Review and Measurements of Topping DX3Pro DAC and Headphone Amp

[finneybear]

Which OpAmp swap stops the thread from being overrun with hyperactive weirdoes who make 8 consecutive uninterrupted posts of solipsistic blather in a single hour?

I stopped by here once a day or sometimes once a few days. Is posting all replies in one shot a big problem to you?

 

[finneybear]

Very interesting, also a very clean work. I wonder if you could "inject" a 20KHz square wave somewhere at the input of the LPF and measure the output at the RCA plugs with a scope (of course, repeating the test with 10KHz might be even better). It could be helpful to see both IN and OUT traces in overlay and see the attenuation and phase delay/shift. Of course, before vs. after measurements would be nice to compare.

Funny thing, I usually notice that increasing amplifier's bandwidth might help me in getting more micro-details and cleaner sound, not vice-versa. It's odd that you find the sound better now, with a lower bandwidth, so the above "square wave generator & scope" test might help in determining the actual reason (if any). Usually manufacturers are limiting the bandwidth just to be sure that their devices will not oscillate, especially opamp-swappable equipment, so increasing bandwidth sometimes might help.

The design goal of LPF is different. It's actually to make square wave less squarish. Topping engineers chose standard X4 sampling frequency, around 178KHz, as the roll off point. 4493's datasheet suggests any FC point from 120K to 170K is good. For DSD, 4493 even has a LPF inserted internally with FC at 50K. All those 130KHz, 178KHz, are way above what human ears can hear. LPF's job is to remove those ultrasonic noises effectively. 178KHz is a bit too high, and OPA1612 is a bit top happy, I lowered it a bit to follow datasheet's suggestion.

 

[finneybear]

Just got in touch with the company's validation lab which has a few APx525. I think I will just have them to do a test on DX3. This is more convenient to me.

 

[simonchretien]

My fixed DX3 has been running non-stop for 4 days now. Solid stable.

Doesnt mean much, mine shuts down every 1 or 2 weeks, running non stop or not. Been doing that since december.

 

[pejakovic1]

Since the Auto Off feature isn't working at all, or just works randomly, maybe this feature is what actually makes the units shutdown randomly. And the complete failure of units is unrelated to that.

 

[amirm]

Just reporting that the unit Yue sent me has been solid as a rock. Also that I have been communicating with Topping and they have broken units and are marking progress on what is wrong with them.

 

[vincent_emerald]

Just reporting that the unit Yue sent me has been solid as a rock. Also that I have been communicating with Topping and they have broken units and are marking progress on what is wrong with them.

Hope we hear from them sooner on what went wrong. OR if they prefer to disclose, which they would not ...

 

[trl]

The design goal of LPF is different. It's actually to make square wave less squarish. [...]

Rounding-up the corners of the square-waves will make the sound a bit "warmish" and after 16KHz trebles will start to roll-off a bit. I think that reducing the LPF cut-off might affect sound-neutrality of this audio equipment.

However, if there's a way for you to post some measurements before vs. after the modding (or at least after the modding) it would be awesome, for a better understanding of the sound change, just in case some of us might think to do this modd or not. Thank you!

 

[777]

Here is my mod for those who do not need the headphone amplifier.

 

[Yuno]

Since the Auto Off feature isn't working at all, or just works randomly, maybe this feature is what actually makes the units shutdown randomly. And the complete failure of units is unrelated to that.

Auto off works perfectly for me.

 

[777]

Here is my mod for those who do not need the headphone amplifier.

R2 must to be removed because after it there is a resistor=10kohm to the ground (input impedance of the OPA2140). So, the biggest problem is the network around OPA1612. The resistors are too small and the output current it is not enough or maybe trigger the current limiter circuit.

Some words from the OPA1642 datasheet : "The output current of the OPA164x series is limited by internal circuitry to 36 mA and –30 mA (sourcing and sinking), to protect the device if the output is accidentally shorted. This short-circuit current depends on temperature; see Figure 26. Although uncommon for most modern audio applications to require 600-Ω load drive capability, many audio operational amplifier applications continue to specify the total harmonic distortion (THD+N) at 600-Ω load for comparative purposes. Figure 7 and Figure 8 provide typical THD+N measurement curves for the OPA164x series, where the output drives a 3-VRMS signal into a 600-Ω load. However, correct device operation cannot be ensured when driving 600-Ω loads at full supply. Depending on supply voltage and temperature, this operating condition can possibly trigger the output current limit circuitry of the device. "

If retention of the OPA1612 is desired, then R3=R4=4.7kohm , R5=R6=R7=R8=6.8kohm , C1=C2=220pF (NPO, COG) and obvious, remove R2. If you want headphone amp too, the input resistance to the ground of the OPA2140 can rise up, over 20k...30kohm.

 

[trl]

Here is my mod for those who do not need the headphone amplifier.

I am a bit confused, so basically you bypassed the 2nd opamp that probably goes into the output buffer, right?
It's difficult for me to understand it without having the DX3PRO in fornt of me, sorry...

 

[777]

I am a bit confused, so basically you bypassed the 2nd opamp that probably goes into the output buffer, right?
It's difficult for me to understand it without having the DX3PRO in fornt of me, sorry...

OPA2140 is the op-amp from the headphone amplifier. It pick-up the signal from the output of the OPA1612 through two resistors of 100 ohm each in series. At the (+)input of the OPA2140 there is another resistor (10kohm) to the ground.

 

[Dmytro]

Hi @TP-Wong,

I've also faced an issue with DX3PRO stuck in permanent standby after 10 minutes of listening to music on new device. The symptoms are the same as shown by @david99 in video.

My device has serial number 1808593066 and headphones are Hifiman Sundara with impedance 37 Om. Device came with firmware v.1.03 and was successfully updated to v.1.04. DX3PRO was with music turned off when 'pop' sound came out from headphones and device went into permanent standby mode.

Should I open a dispute and return DAC to seller (HIFI College Store shop on AliExpress) or should I send it to Topping directly? How can I avoid paying shipping cost, as it's a large amount to send from Europe to China?

 

[noobie]

As I have mentioned, it is a good idea for Amir to do the measurements for a consistent result, not that I do not have AP to do test. And I can predict the result will be pretty much aligned with what other people have got - much less noise spikes, etc. I plan to swap the XO for lower phase noise ones though.

My fixed DX3 has been running non-stop for 4 days now. Solid stable.

Sorry, I am a little confused by your reply. Are you willing to ship your modified unit to @amirm ?

 

[pacman]

https://www.aliexpress.com/item/TOP...io-Decoder-XMOS-XU208-AK4493/32956563439.html

 

[Wolven]

My DX3pro has now turned itself 4 times. I contacted the company two weeks ago but no response.
So, what have they fixed with the 2019 version?

 

[bellyofthebizd]

https://www.aliexpress.com/item/TOP...io-Decoder-XMOS-XU208-AK4493/32956563439.html

might be just marketing bl

 

[amirm]

might be just marketing bl

Yeh, these vendors jump the gun all the time....

 

[noobie]

There does not appear to be any notes on the Topping website that there is a new model of DX3Pro...