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Review and Measurements of Topping DX3Pro DAC and Headphone Amp

david99

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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.
 

nebula

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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.
 

Klenfo

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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

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

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.
 

yue

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I plug and unplug my headphones often and that has not had any impact.
Topping already has two fully broken units shipped back. Let's see what they will find.

They sell a lot of units in China too but none of the Chinese customers experience this issue.
 
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mikehoopes

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How to you measure whether the output voltage is fluctuating? I measured the PS that came with mine and it was 15.1 every time. Forgive the noob question, but would that voltage output change when plugged into the device?
My wall wart isn't easily accessible right now. I think people have been saying it's rated for 110-220 Vac, so that would mean that it's regulated.

What instrumented tests, DX3 Pro with headphone-type load, have we done so far that focus on that much-maligned 15 VDC wall wart?
 

yue

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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.
I would say it's very unlikely. Topping's device code is 0X8877 and producing this sequence (0b1000100001110111) randomly via IR inference at the same frequency is already very hard. Not to say the sequence should be added before the actual button code and its inverse code.
From the youtube video people posted online it's unlikely that IR could be a cause --- most people are not able to turn it back on until a full power cycle. Other people has weird frequent USB connect/disconnect, while in normal situation the device should always be shown connected in computers, even when it's off.
 

Yuno

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most people are not able to turn it back on until a full power cycle
I don't really agree with this, from what I see a lot of the people seem to have the same kind of "harmless" issue that I do - simple shutdown that just requires to press power button. My only fear is that at some point this harmless issue will cause my dx3 to not power again.
 

yue

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I don't really agree with this, from what I see a lot of the people seem to have the same kind of "harmless" issue that I do - simple shutdown that just requires to press power button. My only fear is that at some point this harmless issue will cause my dx3 to not power again.
Different units have different behaviors.
 

chrisliuboy

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yue

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Hmm, I am little bit concern about this now, I keep my old dac running 24x7 for 5 years already and it's still working fine, I thought I will never hear a temperature related concern on any solid state amp.
depends on the design. a current over the critical level can break down the pn junction irreversibly.
If all solid state amp are as safe as you described, there's no need to add heat sink onto it. But most expensive "shiny" headphone amps do have heat sinks. class A headphone amps such as Oppo HA-1, generate huge amount of heat.

Good headphone amp design, on the contrary, does not produce noticeable heat at all. I have been using Objective 2 since when it was invented by nwavguy, and the opamps never generate any amount of heat noticeable by me at all throughout the years. I touch them with my fingers and they run cool even in hot summer.
 
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kotgnk

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Topping already has two fully broken units shipped back. Let's see what they will find.

They sell a lot of units in China too but none of the Chinese customers experience this issue.
I sent the same back to China. So, they already have three devices.
 

Yachary

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By the way, I find the reason of mine "burn in". My power amp has HPF switch on back side: off, 20 Hz, 40 Hz. And I don't pay attention for it, thinking bookshelves don't play below 40 Hz. But sometime switch it. Yesterday I switched it to 20 Hz and heard "unburn" sound. So, I'm not going crazy, but my amp want to)
 
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y845133y

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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.).
If the DX3-Pro circuit is same as Heres's an example of an extremely similar circuit. Maybe the diode was broken which is for controlling to turn off the BJT.
HP.png
 
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