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chchyong89 7th October 2010 04:19 PM

Learning towards MINI DAC
Hi, I am new in DAC but i would like to give it a try during my school holiday.
My goal is to create a mini USB-key size DAC in a very low budget that every students can afford the bill and built themself a unit to play! Stepping this journey, I hope any of you willing to give me some guides.:rain:

I know nuts about this, but i would like to show you guys what i am thinking,

However, i have no idea on the upsampling parts that which should fit the bill and the quality.
There are few IC in my brain which are:
*Or something better?

For DAC section, i have no idea AK4396 is better or CS4398 is better. The reason i choose them because both of this is the cheapest performer that i know. Any other suggestion guy?

Here is the output stage i would like to try after i read up a lot of results from google, AD8620 is used because i really need a smd size and capable to duty below 5Vdc (USB)

Is there anything wrong or any parts can be remove to minimized the parts count without degrading the output quality ? So that i can have my PCB as smaller as possible:usd:

One question, it there any output stage using discreet design that can work on USB power?

My utmost thankful to all of you who read this:rolleyes:

qusp 7th October 2010 05:41 PM

I dont think AD8620 will be happy with 5vdc, let alone something discrete. if you are planning to run from the USB bus power with such small parts count and low current. I think you are being too ambitious

nightanole 7th October 2010 05:56 PM

So your basicaly making a usb only amb gamma 2.

Might as well copy some of the design since its for your own personal use. They have all the parts you need. You just need to simplify the design down to just usb and pick your dac.

By the way usb 5v is very noisy so i hope you know your way around ferrite beads and ldo 4.75v regulators.

Also check out the grub dac and bantam dac since they use some of the parts you listed for usb.

chchyong89 7th October 2010 11:24 PM

I think i better don't use the gamma 2 output stage without amb's permisson. Because i want to fabricate pcb layout myself which is not using his PCB, it's not good if i continue with his design:rain:

Any others good output stage that's is open publication that i can take a look for reference?

chchyong89 8th October 2010 12:28 AM

I think i got what you meaned, by the way, do the following circuit seem fine?

For the ferrites beads, I think it will be not a problem for me

nightanole 8th October 2010 01:21 AM

it should go like this:
usb power = 4.9-5.1 volts
then a ferrite
then a decoupling cap (.1uf)
then the 4.75-4.5 volt regulator circuit
then you run your regulated to your opamp,analog dac section, and to your 3.3v regulator for the digital section of the dac.

You dont need 470uf on the output unless your driving headphones. if your driving something normal like a 10k pot then stick with 15uf-30uf.

Also i havent checked out the opamp yet, but if your running less then 5volts into it you need to run it below unity gain, and have a opamp thats stable below unity gain. If you dont then when the dac maxes out, the opamp will clip. Id shoot for 1-1.4rms output. If you sit safe at 4 volts of swing, thats 1.418rms.

While i havent tryed this, you could try. run the 5volts usb into the opamp via a ferrite and a decoupling cap. Opamps are very good at rejecting power supply noise (dacs are the opposite). so you would run regulated 4.5v into the analog dac, and run unregulated 5v into the opamp with unity gain.

chchyong89 8th October 2010 02:23 AM
Is this correct? Both the regulator chosen has high PSRR and low noise, i think it's pretty decent to use.

You are right, since the using of IIS, volume control no longer able to control under windows anymore, it will be better to change the 470uF into 20uF with a pot afterwards.

Thanks a lot for the guide :-*

nightanole 8th October 2010 11:07 AM

the .1uf needs to goto ground, like your first 2 drawings. Other then that it looks good.

Ken Newton 8th October 2010 11:58 AM

If your design includes the AD1896 for upsampling you will get excellent source jitter rejection as a side benefit.

riktw 8th October 2010 12:28 PM

if you want to make it small, good luck soldering
0402 resistors are doable by hand.
you would need a 4 layer PCB with IC's on both sides to keep it small
for price, if you make enough PCB's its not to expensive :)

and for the DAC's, maybe a wolfson dac?
the WM8521 is cheap (1,90 euro's at farnell for 1) kinda small, 14 pins
else the WM8501, harder to get but also not to expensive and also 14 pins
bit higher quality then the WM8521
no need for an opamp gain stage, works on 5V
downside is that the wolfson dacs have a lower SNR and higher THD
but i doubt you will notice it with the USB power supply ;)

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