No, it is not wrong, please don't touch.
C82 sets a pole in the inverting connection of U24 by using the feedback loop. The same cannot be done in the non-inverting connection, so it is done passively by C75||R130 in a voltage divider with R102. This creates the same pole in the inverting and non-inverting connections.
However, to do it passively costs voltage swing and therefore you need more gain in the non-inverting connection. Hence U24A needs a larger value feedback resistor than U24B. Why it is not exactly twice the value must have been determined by experimental means.
p.s. Coris, this is a good example of why you SHOULD NOT correct/modify the Oppo as long as you sit on your elbow.
C82 sets a pole in the inverting connection of U24 by using the feedback loop. The same cannot be done in the non-inverting connection, so it is done passively by C75||R130 in a voltage divider with R102. This creates the same pole in the inverting and non-inverting connections.
However, to do it passively costs voltage swing and therefore you need more gain in the non-inverting connection. Hence U24A needs a larger value feedback resistor than U24B. Why it is not exactly twice the value must have been determined by experimental means.
p.s. Coris, this is a good example of why you SHOULD NOT correct/modify the Oppo as long as you sit on your elbow.
Well, your opinion... With my output module, fully differential and symmetrical the Oppo player it perform and sounds at much higher level, with unprecedented soundscene fidelity and precision.
I have touched and corrected (so in elbow...) this "very scientifically design" which deliver a extremely poor soundscene and a mediocre sound quality, and the results was/are only excellent.
This is a good example that not all the time the theoretical approaches it fit perfect with the human perception of the sounds and music.
This so sophisticated design is not to be found as recommendation in the DAC chip datasheet itself.
I may give you many examples about design faults in this player, but I`m not interest to make it publicly, as I correct it (so in elbow...) in may mods. The results are only excellent so far...
I may wish you to feel happy with the right "poles" in your unmodified device...
P.S. BTW, Oppo itself gave up this I/V design in their HA1 DAC/headphone amp, and this it sounds a little better than the DAC approach in 105 models...
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Indeed, good point. Why should be different the I/V for multichannel board, than for stereo board? It is actually the same DAC chip, the same I/V opamps, and it should be the same processing quality both cases...
I just wonder, if I can make R30 and R33 equal to have "less than 10mV".
It is 1,26V there now.
It is 1,26V there now.
You should do so to have the lowest possible offset level before the AC coupling caps (nearest to 0,000v).
As I remember, it should not be a such high DC level on outputs... It can be something wrong somewhere... Is quite long time ago I have been involved in these details. Now I just don`t care about what is there, but I remove all the necessary components and mount in place my modules...
Original design it have an offset control circuit for these opamps. This circuit (copy/paste from the ES9018 datasheet) is meant to balance the output DC offset for a optimal value, but because production and components tolerances, the offset is not all the time the same for every single device. This was the reason Oppo chosen the AC coupling caps on outputs for 105/105D models. In my opinion this offset control circuit, which it is centred on a DC value, but not a more safe and stable ground, is one of the designs issues here.
I may suggest first to try to adjust the offset using that global control circuit, and observe if the DC levels it react at your adjustments. If no reaction, then is something wrong somewhere... You may measure first all the outputs on the stereo board to have an idea about the overall situation. Then try to do something to lower the offset or find out what it may be wrong in this area. You can for sure experiment with another values for that resistors, and then even ground the appropriate opamps pins to have a stable input value for the offset control.
As I remember, it should not be a such high DC level on outputs... It can be something wrong somewhere... Is quite long time ago I have been involved in these details. Now I just don`t care about what is there, but I remove all the necessary components and mount in place my modules...
Original design it have an offset control circuit for these opamps. This circuit (copy/paste from the ES9018 datasheet) is meant to balance the output DC offset for a optimal value, but because production and components tolerances, the offset is not all the time the same for every single device. This was the reason Oppo chosen the AC coupling caps on outputs for 105/105D models. In my opinion this offset control circuit, which it is centred on a DC value, but not a more safe and stable ground, is one of the designs issues here.
I may suggest first to try to adjust the offset using that global control circuit, and observe if the DC levels it react at your adjustments. If no reaction, then is something wrong somewhere... You may measure first all the outputs on the stereo board to have an idea about the overall situation. Then try to do something to lower the offset or find out what it may be wrong in this area. You can for sure experiment with another values for that resistors, and then even ground the appropriate opamps pins to have a stable input value for the offset control.
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There is no Offset circuit on that scheme. How it can be found on the stereo-board? How it can be adjusted?
