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Old 4th May 2013, 07:51 PM   #381
Coris is offline Coris  Norway
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Tested 105 DAC with 108Mhz clock. The main processor it still have its own 27Mhz oscillator. I do not have yet the divider by 4 to get the right clock out of 108Mhz oscillator.
It work just wonderful! No mater one or another will/still say, there is very obviously that higher clock frequency for ESS9018 it improve the quality of the sound dramatically.
The test it were made by only replacing the old oscillator with 108Mhz one. The clock circuitry have to be modded accordingly for best functioning. I did not yet, and used the Oppo`s design as it is for instance. I still have some random drop out, but out of those, the improvement in sound using this high frequency clock is huge. Specially in soundstage, details, separation and definition.
It seems that the differential circuit used to send out the clock to the multichannels DAC it have some problems with 108Mhz frequency, even though the chips used are specified for 200Mhz. It may be the imperfection of my testing setup, which it cause this... When will come the divider I will do it right this mod...
As a conclusion, everything point to 108Mhz clocking/dividing as the best way in this case.
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Old 5th May 2013, 09:24 PM   #382
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[QUOTE=Coris;3473787When about AC coupling reasons, I may say that I'm not (yet) satisfied with your possible explanation. If it were to have DC offset on unbalanced outputs (RCA), then it were reasonable to use AC coupling only on those outputs. This player is entirely AC coupled, even on balanced stage. So...
As one can notice, the unbalanced I/Vs on the RCA channels are symmetric designed (unbalanced I/V resistors), and have nothing to do with the phases (you show in your pic) coming from the DAC. We talk here about unbalanced output, but I think that the phases coming from the DAC differential outputs it may be symmetric and equal treated by the I/V converter. I still do not get the advantages of 50% unbalanced I/V conversion, which is reflected further in the summing/final opamp. There is a phase from DAC differential output which is 50% bigger level than another one after this I/V stage...

So, we may still finding the right explanation... It should be easier to have an answer from an Oppo designer here[/QUOTE]

FWIW: My best guess as to the Oppo designer's intentions here is that he might have deliberatly chosen differing resistors on the I/V op-amps so as to unballance the circuit, and lessen the second harmonic cancellation effects. He might have tried this to "sweeten" the sound slightly.
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Old 5th May 2013, 10:01 PM   #383
Coris is offline Coris  Norway
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I think your supposition it seems reasonable. It may be this a possible explanation, but...

As their design is, and how those channels are functioning (RCA channels), I appreciate that it may be enough difficult to be heard such delicate details of sweetness in sound on that output. In original design the soundstage is very poor, the definition is also low, and even the fidelity is not as high that a listener could hear it that sweetness or not in the resulting sound.
There is need of quite large modification to make the RCA channels and the DAC to sounds good...
In my analize of that circuit, I can see that one of the phases (out of the I/V converter) it have a double level comparing with another one coming from DAC differential output. The resulting AC signal it have the + or - part in it higher (unbalanced) than the opposite. This is about resulting AC signal after the output caps. Let`s not forget that the coupling caps isolate the DC from AC on that outputs. Or let pass only the AC out.
There is specified in datasheet of ESS9018 (and this is enough obvious in such differential design) that the signals out of the DAC it have to be treated symmetrical/identical, to benefit of the DAC specifications and design.
I really think that there is a really mess on that output, because this resistors unbalance in its I/V converter. And this it may be reflected in quite obvious poor soundstage on RCA.
So let`s waiting for more opinion on this subject before a conclusion...

Last edited by Coris; 5th May 2013 at 10:13 PM.
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Old 6th May 2013, 01:34 AM   #384
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Quote:
Originally Posted by Coris View Post
I think your supposition it seems reasonable. It may be this a possible explanation, but...
I have another theory, that it has to do with slew rate problems that are inherent to opamp/feedback I/V - I remember well nodding my head when Charlie Hansen of Ayre on the Hi-Rez Audioasylum forum fingered this as a major contributor to 'digital' sound and found myself saying "hear hear."

Also, using single phase means 780 Ohm output from the DAC and that in some say that they find single phase sounding better, BUT they all have something is common, they are using opamp/feedback I/V, or "virtual earth" rather than real earth. I can see what they, Oppo, are doing is helping to attenuate or reduce slew rate induce distortion, that is that less "heat" is seen by the opamp. At very high frequencies, the feedback simply cannot respond fast enough, they also have an internal comp cap that induces 90 degree phase angle that eventually erodes beyond 90 degrees causing even worse headroom at HF. Even well before it gets truly bad, it still starts to make things sound flat and grey, the colours gets bleached etc.

My suggestion is using this arrangement below - zero feedback. The gain block is actually based on a zero feedback Phono Stage sans RIAA EQ - the two resistors sum at around 6 Ohm, which just happens to be about the source impedance of a very fast Ortofon MC cartridge. This is no coincidence.

Cheers, Joe
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Last edited by Joe Rasmussen; 6th May 2013 at 01:43 AM.
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Old 6th May 2013, 08:38 AM   #385
Coris is offline Coris  Norway
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For instance I have this comments at Joe`s theory.

