Topping A90 Discrete (A90D) - Teardown and personal thoughts

[kevin gilmore]

this was the schematic of the nfca module as used in the eha5. so the 90d may be slightly different as it probably does not have the 18khz filter.
and the volume pot is replaced by a discrete relay attenuator. high res pictures posted elsewhere. too big to fit here.

 

[mrjayviper]

Everything is straight forward, but after taking off the back plate you will need to figure out a way to easily disconnect the two ribbon cables coming from the rotary knob and display.

Worst part is to get the two screws from the front plate off, given that you'll need a very long and very thin screwdriver (the one from iFixIT is shorter and thicker, even with the longer adapter included).

Chances to damage the ribbon cables and/or to not be able to put everything back are quite high, so I strongly don't encourage anyone to teardown this device!

BTW, why drilling the top case for? I measured quite low temps on top, even after driving at insane levels two planars at the same time the temps were like around 40C. My Matrix HPA-3B was hitting 60C when I was driving two planars for testing.

thanks for the reply. my worry is those 2 ribbon cables. removal might be easy but putting it back is my worry.

 

[trl]

Putting back the ribbons can be easily done from front side, given that you will need to remove the front plate anyway. So worst part now would be figuring out a way to place back the two screws in the corresponding locations from the front plate. Worst case scenario is to not be able to fix back the front plate (fix the feont plate with a couple of small scoth tape pieces).

However, if you can find a long enough and very thin screwdriver you should be able to place those two tiny screws back. I was using the iFixit screwdriver + the 150 mm Flex Extension and it was a PIA to put back those two inner screws, so anything longer and thinner than that would be way better for this job.

 

[mrjayviper]

Putting back the ribbons can be easily done from front side, given that you will need to remove the front plate anyway. So worst part now would be figuring out a way to place back the two screws in the corresponding locations from the front plate. Worst case scenario is to not be able to fix back the front plate (fix the feont plate with a couple of small scoth tape pieces).

However, if you can find a long enough and very thin screwdriver you should be able to place those two tiny screws back. I was using the iFixit screwdriver + the 150 mm Flex Extension and it was a PIA to put back those two inner screws, so anything longer and thinner than that would be way better for this job.

do you still have the amp in "pieces"? can you please take a pic of the front pieces and the front pcb just to give me an idea on what's involved in putting it all back together?

thanks again!

 

[trl]

The headamp has been assembled back a few hours after I had it disassembled for this teardown review, but you can look on the first page and check the pics with the temperature measurements and you can clearly see there the front panel and the top of the PCB with the two ribbon cables connected.

 

[Music1969]

Any teardown of Topping A70 Pro coming @trl ?

I believe it is even better amp, and cheaper !

See here: 8 minutes ago

 

[audiofun]

Any teardown of Topping A70 Pro coming @trl ?

I believe it is even better amp, and cheaper !

See here: 8 minutes ago

I would like to see a teardown too. but even with that we may still have limited knowledge, as the main parts are sealed in modules. I lost interest in buying (and teardowning) topping products after they transitioned to use those modules. To me this is a stupid move --- causing a lot of product issues, and not enough to prevent competitors learning their designs.
I would say they have similar technology, both use PBSS305 as output transistors. but unlike the complex discrete circuit here, A70 Pro sealed module is perhaps just using op amps.

 

[trl]

Any teardown of Topping A70 Pro coming @trl ?

I believe it is even better amp, and cheaper !

See here: 8 minutes ago

The A70 Pro seems to have capsulated T'ang-ku modules, while A90 has capsulated NFCA modules, like the ones used in the DX9 below (which are naked and not capsulated):

​

However, you can check https://www.audiosciencereview.com/forum/index.php?threads/topping-a70-pro-hp-preamp-review.44636/ and also the graph published by Amir as well:

​

I suppose that the newly developed T'ang-ku modules are still Nested Feedback Composite Amplifier type, but more details can also be found here: https://www.tpdz.net/productinfo/1009982.html. Perhaps @JohnYang1997 would like to share more with us or perhaps to update https://www.audiosciencereview.com/forum/index.php?threads/topping-a70-pro-hp-preamp-review.44636/ with a few inside pics?

