S/N ratio Balanced input vs. Unbalanced input

@atmasphere What you said make sense. I will leave it if this not a defect, just not perfect.  Thanks 

@auronthas The reason your amp is noisier with the balanced input is that the amp itself has a single-ended input; its not internally balanced. So the balanced input goes thru a separate circuit which adds noise.

IMO/IME this is a sloppy way of doing things since the balanced operation is more of an afterthought whereas again IMO it should be the star of the show.

Normally if the internal circuitry were balanced-differential, the single-ended input would be noisier as there would be less noise cancellation.

This also explains why there is less noise when the balanced DAC is connected; the opamp that does the balanced to single-ended conversion is able to pick up noise with no input load.

Are you sure other sources into the amp don’t give the hiss?

@o_holter Ya, I tried my old Sony CD player which connect to integrated amplifier via RCA, I did not notice any hiss near tweeter.  I will do fast "switching" from balanced input (Ares II DAC) and RCA input (Sony CD player) to test the hiss noise.

adding "Cable Clamp Clip RFI EMI EMC Noise Filters “ 

@westcoastaudiophile my audio equipment are connected to a good power conditioner of Novaris brand.  I would think EMI issue shall not be the case, wouldn't it ?

since hiss is not volume cntrl dependent, you may deal with EMI issue. 

adding "Cable Clamp Clip RFI EMI EMC Noise Filters “ to analog bal/unbal cable, close to the amp inputs,  sometimes helps.

I wouldn’t worry about it but I would be curious. Even if not so loud, the hiss should not be there. I am allergic to anything that gives more digital glare, and the hiss may be a suspect, even if not much notable by itself when playing music in the listening position. So I would wonder, why does this happen. Does the DAC behave that way with other amps also? Are you sure other sources into the amp don’t give the hiss? You’ve said its the same from xlr and single ended inputs. If you have switchable inputs between sources on your amp - the same across these, also? The fact that the hiss does not vary with the volume level makes me pause. Something wrong in the DAC? Or mismatch, amp / DAC?

I just tested in my secondary system, with a Ming Da integrated amp, with a few small DACs including the Fiio x3 and Huawei p30. Aurum Cantus speakers, with top notch ribbon tweeters well able to tell me what goes on. No hiss, but some hum. Varying with volume. Below the "worry" border, though - only heard clearly at max volume.

If hiss comes from the DAC and is independent of the volume pot, then likely DAC is injecting some electrical noise into amplifier.  I wouldn't worry about it, since not too many amps are completely quiet with the ear on the tweeter.

No more hiss if DAC is disconnected

What happens if you disconnect the DAC from your amp? Hiss still there?

@o_holter yes, the hiss is constant, with no variance on volume, the hiss is there with power standby on my DAC Ares II , only it’s gone when I unplug the power cord

So its not the connections. And the hiss is constant, regardless of the volume level?

Can you hear it from distance of 1m?

@kijanki Nope, only audible at near field,  close to tweeter.

If this is not abnormal, then I am relief.

Auronthas - can you compare the hiss, changing to single ended input?

@o_holter since my Ares II manual stated only XLR or RCA can be connected at one time, I have tried RCA before, and I can hear the same hiss.

Auronthas -  can you compare the hiss, changing to single ended input?

If you hear noise with ear on the tweeter it is normal.  With my limited experience only some amps are completely noiseless.  Can you hear it from distance of 1m?

@kijanki the reason I ask is I can hear noise (hiss) from tweeters when my balanced input (Denafrip Ares II) is connected while music is stopped playing. Volume changing not affected the hiss sound. 

@kijanki I just check E270 vs E260 technical paper,

E270 noise voltage is 35microV at -30dB volume position

But in the above E280 technical paper, E270 noise voltage is 41 microV.

I am more confused now.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.accuphase.com/technical_information/e-270_technical_information.pdf&ved=2ahUKEwjtyazZz-j4AhV-wzgGHZfuC8QQFnoECA4QAQ&usg=AOvVaw1aVU67BSPqeah_5DXshwqG

I am confused as well.  Balanced input suppresses common mode noise, but S/N measurements were taken with inputs shorted.  I don't see any reason why balanced should be worse, assuming similar input level.

@kijanki Thanks for pointing out. I hope so.

But, when i checked the previous model E270, the S/N ratio for balanced input is 91dB, unbalanced input (high level input) is 108dB.  

I am confused.

It has to be typo.  On page 5 of their technical paper they show 107dB for BAL-CD input.