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Review and Measurements of Topping DX3Pro DAC and Headphone Amp

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I had a set of Kanto Yumi speakers that did the same thing people are reporting about the dx3 powering off while in use. In my opinion the problem is with the auto shutdown feature when music is not detected. Either the signal is not strong enough for this feature to detect the music playing or it has gotten degraded or become damaged maybe from too strong of a signal.

Either way in my opinion this issue is the auto shutdown feature not functioning correctly.
 

Wolven

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First time I got random shutdown I was not using driver but had latest firmware. Other 2 times it happened I was using driver and latest firmware.
I had the unit turn off twice since late November, with new firmware. Both times in DAC mode. Last time while playing in Foobar, previous time cannot remember.
 
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Hey everyone. I wanted to share my findings in performing failure analysis on my failed DX3pro in the hope that others may find this information useful.

I purchased a DX3pro (SN 1812594045) from an eBay seller and have been using it primarily with Shure SRH1540 headphones (46 ohm) for the past month at work with the stock wall-wart PSU. I never unplugged the unit during this time, but let it automatically transition to and from standby based on whether or not an audio stream was being sent from my computer. Last week, I returned to my desk from a meeting to discover that it had suffered a failure similar to those others have been describing: the right channel of my headphones was producing only a hissing noise, and upon removing the headphone plug from the DX3pro's jack, there was a loud 'pop' and the DX3pro went into standby mode.

In the case of my particular unit, it appears the right channel of the headphone amplifier has failed and is outputting approximately -9.5V DC on the right channel of the headphone jack. The left channel appears to be operating normally. I traced the headphone amplifier circuit and it is a fairly straightforward op-amp based design with its output boosted by a single complementary BJT stage (2SB649/2SD669). Heres's an example of an extremely similar circuit: http://sound.whsites.net/project113.htm

On my unit, it appears the PNP transistor to the -10V rail on the right channel has failed with a short from collector to emitter, resulting in the DC level present at the headphone output. I don't have good root-cause on why this transistor failed, but I suspect either a design issue (such as excessive bias current resulting in excessive heat and consequent damage) or a part quality issue. I'll keep working on this tomorrow to see if I can identify any issues.

Also FWIW all other functions of my unit still appear to be working normally (user interface, entering/exiting standby, etc.).
 

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yue

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Hey everyone. I wanted to share my findings in performing failure analysis on my failed DX3pro in the hope that others may find this information useful.

I purchased a DX3pro (SN 1812594045) from an eBay seller and have been using it primarily with Shure SRH1540 headphones (46 ohm) for the past month at work with the stock wall-wart PSU. I never unplugged the unit during this time, but let it automatically transition to and from standby based on whether or not an audio stream was being sent from my computer. Last week, I returned to my desk from a meeting to discover that it had suffered a failure similar to those others have been describing: the right channel of my headphones was producing only a hissing noise, and upon removing the headphone plug from the DX3pro's jack, there was a loud 'pop' and the DX3pro went into standby mode.

In the case of my particular unit, it appears the right channel of the headphone amplifier has failed and is outputting approximately -9.5V DC on the right channel of the headphone jack. The left channel appears to be operating normally. I traced the headphone amplifier circuit and it is a fairly straightforward op-amp based design with its output boosted by a single complementary BJT stage (2SB649/2SD669). Heres's an example of an extremely similar circuit: http://sound.whsites.net/project113.htm

On my unit, it appears the PNP transistor to the -10V rail on the right channel has failed with a short from collector to emitter, resulting in the DC level present at the headphone output. I don't have good root-cause on why this transistor failed, but I suspect either a design issue (such as excessive bias current resulting in excessive heat and consequent damage) or a part quality issue. I'll keep working on this tomorrow to see if I can identify any issues.

Also FWIW all other functions of my unit still appear to be working normally (user interface, entering/exiting standby, etc.).
That's very interesting finding! Actually I found different units have different behaviors when failing:

- some units failed on the left channel rather than the right one you are experiencing. See https://www.audiosciencereview.com/...ac-and-headphone-amp.4967/page-73#post-132473

- some units automatically shut off without producing the hissing noise that you experienced, see https://www.audiosciencereview.com/...c-and-headphone-amp.4967/page-138#post-150264

- some units are not able to turn back on again, while you can still turn it back on. see https://www.audiosciencereview.com/...ac-and-headphone-amp.4967/page-67#post-128948

- some units such as @Toku's and mine, don't enter standby mode, they just stopped producing noise in the middle of a track. see https://www.audiosciencereview.com/forum/index.php?threads/dx3-pro-issues.6449/#post-143382

This is so mysterious!

For the first time we are able to get a fully dead unit not returned to the seller. You can contact @TP-Wong or <[email protected]> and he would be happy to investigate!


the right channel of my headphones was producing only a hissing noise, and upon removing the headphone plug from the DX3pro's jack, there was a loud 'pop' and the DX3pro went into standby mode.

did the pop come from the relay?

My assumption is that while you are unplugging the headphone, it creates a huge amount of current (because it's 10v dc, and there's short period of time that the headphone jack will create a short circuit when plugging/unplugging. and to make it worse, the output impedance of the device is super low.) That current essentially put the chip (very likely STM8 chip. xu208 is also possible) into shutoff mode.

Very likely the transistor was already broken by overcurrent when you heard the hiss noise. Topping intentionally use low output impedance design. I guess the elimination of the protection transistor makes it too easy to fail when using low impedance headphones.

@parkerlewis @haroharo @Stein @exaudio @david99 @Wolven quick question --- when your DX3 died, what headphone were you using? Are they low impedance headphones?
 
