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Review and Measurements of WesionTEK Khadas Tone Board DAC

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Feb 5, 2019
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Add my thanks to Marvin for the photo. I saw the summer IC, pulled up the schematics and there it was. No wonder the (not totally read) schematic wasn't making sense. I'm not familiar with DAC circuits, so I also must ask, is it normal for the U15/U17 opamps to be biased with such an offset?
It's interesting biasing indeed. On my over-simplified-schematic had it marked as 3.3V but that's the AVCC_R rail, in reality it goes thru a resistor divider with 10k/3.3k ohm so the bias on the non-inverting input of RT6862D is 0.82V. The output from ES9038Q2M is a differential signal with zero at AVCC/2 so that is 3.3/2=1.65V with full scale out being 0.906xAVCC peak to peak. So that is 0.906x3.3=2.99V (let's say 3V) peak to peak meaning full output from the DAC is centered at 1.65V with peak at 1.65+1.5=3.15V and bottom at 1.65-1.5=0.15V. And that signal is then biased up 0.82V at RT6862D. Just a note that the opamps are running at +-5.5V provided by R1286K010F (datasheet https://www.mouser.com/datasheet/2/792/r1286-ea-1076068.pdf).

So I guess they wanted a higher balanced signal to convert to single ended with RT6863?
 

mikoy

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Feb 7, 2019
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Sorry to see you got markings backwards. I'm actually thinking going with something like this. Seller is offering everything needed to customize it to our needs:

Length: can be changed to any length
Color: Can be oxidated to any color
Drilling Hole: holes on the plates,hole milling,holes on the body,according to your drawing
Printing: Silk screen printing or Laser typing according to your drawing.


I'll ask about the final price with holes on the plates... and if it's reasonable I'll probably try going with it in black color.
I asked as well but minimum order quantity is a 100!
 

Nango

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I have the same problem. Thing is the wrong way around and the finish quality is abysmal. Wouldn't recommend the product.
Actually, no, it is not a joke, mine also wrong side labeled and, as you say, the finish and quality of the aluminium ($ 30) is the worst I have seen in many years. The only +ive is the TB wont be exposed to dust anymore, thats it.

I can't recommend and I dont buy any Khadas anymore without a proper case!!!

tb_box.JPG
 
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Feb 8, 2019
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It's interesting biasing indeed. On my over-simplified-schematic had it marked as 3.3V but that's the AVCC_R rail, in reality it goes thru a resistor divider with 10k/3.3k ohm so the bias on the non-inverting input of RT6862D is 0.82V. The output from ES9038Q2M is a differential signal with zero at AVCC/2 so that is 3.3/2=1.65V with full scale out being 0.906xAVCC peak to peak. So that is 0.906x3.3=2.99V (let's say 3V) peak to peak meaning full output from the DAC is centered at 1.65V with peak at 1.65+1.5=3.15V and bottom at 1.65-1.5=0.15V. And that signal is then biased up 0.82V at RT6862D. Just a note that the opamps are running at +-5.5V provided by R1286K010F (datasheet https://www.mouser.com/datasheet/2/792/r1286-ea-1076068.pdf).

So I guess they wanted a higher balanced signal to convert to single ended with RT6863?
To fully understand, you have to complete the circuit with ESS's output impedance Rdac. You will see RT6862D actually work as an active amplifier/filter and its output offset due to the input bias, Voffset = Vinl_r * (1 + 806/774) = 3.3 * 3.3/(10 + 3.3) * (1 + 806/774) ~= 1.67V; Now at full scale the two RT6862D output voltage will be -3.15 * 806/774 + 1.67 ~= -1.61 and -0.15 * 806/774 + 1.67 = 1.51; So the common mode voltage is already very close to ground, this will improve the output of differential amplifier/filter RT6863 - better CMRR, better linearity.
 
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Dec 22, 2018
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bbt8888, thanks for the reply. I see that you used the dac output voltage mode. If the current mode was assumed, the Voffset would be halved. How do you know which one to use?

Having an offset voltage forces current (Voffset/(2*R32) to flow thru R32 and R33 and the outputs of the connected opamps for no signal. The offset determines a kind of Class A biasing (1.67/2*806=1ma). That's my guess.
 

