customizing soundcard-- advanced DIY hotrodding

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Svart

Well-known member
Joined
Jun 4, 2004
Messages
5,134
Location
Atlanta GA USA
excellent. i thought of this too for my sound card, however the bitrate and sampling are much too low so i'd need to choose another card. what card are you using?
 
[quote author="buttachunk"][quote author="SonsOfThunder"]curious to know if you know right off if the D/A output is voltage or current? [/quote]
is this a trick question ? :green:
it's voltage[/quote]

Hi Butta'
No it wasn't a trick question...many DACs are current output...I looked this data up and you are correct, it is differential voltage out. Your biased buffer looks cool. I am curious that they show cap coupling between the DAC and the LPF/buffer, while you have chosen to move the cap to the output. Any comments on why?

Thanks!
Charlie
 
[quote author="buttachunk"]i just laid out the output buffers-- they bias the
http://img.photobucket.com/albums/v251/buttachunk/classaoutputbuffercopy2.jpg
[/quote]
In the sigma delta ADC s external lowpass are not good thing.
The sigma-delta have lowpass inside.
(Only some computer card-producers leave capacitor - legs
alone, you can read ADC datasheet and solder caps.)

I have also modified sound - card in my comp.
It is sounblaster Live (price: 10 dollars :) )
with cool sigmatel ADCs (Soun blaster uses it only
in several series)
As input I use CD-ROM (have floating ground)
as output I only solder SMD connector near sigmatel and
cuts wires after it. Near external connector I have tantalum caps.
 
[quote author="buttachunk"]i just laid out the output buffers-- they bias the opamps into Class A, and should sound phat :green: .
includes low pass filter (as per the mfg's datasheet)

http://img.photobucket.com/albums/v251/buttachunk/classaoutputbuffercopy2.jpg

i will post the input buffers soon[/quote]

Having done similar "Class-A" upgrades to opamps there is something I have repeatedly experienced with all these circuits. If you ever load it so that the output comes out of single ended mode your signal goes to hell. The transitions between (and near) the biasing modes are NOT musical at all. I am pretty sure you know this and bias with enough current so that during typical use the load never sinks enough current to allow that.

Cheers,
Tamas
 
[quote author="buttachunk"]TK@

yes-- "oldschool" resistor biasing can lead to problems in this case because of the opamp output's sensitivity to DC. the constant current source is far more linear and far more accurate than say a 1% 6k resistor from the VE- to opamp out. from my reference materials, the ccs should be set to 3-5 ma for class a bias without nasty side effects. :wink: (getting too hot or sounding nasty)

having said that, i like resistor biasing for some less critical-current transistor stages-- sometimes the "slop" factor makes it sound vintage.. the "warmth" of 20% tolerances!!! :green:[/quote]

I have to respectfully disagree. The switch from single ended to symmetrical output creates a spray of odd harmonics regardless of the biasing method used (resistor vs. CCS). It never sounded like "warmth" to me, but you may be after high frequency distortion so I will not argue about the sound . A thirty foot cable can cause enough capacitive load for all the current (5ma) to be sinked to charge the transmision line. At that point the output switches from single ended Class-A to symmetrical Class-B. Actually a single ended Class-A output with constant current source cannot be more efficient than 25% so most of the power ends up as heat and even less power is available to drive the load. That is the reason why this sort of opamp biasing is never used without a subsequent buffer (even in the Audiophool world). However, if you give it 5ma and make absolutely sure that you will never draw more than a mA from the output it will work just fine.

Cheers,
Tamas
 
Chutta-Bunk...

A quick question (and possibly a correction)?

"Me Julie"? -If that's supposed to be a British thing, sort of the equivalent of the Aussie "Me Shiela", then I think you might possibly have the wrong name...

Where I came from, it was always "Me Judy"...

I think that Mark Burnley should confirm this...

Keith
 
Keith,

I think we're talking "respect wid 'yo Staines Masseeve"

...Ali G-isms rather than local dialect?? :?

Some of those Ali G moments were almost painful...like when he met Boutros Boutros-Ghali-Check This

:green:

Mark
 
Ah. Good stuff.

Having never seen the show, I'm not familiar with the lines.

I dumped cable TV last year when we moved house, meant to investigate sattelite as an option, but 3 months went by without getting anything hooked up and then, well... I sorta didn't miss it! -For $10 I got a TV antenna with usable gain, and that's all I've needed for the local channels during the hurricane. (in fact it dodn;t go out like the cable did, and it worked when the cloud cover was thick, unlike the sattellite! -It did get a little snowy during the downpour, but that's all!

The show looks pretty funny though. :)

Keith G.
 
I still can't figure out if I like Ali G. or not. I admit, I find some appeal in what he does. Making fun of world leaders in so public a way is always welcome by me.

He's either the world's smartest stupid man, or the world's stupidest smart man. :green:
 

Latest posts

Back
Top