PC to DAC connection?

[zhai]

Hey all, I have a problem that's bugging me for a long time.

I have a NAD 2400 amplifier, and I tried hooking my computer sound card's analog out to it. Then the 2400 died.

Had it fixed, suspected the sound card of being to blame, so I got a USB soundcard which was supposed to be well electrically insulated, and connected it to the amplifier. Then it died again.

So now my best guess is to get an optical signal from the PC to a DAC, which I wanna build. But I hear from everywhere that this is no good if you want to have good signal quality.

So what other options are available if I wanna be sure my obviously sensitive amplifier won't get killed? Would a USB connection to the DAC while not using power from the PC be a solution?

Is optical SPDIF really that bad? Or is it ok if it is done well?

Thanks.

[peufeu]

got a USB soundcard which was supposed to be well electrically insulated

USB isn't insulated, these things derive power from the PC, so the PC ground is connected directly to your audio ground, and all hell breaks lose.

By the way, your PC needs a new power supply (next time, maybe instead of burning an amp it will electrocute you ?)

Wired SPDIF normally uses an insulation transformer so you should be safe (just check that your gear does include one !)

[seoman]

Optical could give some more jitter but i doubt if you can tell the difference. aspecialy since 99% of the pc users don't have a desent soundcard.
No analog output of a soundcard can outperform a optical spdif connetion.

Why why why do people think that usb sould give you cleaner sound.
It's just as terrible as any pci card or onboard card.
It is always connected to the same crapy supply.
wich is most likely the reason that your NAD died.
(NAD has to scratch his head over this!!!!!! bigtime!!!!! )
Any usb connection with or without external supply is still 100% connected to that floating ground!
PCs need a earth connection to prevent it's ground from floating.

Using the optical out is the best solution.
And those theoretical losses due to the optcal conversion is really no problem. especialy when you compare it with NO sound at all and a broken amplifier.

[FastEddy]

" ... your PC needs a new power supply ..." Agreed.

There are of course several levels of quality ... I'm listening to Muddy Waters "Folk Singer" right now on my Apple MacBook, a really great DVD-A digital convcersion of the original analog master tapes. The sound is not nearly as "fat" on the Apple DVD player as on my Pioneer DV-525 ... the reason is ...

The DVD-A is 24 bit / 96K on one side and 24 bit / 192 on the other. The Apple passes the DVD-A information through their Digital to Digital converter to SPDIF Optical (Apple LossLess), and the 24 bit information gets chopped down to something like 16 bit / 44K or 16 bit 48K, ... becoming no better than CD quality .... and a with a significant loss of dynamic head room. (from 140 db down to, I believe, around 85 db = )

So: 1) fix you PC to be sure it works with what you have, 2) consider making DIY improvements to you USB "sound card" ... or 3) possibly consider getting some kind of higher resolution PC to Analog adapter.

I for one don't intend to ever buy CDs again now that I have heard the obvious superiority of DVD-A / SACD / HDAD / ... (My favorite PC to Analog DAC adapters are via the FireWire 1394 connection, not USB ... But there are plenty of very good USB DACs ... just try to get 24 bit / 96k as a minimum.)

[mrshow4u]

How did the NAD die?

Was it burned grounds, or shorted outputs?? Ive seen plenty of NADs blow up all on their own. Maybe link the PC chassis to the NAD chassis through a 1.5k resistor and measure the voltage across it. See if theres current down the ground path.

It could be some spurious clocking noises going down the signal line causing the NAD to oscillate, causing common-mode conduction, then transistor death.. Do you remember the NAD getting really hot? Maybe poor analog out filtering?

Measured on an Ap System 2, optical jitter is always higher than coax. Normally, the levels are several magnitudes lower than what the AES deemed audible. I am happy using optical. ...1 less ground loop to worry about.

[FastEddy]

When it comes to PC to Analog and anything down stream pops, the first suspect is the PS power supply.

PC power supply problems:

* They are notoriously dirty, noisy beasts and for quality audio will never ever work right unless replaced with something twice as healthy with much better filtering.

* If the PC has a lot of extra equipment (multiple drives, lots of plugins, etc.) the PC PS is probably at or close to its limits = making it even more dirty, noisy. (every PC supply I have ever seen is overloaded from the get go.)

* The reliability of most clone box supplies is always in question and is the most common cause of PC problems.

* PC supplies are all switching supplies and should never be used unisolated from the DAC = sorry, but that's a fact, jack.

Dump it, get another one, unload yoyr system of extra peripherals and hook that NAD back up ... then consider what has to be replaced.

[jameshillj]

... and should never be used unisolated from the DAC....

Eddy, could you expand on this a bit, please
- do you tie the DAC earth, case and gnd plane layers etc to the usb earth (0v computer), or just the 0volt input to the chip and use a standard in box p/s for the usual DAC functions?

[jameshillj]

... and could you, or anybody else direct me to any appropriate link where this subject is / has been under discussion? jh

[zhai]

I guess I was just a victim of an unscrupulous salesman about that "usb insulation" thing.

Well I did replace the power supply with a high quality (SeaSonic), but I'm still going to be wary of connecting it electrically to my amplifier, even if both are grounded... can anyone tell me that if I did that, there'd be no chance of killing my NAD again?

What happened when it died was that the channels first started to jump down in volume, then a bit later they faded completely. No extreme heat or any other symptom than that.

So what I plan on doing is to build a DAC with SPDIF TOSlink input, get a "pass-through" sound card with optical out for my PC and hopefully be happy. I'll probably get the DDDAC for this purpose. Doede tells me he can include a TOS input, so everything should be good

Oh, and at some point I wanna make a DAC which can handle 24/196, but for a first project I think DDDAC will be nice.

[seoman]

Was your PC grounded/earthed ?

When connecting a non-grounded pc you better unplug the PC first, (switching off will leave the power supply still active) before plugging the audio cabels.
RCA plugs connect the signal first and then it's possible that a high voltage is applied to the analog switching IC or Volume IC.
They die when a signal (higher than the supply) is applied.