Aibo

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Nov 4, 2018
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Would interested in this as well. Do you have the Generic version or the VIMs
version?
Generic version. You get all the connectors in the bag so you can solder them anytime later if needed.

I asked as well but minimum order quantity is a 100!
Wow, that's not gone work then. Thanks for the info. I'll probably buy any pretty box and try to find some local guys that can do CNC machining.
 
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bbt8888, thanks for the reply. I see that you used the dac output voltage mode. If the current mode was assumed, the Voffset would be halved. How do you know which one to use?

Having an offset voltage forces current (Voffset/(2*R32) to flow thru R32 and R33 and the outputs of the connected opamps for no signal. The offset determines a kind of Class A biasing (1.67/2*806=1ma). That's my guess.
(1) Whether 9038 operate in current or voltage mode is completely determined by external circuit, there is no register/settings inside the chip to configure the operating mode. The internal output stage will be modeled as Thevenin voltage source all the same --- "DACs are as described, namely a Thevenin equivalent to a voltage source linearly between AGnd and AVcc having an approximately 800Ω output impedance" (Technical Details of the Sabre Audio DAC, http://www.esstech.com/files/4314/4095/4318/sabrewp.pdf). Also you can refer to "https://www.diyaudio.com/forums/digital-line-level/314935-es9038q2m-board-post5297231.html" and "https://www.diyaudio.com/forums/digital-line-level/314935-es9038q2m-board-23.html#post5343340"

(2) The TB circuit is a standard I/V stage + differential to single end conversion, so it obviously operate in current mode. To understand how it work, you can refer to TI application note "sboa237 - HiFi AudioCircuitDesign" and "sbaa333 - Current-to-voltage converter circuit for audio DACs".

(3) The bias (virtual ground) setting is decided by a lot of factors: DAC chips, op optimal operating range, etc. Eg. some TI dac chips can only source current so you have to connect bias to GND, 9038 doesn't have this limitation though.
 
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Actually, no, it is not a joke, mine also wrong side labeled and, as you say, the finish and quality of the aluminium ($ 30) is the worst I have seen in many years. The only +ive is the TB wont be exposed to dust anymore, thats it.

I can't recommend and I dont buy any Khadas anymore without a proper case!!!
Hello,

We are really sorry about this problem.
This batch was made from a new factory we was not used to work with.

During our tests we didn't found reversed unit printed in the wrong side.
As all units has been sold in 3 days, we didn't had the time to notice the problem and remove them for sale.

We will offer refund for all reverse printed units, affected customers can contact us.
We will use another factory for next batch.
 
Joined
Jan 14, 2019
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Actually, no, it is not a joke, mine also wrong side labeled and, as you say, the finish and quality of the aluminium ($ 30) is the worst I have seen in many years. The only +ive is the TB wont be exposed to dust anymore, thats it.

I can't recommend and I dont buy any Khadas anymore without a proper case!!!

View attachment 21555
Hi, I´ve also bought this case. The front and back pieces are interchangeable, so i don´t understand why was assembled that way. We just have to switch it... I have the same case with the same lettering...The only down point besides the size and thickness of the metal is that the small hole made to the operating led is way to the left and i´ts not alligned so i can´t see it.
 

Nango

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I tried all ways but labelling is always wrong side and the white ked is not visible. It is not that drama but simply annoying. I won't send it back as it costs the shipping more than the item itself.

I received also a 5% voucher on my account for upcoming purchases with them which doesn't really help.
 
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About the screen printing inversion, simply swap the front and back panels.
In this case, the card can not be attached to the bottom panel without drilling new holes.
But that's not a big problem because the main fixture are the RCA connectors.

About the led hole, it was made to add a 2mm round led soldered on the PCB.
But you are right, it's easier to use the onboard one by drilling a hole in front of it.
And we should have illustrated it in the manual.
 
Joined
Jan 17, 2019
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I just drilled one hole on the bottom. Don't really need three post on the board in this case. Will do for the time being. Been thinking about modding the case on my receiver and mounting it there. Be pretty sweet to have a built in tone board on a commercial avr
 

Nango

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Hello,

We are really sorry about this problem.
This batch was made from a new factory we was not used to work with.

During our tests we didn't found reversed unit printed in the wrong side.
As all units has been sold in 3 days, we didn't had the time to notice the problem and remove them for sale.

