgrade the Monster IC anyway as that is what's available now....If I get a quality shield IC and that fixes the Humm....is that ok or do I run the risk of some problems....

There must be many that run multiple dedicated ports....this problem can't be uncommon I would think. Is there a better configuration as to matching particular componets to ports....Amp-preamp....DAC-amp or amp-amp and so forth.

Hi Roger,

I would think that if you install a different ic that fixes the problem, you should be all set. Probably what would be happening is that the different ic would have a lower shield resistance, which would essentially short out the ground offset between the components it is connected to, and thereby reduce the extraneous ground currents.

My own philosophy about power distribution is to connect everything in the system to the same dedicated ac outlet, that is isolated from everything else in the house (refrigerators, air conditioners, etc.). I do that to avoid the very type of problem that you are describing.

But I'm probably in the minority among those who focus seriously on power distribution. Most people put purely digital components on separate dedicated runs, to prevent cross-coupling of digital noise into analog signals. It's probably debatable as to whether a dac is a digital or an analog component. I would consider it to be analog, to prevent its outputs from being contaminated by noise from digital transports and other purely digital things.

Many people also put their power amps on separate dedicated runs, because of their large and fluctuating current requirements. But as you appear to have found, that creates the risk of ground offsets relative to the preamp.

I guess the bottom line is that some experimentation and trial and error tends to be necessary.

-- Al
Al thanks for all your help....I think I have a better understanding now...appreciated greatly.

Just thought I would post this for reference