eziitis
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- Mar 5, 2019
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I am afraid changing capacitor value will not be big help here...Yep, the 100uf value used in DX3 is bad, too. 4493 is suffering with all the ripples.
I am afraid changing capacitor value will not be big help here...Yep, the 100uf value used in DX3 is bad, too. 4493 is suffering with all the ripples.
kind of OT, but it would be very helpful if Topping would provide schematics. such a request is not so silly as it may sound. for instance Khadas tone board has all schematics public, and I can say from the point of EE they have done very good job. yes there is a switcher for opamp power as well, but it is not so critical, because opamps have high PSRR. another matter is impedance of course .... nevertheless the critical AVCC comes from a dedicated reg and is pretty clean in fact.
What is not certain is if all of this is oversight or part of the market plan - given the number of people who have complained about issues I'm inclined to think it's a bit of both.
the PSRR is very poor once you enter switching frequency
good points indeed unfortunately sending mod unit elsewhere for measurements is absolutely impractical for me.
so if the thread is about measurements, and the DAC performance as it is in original state has been measured in very beginning, what more we can measure?
in order to come up with sensible mods one should identify critical points, and at the moment it appears VREF to me. so I am putting back those
TPS54331 switchers, what I prematurely removed in favour to linear PS and will try to measure what noise we have on +5VL/R test points. I would say first one should look for presence of switching frequency and signal frequency. upon the extent of contamination one can decide whether and how things could be changed. anyone with a decent scope willing to join this measurement?
kind of OT, but it would be very helpful if Topping would provide schematics. such a request is not so silly as it may sound. for instance Khadas tone board has all schematics public, and I can say from the point of EE they have done very good job. yes there is a switcher for opamp power as well, but it is not so critical, because opamps have high PSRR. another matter is impedance of course .... nevertheless the critical AVCC comes from a dedicated reg and is pretty clean in fact.
... What is not certain is if all of this is oversight or part of the market plan - given the number of people who have complained about issues I'm inclined to think it's a bit of both.
It is not the amount of THD, it is the shape of the curve. After signal going through the cap, the distortion amplitude changes among different frequencies. The impedance curve is another important factor, too. Then after the cap, if the signal gets amplification, the THD will go up again. This THD is just a component of the signal chain, not the final THD number of the whole circuit. From the curve we can see coupling cap would degrade the low frequency signal quality more. How serious the problem is, all depends on what's at the next stage. If the cap is for the final output, things may be OK. But as the output coupling cap for DX3's 4493 output, it can be a problem.
The mod is mainly to fix some poor engineering decisions in DX3, not to lower noise floor or to reduce distortion, etc.
The linear supply will certainly improve the DX3.
@eziitis no doubt the original unit has been measured by @amirm quite extensively. I also don’t doubt that some on this thread have the means and possibly backing from others to do testing. But as the thread and the whole forum are founded on @amirm measurements, would be appropriate protocol to have confirmatory measurement done by him on improved units...
As I am not aware of your situation I don’t know what complexities are involved in you or others shipping a modified unit to @amirm. However, if it is cost, I and maybe others might volunteer to donate some of the funds necessary to get units shipped if it is not too exorbitant.
In all I note that there are two flavors to issues - improvements to the performance of the unit (what I am referring to) and reliability of the unit. The improvements are subject to relatively rigorous analysis (you, @finneybear, @amirm and others can drink some beer/wine and debate what measurements to do).
The reliability... I am afraid most of what has been discussed on this thread falls into the category of anecdotal evidence. It would be fantastic if Topping were to give us a failure rate number, but I can understand the corporate mindset and realize they are probably not likely to (they are a for-profit enterprise with competitors, after all). Earlier in this modern rendition of “War and Peace” a Topping rep commented that there were no failures returned to them, but I am sure with more units sold and more time they now have some and can calculate their failure rate. But we probably won’t hear a number. If a Topping rep is reading this, maybe they would be willing to tell us if the DX3PRO failure rate is higher, equal, or lower to other units they sell (though cost differences likely skew that).
And my own little unit keeps on chugging along...
Finally done with the LPF. Use only one set of outputs for each 4493:
View attachment 22915
[...]
The FC point is now around 130KHz, down from 178KHz.
[...]
The paper is quite vague on detail as I noted but you can read it from the link provided. My sense was that speakers were used to generate noise or something like it.Was the test done while knocking on the ceramic caps? If not, then I think the test is valid as piezoelectric effect clearly exist.
@eziitis no doubt the original unit has been measured by @amirm quite extensively. I also don’t doubt that some on this thread have the means and possibly backing from others to do testing. But as the thread and the whole forum are founded on @amirm measurements, would be appropriate protocol to have confirmatory measurement done by him on improved units...
What problem? THD+N is -106 dB. 2nd harmonic distortion is at -110 dB.
sorry, what kind of HF signals we are talking about in an audio application? I would kindly ask to stop confusing people knowing even less that use of DIP8 opamp package in an audio application is a major design fault. just opposite, it may have even some benefits as it allows more solid power traces.
I am afraid changing capacitor value will not be big help here...
But are you talking about lowering the final amount of harmonic distortion?
Because earlier you wrote:
And I'm getting seriously confused