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.@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.
I plug and unplug my headphones often and that has not had any impact.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 can certainly stress test the amp using lower impedance dummy loads.
Topping already has two fully broken units shipped back. Let's see what they will find.I plug and unplug my headphones often and that has not had any impact.
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.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?
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.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 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.most people are not able to turn it back on until a full power cycle
Different units have different behaviors.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.
Hmm, I am little bit concern about this now, I kept my dac/amp 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.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
I plug and unplug my headphones often and that has not had any impact.
depends on the design. a current over the critical level can break down the pn junction irreversibly.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.
I sent the same back to China. So, they already have three devices.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.
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.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.).
I simulated the headphone circuit is normal work as below.
View attachment 22004
Output waveform:
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When the diode (DL2) is broken.
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The output waveform is Negative.
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