OK...
When you say "cannot hear when listening" I assume you mean that you don't notice it when there's music playing.
First of all, ALL amplifiers have some small amount of internal background noise, which is going to be made up of hum and or hiss.
With a good amp this background noise should be really low - but it will never be zero.
Your Klipsch Heresy's are VERY efficient.
That means that they will tend to make even tiny amounts of hum or noise obvious.
And this will be more true if your room is relatively "live".
And, of course, it's going to depend on how close you're sitting to the speakers.
(I would expect to hear noise, from a few feet away, with efficient speakers.)
It's also worth mentioning that there will usually be more noise with a more powerful amplifier.
S/N ratios are RATIOS....
So, if you have a 20 watt amp with a S/N of 90 dB, and a 200 watt amp with the same 90 dB S/N...
The 200 watt amp will be ten times as powerful but it will also make 10 times as much noise.
(You would need a 200 watt amplifier with a HIGHER S/N ratio to have an equally low amount of background noise.)
Without worrying about the numbers this means that "all else being equal" a more powerful amplifier will make more noise.
Therefore, in a really quiet room, I wouldn't be surprised to hear a tiny bit of noise when the music isn't playing.
So, to that degree, this may be normal.
(And the only real "solution" is to turn the amp off when you're not listening to music.)
Now, all that said, there are a variety of ways in which MORE hum can find its way into a system.
So, while some hum could be coming from the amp, some of it could be coming from the preamp, or the interconnects.
And there could also be some sort of 'ground loop" or other "ground issue" between the amp and the preamp.
So...
Make sure your interconnects are nice and tight (try unplugging and reconnecting them).
Try moving your interconnects a little bit (especially if they rest next to a power cable).
See if the hum goes away or reduces when you disconnect the amp from the preamp (if it does then you may have a ground hum issue we can look into).
(The hum you hear may be coming from multiple sources... so eliminating one or more of them may REDUCE it even if it doesn't eliminate it.)
Keith
I have an older XPA-2, Gen 1 my first powerful amplifier. Speakers are Heresy IV's, PT1 pre. I getting some hum from the Heresy's, cannot hear when listening although wanted to know more about this, can it be controlled, or eliminated?