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yue

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In my opinion the problem is with the auto shutdown feature when music is not detected.
This is clearly not the case. Mine stop producing sound in the middle of a finale coda, which by no means it cannot detect the music.
Other people experienced the shutdown and are not able to turn it back on.
 
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That's very interesting finding! Actually I found different units have different behaviors when failing:

- some units failed on the left channel rather than the right one you are experiencing. See https://www.audiosciencereview.com/...ac-and-headphone-amp.4967/page-73#post-132473

- some units automatically shut off without producing the hissing noise that you experienced, see https://www.audiosciencereview.com/...c-and-headphone-amp.4967/page-138#post-150264

- some units are not able to turn back on again, while you can still turn it back on. see https://www.audiosciencereview.com/...ac-and-headphone-amp.4967/page-67#post-128948

- some units such as @Toku's and mine, don't enter standby mode, they just stopped producing noise in the middle of a track. see https://www.audiosciencereview.com/forum/index.php?threads/dx3-pro-issues.6449/#post-143382

This is so mysterious!

For the first time we are able to get a fully dead unit not returned to the seller. You can contact @TP-Wong or <[email protected]> and he would be happy to investigate!





did the pop come from the relay?

My assumption is that while you are unplugging the headphone, it creates a huge amount of current (because it's 10v dc, and there's short period of time that the headphone jack will create a short circuit when plugging/unplugging. and to make it worse, the output impedance of the device is super low.) That current essentially put the chip (very likely STM8 chip. xu208 is also possible) into shutoff mode.

Very likely the transistor was already broken by overcurrent when you heard the hiss noise. Topping intentionally use low output impedance design. I guess the elimination of the protection transistor makes it too easy to fail when using low impedance headphones.

@parkerlewis @haroharo @Stein @exaudio @david99 quick question --- when your DX3 died, what headphone were you using? Are they low impedance headphones?
Hi Yue,

I was using Bower Wilkins P5 S2 - 22 ohm adn planning using Bower Wilkins P9 also 22 ohm when I will buy new one. My question is. Is this DX3 PRO like dangerous for low impedance HP?

Thanks.
 

yue

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Is this DX3 PRO like dangerous for low impedance HP?
My suspicion is broken unit / random shutoff unit are caused by over current --- probably the circuit is not good enough to handle low impedance headphone + a zero output impedance. Seems most of you guys who have a dead unit use low impedance headphone, this further makes my assumption more likely to be true.
 
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My suspicion is broken unit / random shutoff unit are caused by over current --- probably the circuit is not good enough to handle low impedance headphone + a zero output impedance. Seems most of you guys who have a dead unit use low impedance headphone, this further makes my assumption more likely to be true.
Makes sense for me. So if it is true this means that for this to be fully remediated we need to wait for topping to come with redesign of DX3 PRO
 
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My assumption is that while you are unplugging the headphone, it creates a huge amount of current (because it's 10v dc, and there's short period of time that the headphone jack will create a short circuit when plugging/unplugging. and to make it worse, the output impedance of the device is super low.) That current essentially put the chip (very likely STM8 chip. xu208 is also possible) into shutoff mode.
Based on your assumption, I think it is at least good practice, although not a complete avoidance of issues, to power off the unit before plugging/unplugging the headphone.
 

Yuno

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Incidentally my unit just shut off for the 4th time now. Frequency about once per 3 weeks. So now I can fully agree that we can cross PSU from our list, as I was using Meanwell GS25A15-P1J (15V, 1.66A) since the beginning of this month. Also no other remotes in sight.
I guess one possibility is remote is faulty and sends signal to power off on it's own, but I would really doubt it. I'm connecting dx3 pro to APC ups, maybe that is a factor too, but frankly if anything this should be a positive since it regulates power somewhat (it's standard offline back-ups).
 

777

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Jan 1, 2019
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Hey everyone. I wanted to share my findings in performing failure analysis on my failed DX3pro in the hope that others may find this information useful.

I don't have good root-cause on why this transistor failed, but I suspect either a design issue (such as excessive bias current resulting in excessive heat and consequent damage) or a part quality issue. I'll keep working on this tomorrow to see if I can identify any issues.

Also FWIW all other functions of my unit still appear to be working normally (user interface, entering/exiting standby, etc.).
In my Dx3Pro the bias current it is 0.0075V/4.7ohm=1.6mA on each channel, left and right.
 
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Wow, I hope my unit is not the next to fail (using low impedance as well, Fidelio X2HR).
Had a few random shutdowns but they were a few weeks apart like the others here reported. Hasn't happened since I disabled the auto-standby and began powering the unit on and off via remote.
 
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Just I wrote yesterday - no self shutdown during last month of use of this device. Today it happened right during play youtube video.:D
 
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amirm

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@amirm,

Could we know ohm value of headphones you are using with your two units? Also were you using it already with low impedance ones?

Thanks.
My everyday headphone is AKG K92 with rate impedance of 32 ohm (use it because it is closed back to block equipment noise). It is very efficient though so I am down in -30 dB or lower for background listening.

I can certainly stress test the amp using lower impedance dummy loads.
 
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amirm

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Can you guys with shutdown put a piece of tape in front of IR sensor and see if it still shuts down? Some monitors emit IR that can cause the receiver to do things.
 
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amirm

amirm

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My suspicion is broken unit / random shutoff unit are caused by over current --- probably the circuit is not good enough to handle low impedance headphone + a zero output impedance. Seems most of you guys who have a dead unit use low impedance headphone, this further makes my assumption more likely to be true.
I plug and unplug my headphones often and that has not had any impact.
 
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