Topping DX3 Pro v1 và v2

TLDR:Is the DX3 Pro a bit underpowered for the Sundara? Will I gain anything significant by going for a different DAC AMP?

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So i'm pretty new to the 'better headphones' game and recently bought a Hifiman Sundara.

Plugging it into the back of my pc, It sounded better than the Sony MDR 7605 that I was using previously, but it didn't play very loud. I decided to look into buying a small DAC + AMP to sit on my desk, expecting a nice bump in audio quality too. [i prefer a 2 in 1, since there is a lot of stuff on my desk already]

I bought a Topping DX3 Pro, based on the raving review that Amir from audiosciencereview.com gave it. I only realized later that i have the v2, while the review was about the v1, which is supposedly measures a lot better.

I must say i'm a bit underwhelmed by the difference between the pc output and the topping dx3. It does play louder, but i need to crank it up quite a bit in order to do that [-20db at +9.0 gain settings, then play at 60% in windows]. Maybe the Realtek ALC1220 on my mainboard wasn't that bad to start with, but still, I expected a bit more.... fullness?

The bass on the MDR 7605 was quite prominent. The Sundara sounds a lot cleaner, but it feels a bit thin on bass to me. Worth noting: These are my first open backs.

So i was wondering, is the DX3 Pro a bit underpowered for the Sundara? Will I gain anything significant by going for a different DAC AMP?

So I got another DAC here at home - purchased through usual retail channels of course :-].

The Topping DX3 PRO [~US$220] is a device meant for those who want wired [S/PDIF TosLink, Coaxial, USB] as well as flexible Bluetooth 5.0 wireless input. There are 2 versions of the DX3 PRO out there - the earlier version reviewed/measured at Audio Science Review by Amir and the newer one which I have here with LDAC support [Sony-developed "high resolution" Bluetooth CODEC, also measured by WolfX-700] released in late 2019.

At some point, I figure it would be interesting to compare how the various Bluetooth codecs perform since this device can accept the lowest common denominator SBC, plus AAC, aptX, aptX-LL [Low Latency], aptX-HD, and LDAC audio - about as broad a range as I've seen among Bluetooth DACs [here's a good primer on these acronyms].

For today, let's examine the device's standard DAC performance and run it through my typical procedure with a few new measurement variants to see how it performs.
Here's a top view of the box with the antenna sticking up - notice the "Hi-Res Audio" stickers - one for the standard hi-res DAC, another for the aptX-HD and LDAC wireless hi-res.

It's a pretty nice solid metal box. Plastic remote with a good clicky feel to the buttons. Here's a picture of the remote with the rear of the DAC:

Notice that there are 2 S/PDIF coaxial, and 1 TosLink digital inputs. Regarding the remote, while light weight, the buttons are responsive. Right/left buttons to change input. The "M" button switches from 0/+9dB gain on the headphone amp. "FIR" for filter options. "M" for toggling auto-standby if not in use for a few minutes or no input signal.

A small switching 15V/1A wallwart power supply is included of course. Notice that it only has unbalanced RCA outputs at the rear with a 3.5mm headphone jack out front. I believe 3.5mm jacks are more convenient these days for most home users than 1/4" jacks although I do find 1/4" more robust if we're going to call this a "PRO" product. The output setting is quite flexible with choice of RCA +/- headphones active. Also, the RCA out can be set as direct line out or pre-amp mode with volume control which is a nice touch.

The DAC uses dual AKM "VelvetSound" AK4493 chips for conversion [spec of -113dB THD+N / 126dB DR]. XMOS XU208 USB controller to handle up to DSD512 [DSD256 DOP] and PCM 768kHz. Qualcomm CSR8675 Bluetooth chip to support the various audio codecs. Remember that Qualcomm purchased CSR, the makers of aptX back in 2015 so it makes sense that this chipset supports the range of aptX flavors. Headphone out amplification uses the TI TPA6120A2 [spec -112.5dB THD] with 0dB and +9dB gain settings available. The spec says up to 700mW into 32Ω load. Given the price, this is a capable DAC.

