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Topping D90 MQA - teardown

trl

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Topping D90 MQA - teardown

This is the MQA version of the D90 reviewed by Amir here: https://www.audiosciencereview.com/...ds/topping-d90-balanced-usb-dac-review.10519/ back in Dec. 2019. As per the above measurements “the D90 is instrument grade digital to analog convert and can be used to test analog audio gear”.

The case is made of aluminum, black anodised, with dedicated grounding points without coating. I can see three grounding points on the back plate, but also couple of more additional grounding points on the bottom too.

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Top view of the motherboard.


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Bottom view of the motherboard. Notice the copper grounding points and the PVC isolation from backside, to prevent any possible short-circuits.



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Rails for the board to fit inside and also for the screws.
Grounding is done through this part of the case too, via the screws from the back and from the bottom as well.



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One of the two grounding points from the bottom of the case
The inside power wires are well routed and the isolation is perfectly done, without getting worried of a future short-circuit or touching the case if the device is wrongly manipulated or falls down on the floor, then plugged into power socket again. I do love the transparent-matte isolation PVC sheet from the bottom, just between the bottom of the PCB and the aluminum case. This is minimising any possible short-circuit if something bends or falls inside the DAC (low probability, but I do love the idea anyway).

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Common-mode rejection filter, 120/230V switching board, transformer. Notice the well done wiring job with good isolation around.

I do like to see linear PSU inside such a small DAC case, with the a 120/230V switch on the bottom of the case. The transformer seems beefier then needed, so probably oversized a bit, which is usually a good thing. It is followed by couple of bridge regulators made of 8 x SS34 fast 3 A Schottky diodes. There are three big Nichicon capacitors, 3300uF/25V each, used to lower the AC ripple.

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Fast 3A Schottky diodes and big FW Nichicon capacitors.

Two ON-SEMI LM317D2T linear regulators followed by SMD capacitors are lowering AC ripple & noise, then used on both rails of the digital side from the middle of the board. Of course, smaller regulators might be seen on the board, for chips that requires different input voltages.

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LM317 linear regulators followed by SMD caps.

TPS7A47 and TPS7A33 are +/–36 V, 1 A, Ultralow-Noise linear voltage regulators and are used, one on each rail, to power the D90 analogue parts and the DAC chip (the right side of the board).

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Texas Instruments low noise TPS regulators.
(I needed to use lot of Isopropyl alcohol spray to clean this board's corner, probably due to some resin left over).​

Couple of Accusilicon AS318-B Series Professional Audiophile Crystal Oscillators, about 50 USD each. One is 45.1584 MHz and the other one is 49.152 MHz, very low noise both (-100dBc).

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Accusilicon clocks.

The DAC used is from AKM, an AK4499EQ 4-channel DAC. The opamps following the DAC chip are four OPA1612 used in I/V conversion and as buffers we can see three LME49720. Just near the XLR & RCA plugs we can spot three muting chips (37190 1941U 16-pin IC) that can be easily activated by remote’s MUTE feature. Four Japanese Nichicon 3300uF/25V capacitors are used to lower the noise in analogue domain from the AKM DAC chip.

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The three LME49720 opamps and the 16-pins muting chips (not sure what model are these).


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AKM AK4499EQ DAC chip, TI OPA1612 I/V opamps and the big 3.300uF Nichicon caps.


USB downstream traffic is handled by the multicore microcontroller XMOS U11690C20 which is part of the XU216-series vs. the XU208-series on the non-MQA version.

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XMOS, ALTERA, ARM and the AK4118 chips.


A “Complex Programmable Logic Device (CPLD)”, ALTERA MAX-II EPM240T100C5N, can be easily seen on the board. This is a programmable device that contains a non-volatile memory inside and is probably used inside D90 to deal with digital processing. Topping advertiser states “clock processing and signal optimisation” and “combines with the accusilicon femtosecond to bring a lower jitter effect”.

AKM AK4118AEQ is a 192kHz 24bit Digital Audio I/F Transceiver used for the S/PDIF output (OPT/COAX/AES). Murata 78601/1JC isolates the S/PDIF input from the board, this a common thing to do when BNC or COAX plugs are installed.

