You are almost certainly hearing the noise floor....
EVERY electronic component, including a plain old piece of wire, has a noise floor (it's really low for a piece of wire - but not zero).
In a device that has lots of components, like an amplifier, you hear the combined noise floors of all of them - and they interact with each other in complex ways.
Of course, some are far lower than others, and many things can determine whether you can
HEAR the noise floor or not.
Human hearing has a "sensitivity floor"... so, if the noise floor is below the lowest level you can hear, then you can't hear it.
Human hearing also has a remarkable powerful built-in "automatic gain control" feature.
Spend an hour in an empty abandoned cave and the sound of the blood rushing through your veins will become deafening.
Spend a few hours at a Blue Oyster Cult concert and you probably won't hear the engine when you start your car on the way home - at least for a day or two. (Been there; done that.)
In general, for a given level of "quality" and "design", the noise floor of any amplifier or similar device is proportional to the output power.
If you have two amplifiers with a S/N ratio of 100 dB, and one of them is 100x as powerful as the other, then the one that is 100x as powerful will also be 100x as noisy.
(You cannot agree or disagree with that statement because it is simply another way of stating what the numbers I quoted actually
mean.)
If you want an amp that is more powerful, yet no noisier, then you need an amp with a higher S/N ratio.
Note that you are hearing the combined noise floors of every component in the signal chain.
If you disconnect the amplifier from everything else, and you hear a certain level of hiss, which remains the same no matter where you set the volume control then.....
1) That noise is originating or "being realized" in the stages of the amplifier after the volume control. (If it was coming from before the volume control then the volume control would affect it).
2) It could still be some sort of "interference" getting to the amplifier from outside - like line noise, or the circuitry in your cell phone. (If it's that, then it will usually go up and down over time, or when you move the amplifier to a different spot.)
If the noise level goes up and down when you turn the volume control, but goes away when you disconnect your source, then it's coming in from your source. (If so, then it could be the noise floor of your source, or lots of other stuff.)
If it goes up and down when you turn the volume control, but
DOES NOT go away when you disconnect your source, then it's probably coming from the stages of the amplifier before the volume control (if there are any).
Also note that speakers and headphones vary
VERY WIDELY in terms of efficiency.
So, of you have an IEM with an efficiency rating of 105 dB/watt, and one with an efficiency rating of 95 dB/watt, the same noise will
SOUND 10 dB louder on the one that is 10 dB more efficient.
Also note that most headphones have a rather NON-flat frequency response.
This means that each one emphasizes certain frequencies and de-emphasized others.
So, if your particular headphone has a frequency response that's "up 10 dB at 10 kHz" it's going to sound bright.
And, since most noise occurs at high frequencies - like around 10 kHz, the same amount of hiss from the amplifier will sound louder on the headphone that sounds bright.
(And, since that noise is occurring after your equalizer, even if you use an equalizer to turn down the treble so it isn't so sharp, the level of the noise will remain the same.)
All this means is that some particular headphones emphasize (or "are more sensitive to") noise than others.
(If you're using speakers, not only are different speakers very different, but the room makes a
HUGE difference; of course that isn't true with headphones.)
Also note that different people have
VERY different
PERCEPTIONS of noise.
The best vinyl album has a S/N ratio of about 70 dB (about a zillion times worse than the A-100).
You will
ALWAYS hear the noise go
WAY UP when you put that needle down on a vinyl album.
This is one reason why some folks can't stand vinyl; others don't notice it at all.
Ditto for cassette, and even open reel, tapes.
(Also note that, for many people, our sensitivity to high frequencies like noise may decrease with age.)
As a headphone amplifier, the A-100 is
VERY powerful..... think the difference between a nitro-powered dragster and your family sedan (the A-100 is the dragster).
And,
FOR AN AMPLIFIER IN ITS POWER CLASS, the A-100 is very quiet.
However, the A-100 is still a remarkably quiet
dragster... and not a quiet
family sedan.
Most headphone amplifiers are more in the "tricycle class".
(The headphone amps in most of our units, like the PT-100, fall squarely into "family sedan" range.)
That's why the A-100 sounds so much
BETTER with so many headphones (especially the ones that really need a powerful amplifier to sound their best).
(Think of putting on the jumpers as connecting the turbocharger.)
But it's also
NOT going to be as quiet as some other amps with some headphones.
With the A-100, the same output runs both the speaker outputs and the headphone outputs.
If you connect it to a pair of speakers instead of headphones you'll find that, compared to other speaker amps, it is
VERY quiet.
And if, when it comes to headphone amps, you're more of a "family sedan" sort of person....
Or, if you really want a sports car that drives like a dragster, but is as quiet as your family sedan, and you have the budget to pay for it.....
Then the A-100 may not be for you... which is why we have a "no fuss return policy".
But, if you've had two A-100's, and they both perform exactly the same, even with no source connected, then it's pretty likely that they're working as they should.
(And, if you haven't already, you really should try connecting your
SPEAKERS to your A-100.)
Obviously I am not sure of the situation and I don't have time to read back six pages but I own a dozen Emotiva amps and none of them are noisy. My guess is it is something with your wiring, cables, headphones, etc that is causing the hissing. I don't own an A-100 so I can't begin to break things down with you on it. I have heard mixed results on the PT-100 and not much at all on the TA-100. I would try different cans, different wall plugs, different cables, speaker wires, etc to make sure the hiss doesn't follow one of the possible culprits. However, I am not one to rule out two bad units....it can happen.
I use my XDA-2 as a headphone amp at times and also have a dedicated Schiit Fulla 2 that I recently purchased. The Fulla 2 sounds great but if you have a plug wire crossing a charging wire you get noise. I think the whole headphone amp thing has faults. I can say through any of my XDA-2 I have absolutely no hiss, no noise, no nothing but clear precise music. Maybe a DC-1 for you would do the trick as far as the headphone issue.
One way or the other, hate to see you going through this. Nothing sucks more than sitting down to listen to your favorite tunes and have an inherent noise coming through that you cannot explain.
Tim
Thanks for the sympathy. It’s frustrating, to be sure.
I’ve tried pretty much everything you suggested. Different headphones, different cables, unplugging everything but the power cable and even using a different outlet in my house. None of them made any difference.
I’ve done some A/B testing between the audio quality coming out of the PT-100 and A-100 and the A-100 is so much better. But the hiss just kills it for me. With much of the music I listen to, the hiss ruins the experience. The quiet parts are supposed to be quiet. The hiss is so prominent that even during some of the not so quiet parts, I can hear it. And it’s not just me - the hiss just isn’t there when listening through the PT-100.
So, now, having had 2 bum (?) A-100 units, I’m looking around at my options. Integrated amps are a possible solution but I’m sure I’ll be missing the musicality of a dedicated headphone amp. I’m going to head to my local Audio Advice this weekend and try out what they have on offer. I may pick up something just to get audio through my speakers that also includes a headphone jack and keep searching for a dedicated headphone amp. Or I may return the PT and A-100’s and get a TA-100 for the speakers and keep the search going for a headphone amp. I don’t know. This is, honestly, exhausting. :/
