ES9038Q2M Board

[DPH]

None taken! It's really for the best as it's certainly safer to be thorough than otherwise, especially when describing a schematic by looking at a pcb. That's regardless one's experience level.

You've certainly been busy with this board!

 

[abraxalito]

There is also a photo showing the external SRC PCB and Arduino microcontroller for it. Wish I could find an inexpensive alternative that other people could use if they wanted.

Would this one fit the bill? - its just over $40 : https://item.taobao.com/item.htm?sp...6BaMG6b&id=12809416535&ns=1&abbucket=3#detail

 

[Markw4]

abraxalito, Yes, thank you! It is exactly the right thing. An SRC4392 is rated for harmonic distortion down at -140dB. Don't know how you found it, but good work. I will have to see if I can figure out how to order one to try.

 

[Markw4]

Actually, not speaking or reading Chinese I have no idea how to order something there.

 

[abraxalito]

I've sent you PM about it

 

[vacuphile]

Mark,

Did you put small resistors -2 Ohm or so - between dac and opamp? I found that doing so halves the distortion. 6dB improvement for the price of two resistors, not bad.

 

[TioFrancotirador]

Look at this post:
http://www.diyaudio.com/forums/pc-based/302687-es9018k2m-es9028q2m-9038q2m-dsd-i2s-dac-hats-raspberry-pi-19.html#post5385664

 

[Markw4]

Haven't tried it yet, too many things going at once. But, I will. Very interesting observation.

 

[Markw4]

Mark,

Did you put small resistors -2 Ohm or so - between dac and opamp? I found that doing so halves the distortion. 6dB improvement for the price of two resistors, not bad.

A question for you: when you say 2 small resistors halve the distortion, I assume you mean 2 per channel? If not, I may be missing something.

 

[Markw4]

Look at this post:
http://www.diyaudio.com/forums/pc-based/302687-es9018k2m-es9028q2m-9038q2m-dsd-i2s-dac-hats-raspberry-pi-19.html#post5385664

Looks like that was for a version 1.04 DAC. The current version appears to be 1.06.

Regarding use of a controller, the 1.06 DAC doesn't seem to need one. It appears to adjust automatically to the input stream with the user only needing to select a hardware input using the jumpers, or maybe using a switch instead which has been wired up to the jumper posts.

 

[vacuphile]

Hi Mark

Yes, two per channel between the DAC and the opamp, so one for the + and one for the - dac output. I was very surprised with the results; will post measurements, time willing. But I couldn't go below 2.7 Ohm because the board froze for unrelated reasons. Some further experimentation may be required to find the optimum point.

I also tested this with the 9018 board, but in that case any resistance added in the path between opamp and dac produces more distortion.

 

[cdsgames]

Hi Androa

I don't think it matters so much, all you need is a good reservoir of electrons. I will check the datasheet and get back to you

 

[cdsgames]

.

The tiny PCB attached vertically by one end of the AVCC opamp has two sets of 10k SMD resistor voltage dividers and two 10 uf organic polymer filter capacitor cans you can see from their sides. That is the reference voltage divider.

I am thinking about the Vref. How about changing the resistor divider with a Vref IC ? I think that could improve THD

 

[Markw4]

Vref should work best at the quiescent, or 1/2 of full scale in this case, DAC output voltage. That, in turn, is dependent on AVCC whatever it happens to be.

It is not so important for Vref to be at an exact, pre-determined, fixed reference voltage.

 

[cdsgames]

Agreed but its important not to fluctuate . I will do some tests this week using the TI VREF monolithic ICs

This is an interesting link in regards with Vref and THD impact (for ADC)
http://www.ti.com/lit/wp/slyy097/slyy097.pdf

 

[Markw4]

The application note is for a totally different kind of circuit. Not the same thing at all.

 

[oversimon]

Could someone show me the easiest way to put the Dac in current mode?
I followed the advice of Madds1 post # 355 but the indicated resistance seems irrelevant, I tried all the values between 0 and 3.2M.
I'm a beginner, could you show some images too?
Any suggestions?

 

[Markw4]

Do you know how to read schematics?

 

[cdsgames]

Mark,

Did you put small resistors -2 Ohm or so - between dac and opamp? I found that doing so halves the distortion. 6dB improvement for the price of two resistors, not bad.

I will also test this finding...will report back .

 

[oversimon]

Do you know how to read schematics?

Yes,
Thank You.