ARM STM32F030 microcontroller from the board features an Arm® Cortex®-M0 core inside that runs at speeds up to 48 MHz. I guess this CPU is the main “core” of D90’s board, taking care of all the commands coming from the computer host or from the external sensors/switches, since pressing the Power ON/OFF, play and decode PCM/DSD/MQA till all the commands available in the LCD menu.

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Screen menu has only two rows, but it's clear and visible, with three brightness settings.

This DAC can natively decode PCM32bit / 768 kHz and DSD512 natively via IIS and USB inputs, as well as Bluetooth 5.0 transmission 24bit/96kHz LDAC, AAC, S-BC, APTX, APTX LL, APTX HD via the Qualcomm CSR 8675 chip.

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The multitude of In/Out ports. Notice the left & right grounding points and the one from the right side of the AES socket.
Grounding of the case is done when screws are inserted.

D90 has a nice case and a very informative front screen, with enough menu settings. Thesycon ASIO drivers are working perfectly and without any skipping or audio drops. The BT5.0 with LDAC support sounds fine when streaming audio from my phone. The inside wiring and shielding are done with care and responsibility and the soldering is very well done too. Plugs & sockets are of a very good quality and includes both balanced and non-balanced outputs as well as several inputs too, good Nichicon caps can be spotted, so I can not see any flaws.

However, I’d like to have the Bluetooth module completely shut-down, but I guess this is not possible, because it doesn’t seems to have a small SMPS inside to take care of power management. So, unless I want to use the back power switch the BT adapter, and probably other chips from the board, will remain powered ON (very low consumption anyway).

Also, having the power switch on the back, without easier access sometimes, I’d like to see a menu option for the D90 to remain powered-OFF by default instead of existing power-ON, so when I push the power button from back I’d like the D90 to stay OFF until I power it ON from the remote or from the front button.

Remote control is nice, not too small like the one from Apple TV and not too big like TV’s remote. I’m not in love with it’s narrow angle of operation, but I can definitely live with this and if I point the remote straight to the D90 it operates as it should.
 
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Tokyo_John

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This is a fun teardown and discussion, thanks for sharing it!

I noticed an interesting review and mod description on the D90 (pre-MQA version) at Amazon Japan, which translates to...

With AK4499 installed, it was purchased to replace the AK3399 DAC.I'm having fun with IIS input and SPDIF input.I am using it in DAC mode.

At first, it was honestly sound “I wonder if this is something like this”.I thought, “Is this because the price is also a price?”, but when someone pointed out that “I'm using Bluetooth with Bluetooth turned on”, I quickly turned off Bluetooth.Then a slight smear of the sound is taken out, and the original sound seems to have come out.This is good, isn't it?It is a bluetooth of Uri, but it is recommended to turn off if you enjoy a higher sound quality.

Still, it felt that the original of the AK4499 could not be demonstrated, so I opened up and replaced the output stage op amp with OPA1692.This was perfect, and it became a fresh and energetic sound that I don't think of the same DAC.The next retrofit is to replace the I/V conversion op amp around the DAC chip with the OPA1602, which has a margin of input current compared to the default.

So they swapped the LME49720 op amp to OPA1692 and claim to achieve a significant change, a "fresh and energetic sound" that isn't "the same DAC" any longer.

Searching for LME49720 and OPA1692 returned this interesting TI thread from 5 years ago, discussing that the LME49720 was going out of production at that time, and somebody recommended using the OPA1692 as a substitute/replacement...
https://e2e.ti.com/support/audio/f/audio-forum/457875/lme49710-and-lme49720-end-of-life

As far as I can tell, the LME49720 has a solid reputation for delivering clean detail. However, being out of production, it must be that Topping has managed to procure a huge stockpile of these legacy TI op amps, if they are using them in their flagship DACs. Perhaps when they run out of these in the future, then they may have an intriguing option in the OPA1692?

It almost makes me want to tinker with mine.