The LM4265 opamp slew rate is specified at 20V/µs. This slew rate is strong attenuated by the caps (original design) in the feedback (paralleled with the I/V resistor). The resulting slew rate at the I/V output it may be quite low anyway.

Although an gain of 250 in this stage it may (in my opinion) increase too much the noise... But I think to give it a try.
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Old 6th May 2013, 10:28 PM   #386
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Yes, noise can be a factor with gains like this. I had the first VSE modded Yamaha in the US here for more mods. The gain was set for 1Vrms. I could hear the hiss from the circuit at 6-7 feet away at listening level. I removed half of the resistors to ground and got 2VRMS. Then I could hear the noise at 3 feet from the speaker.....not too bad. The circuit I was using at the time in my Oppo with 2V out gave no hiss.....no noise.....at least 20db or better signal to noise than the VSE circuit. The AD844s used without feedback is very clever. Sound wise not to bad either.
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Old 9th May 2013, 01:32 AM   #387
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Quote:
Originally Posted by Ric Schultz View Post
Yes, noise can be a factor with gains like this. I had the first VSE modded Yamaha in the US here for more mods. The gain was set for 1Vrms. I could hear the hiss from the circuit at 6-7 feet away at listening level. I removed half of the resistors to ground and got 2VRMS. Then I could hear the noise at 3 feet from the speaker.....not too bad. The circuit I was using at the time in my Oppo with 2V out gave no hiss.....no noise.....at least 20db or better signal to noise than the VSE circuit. The AD844s used without feedback is very clever. Sound wise not to bad either.
Using 844's without feedback is a long way from clever and also doesn't
take full advantage of the DAC. The 844 has very low internal bias currents
which will basically make a nice euphonic distortion box when used open
loop.

In grounded base / virtual gnd configuration as per the other thread using
1704, the improvements gained via stacking 844's confirm my statement.
By stacking, you are effectively creating a virtual single chip of higher bias
current. I have spoken to Joe about this years ago suggesting a discrete
circuit to be a better option. The one advantage of 844 is it has very low
offset so can be set up direct coupled with some additional circuitry.

In non inverting mode, ie; voltage mode same applies, internal bias currents
will mean for a gain of x 250 there will be a lot of distortion. This will be all
low order so the euphonic thing will be in action.

Squeezing everything down to 2x3 ohms will result in a pretty big reduction
in dynamic range of the chip. Quick calcs estimate the chip will go from
>125 dB DR to around 90dB.

Does this matter is a big question - ATM the best replay I've heard is analog
tape, having all of 70dB DR (if you are lucky) and lot's of distortion - so I
suppose that's audio for you!

Z
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Old 9th May 2013, 02:09 AM   #388
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Quote:
Originally Posted by Coris View Post
Although an gain of 250 in this stage it may (in my opinion) increase too much the noise... But I think to give it a try.
Excuse me, but did I ever say that I use a gain of 250?

I am discussing a thought-experiment re a single (or per phase) and I already did mention the need to attend to noise.

Of course I am NOT suggesting a noisy solution. Wherever did that idea come from? Cheez...

C'mon - I wasn't born yesterday.

Anybody is welcome to come here and stick their heads right inside the cones of my rather efficient speakers !!!
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Last edited by Joe Rasmussen; 9th May 2013 at 02:13 AM.
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Old 9th May 2013, 03:40 AM   #389
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Yes, indeed. Your post above shows the circuit with X250 in it.

The original VSE circuit you used in the Sony and Yamaha players used 844s with no feedback (one per phase). I have the schematic here. It was noisey with the Burr-Brown DAC in the Yamaha. If you are using a different circuit that is less noisey than that circuit....it would be a good thing.

What I use is a single J-fet buffer (current sourced with another J-fet, you know the basic B1 direct coupled circuit...been around for years and years).....yes, I only get 1V RMS per phase but....oh my, the palpability is through the roof. Every part needs to be state of the art and using the best shunt regulators with no electrolytic caps on the output of the regulator. Super simple....super good. As long as you use a preamp, you are fine. Passive preamp use or directly to amp use may not have enough volume. Try it! Never heard better, including transformers, other discrete stages and the VSE 844 circuit.
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Old 9th May 2013, 04:03 AM   #390
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Ric

What you say has NOTHING to do with me. Unless I have that Yamaha player here I can make ZERO comment. So why are you AGAIN having a go at me - on the basis that a diagram shows "x250" which was not intended to be extrapolated into something you found in a Yamaha player I have NEVER seen.

I have never done a Yamaha in the way you describe. You are describing something seriously defective and ascribing it to me, who have not laid a hand or eye on it?

I am quite willing to be judged by what *I* do, in fact I am all the time.

It seems to me that YOU, Ric, are constantly trying to find an angle to have another go at me. Now I cannot even do a theoretical schematic (not an actual circuit), and once again you POUNCE !!! ???

IF you are trying to silence me? Then maybe that is working, so that I cannot freely express myself with the thought "oh oh, maybe I will get another slur from Ric?" - then I shall not have anything to do with this forum again.

That's all.

Too bad, because I do believe I have contributed something.

But I don't need this. I don't rely on this forum and is kept quite busy enough by people who appreciate what I do.

And not one has complained about noise? Where in the netherworld did that come from?
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