 

[Music1969]

How is A90D QA/QC now?
Have they fixed all early issues?

 

[trl]

I'm using my A90 Discrete only a dozen of hours per year, sorry. However, D90 MQA seems rock-solid till now, although I'm using it only about 100h/year, so probably not much enough to tell if it's reliable or not over the years.

P.S.: The only audio devices I'm using daily are Marantz Cinema 70s, followed by Yamaha A-S701, ASUS Essence One MKii and some Burson gear.

 

[ReinhardS]

While it's great that the Chinese are making high-quality hi-fi affordable, there's still so much expensive nonsense involved. Nobody needs a balanced XLR connection for short distances at home. Especially not when the volume control is apparently asymmetrical as here [1] - a big CON for me. In a compact housing, the space could be better used for multiple RCA inputs. The discrete design only increases the probability of failure; the measured values were already perfect with the A90. I would have preferred a signal path without electrolytic capacitors. The placement of the 85-degree Nichicon BP electrolytic capacitors directly on the power amp heatsink is also questionable.

Thanks for the insights, @tri

would be great to get some detailed instructions how to open this device.

[1] It seems the signal is converted to asymmetrical before the potentiometer and afterwards again to symmetrical,. Here are regular op-amps used, why the effort with discrete op-amps after this stage then?

 

[trl]

I am only using balanced inputs in all of my home setups due to rather longer distances used and the nearby power cables. Probably for most people the non-balanced wires could be just fine, but when you want to squeeze the best SINAD possible then going XLR might be an option for some. Also, most studio monitor speakers are calibrated for balanced setups, so best SNR is achieved with 4V RMS on its inputs.

Output stage heatsink is heating less than 50C, so the 85C caps from nearby should be fine for 10 years or even more.

I don't recommend you to open the case due to the volume control ribbon that can be easy to break; also, putting the ribbon back it's quite difficult too, same for the front plate screws (a very long and thin screwdriver might be needed).

 

[ryanuk]

Thanks for this teardown! I just picked up a used one earlier this year, and I'm using the balanced XLR on the front panel, but after knocking it with my knee, it has now become a bit loose and a slight knock makes me lose one side of the headphones. I'd love to get it fixed, but support just asked me to ship it to China! As it's working mostly and I'm using it every day (and it's out of warranty anyway), I'd love to repair it.

I know you advise against it, but what tips do you have for removing and reattaching the ribbon cable(s) / case so I can access the XLR socket on the front? Can you let me know what tools I should get, and how the ribbon connector is taken off / put back?

Thanks!
Ryan

 

[trl]

Ryan, is quite difficult and risky to to this and you might also void the warrant y and even break the device completely.

However, a really long screwdriver would be needed, preferable thin too, to be able to easily protrude inside to screw / unscrew some screws in there. A frontal light would be needed too, spotty if possible, not floody, to better see inside the case while using the screwdriver. IIRC there's like one inch left after you open it up, until the ribbon starts to pop-up from there.

BTW, what's the cost to ship it to China?

 

[Guy.Cohen]

Ryan, is quite difficult and risky to to this and you might also void the warrant y and even break the device completely.

However, a really long screwdriver would be needed, preferable thin too, to be able to easily protrude inside to screw / unscrew some screws in there. A frontal light would be needed too, spotty if possible, not floody, to better see inside the case while using the screwdriver. IIRC there's like one inch left after you open it up, until the ribbon starts to pop-up from there.

BTW, what's the cost to ship it to China?

Hi,

Thanks for your very nice contribution and screenshots.
Question: is this preamp making debalance before R2R volume? It seems yes by the opamp in between the 4 green bipolar.

Thanks