The older V1 model used the TI OPA2140 opamp to drive the headphones.

Similar to the Topping D10 previously measured, the manual comes with some measurements already printed for you - nice to see, audiophiles need not be phobic over numbers and charts :-]

Nice OLED display - easy to read volume control setting. Topping D10 on top.

As usual, let's start with the "microscopic" tests. Right off the bat, we see that this DAC provides us with a number of digital filter options. To be honest, while it's nice to have choices, unless I'm purposely fooling around with stuff like the custom intermediate filtering, I'll listen with standard linear phase, steep filters. Typically these provide best flat frequency extension and the linear phase setting will not add phase shift/group delays in the time domain.

For the DX3 PRO, this means filter setting F-1 [labeled as just "F1" in my diagrams] would be my focus for the majority of these measurements and when listening. So with the DAC set at F-1, this is what a 1kHz 0dBFS sine wave and -3dBFS square waves look like off the rear RCA outs [connected by USB from Raspberry Pi 3 B+ running Volumio]:

As you can see, the output is a standard 2.1Vrms at 0dBFS. Channel balance is excellent with the 2 channels precisely overlaid in the sine waveform. For the square waves, as expected, with the filter set at linear phase, pre- and post-ringing are symmetrical. So, for filter F-1 setting, the impulse response looks like this:

Note that "absolute polarity" is maintained. Here's the "Digital Filter Composite" [DFC] consisting of an overlay of various signals that can help us understand the digital filter better in the frequency domain, based on discussions with Jürgen Reis. This is an extension of what Stereophile has been doing:

Looks great; for context, compare this to the AudioQuest Dragonflies. The filter is reasonably steep with minimal imaging artifact from the 19 & 20kHz tones or wideband white noise. Already we can see that IMD would be quite low. Furthermore, this filter has enough intersample overload protection to prevent anomalies with the 0dBFS white noise signal. Certainly an excellent performing digital filter among the DACs I've evaluated over the years. This is of course just filter F-1... The DAC provides 6 settings total, here are my descriptions rather than using the AKM or Topping language which can be a bit vague:

     F-1 = Linear Phase, Sharp Roll-Off

     F-2 = Linear Phase, Slow Roll-Off
     F-3 [Default] = Minimum Phase, Sharp Roll-Off
     F-4 = Minimum Phase, Slow Roll-Off
     F-5 = "Super Slow" Roll-Off - essentially non-oversampling
     F-6 = "Low Dispersion", "Short Delay" - Intermediate Phase I didn't bother testing them all with DFCs, but here are the impulse responses for F-2 to F-6:

For the most part, the filters are as per the descriptions. Of interest, the F-5 setting is useful if you want to listen for a NOS-like sound. I'm not even sure why they call it "Super Slow Roll-Off" - it's essentially unfiltered! And the F-6 "Low Dispersion" is an intermediate phase setting with moderate steepness. Since F-3 is the default and I assume many people will just listen with that setting, here's the DFC graph:

While the steep roll-off is the same as F-1 above, notice that it doesn't handle "intersample overs" as well and we can see this showing up with the 0dBFS wideband white noise signal.

As I said above, for those who love the sound of Non-Oversampling DACs, Audio Note's silly misnomered "1x oversampling", stair-stepped waveforms, or the "euphonic distortion" that this might bring with copious ultrasonic imaging/"aliasing" artifacts, check out setting F-5 and this "beauty" of a DFC graph and stair-stepped 1kHz sine wave:

The headphone output is indeed quite powerful. It's capable of pushing 4.6Vrms into a 30Ω load at the +9dB gain setting [filter setting F-1]:

So that's a good 700mW as per spec. The one disappointment however which the WolfX-700 measurement/review found was that the output impedance unfortunately is rather high:

That voltage drop from Open to a 30Ω load [1kHz sine] calculates out to an output impedance of 10.4Ω. The specs sheet rated the headphone output impedance as "