There are some opamps pins which goes to "OFFSET" somewhere... They did not designed down all the details of course, to minimise the disclosing of their "secrets"... There may be for sure a sheet which it may shows the offset mechanism, but that sheet it was not leaked out (yet...).
So, if you may follow the traces on the board (hopefully there are very few inside traces in this model design), then you will find out quite much about how it works that offset circuit and how it may be adjusted. Mainly that offset pins are tied to a DC level, which is possible to adjust it somehow.
As I pointed out previously, the best is to dismiss that offset circuit and connect the offset pins to ground. Then try to adjust the offset on the outputs, having already a very stable input/reference for the offset input pins.
There is a lot of work to find out what is not on the schematics, but the positive aspect in all this is that you may learn quite much about the device. And even more, you will find out about lot of another design faults...
So, if you may follow the traces on the board (hopefully there are very few inside traces in this model design), then you will find out quite much about how it works that offset circuit and how it may be adjusted. Mainly that offset pins are tied to a DC level, which is possible to adjust it somehow.
As I pointed out previously, the best is to dismiss that offset circuit and connect the offset pins to ground. Then try to adjust the offset on the outputs, having already a very stable input/reference for the offset input pins.
There is a lot of work to find out what is not on the schematics, but the positive aspect in all this is that you may learn quite much about the device. And even more, you will find out about lot of another design faults...
Coris, you said in an earlier post that you did not understand why these two resistors had different values.
Subsequently, I explained to you and others why this set up makes perfect sense and should not be changed
Therefore, what I wrote is not an opinion, but a factual statement, based on understanding how these circuits work. When you subsequently try to ridicule this explanation, perhaps because it flies over your head, well, that triggers a desire for action in me.
By your not-understanding this simple design feature, you demonstrate a fundamental lack of understanding. This while you try to present yourself as an authority in the field. Quod non. You are trying to sell ill thought out stuff to the gullible.
This is made obvious because of what follows in your response. It is just a sales pitch for the wares you peddle, lacking any verifyable fact. Mere humbug about sound stage and what have you.
I want to warn the readers on this site against people like you. You have a financial interest. Therefore, I think your utterings should be moved to the vendors forum. That way, it will be obvious to all that you are trying to make a buck. Nothing wrong with that per se, but it has at least to be clear that you are doing so. I therefore call on the moderating team to move this thread to the vendors forum.
Coris makes deep research on the subject. And his experience is very useful for us. It doesn't matter, whether some of his ideasn are right or no, if you are able to check it yourself.
The main goal is that he shows a possible way. And for sure he can have some know-how, that he doesn't want to open in commercial purposes. I don't think he'll intensionally distort the results of his research.
Well, I shouldn`t answer to you this time, but I would like to make some corrections to your speech:
First, I meant is your opinion about your expression "sit on elbow" (referring to my meaning), but not regarding to your explanation about that resistors. I do not ridicule it, at all, but I answered with my opinion that not all the time what is made by the book (that design) it may fit the real world. And if you may appreciate that a "pole" correct circuit it may sounds better, then be happy so, and that`s all.
Second, I do not sell anything through this thread. I`ve made my mods, and I presented here for other knowledge and inspiration. I do not advertise for one or another solutions presented here, but I sustain my approaches. I suppose everybody should be free to do so, here and there.
I do not have any financial interests in this thread, as you malicious pretend, to sustain your interventions to the moderator team. This is only your (and single so far) opinion and assertion.
Actually I may guess your intentions, and work, to shut down this thread/discussion which it may not be very comfortable to this Oppo manufacturer. As nothing in this world is perfect, this device is a part of this world too, and it should not be a crime to modify it so as one may want and presnt it here his results (which it may be better or worse). So it is, and one or another should accept the rules of the game, without such reactions.
Your vehemently (quite OT) post is only regrettable (my opinion...).
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Did you really have to say that? We need to reduce the aggro level on diyaudio.com
vacuphile may I ask what it may be in your opinion the stages in this player which it may be, or it need to be moded/tweaked? As I understood, your appreciation is that the stereo stage is perfect as it is.
I think that the Oppo 105 is well engineered and that the full potential of the parts being used is being realized. Earlier in this thread I pointed to some independent measurements which confirm this.
Lacking engineering wherewithal and adequate measuring capabilities, you cannot realize any improvements whatsoever.
Because you hinted at that earlier, let me make very clear that I have no connection to Oppo. I even don't know what country they are located. But their product speaks for itself.
Stereo image is a red herring.
