| Originally Posted by germanium /img/forum/go_quote.gif correct |
| Originally Posted by applegd /img/forum/go_quote.gif For my STX, I will do some reverse engineering later to see the complete details. These two caps are just there to form high pass RC filter for blocking the DC. |
| Originally Posted by germanium /img/forum/go_quote.gif True but they do have an impact on sound quality. Enough to bring the performance up to anouther level. Most of the shorcomings compared to the more expensive DAC in the stereophile article can be traced to these caps. |
| Originally Posted by applegd /img/forum/go_quote.gif Remove these caps will pose DC offset risk to at least some of the card too. Not every Head-Fier has DMM in hands. |
| Originally Posted by germanium /img/forum/go_quote.gif The D.C. offset risk is only to any outlying equipment as this only feeds the RCA jacks. D.C. offset is very low on these cards though I do understand your trepidation in doing this mod as some equipment is sensitive to D.C. offset. The D.C. offset I measured is so low that even those amps that are sensitive would have no problems. Less than 2 millivolts in my case. Many amps have more than this coming from thier own input! |
| Originally Posted by applegd /img/forum/go_quote.gif Yes. Your points are same as what I want to say in my reply "Remove these caps will pose DC offset risk to at least some of the card too." |
| Originally Posted by germanium /img/forum/go_quote.gif You missread me. The D.C. off set coming from the input of the following amp is of no consequence as its current is very very low & is protected by at least 1Kohm of resistance at the input of the following amp. The opamp on the card can easily handle this amount of current & is therefore no threat at all to the card. I have been doing this mod for years & have yet to have a single problem as a result of it. |
| Originally Posted by applegd /img/forum/go_quote.gif Focus on the technical stuff here.
When we worry about the DC offset of a source(in this case it is STX), it is common sense that the DC offset is at the output(In this case, it is RCA output jack) of the source(STX). For your case, less than 2 millivolts DC offset at RCA output of STX. But you can not guaranty all the rest STXs around the world MUST have such low DC offset. ASUS Hardware developers are not nuts, these two caps there have their meaning to the circuit, although they also introduce the problems such as phase shift, decrease in sonic clarity etc. The problem caused by the DC offset is not against STX card itself. A lot headphone amps are DC coupled without input caps. If my STX RCA output has 5mv DC offset, and I use DC coupled headphone amp with gain 11, personally I won't be comfortable to let my HD650 to deal with about 55mv DC offset at the headphone amp's output jacks. If we remove these two caps from the STX board then short the pads, we avoid cap related issues in audio path,then no phase shift, no decrease in sonic clarity etc. But we have to keep in mind that we risk damaging our expensive headphones if we do this. STX that has a low DC offset now may develop a problem tomorrow. |
| Originally Posted by germanium /img/forum/go_quote.gif Bear this in mind also that since many amps already have some D.C. offset of thier own if the D.C. offset on the Xonar card is lower than the D.C. offset of the input of the following amp then the D.C. output of the following amp will in fact also be lowered as the D.C. offset of the input of the following amp will be largely neutralized by the buffer amp on the STX-ST card. D.C. offset at the output of the following amp tracks the input D.C. offset times whatever the gain is if it is also D.C. coupled. So in that case D.C. coupling of the Essense cards will actually neutralize the D.C. offset in the following amp & improve its performance not degrade it if the xonars D.C. offset output is less, but this only works of course if there is no cap. |
| Originally Posted by germanium /img/forum/go_quote.gif 55mv D.C. offset is not going to hurt any headphone extant, not even low impedance ones let alone a high impedance one like the HD650. These the high impedance would limit the current to .000018 amp or .000001 watt into 300 ohms. & if there is D.C. offset at the input of the following amp that is greater than The D.C. offset of the output of the Essence cards leaving the cap in will actually do more harm than removing it if the D.C. offset of the input of the following amp is significantly higher. |
| Originally Posted by germanium /img/forum/go_quote.gif The Essense card should easily & safely be able to nuetralize up to 500mv of D.C. offset at the input of the following amp. This is more than the card will ever see with any normal operating amp. The only problem arrises if there is a failure of the following amp or the output section of the card fails. Both of which are quite unlikely though not impossible. 500mv of D.C. through a 1Kohm resistor would only be about .5 milliamp & that is all the current the output of the card would have to absorb in this worst case senerio. Far below it's capabilities. |
| Originally Posted by applegd /img/forum/go_quote.gif The big concern is the DC offset at the output of the DC coupled headphone amp and whether the DC offset impacts the sound quality, or even burn the headphone. It is just the headphone owner's preference. As long as the DC offset voltage does not actually burn the headphone, someone might still "enjoy" the headphone even the DC offset also affect the dynamic range of the sound. Not sure how many head-fier/DIYer can allow 500mv DC offset into his/her HD650 as it is obviously way tooooo high. Usually DIYer prefer the DC offset at headphone amp output less than 20mv if possible. |
| Originally Posted by germanium /img/forum/go_quote.gif you wanted technical information, I give it & you turn it around into something different from what I'm actually saying. Anybody that reads what I was saying with an open mind would actually see what I'm saying the 500mv was a worst case scenerio for the card to have to absorb which I said it would likely never see. Not talking of D.C. offset to the headphones in that situation but a very very unlikely situation involving just an unreal D.C. offset coming from the input of the following amp. In anouther situation I have actually seen 1 volt of input D.C. offset nullified by the output of the previous amp. This D.C. offset was self contained inside A powered speaker & never exposed to the outside world so again not a situation that the card will actually see. This can also be an advantage & is actually used by none other than bob carver to bias the output of his opamps to pure class A operation. |
