The Untold Tales – Asus Xonar HDAV Opamp Power Supply

 

Here’s something that will catch out the unwary.  While attempting to upgrade the opamps on my Asus Xonar HDAV and H6 daughter board, I discovered that there was a limit to the amount of discrete opamps (from Burson Audio) that the card will take – and I’m not just talking in terms of physical space!

So here’s the story.  I had already upgraded the stock opamps in the main card to the Burson Audio discrete modules (check out http://www.bursonaudio.com) with some pretty speccy results.  So naturally, being me, I wanted more, and so I purchased some additional Burson modules to upgrade the filter (forward) section opamps for the centre/subwoofer, side surrounds and rear surrounds as well as the I/V section opamp for the centre channel on the H6 daughter card.

Initially, this seemed to work well, but on closer listening, I noticed that there was some crackle evident particularly in the centre channel.  Also more distortion than I would have expected from my newly acquired Anthem PVA7 and Paradigm CC490 centre channel speaker.

Frustrated, I went back to the Burr Brown OPA627AP opamps on the daughter card and everything seemed to work without any crackling (although, as good as the Burr Brown’s are, I had lost some detail and tone ).  I tried all the Burson opamps again with the same results, so at this stage I thought the drivers might have been the issue.  I uninstalled the existing drivers and then tried to install some unified Xonar drivers that I found only to find that they wouldn’t even detect my card!  Gaaaahh!  Same thing happened with the drivers direct from Asus when I tried to reinstall them – again, Gaaaaahh!  Removed the Burson’s, put the Burr Brown’s back in, reinstalled the Asus drivers and everything detected and installed fine.  Tried a few combinations and found that the drivers would not install with any more than 2 discrete opamp modules on the daughter card (in addition to the 3 on the main card).  Everything was pointing to an inadequate power supply to the daughter card (which is sent through the ribbon cable).

 

I have the power!  (Or do I?)

The Burson’s are designed to run at a minimum of +/- 12V which is what I thought the Asus was running at (seems logical as it was taking its power from both the PCIe +12V supply and the additional molex +12V supply – don’t know where it gets the –12V from, but hey, I’m not an electrical engineer!)  So naturally, I thought that the upgraded opamps on the main card were drawing too much power and reducing the available power left to run the upgraded opamps on the daughter card.  My idea was to locate the +/- 12V opamp power supply pins on the bridge connector, “disconnect” those from the ribbon cable and attach a +/- 12V direct power supply from an additional cable from the main PC power supply.

My first lack-of-knowledge hiccup – a molex connecter on a PC power supply only includes +12V and ground, but no –12V.  Hmmmmm…

After hitting this wall, I thought that I might as well see if I can locate the pins anyway.  I found a +12V, but no –12V – WTF?  Checked a few more pins, found the standard 3.3V and 5V pins as well as some strange pins running at +/- 8V.  “Surely not?” I thought.  Checked the V+ and V- pins directly on each opamp, and yep, +8V and –8V.  I’ve said it before and I’ll say it again - Asus, you fools!!!  I still thought it might have been some sort of voltage drop from a lack of supply from the main card, but I checked the opamps on the main card, and again, +8V and –8V.

F#*k!!!

 

Where to from here?

Well, I’m seeing 3 options.  The first one I’ll definitely take, but the other 2 I’ll investigate just out of curiosity and if I can save up some money.  After all, I’d like to let others know of my experiences so that if anyone decides to take up the challenge of following in my footsteps, they hopefully won’t run into the same challenges.

Option 1 – Build a custom +/- 18V power supply to run the opamps

I’ll definitely need some advice and help in this area.  Working with mains AC voltage is not something I’m exactly qualified to do, so I may have to delegate.  At the end of the day, if I can get something that I can connect the +/- power pins (pins 8 and 4, respectively) on each of the opamps to, then I’m pretty happy.  Even happier if this power supply is regulated to within +/- 1% or better.

Option 2 – Buy an M-Audio Delta 1010LT card

This card has 8 analogue outs and is generally regarded as a very good sounding card.  Mind you, I believe it uses the NJM2114D opamps found in the I/V section of the Asus, so could be pretty sub-standard to what I am wanting to achieve.  Although given that this is a PCI card, and PCI supplies –12V as well as +12V, maybe it can at least provide the appropriate power to run everything.

Option 3 – Buy 2 Lynx 2 B cards

These cards are apparently awesome.  2 analogue inputs and 6 analogue outputs, runs on PCI (again, hopefully, can provide decent power to the opamps), and lots of professional praise from many high-end users.  Trouble is, at $899 a pop, this will take a while to save up.  They use (again, I may be wrong) the Analog Devices OP275 opamps which I haven’t as yet heard.

 

Well that will do for now.  More stories to come, as well as the continuation of the main story – stay tuned!