simple unbal to bal converters

livingnote said:

Well what I will be doing later this week is to make a little I/O board thingy in SMD, I consider it handy in general to have one of those for general in-outing. You know, fits on a postage stamp and does balancing duty, maybe mountable to a print XLR directly or hijack it and stick it into your 'puter as mentioned.

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good idea!
Why haven't i thought of the onboard card before?  ???
For test purposes this would be more then enough, maaybe for real snr and distortion the onboard card will not do the job but what the hell.
I have my terratec card working under vista now but really unstable and hardly useable.
The IO box is working brilliantly and clean BTW!

>>>> There's 12v and 5v supply sources in abundance.

If using +/- 12V from the computer PSU (via molex) I think that rails need to have extra filtering. Don't have the link for that, sorry.

If going with SMD, that may mean the need to mount the 1W filter-resistors tru-hole. And/or add some chokes on the rails.

Texas' DRV134 and DRV135 are also an option.
http://focus.ti.com/docs/prod/folders/print/drv135.html

Just got back from Neutrik. What I'll be working with is the NC3 m/f B V and H, so you can have the pcb soldered on either vertically or horizontally. I really like the B series for the metal flange and the self-tapping screws, and that you can stick them in from the back, making for easy work to change the entire I/O module if you so please.

Here's a link to Intel's spec for Front panel audio: http://www.intel.com/support/motherboards/desktop/sb/CS-015851.htm

Basically there are two specs, the old one, AC97 and the new one Intel High Definition Audio, but they use the same header.

A white paper on HDAudio is here: http://www.intel.com/design/chipsets/hdaudio.htm

Here is a more inclusive document on front panel connectors: http://www.formfactors.org/developer%5Cspecs%5CA2928604.pdf

Basically its a 2x5 header with one pin missing for a key.  The AC97 application is pretty straightforward with mic inputs, headphone outputs and a "filtered" +5v (sorry no 12v here unless it is part of the mic bias, but I think that's much lower).
The HDAudio spec is a lot more convoluted because it includes some circuits for sensing what is plugged in. P25 of the last document above has a pretty good schematic.

Hope this is useful.

Now to get that XLR somehow stuck into the front or back panel - maybe a D-Sub breakout cable if that hasn't been mentioned yet...attached on-board to a little card and PCI metal thingie. Had that on my old M-Audio card years ago, albeit unbalanced.

oh and fantastic documentation, dcharrison, thanks!

Cheers!

Digital audio labs manages to get 1/4" connectors on a plug-in card, but XLRs will probably need to go in a bay.  I'd hate to see any audio run very far unbalanced inside a PC.  Maybe the circuit could ride on the header and the connector could fit in a bay.  A blank bay cover would work, depending on how sturdy it is.

There is even this outfit that makes modular i/o ports for bays:    http://www.frontx.com/

Perhaps, while you are at it, stick a pot on the unbalanced side.  Everybody would like to have a volume knob for their PC!

audiox said:

2 x unbalanced-to balanced & 2 x balanced-to-unbalanced converters on one pcb:

http://audioxxx.googlepages.com/bal_card_block_diagram.pdf
http://audioxxx.googlepages.com/bal_card_schematic.pdf
http://audioxxx.googlepages.com/bal_card_layout_designations.pdf
http://audioxxx.googlepages.com/bal_card_layout_values.pdf

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i was wondering, would there be any differences if i use one  NE5532  for left and one for the right channel.
on your schematic, you share them. is thee any specific reason for it.

kam

kambo said:

i was wondering, would there be any differences if i use one  NE5532  for left and one for the right channel.
on your schematic, you share them. is thee any specific reason for it.

kam

Click to expand...

Should not make any difference....

thank you,

i am gonna build this circuit for eliminating hum on Roksan LIII amp;

lynx aurora =to=> presonus central station to ====>
Roksan LIII amp (phono input) hum
bryston 3 (XLR in) no hum

am i on the right track....

Well, what exactly do you mean by Phono input?

oops sorry,
inputs are  RCA, unbalanced on Roksan LIII.

Ok, as I understand it your question "Am I on the right track" means something like:

"is the hum caused by the fact that the Roksan LIII amp has a unbalanced RCA input".

Well, I don't know what the schematic of the  Roksan LIII amp looks like. It can be a design flaw, a wrong grounding scheme, or maybe your unbalanced cable is picking up hum.
I'm just guessing here...

You might also want to look at the THAT 1240 line receivers.  

http://www.thatcorp.com/datashts/1240data.pdf

unbalanced cable is only 10inch. and roksan has common ground (as roksan said)

i built one balance to unbalance circuit and will post back the result next week

thank you
kam