We will offer refund for all reverse printed units, affected customers can contact us.
We will use another factory for next batch.
Don't need a refund, shit happens, it is simply a pity.
 

Roen

Senior Member
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Oct 14, 2018
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About the screen printing inversion, simply swap the front and back panels.
In this case, the card can not be attached to the bottom panel without drilling new holes.
But that's not a big problem because the main fixture are the RCA connectors.

About the led hole, it was made to add a 2mm round led soldered on the PCB.
But you are right, it's easier to use the onboard one by drilling a hole in front of it.
And we should have illustrated it in the manual.
I don't believe a product that's being sold as "made to fit" needs any user modifications to fit said product.
 
Joined
Nov 6, 2018
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About the screen printing inversion, simply swap the front and back panels.
In this case, the card can not be attached to the bottom panel without drilling new holes.
But that's not a big problem because the main fixture are the RCA connectors.

About the led hole, it was made to add a 2mm round led soldered on the PCB.
But you are right, it's easier to use the onboard one by drilling a hole in front of it.
And we should have illustrated it in the manual.
Why not make a front panel with an opening for using the onboard led as an option?
 

BYRTT

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Nov 2, 2018
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...the small hole made to the operating led is way to the left and i´ts not alligned so i can´t see it.
...and the white ked is not visible...
...About the led hole, it was made to add a 2mm round led soldered on the PCB. But you are right, it's easier to use the onboard one by drilling a hole in front of it. And we should have illustrated it in the manual.
Why not make a front panel with an opening for using the onboard led as an option?
To fix that LED light for first batch with the non alligened hole suggest one could glue a small piece of clear plastic material say acrylic or glass on the back of front plate behind the 2mm hole so that onboard smd LED will shine up in the glued piece of acrylic and be viewable thru the hole, other sollution could be grab cut and glue one of those cheap TOSLINK fibre cable as other members showed pages back and republished below.

1000.png
 
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m8o

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Jan 28, 2019
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Khadas Tone Board is only one model from Khadas Family, and we suggest user could buy Khadas Tone Board along with the Khadas VIMs for SPDIF in/out can enjoy high resolution audio and 4K video together. That we need to consider the compabilty of Khadas Tone Board and Khadas VIM Boards. Through Khadas Docs, you could get the user manual along with the below details:
Other docs can be check on our Docs.khadas.com​
Hello,

Please correct me if I am mistaken, but I believe you are a representative of Khadas? If not, please ignore this question.

But if so, have you considered producing a version of this DAC that is a Raspberry Pi [RPi] HAT? If it can take input from the RPi as well as maintain s/pdif input it has now that would be ideal.
 
Joined
Jan 18, 2019
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My Khadas is on the way. I'll compare it directly to the DX3 Pro (modified and unmodified).

Since I'm in China it's hard to get the audiophonics case delivered in time so I decided to modify one on my own from a taobao shop.

【88*38 线路板diy铝合金型材盒子/电子电源铝盒/仪表仪器铝外壳体】https://m.tb.cn/h.3uAvHFW?sm=4b66e3 点击链接,再选择浏览器咑閞;或復·制这段描述¥BMKDbt8kGWL¥后到淘♂寳♀[来自超级会员的分享]

70mm version. Almost the same as audiophonics uses.

Screenshot_20190212-033328.jpg

Screenshot_20190212-033819.jpg


82mm in width. The board should just slide in. All that's left for me is drilling some holes in the right places. Shouldn't be too hard.

I'll post back I'd it works out and how to do it.
 

Attachments

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Jan 18, 2019
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Did anyone measure if there is an improvement of using a seperate power supply with the Khadas?

In looking into this LPS that can take USB in and out to feed it over one cable with clean juice.

【USB 电源净化器 过滤噪声 25W直流线性电源 数字界面 CAS】https://m.tb.cn/h.3FkMKwb?sm=d94af6 点击链接,再选择浏览器咑閞;或復·制这段描述¥6ZO4btP70K7¥后到淘♂寳♀[来自超级会员的分享]

Screenshot_20190212-143329.jpg

Screenshot_20190212-153629.jpg


I am using a USB purifier in between so I'm just wondering if it would be worth the investment.
 
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