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Wanna discuss what's inside the DX1? I took some pictures!!!! (edit: and they're here now lol)

mike7877

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They're all on extreme angles and hyper zoomed so I could read the characters on the tiny chips wayyyy inside because I couldn't get the board to slide out without a special screwdriver. The pictures are too ugly and there are too many missed shots for me to pick through to find the few, least blurry gems. So you only get the results! edit: Voodooless wrote me a persuasive essay on why I should post pics, which basically boiled down to "pics or it didn't happen", so I did the work of loading a folder on my phone with tens of thousands of images in Windows Explorer so that I could let them all load first then scroll to the bottom and copy the last ~100 to my desktop to search through them, resize, thencut the relevant parts out to make an ugly collage (in post 3) so my thread wasn't all for nothing! /edit


The AK4493S looks to be an AK4493S!

And surprise, surprise, there are a total of three (3) op-amps! ! !
Two are by the headphone jacks, and one is between the AK4493S and RCA jacks.

The op-amps are some little known (to me anyway) Chinese options. They're spec'd pretty well from the single datasheet I was able to find,

32 ohm headphones: -114dB THD+n
High impedance out @ 3.16V RMS: -116dB THD+n

1697971644390.png


Topping measures and specs their stuff properly as far as I've been able to compare. 0.0002% THD or -114dB is given for both 300 ohm headphones and RCA outs. 0.0003% THD or -110dB is given for 32 ohm headphones.

I don't know how the op-amps are wired - if the 1/8" and 1/4" are in parallel and each op-amp is dedicated to one channel, or, if each jack gets its own op-amp for better separation with low impedance loads. Separation/isolation is given in the datasheet as -140dB, but that isn't with 32 ohms on the output (and this can make a difference, but I'm not sure in this case).

The op-amps are capable of 100mA continuous per channel, and since the 32 ohm 200mW at -110dB THD+n, and 280mW peak (-40dB THD+n) are 80mA / 94mW respectively, power handling doesn't seem like it has to be a reason.

Maybe there are two chips for the headphones to increase cooling! Maybe RT6863D needs to be heatsinked to put out 280mW x2 continuously at -110dB THD+n. At just 1.7mm x 1.5mm x 0.3mm, it can't weigh or dissipate much......

It wouldn't surprise me at all if heatsinking a single RT6863D in a way that it wouldn't become detached after 4 years of light use or a big bump, would cost more than buying two RT6863Ds and the extra ~12 SMDs the second op-amp required.

CTR makes the pot.

The power supply section (5V filter + boosting and whatever) is well designed. There's a good number of caps, coils, and smaller caps, resistors, as well as (what appear to be) a few transistors. There seems to be a better either filter + boost, or just filter on the 5V USB, and from there, there are really simple buck or boost converters right before the op-amps (3 identical). There isn't even an IC from what I can tell for the power sections right before the op-amps. This says to me that the active components were chosen very specifically, with the passive parts perfectly complimentary to maximally filter switching noise. No off-frequency noise from the PC PSU made it through the 5V USB filter/filter+boost (or whatever it is), so the final stage was able to be kept pretty simple (cap, coil, smaller caps, and some resistors probably for filter cap current limiting)

I'm going to put it back together now that I've solved the mystery!

DX1 - off-brand op-amps which are surprisingly excellent!
 
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mike7877

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I've been wondering a bit since I looked inside...
There are 5 switch-mode voltage regulators in there. Or at least 4 + an active filter of some kind...
This is all inside a sealed aluminum chassis...
With a DAC and op-amps also inside, mere centimeters away...

How the EFF is -114dB THD+n possible, especially with a -114dB THD+n DAC + -114dB THD+n op-amps?!?!

You'd think the best result would have to be -111dB, unless Topping got the DAC and the op-amps to perform 3dB better than their datasheets suggest, right next to all those fast-switching transistors!

And in a metal box, no less!

Is anyone else as amazed as me? Especially after looking at the voltage regulators. Yes, they're all together in the middle, but otherwise, they look like nothing too special, just a bunch of optimally sized capacitors and current limiting transistors and short traces and low current.

BUT...

they're mere centimeters away from the low noise parts, and really only use a few extra ceramic capacitors.

Not to downplay what Topping achieved for $100USD to the consumer at all, but literally every other manufacturer should be extremely embarrassed. I'm thinking this is class action territory for anyone who's spent more than $500 on a DAC since 2003.

No new physics has been learned or applied
No new material science developments utilized in design.

Just 5 years ago for $100 you would expect -20dB worse
 
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