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Double amping: Is it dangerous?

post #1 of 20
10/17/12 at 2:47pm
Thread Starter 

So I have a bit of a situation here.

 

I'd like to hook my STX to my Asgard via headphone out to RCA to take advantage of Dolby Headphone for games.

 

The problem is, when I do this and play Borderlands 2 there is this buzzing noise present. When I switch from normal, to high gain, to extra high gain the buzzing starts at the exact same point on the volume knob. So if I play at extra high gain then the buzzing starts at a point above my listening level, but at normal gain the buzzing gets to me. This buzzing is only when I play this game(haven't tried any other games yet), but not when I play music. So I'm not sure what's up with it. 

 

Strangely enough extra high gain seems to have the same volume as RCA to RCA also...

 

 

But anyways, to my actual question:

Is putting a 7Vrms output at 10 Ohms into the Asgard dangerous or damaging to it?

 

I haven't noticed a degradation in sound quality yet in doing so.

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post #2 of 20
10/17/12 at 3:40pm
Thread Starter 

Well I asked this to Schiit and they said it was cool.

 

But I would like to know if any of you have any idea what the hell is going on here. Pretty weird problem.

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post #3 of 20
10/17/12 at 4:00pm

don't know if it's the same on your STX, but CMSS-3D works via RCA line out on my Titanium HD.  did you try the line out on your STX to see if DH works?

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post #4 of 20
10/17/12 at 4:08pm
Thread Starter 
Quote:
Originally Posted by Porter1 View Post

don't know if it's the same on your STX, but CMSS-3D works via RCA line out on my Titanium HD.  did you try the line out on your STX to see if DH works?

I really wish it did, but Asus made the assumption that nobody would ever use RCA line out for headphones. The only option is Dolby Virtual Speaker which clearly isn't designed for headphones.

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post #5 of 20
10/17/12 at 4:09pm

There should be a way to set your soundcard for line-out instead of using the card's amp stage. That way you won't be double amping.
 

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post #6 of 20
10/17/12 at 4:24pm

The double amping is not really a concern in of itself.

 

You're probably getting ground loop issues, since you're connecting what's supposed to be 0V from the computer (sound card headphone out) to that of the amp (input jack).  Probably the increased CPU and/or GPU load is dirtying the ground from the computer.  Keep in mind the high currents involved (tens if not hundreds of amps), switching at a really high frequency.

 

Are the amp and computer plugged into the same outlet/strip?  If not, try that.

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post #7 of 20
10/17/12 at 5:06pm
Thread Starter 
Quote:
Originally Posted by mikeaj View Post

The double amping is not really a concern in of itself.

 

You're probably getting ground loop issues, since you're connecting what's supposed to be 0V from the computer (sound card headphone out) to that of the amp (input jack).  Probably the increased CPU and/or GPU load is dirtying the ground from the computer.  Keep in mind the high currents involved (tens if not hundreds of amps), switching at a really high frequency.

 

Are the amp and computer plugged into the same outlet/strip?  If not, try that.

 

Yeah they're plugged into the same strip. Jason at Schiit suggested getting a 3 to 2 prong adapter for the Asgard, but after saying that the buzzing wasn't there with RCA out he said that probably wasn't it. I'll get one anyways and see if that does anything since they're like 3 bucks.

 

But keep in mind that this buzzing does not occur when no applications are running. Only in Borderlands 2...

 

Quote:
Originally Posted by OJNeg View Post

There should be a way to set your soundcard for line-out instead of using the card's amp stage. That way you won't be double amping.
 

There is, just not while still using Dolby Headphone. I use line out when listening to music but I really like Dolby Headphone for games.

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post #8 of 20
10/20/12 at 8:17am
Thread Starter 

A little update: It was in fact ground loop related. Picked up a 3 to 2 prong adapter for $0.50 and gave it a shot and it worked.

 

While there WAS some humming going on with RCA to RCA before, I assumed this just had to do with it being turned up above its snr rating or something. The buzzing is something completely different and I guess was probably just caused by more GPU load. 


Edited by chewy4 - 10/20/12 at 8:19am
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post #9 of 20
10/29/12 at 9:01am

Such a shame asus doesn't let you use the RCA outputs for headphone surround.

