[Roxim5]

I have the new AKG K553 Pro's and an SMSL SD793-II. I know that these headphones do not need an amp technically, but I wanted to get one for future headphones as well.
 
Headphones work great through direct output from my computer and my work computer. At home, I have the AMP connected to my computer through a TOSLINK cable. The headphones are connected to the 1/4" plug on the amp through the adapter that was provided with the headphones. After I changed the output on the computer to digital and turned up the volume knob on the amp and play something, sound only comes out of the left side of the headphones at expected volume. The right side is so faint it is almost not audible. If I listen closely, I can hear something. Sounds as if the headphones are only receiving mono audio and not stereo. So this is the issue I am having.
 
Things I have tried:
-Plugged the headphones directly into the computer, works as expected. (Headphones are not the culprit)
-Using the 1/4" adapter, plugged headphones into another adapter 1/4" to 3.5mm and plugged into computer. Worked fine. (1/4" adapter is not the culprit)
-Changed settings back and forth in the Windows Sound control panel in order to try and resolve the issue without luck.
 
Components:
AKG K533 Pro (w/ included 1/4" adapter)
SMSL SD793-II
Monoprice 6' Premium TOSLINK cable
Realtek High Defninition onboard Audio w/ latest drivers.
 
Let me know if you guys need any more information.
 
Thanks for the help!
 
EDIT: SMSL amp is the culprit. Had to return it and get something else.

 

[cel4145]

SMSL products have a reputation of poor reliability (I don't recommend them).

However, the trick to figuring out the problem is further elimination of things that are not the problem.

Could be the SMSL doesn't like the adapter that came with your headphones. Try a different adapter or different set of headphones with the larger plug.

Try the SMSL with a friend's computer that has optical to make certain that it's not an issue with your computer.

Do all those things, and you'll know where your problem is

 

[Roxim5]

I am going to have a coworker test it out on his computer as well. He has different headphones with a different 1/4" adapter, as well as another TOSLINK cable to test with. So I we will know definitively where the problem lies by Thursday.
 
I already suspected the SMSL as the culprit but wanted to get another persons input on the situation. What DAC/AMP do you recommend to replace this one with? Sub $100 if possible, preferably with optical input.

 

[PurpleAngel]

  I am going to have a coworker test it out on his computer as well. He has different headphones with a different 1/4" adapter, as well as another TOSLINK cable to test with. So I we will know definitively where the problem lies by Thursday.
I already suspected the SMSL as the culprit but wanted to get another persons input on the situation. What DAC/AMP do you recommend to replace this one with? Sub $100 if possible, preferably with optical input.

 
Did you try setting the Realtek computer audio to "2-channel" and "speaker" output?
Just to see if it makes a difference for the SMSL.
 
For replacing the SMSL.
Creative Labs Sound Blaster Z sound card ($65-$85)
 
Asus Xonar DX sound card (used, $50), combined with a FiiO E11K headphone amplifier ($60).
The E11K is a better headphone amplifier, then the one built into the SB-Z.
 
FiiO E10K ($76) or Schiit Fulla ($79), both are USB-DAC-amps.
USB bypasses the sound card features (both on-board and add-on).

 

[kramer5150]

(Stupid suggestion warning)  Make sure your L/R balance control on your computer is set even-steven.  Stupid as it sounds, I have made this mistake before 8^)
 
If you have a DVD player and CD in the house, plug its coax-digital output into the DAC, do the same with the TOSLINK output on the back of the DVD player.
 
If you have a whole nother' amp ,or stereo receiver you could try and plug the SMSL RCA line outs into that.  If they work then theres definitely something wrong with the headphone amplifier section.
 
That amp has a socketed OP amp on the analog stage, you might want to try and re-seat that.. or roll in a known good one.
 
Outside of that, I can;t think of anything else.

 

[cel4145]

It's not going to be your toslink cable. If that were having problems, it would affect both channels about the same.

