WOT: Sound card noise

[CurtZHP]

So, I've been experimenting with a couple different sound card arrangements. Mostly to give myself something to do when things get slow at work. Fortunately, the engineering shop at a radio station is a great resource when one wants to tinker. Anyway...

Got a workstation sitting here that is pretty much just like the one I have at home in terms of internal hardware. I had a spare Digigram VX882HR sound card sitting on the shelf, and I was curious as to whether it was a viable solution for a home studio rig. (We use them in the backup on-air system. These and other Digigram cards are used in a couple popular automation systems.) So, I was fooling around with setting up aux headphone mixes in SAW Lite, something I've been meaning to figure out anyway. Works great, by the way! But as I'm listening to the phones, when nothing's playing, this rig is noisy! Hiss galore! I've listened to tapes quieter than this!

I figure it's the little battery powered headphone amp I'm using. I replace it with a decent Rolls half-rack unit that has an actual power supply. A little better, but still a bunch of hiss. I start wondering if it's the sound card; so I grab another VX882HR. Same thing. Bleh.

Sitting on the shelf next to these $2000 sound cards (No lie! We paid close to that much for them new!) is a little $150 Focusrite Scarlett 2i2 USB interface. I plug that in, hook up the same headphone amp, and the hiss is GONE! I have to turn the volume up on the amp almost all the way to hear any noise. I hit play in SAW, and the music is plenty loud. I run the monitor level control on the Focusrite all the way up, and the noise floor doesn't change a bit.

Am I to believe that a $150 USB interface has better noise performance than a $2000 professional "broadcast quality" sound card??

Or am I jumping to conclusions and missing something?

[Dave Labrecque]

I'd bet something's wrong. The specs on that card say THD+noise is at -94 dB. I would check gain staging and impedance from the card's output into the headphone amp of choice. But that's just me poking in the dark, as my electronics knowledge is limited.

No dedicated headphone output on that card, right? You're just using a pair of the analog line outs?

[Microstudio]

I think is would be the drivers for those cards or the settings for those cards that would be causing the sound issues.

[CurtZHP]

I'd bet something's wrong. The specs on that card say THD+noise is at -94 dB. I would check gain staging and impedance from the card's output into the headphone amp of choice. But that's just me poking in the dark, as my electronics knowledge is limited.

No dedicated headphone output on that card, right? You're just using a pair of the analog line outs?

Right. Just running a pair of analog outs to the headphone amp. Balanced connections all the way. I did the same with the Focusrite, even though it has it's own headphone amp (which sucks, by the way...).

I'm almost wondering if it's thermal noise. These cards do get hot.

Back in the old days, Digigram made a card called the Mixart8 that we used in a couple on-air rigs. They had this little 1.5 inch muffin fan on them. Problem was, the fan tended to die after a while without telling you, making the card misbehave in all sorts of odd ways. I finally ended up ripping the little fans off and just putting big 3-4 inch fan cards right next to them, along with hooking up every chassis fan I could. I swear, if the server wasn't screwed to the rack, it would have taken flight!

[Dave Labrecque]

Right. Just running a pair of analog outs to the headphone amp. Balanced connections all the way. I did the same with the Focusrite, even though it has it's own headphone amp (which sucks, by the way...).

I'm almost wondering if it's thermal noise. These cards do get hot.

Back in the old days, Digigram made a card called the Mixart8 that we used in a couple on-air rigs. They had this little 1.5 inch muffin fan on them. Problem was, the fan tended to die after a while without telling you, making the card misbehave in all sorts of odd ways. I finally ended up ripping the little fans off and just putting big 3-4 inch fan cards right next to them, along with hooking up every chassis fan I could. I swear, if the server wasn't screwed to the rack, it would have taken flight!

LOL.

[matt]

You've established that the noise is coming from the sound card. Try installing it in a different motherboard to see if the problem follows the card. If that solves the problem, there is likely an issue with the pci power rails in the current mb or a weak power supply. If this doesn't solve the issue it could be a damaged IC or cap on the soundcard.

[Dave Labrecque]

You've established that the noise is coming from the sound card. Try installing it in a different motherboard to see if the problem follows the card. If that solves the problem, there is likely an issue with the pci power rails in the current mb or a weak power supply. If this doesn't solve the issue it could be a damaged IC or cap on the soundcard.

If I understood him right, he got the same result with two different cards of the same model. But it does sound like the mobo could be suspect, as you suggest.

[CurtZHP]

If I understood him right, he got the same result with two different cards of the same model. But it does sound like the mobo could be suspect, as you suggest.

That's correct. I tried it with two cards of the same model. I am planning on bringing one home this weekend to try it on my own system to see if I get the same result.

[CurtZHP]

OK, so I brought one home and installed it on my own workstation. Ran the first two outputs to my monitor amp (Crown D-75). Ran up the outputs. Seems MUCH quieter. Like what I'd expect. Planted my ear right against the tweeter with nothing playing and heard a very faint buzz. Put everything back the way it was and listened again. Same buzz. Must be my amp. Forgot to bring home the headphone amp to repeat the test as I did it at work. Tomorrow?