 

This was the main reason I went for the Titanium HD instead

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post #10 of 20
10/29/12 at 11:47am
Quote:
Originally Posted by kazaakas View Post

Such a shame asus doesn't let you use the RCA outputs for headphone surround.

 

If you do not intend to use the built-in headphone amplifier, it may make sense to use the Xonar D1, DX, D2, or D2X instead.

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post #11 of 20
10/29/12 at 12:10pm
Quote:
Originally Posted by stv014 View Post

 

If you do not intend to use the built-in headphone amplifier, it may make sense to use the Xonar D1, DX, D2, or D2X instead.


Those can't output headphone surround through the RCA outputs either though, right?

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post #12 of 20
10/29/12 at 1:33pm

Not sure it is worth much, but I double amp my speaker amps.  Preamp out into 5 watt per channel mono blocks which is turn the speaker outs into RCAs and then plug those into another pair of monoblocks.  Works great.  It's called "supersoaking amplification" I'm sure there is a more technical term but that's the only one I'm aware of.  Buzzing could also be due to higher gain.  Each amp adds an extra gain stage to the mix so line level noise is louder.

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post #13 of 20
10/30/12 at 4:19am
Quote:
Originally Posted by kazaakas View Post

 

Those can't output headphone surround through the RCA outputs either though, right?

 

They have no "amplified" headphone output. The front channel 1/8" output jack is comparable to the RCA line output of the ST/STX (~2 Vrms maximum output, 100 Ω output impedance, 220 uF coupling capacitors, and is driven by a general purpose audio op amp like the NJM5532 or LM4562), it just does not use RCA connectors, and does support Dolby Headphone.

 

"Double amping" the headphone jack of the Essence ST/STX can be fine though, if the output level is set correctly. At 2 Vrms and 44.1 kHz sample rate, the dynamic range is still at least 100 dB, which, while less than that of the Xonar D1, is actually good enough if the volume is controlled at the amplifier.

 

One could also use an external DAC from the S/PDIF output of the Xonar, but then the card might just as well be replaced by a Xonar DG which costs less than $30.


Edited by stv014 - 10/30/12 at 4:28am
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post #14 of 20
10/30/12 at 4:36am
Quote:
Originally Posted by colinharding View Post

Not sure it is worth much, but I double amp my speaker amps.  Preamp out into 5 watt per channel mono blocks which is turn the speaker outs into RCAs and then plug those into another pair of monoblocks.

 

It only makes much sense if the preamp out directly to the second pair of monoblocks is not enough to drive them to clipping (or even just sufficient for listening) level, though, i.e. if more gain is needed.

 

Quote:
Originally Posted by colinharding View Post

Buzzing could also be due to higher gain.  Each amp adds an extra gain stage to the mix so line level noise is louder.

 

Adding the extra gain should amplify the signal and the noise from the source equally, though (unless the volume at the source is also changed), other than adding the noise of the new stage as well. An unexpected increase in buzzing or other interference is indeed likely caused by a ground loop.

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post #15 of 20
10/30/12 at 5:27am
Quote:
Originally Posted by stv014 View Post

 

It only makes much sense if the preamp out directly to the second pair of monoblocks is not enough to drive them to clipping (or even just sufficient for listening) level, though, i.e. if more gain is needed.

 

 

Adding the extra gain should amplify the signal and the noise from the source equally, though (unless the volume at the source is also changed), other than adding the noise of the new stage as well. An unexpected increase in buzzing or other interference is indeed likely caused by a ground loop.

 

Well I've a bit of unique situation, which was why I wasn't sure it would help in this situation.  Gain is just fine with the preamp and first pair of monoblocks.  That's not the issue, the first pair of monoblocks were made a driver amps (transformer coupled) so the 6uF output on the Preamp drives an input transformer (first stage) which in turn drives the second stage of transformer coupled monoblocks.  The second pair don't have an input stage (so little amplification on their own) so the first pair of monoblocks acts as the input stage for the second.  In any case I've done this with the first pair of monoblocks and used the outputs into a Portaphile 627 headphone amp.  Sounds great. Everything is grounded back to the equipment rack so that I don't introduce a ground loop issue, with so many gain stages you're bound to increase the noise floor just a tad though. 

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