How Good is ES9018 in Voltage Mode?
I have been using my BII DAC in voltage mode since day one (that is no output stage, the output of the DAC is connected straight to UCD-180HG amplifier modules).
JACQUES HIFI PAGES has a a comparison of the Sabre32-based Buffalo II DAC used in voltage mode compared with AKM AK4397-based Xindak DAC. The reading is at least entertaining…(note: I have edited some of the content I pulled from the website for clarity):
I eventually could buy two 32bit dacs which are scarce , expensive and hard to locate…
I don’t think you need presentation for the 2nd (DAC) one which is the famous Twisted Pair Audio Buffalo II featuring the not-less-famous ESS Sabre 9018 “where-are-you” dac.
This chip seems to be the hardest to locate on the planet and I really can’t understand why. Usually , once a chip is invented, it costs nothing to make a million of them, as it is just a photocopy on carbon wafers. But in this case, it is just like somebody makes them one by one in a small workshop. For example, the Oppo DVD players which supposedly use this chip are always discontinued or not yet available (out of stock?). And Twisted Pair Audio is constantly putting people on waiting lists, while other DACs are available by kilos. Great mystery.
The other one is a masterpiece crafted by small chinese hifi factory Xindak for their 20th anniversary. Quite expensive but made on very high standard as you will see. Let’s start the fight !
THE XINDAK 20TH ANNIVERSARY DAC
This monster cannot sound bad and I really enjoyed it from the 1st minute, with its always musical silky precision.
THE BUFFALO II DAC
In comparison the Buffalo really looks like nothing: a small circuit just like the 25$ generic dac kit from China. It seems well implemented and it has no output section so you hear what comes out from the DAC—(the DAC is) not visible on the picture; it is under the improved analog supply (the AVCC board) according to Twisted pair.
They say the DAC is I (current) out but works great like this….nothing like the classic I-out DACs like the TDA1541 where there’s not sound at all with direct output.
Here is a better photo of the PS used for the Buffalo II setup:
Note the following:
- SPDIF input
- Sabre32 is operating in voltage-out mode
- Only half of the output is used (“single ended” output connection: + and GND): internally, the Sabre32 has 8 pairs balanced dacs (16 dacs in total), each pair provides the in-phase and the anti-phase output. Only taking the in-phase output means that only half of the DACs are being used.
- Based on the photos, the PS is very likely based on run-of-the-mill 78XX linear regulators.
Well I’m sorry to say the Buffalo II DAC beats the Xindak DAC. Sorry because it cost me more money. The Sabre32 DAC circuit does not feature up-sampling but straight out of an old Philips player (with CDM 4/19 of course, you should know my drive taste by now) it really brings CD sound to something I have never heard before.
Of course the Xindak sounds great, silky, analytic but the Sabre, plugged crudely from its output to my amp, is 10 times more analytic… and it was really what I looked for.
2 years in searching a super-precise source for my super-precise Elipson 4140 speakers and it’s done at last. Funny how 40 years separate those speakers with their electronic companion.
Sorry again because to improve my system I should buy another pair of big 70’s Elipson monsters. And again because those buffaloes are as hard to buy as a real buffalo from USA….
The fact that the Buffalo II DAC is not only used in voltage-out mode but it is “crudely” connected to the amp as the reviewer said, says a lot about the capability of the Sabre32 DAC even in voltage mode
According to the Sabre white paper:
The highest performance in terms of THD is via the current mode, but both voltage and current mode provide about the same DNR.
- DNR better than -132 in both voltage and current output modes
- THD: -108db in voltage output mode, -120db in current output mode
THD in the Stereo current mode is limited by the external components and measurement equipment. We recommend using an extremely good op-amp for the highest performance but even an excellent op-amp is the limiting factor in the THD.
Like I mentioned, I’ve been using the DAC in voltage mode since day 1 basically for several reasons:
- Don’t feel I am missing anything. Have been impressed at the clarity of presentation that this DAC provides. (I guess you don’t miss what you don’t know?)
- Lack of motivation (lazyness? :-)) to build-up my Legato 3.1 kit which is still in the box.
- The fact that an output stage has the additional requirements of a bulky bipolar PS and transformer also adds to that “lack of motivation”
- Simplicity of a direct connection from DAC to amp. The “nothing in between” concept sounds really appealing
- And now, in an A/B comparison the Sabre32 DAC in voltage mode beats a very capable DAC
Further, I am still not convinced if an output stage is a “step up” or just a “side step”.
First, the two output stages offered by TPA have their own pluses and minuses. Between the IVY and the Legato, the Legato output stage seems the favorite with respect to sonics. However, the Legato differential input is unlike that of a differential opamp (of the IVY) where there is rejection of common mode noise. According to Russ [post 602]
Legato is simply an I/V stage (actually 2 pair of independent non-inverting I/V stages) output is essentially the same as the input just converted from current to voltage. Pretty much exactly what you would get with a plain resistor at the output pins to GND – only the output of the DAC does not modulate to the same degree because of the low impedance. As with the simple resistor it will come down to the output levels/value matching. If there is a slight mismatch there will be some differential error given a common mode signal. So essentially any common mode signal is still there at the balanced outputs. But that’s what’s wonderful about balanced signals, it does not matter in the least. On IVY-III the output common mode is dictated in large part by the device. That is why it is not a straight up comparison…
One nice thing is because most of the common mode noise on the ES9018 is extremely high frequency (far above audible) the passive filters actually get rid of almost all of it before it can really come into play. So practically the “CMRR” (if you want to call it that) is superb. That’s why its important to have those low pass filters. Even if there is a small error between the balanced halves those very high frequencies in play would have been filtered out.
Second, the THD of the entire audio chain is determined by the THD of the amplifier. According to the specifications of the UCD180HG the best number for THD is 0.008% which translates to -82dB. Better THD measurements at the DAC stage may or may not translate into any perceivable difference after the amp. In addition, the UCD amp is very easy to drive due to its high input impedance.
Third, the very capable Wolfson WM8741 DAC and the PCM1792A, both top of the line from their respective companies, have THD specifications of -100 db. The ESS DAC already beats them by -8 db in voltage mode.
And fourth, I can expect even better performance that the DAC in the review because of the configuration I am using:
- I2S input with lower DPLL bandwidth setting
- Full balanced connection to the amp
- Digital volume control
- Placid shunt regulator powering the DAC
So, as a whole, is there any more real improvement to be had by running the DAC in current mode?