But definitely a good idea to have someone else test it on their computer.

 

[Roxim5]

@PurpleAngel
What is strange is the "configure" button in Windows Sound is not available and is greyed out for the Digital Output that I am using for the AMP. This is where the speaker setup is usually configured. Thanks for the suggestions for replacement amps/dac, I will look into those if my SMSL is at fault.
 
@kramer5150
It is a perfectly legitimate question that needs to be addressed if you do not have that information. I already made sure that there was no balance to left or right. I will be doing some more testing with the AMP tonight once I get back from work. Going to plug the optical out from my TV into it directly and then the amp with my headphones. This should let me know if the computer is at fault. I also have a second TOSLINK there so that will be ruled out as well. I do not have another receiver or speakers to test the rest of the outputs on the SMSL. So we will have to just deal without. As for the socketed OP amp, I am not sure what that is. Can you give me some links to read up on that? Still learning about this stuff.

 

[Roxim5]

UPDATE
I was able to test the SMSL with my TV. Optical to SMSL, headphones connected to SMSL. Headphones worked without issues this time. So it seems the issue lies with the configuration on the computer. I haven't setup audio through the optical output from a computer before, so maybe there is some setting I am just not seeing. I might just disable onboard audio and purchase a sound card to resolve this. Seems the ASUS Xonar is moderately well received. Any other cards you guys suggest?

 

[kramer5150]

I don't see how getting an additional sound card would help.... if it is truly your settings that are wrong, wouldn't that be a system-wide thing and also affect the other digital outputs?

 

[Roxim5]

  I don't see how getting an additional sound card would help.... if it is truly your settings that are wrong, wouldn't that be a system-wide thing and also affect the other digital outputs?

True, if it was a setting in Windows that is the culprit, this issue will still be present. However, I have a stronger suspicion that it is the onboard soundcard or software for it and not necessarily Windows. The software for Realtek is severely lacking. Also, when I press test in Windows Sound options, the bar that indicates line activity lights up for both channels. I may just return the SMSL and get a FiiO E10k instead of a soundcard, this would circumvent the Realtek as well.

 

[cel4145]

I may just return the SMSL and get a FiiO E10k instead of a soundcard, this would circumvent the Realtek as well.

Unless you want the virtual surround features of a sound card, that's probably a good strategy

 

[PurpleAngel]

  UPDATE
I was able to test the SMSL with my TV. Optical to SMSL, headphones connected to SMSL. Headphones worked without issues this time. So it seems the issue lies with the configuration on the computer. I haven't setup audio through the optical output from a computer before, so maybe there is some setting I am just not seeing. I might just disable onboard audio and purchase a sound card to resolve this. Seems the ASUS Xonar is moderately well received. Any other cards you guys suggest?

 
Asus Xonar DG or DGX sound card, maybe find a good price on used, on eBay.

 

[Roxim5]

UPDATE 2:
Further messing around. I was able to get a hold of a sound bar that had optical input. Connected it to my computer to see if the left and right channels both worked. Surprisingly, they worked without issues.
Plugged the SMSL back in, headphones in, both channels worked this time. Used it for a bit, put the headphones down, came back and it was back to just the left side. I think the issue is the SMSL amp. Maybe a loose component or the like. I have initiated a return on this product and will go for something else after I get a refund.

 

[cel4145]

Plugged the SMSL back in, headphones in, both channels worked this time. Used it for a bit, put the headphones down, came back and it was back to just the left side. I think the issue is the SMSL amp. Maybe a loose component or the like. I have initiated a return on this product and will go for something else after I get a refund.

Definitely the best idea. PurpleAngel will tell you he has had issues with more than one SMSL product. Worth it to pay the return shipping for peace of mind at this point, even if it does start working again. Get a Fiio E10K or Schiit Fulla, and you should have no more issues. If you want to hook up any computer speakers, go with the E10K since it has a line out.