Sound Card Recommendations for the iMac

It looks like there is something wrong with the internal sound card in my iMac desktop. The music is now scratchy and mildly jumbled. Having eliminated every other possibility that I can think of - have others been required to replace the sound card and if so . . . .what did you get? Same stock part or upgrade?
With an iMac, there is no internal upgrade, so instead of looking at "sound cards" you should focus on a DAC (which is an "audiophile" term for external sound card). ;)

Which iMac do you have?

If it's an Intel based Mac, it most likely has an optical audio output. If this is the case, I find the optical output to be extremely good, especially when using a nice glass mini toslink cable.

If it doesn't have the optical output, then USB is a great option. You can get USB DACs or a USB to SPDIF adaptor. I recommend the HagUSB.

As for DACs....well....that's a complex issue. They range in price and features, and of course quaity and character of sound. It all depends on you wants, needs and budget.
Hellofidelity: Thank you for the response. I have an iMac 8.1 Intel Duo. It does have optical/usb/firewire capabilities. I am currently using a Pop Pulse USB to SPDIF converter (it also converts the Toslink) which has worked well up until about a week ago. Thank you for clearing up the DAC/external sound card issue. I never did get that straight.

Can I assume then that an external sound card puts "out" a digital signal and then my headset amp and/or big system processor does the D/A conversion?

And finally . . . .let's assume that my internal sound card is the issue then would coming out with USB or Toslink to an external sound card actually bypass the internal sound card?
Question....what kind of system are you connecting your Mac to?

1. Mac OSX uses "Core Audio", which means you don't need a "soundcard" for most applications. "Core Audio" handles audio files extremely well, and this is one reason why Macs are used for professional audio applications. Sound cards can be purchased for Mac Pros, but it's normally for those professional applications that require studio mixing and mastering. Most people that have correctly setup a Mac for music will tell you that they are an excellent music source, just using the standard digital outputs (optical, USB, FireWire).

2. A DAC's main duty is to take those digital outputs and create a good analog output. In the case of music, the DAC should reveal the space and texture of the music, the kind of thing that gives you goosebumps. DACs sound different because they are "tuned" to have a character. I view DACs the same way as phono stages and cartridges. They sound different because the designer is creating a character or style.

3. Some computers don't have standard digital audio outputs (SPDIF coaxial and toslink) so if you want to connect one of those computers to a DAC that only has those inputs or a surround sound processor/receiver, then a USB-to-SPDIF converter can be used. In the case of your Mac, the simplist (and best way IMHO) is just use the optical output into your DAC or processor (if your DAC/processor has an optical input).

4. If your DAC/processor doesn't have an optical input, yet has a coaxial, then I recommend the HagUSB by Hagerman Technologies. It will convert USB to coaxial very well, and is USB powered, so no "wall wart" power supply is needed.
It isn't a matter of wanting to improve on the Mac Core Audio set-up - it has worked wonderfully well for the last 3 years. It is just a matter of trying to correct a sudden degradation in the sound quality over the last two weeks. The problem lies within the Mac itself, not my other equipment, so I am making the assumption that there is a glitch in the basic Core Audio portion of OSX. My thinking was that an external sound card would "go around" the internal Mac and once again restore good quality sound.

Maybe others have had this experience??
Did you upgrade iTunes recently? Have you tried playing music through different players on the iMac? If it is garbled distorted sound it could just be a software issue, I had terrible sound on a Windows XP version of iTunes after upgrading to a newer iTunes version....

I would not think that a bad internal soundcard would affect optical digital out... as the digital signal is just passing through... So make sure you rule out software problems first.
Thank you Arni - Yes, I recently upgraded to iTunes 9 - hadn't thought about that. How did you correct the problem after upgrading to a newer ITunes version? Maybe you are right on the mark.
I ended up reverting back to the previous version (from 7.0 back to 6.5). My wife later got an iPod that was incompatible with 6.5 so I upgraded again, (7.5), and had the same issues all over again. Went to Songbird, which was the only Windows player that could handle apple lossless files at the time.

I have crossed over to the good side now and have an iMac. There as some free alternative players for Macs out there, such as cog, vox,and songbird to name a few free ones. I recommend you download one of these and see (hear) if they sound better than your distorted iTunes.
Good luck,
thanks Arni I'll check into it!! Hope it doesn't destroy all the album artwork!
Hellofidelity and Arni: Just a follow-up note on the solution. I had upgraded to iTunes 9.0 and the trouble started. Today a buddy came over and suggested we see if iTunes had another upgrade. Impossible, I thought - its only been about a week. Sure enough 9.1.1 was available. We downloaded and problem solved. Music sounds great again. Thanks for you input, I appreciated it.
Thanks for the follow-up....hope all stays well and let the tunes keep flowing. ;)
Do either of you know how to go "backwards" and restore an older version of iTunes? As I stated above the improvement with the newest version is good but maybe I'm getting to picky since I still think I'm hearing some issues.
Is it possible your Pop Pulse USB to SPDIF converter has deteriorated?
Tomjoe - that is always a possibility but today I finally figured out the rest of the problem. I had left the iTunes Equalizer on - it is normally off. I was playing around with it a while back. Once I turned it off the music became instantly crystal clear. So I think the problem was twofold - some issues with iTunes 9.0 and the Equalizer. I'm listening now and it sounds great through the headset. It is my experience that listening through the headset is the quickest way to hear a problem.

Thanks again for all of your suggestions - they were valid ideas!