>>>Some of what you are saying is false. The coupling capacitors are in fact not needed in these circuits in order to function properly. Data sheets for the DACs will bare this out.
Just want to clarify that my post was not intended as a flame. I appreciate the amount of work that went into the mod and some of the related information was of benefit to me.
I was not talking about DAC output. I was referring to this quote from the original post:
"Opamps and capacitors are the two worst offenders of sound quality. With any soundcard you can change these opamps to far better ones, remove capacitors no longer needed due to the better opamp, and give it more power by increasing the size of the power supply filter capacitors on the sound card".
This statement has several inaccuracies. Opamps by themselves are highly unlikely to contribute to poor fidelity. Most modern opamps have ideal circuitry and are far superior to circuits built from discrete components. Furthermore, you cannot simply change one opamp for another unless it is a fairly direct replacement.
The audio output opamps used on the X-Fi are already low noise, high performance opamps:
http://semicon.njr.co.jp/eng/product/opamp/NJM2068.html
It's high unlikely that replacing them with the LM4562 will make that much of a difference. Sound quality is often relative to the ears of those listening.
Capacitors do degrade sound fidelity but the degradation is probably not noticeable to the average ear. Caps only degrade the phase shift of the signal between its current and voltage components. However, that kind of degradation is typical of any amplifier since their frequency response is frequency dependent.
In the statement above it claims you can replace caps 'no longer needed' due to the better opamp. That is simply incorrect. The cap is an integral part of the push-pull output stage used in opamps. Output caps are used even in high quality power amps.
A push-pull stage uses two transistors. In the bipolar junction type, they use either two NPNs or a complimentary paired NPN-PNP combo. The NPN pair is more common since it's easier to match two NPNs than it is an NPN to a PNP. When you have a pair operating, only one transistor is running at one time. The input signal is split between them so that the +ve going signal part drives one transistor and the -ve going side drives the other. That is called a Class AB1 amplifier.
With AB1, there is a transition zone as the +ve going output signal changes over to the -ve going signal. The output capacitor helps smooth that transition, otherwise the distorted signal transition sounds raspy through the speakers. It actually sounds like bees, and the distortion region as viewed on an oscilliscope look like 'bees knees'.
Besides that function, the capacitor is required for operation with a single ended power supply. During one half of the signal cycle, the cap stores charge from one transistor, then releases the charge through the other transistor on the other half cycle. Without the cap, the circuit wont work correctly.
The quote above also claims that increasing the size of the filter caps will increase power. Not true. Increasing the size of the caps may even reduce it. The caps are used to smooth out the rectified signal when a rectifier bridge converts the alternating supply voltage to a pulsating +ve voltage. The caps are designed to hold enough charge so that the charge will be released through the load a certain amount before the next rectified pulse. If the cap is too large, it will no longer function with the correct RC time constant.
In another part of the article:
"Replace the sound card's power supply capacitors with larger ones that are at least several times the original value. Quality matters, especially specs like ripple current".
Not true and not worth it.
And again:
"...some of them [opamps] (are??) extremely esoteric, requiring its own special power supply. Some of them plain unstable".
There is no such thing as a modern opamp that is unstable. If you use them in the wrong circuit they might be, however. There is a big difference between an opamp using bipolar junction transistors and one using MOS technology (CMOS). You just can't take any old opamps and solder it into the circuit where another has been removed, just as you can't replace any transistor with any other transistor. Opamps have specialized uses and it's little wonder the author found some unstable.
It takes a lot of experience in electronics and a lot of research to replace one component with another.
Then this:
"I don't have the schematics to the X-Fi so I don't know how to apply them. If others discover new mods I can add them to the list. Short the 22uF caps near each opamp...."
The author admits not having a schematic then advises the reader to short a component. That is just not done in electronics. Before I ventured into an X-Fi circuit, I would make my own schematic and I would not replace or short components till I understood exactly what they did. Even at that, it is not always possible to understand the original design. They may have had trouble with stability during the design phase and added a cap for stability.
Shorting anything is never a good idea in electronics unless one knows exactly what he/she is doing.
From the article:
"...you bypass the opamps completely and use a discrete analog output stage..."
Makes no sense whatsoever. Opamps are superior to discrete-component amps because they can be built on the same silicon wafer. The problem with discrete components is matching the transistors and other components. In an opamp, transistors and components can be matched to near perfection
Bypassing an opamp is not as easy as it sounds. There are components built into the sound card that depend on having the opamp be there as a load or input. Removing the opamp without disabling the circuits could lead to instability. For example, I bypassed a circuit in a TV once by removing it's input and output connectors and disabling a regulator supplying voltage to the circuit. While I was doing something else, with the TV powered off, the sound circuit suddenly started operating. Nothing else was operating, just the sound circuit. It made no sense but such is life in the world of electronics.
Finally....
"Passive Output Mod - like in the discrete mod, you bypass the opamps completely, and use either a transformer or a bandpass filter
Alternatively, you can simply use a RC highpass filter..."
Why would anyone want to introduce a transformer into a high fidelity circuit? The inductance in the transformer distorts the output signals phase just as the coupling capacitor does.
There is an argument among so-called purists that tube amps are superior to transistor amps. That is nonsense, and I have repaired tube amps at one time. The problem with tube amps, besides the unreliable nature of tubes, due to the heat they produce, is the large output transformer required. It acts as a filter that distorts the tube output signal, making it sound soft. People are mistaking a distorted sound for better quality.
You can do the same, if you like, by taking the near perfect fidelity of a well designed transistor amp and running it through a filter.
Why, why, why would anyone attach an RC highpass filter to an audio amp to improve the sound? All you are doing is cutting the lows and passing the noise.
*********************
>>>>Yes there is 2.5 volt on these coupling capacitors but when you bypass them by shorting the caps the 2.5 volts positive gets sent to BOTH the Plus & Minus input of the
OPAMP.
You are likely talking about the DAC output here. I can tell you one thing, almost for sure. If the coupling caps were not required they would not be there. Inter-stage coupling caps are used to keep direct currents from one circuit from flowing through the circuits of other components. Do you think engineers would use them if direct coupling was a superior option?
>>>I've been doing these mods for years with no failure of opamps DAC's or voltage regulators.
As I said, I have no intention of flaming and I applaud your effort. However, I have several decades experience in electronics, having spent several years on the bench repairing every kind of amp from tube amps to transistor amps. I am also highly trained with several years at university studying electrical engineering. All I am trying to do is pass on information that might prevent an inexperienced user from blowing his/her sound card.
I would never attempt your mods blindly without first making a schematic and spending hours researching the effects of the mods.
I do have an interest in modding the connections between various Creative products to make the drives from one work with another.
For example, some card have the Ad_Link connector on the front of the card. I have an SB0550 used with the Elite Pro external model and I'd like to see if the SB0460, with the same Ad_link connector will work with the Elite Pro. I wont try any mods till I am absolutely sure they wont blow anything or compromise the integrity of the original design.