In the basic mod to the Oppo 105 I removed most of the output stage and with all the remaining parts state of the art and a WA quantum sticker on the op amp I was getting some very, very good sound. However, an op amp is still and op amp.....so, I knew there was more to be revealed. After experimenting with various discrete output stages the last few weeks the most simple one wins. I am using just one J-fet as a follower and using my discrete cascoded current sourced shunt regulators to power them. Simply way more real and palpable. More space, greater air, more separation of instruments, more depth, more dynamics, more inner detail, much more palpable, much more real. The only downside to this buffer is that it only puts out 1 volt RMS per phase. If you are using a preamp then you have no problem. If you are using the Oppo directly to an amp or using a passive preamp then you might not have enough gain. The new output stage/power supply is $200 for unbalanced only or $300 for both balanced outs and unbalanced outs (this is in addition to the basic mod price).
Most every DAC under $4000 that uses the ESS DAC chip is using two op amps in series on the output. This would include the Benchmark, Mytek, Exasound, Auralic, Eastern Electric and X-sabre DACs. Burson is using a discrete output stage but it is a very complicated compared to what I am doing. The Wyred for Sound DAC is suppose to be discrete....but since you cannot see the circuit it is hard to know what they are doing. I tried the Dexa discrete op amp (some people use these as an upgrade to the opamps in the Eastern Electric DAC) but it does not have the magic and space of a serious discrete circuit. Because of this I am going to be modding all of the above DACs with my super buffer output stage. Stay tuned. As good as the stock Exasound or Auralic is......imagine it with just one J-fet on the output! DACs that use the Burr-Brown or Analog Devices DACs cannot use this buffer....they need an I-V converter (the ESS DAC is the only DAC chip that I know that has both current and voltage out). However, DACs that use Cirrus, Wolfson or AKM DACs can use this buffer.....so those DACs and players could have this super simple, super transparent output stage.
So, what is the problem with opamps? Nothing inherently. Just the implementation. The audio design engineers at Burr-Brown, National Semi, Analog Devices, THAT, etc. are not audiophiles. They do not know what "sounds good". They design for specs....especially low closed loop distortion measurements. But closed loop distortion measurements have very little to do with sound quality. The only way to get those .0001 percent distortion figures is to make the amplifier have at least 100db of open loop gain and feedback most, if not all of it. The open loop bandwidth of most audio op amps is less than 100hz. So the only way you can use it is with a ton of feedback.....a ton of feedback means a ton of information out of phase with the original signal. This is not good for sound. The best discrete op amps (even good ones like the Burson and Dexa) have very little open loop gain and very high open loop bandwidth....not to mention much higher biasing of the transistors and no current limiters or reverse diodes, etc. for protection. Low feedback or zero feedback designs generally sound much more real. Op amps squash the soundstage and squash the harmonic envelope so things sound slightly dry, two dimensional and compressed......all of them sound somewhat this way. I have listened to at least 20 opamps over the years and they all are just slightly different flavors....some have more detail, for sure. Some have lower distortion, for sure. Some image better than others, for sure. None of them sounds as good as a discrete stage....none of them. Your standard Burson and Dexa discrete opamps sound better. And they are not the best things out there. The advantage of an integrated circuit is that the diodes, transistors and resistors are incredibly small and so are the traces inside. This kind of low inductance implementation if done right would be world class. However, this is not what we have. So, the sonic perfectionist must look to discrete transistor or tube or hybrid circuits to really deliver the palpable realism we all seek. However, since discrete circuits use separate resistors and transistors and have parts large enough to vibrate.....much care must be taken. One wrong brand of resistor (yes, they all sound different) or one vibrating undamped long bare wire and your discrete stage might not sound as good as an opamp. But carefully done discrete stages are simply more real sounding. Most all recordings are done these days using ADCs that have op amps on the input. Imagine how much better the music would be if all ADCs and DACs had discrete audio stages. The Behringer DCX24/96 is simply incredible once you update the analog stages.....stock it is veiled. As far as I know there is not one all out state of the art preamp or amp that uses opamps.....none....for good reason. There are a couple of excellent preamps by Rowland and Levinson that use opamps.....but I would not call them state of the art.
Check out the mod page for more details: http://www.tweakaudio.com/EVS-2/Oppo_105_Mods.html
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