EDIT: I found 2 blog posts describing the mods from the author of the Amazon review, you'll have to use Google translate if you don't read Japanese. The second one describes swapping the input stage op amps...
http://mark-create.cocolog-nifty.com/blog/2020/07/post-f26340.html
http://mark-create.cocolog-nifty.com/blog/2020/07/post-8619cf.html
 
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Veri

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Searching for LME49720 and OPA1692 returned this interesting TI thread from 5 years ago, discussing that the LME49720 was going out of production at that time, and somebody recommended using the OPA1692 as a substitute/replacement...
https://e2e.ti.com/support/audio/f/audio-forum/457875/lme49710-and-lme49720-end-of-life

As far as I can tell, the LME49720 has a solid reputation for delivering clean detail. However, being out of production, it must be that Topping has managed to procure a huge stockpile of these legacy TI op amps, if they are using them in their flagship DACs. Perhaps when they run out of these in the future, then they may have an intriguing option in the OPA1692?
LME49720NA is very much "in production" still. That news from 5 years ago must have been incorrect.
 
OP
trl

trl

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So they swapped the LME49720 op amp to OPA1692 and claim to achieve a significant change, a "fresh and energetic sound" that isn't "the same DAC" any longer.
This is unity-gain output buffers, so expect no difference in measurements when swapping buffer opamps for line-level outputs. This is a DAC that already has high perf. opamps inside, I'm talking about OPA1612 for the I/V stage, so definitely choosing LME49720 in output buffer was not done from frugality, but from technical reasons.

If you're looking to how well D90 measures, you will understand that these output buffers are not the weak chain link of this device. Also, these days every mod needs to be backed-up by some sort of measurements, so everyone can compare how the device measured initially vs. after the mod was completed. From my perspective there's nothing to improve in this DAC in respect with THD+N and as it's already having a SINAD of 120 dB I really doubt that any human can actually measure by ear differences, unless after the mod the SINAD drops below 90 dB. :)
 

Anton De

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Does someone know what are those 16 pin muting chips in the output? I plugged a 48v mic cable into dacs output so I guess I need to change those..
 

Larry B. Larabee

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That's a nice looking insertion ratio on the board.
 
OP
trl

trl

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I can't remember, there're probably some screws on the back plate; you can look under the rubber feet too.
 
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trl

trl

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I just added a headphones amplifier on top of this DAC, so first thing I did was, of course, a teardown: https://www.audiosciencereview.com/...te-a90d-teardown-and-personal-thoughts.48717/.

Pairing them together was taking a couple of seconds, just a pair of decent and short XLR-XLR cables coming from D90MQA to A90D and a longer pair of XLR-TRS cables getting from A90D to my active subwoofer that controlls the active speakers as well.

Controlling the active speakers from the preamp included in the A90D is like a breeze, given the remote control and the rotary knob. When I was controlling the active speakers directly from the D90MQA I always forgot to turn down the volume from 0 dB to -20 dB and almost blew my speakers out, so A90D comes in handy to help in this matter.
 

Andy74

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Can Any one Help Please. I plugged the Topping d70s into 230v UK outlet without changing the volt selection switch. I didn’t notice that the volt selection switch was in
IMG_2350.jpeg
IMG_2358.jpeg
115v. The unit made a buzzing noise, and then died. I opened the unit and i saw the big blue (? Transformer) bulge In 2 places. See photo attached. What could be the spec of this thing and where would i get a replacement. Any advice will help. Thanks.
IMG_2350.jpeg
IMG_2358.jpeg
 

Roland68

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Can Any one Help Please. I plugged the Topping d70s into 230v UK outlet without changing the volt selection switch. I didn’t notice that the volt selection switch was inView attachment 326737View attachment 326738 115v. The unit made a buzzing noise, and then died. I opened the unit and i saw the big blue (? Transformer) bulge In 2 places. See photo attached. What could be the spec of this thing and where would i get a replacement. Any advice will help. Thanks. View attachment 326737View attachment 326738
Please post a picture of the bottom of the board.
 
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