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ODAC - general and technical discussions

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I'm wondering why the Cbyp cap on the MIC5205-3.6YM5 (pin 4) was omitted? Does it run better without it? Or would it improve noise to add it?

Hi,

A quick history lesson:

The original design used a 3v3 ADP151 which does not need a bypass. When it was decided to push the output voltage to 2Vrms NwAvGuy moved to a 3v6 regulator and decided on the MIC5205. It had the same footprint as the ADP151, SOT-23, and when NwAvGuy tried it out he was able to reach the 2Vrms target.

Yes, the MIC5205 has a bypass for noise reduction but the lack of the capacitor was not noticed when the board underwent analysis. The ODAC noise floor is at the limit of the DAC and I am not sure if the addition of the capacitor would have improved the numbers. That being said there is plenty of room for an adventurous individual to scrap a ground pad and add the recommended 470pf capacitor. ( 0805 size would be fine).

Regards,
George Boudreau
Yoyodyne Consulting
 
Hi,

A quick history lesson:

The original design used a 3v3 ADP151 which does not need a bypass. When it was decided to push the output voltage to 2Vrms NwAvGuy moved to a 3v6 regulator and decided on the MIC5205. It had the same footprint as the ADP151, SOT-23, and when NwAvGuy tried it out he was able to reach the 2Vrms target.

Yes, the MIC5205 has a bypass for noise reduction but the lack of the capacitor was not noticed when the board underwent analysis. The ODAC noise floor is at the limit of the DAC and I am not sure if the addition of the capacitor would have improved the numbers. That being said there is plenty of room for an adventurous individual to scrap a ground pad and add the recommended 470pf capacitor. ( 0805 size would be fine).

Regards,
George Boudreau
Yoyodyne Consulting
Absolutely great reply, thanks!

Looking forward to buying one of these....
 
The noise on C101 is about 30mV p-p on my scope but that probably includes some radiated noise which is well above 1mHz. I really cannot see much below 1 MHz apart from a 20mV ripple which I think is due to the charge pump. You can get rid of this ripple with a 100uF electrolytic but I cannot hear any difference. The power up current may exceed the USB limits with this in place or it may simply be current limited by the regulator.

I wonder if anyone else has been able to increase the value of the post filter resistors R102 and R103. I increased mine to 1k (my lowest value above 220R) which I think lowers the knee frequency by a factor of 3 and reduces measured output at 20kHz by 5% ( is the 0.4 dB?). I now find the ODAC/O2 a lot easier to listen to. I have yet to wire the 2 resistor values to a switch so that I can blind test.
 
Humble pie time. I wired 1k and 220R resistors to a switch and flicked between them. I was not able to detect any difference between the positions. I could not even detect the change in volume due to the change in resistance (<.5dB) to get a clue which resistor was in use. I tried with NMJ2068, 5532 and LM4562 and I still could not tell the difference.
 
How much voltage can this DAC handle?
Actually what are the MAX and MIN voltage that can take to work properly?
Thank you.

The MIC520x regulator is rated for a MAX +16volt input. However, input voltage is only one consideration when talking about a regulator. This is a very small device and it is not capable of dissipating much heat. The controller has its own regulator and consumes approx 100ma while the ES9023 only uses 30ma. Running with the 5volts from the USB port both regulators are well within operating limits.

George

George
 
The MIC520x regulator is rated for a MAX +16volt input. However, input voltage is only one consideration when talking about a regulator. This is a very small device and it is not capable of dissipating much heat. The controller has its own regulator and consumes approx 100ma while the ES9023 only uses 30ma. Running with the 5volts from the USB port both regulators are well within operating limits.

George

George

Thank you, I understand that.
I would like to try a different power source and I can't find easily one rated at 5V. It's easier to find 6/7V sources. Do you think would that be too much? Did you ever tested the DAC with higher voltages?
 
Thank you, I understand that.
I would like to try a different power source and I can't find easily one rated at 5V. It's easier to find 6/7V sources. Do you think would that be too much? Did you ever tested the DAC with higher voltages?

OK.. a 7 volt supply will double the power dissipation and be very near the upper limit for the U103 regulator. I cannot say how hot the chip would be but I expect it to be very very warm. The ES9023 DAC regulator, U101, will be fine at 7 volts.

If you plan on powering the ES9023 separately you will need to break the trace leading to L100 and apply your new power source between L100 and ground.

DO NOT attempt to feed 7volts to L100 without breaking the trace on the back side of the board or you will damage your PC.

::WARNING:: This has not been tried before and you could smoke your ODAC, PC or external power supply.

Have fun :)
 
Hi George, concerning the addition of the bypass capacitor I would suggest that people don't bother! The cap actually reduces the amount of feedback at high frequencies. I tried adding 220pF to pin 4 of U101 with the 22uF in C101 and the ripple increased to over 100mV in the MHz region (why do I never write this stuff down?) i.e. the regulator with the bypass capacitor is too slow and cannot compensate for the periodic discharge of C101 by the charge pump (and maybe oscillates?). You can see the error signal on pin 4. It is a bit unclear from the description on the Micrel document what the noise cap does but he diagrams show that it filters the feedback signal.
 
It should be no problem to use 5m phono cables. The output of the DAC is designed to drive 4700pF but the ODAC has some extra series resistance and 2200pF in the output filter. 500-1000 pF of cable capacitance should not make any difference to the sound and might even make it smoother.
 
Hi guys, first post here, complete newbie to DIY in general.

I was wondering, is it possible to get the ODAC PCB board fabricated? I live in a part of the world where quality audio is something no one has even heard of yet and I want to start off by introducing people to the ODAC and O2. While the O2 amp can be DIY'd, the ODAC can't and I was hoping there's a solution to this. The US$99 preassembled boards are too expensive regionally, and there are no PCB schematics that you can use to fabricate the boards with.

Can anyone advise me on what to do? If I cannot get the schematics, then some OEM solutions or bulk sales would be nice. George if you're reading this, would love some guidance here.
 
Hi guys, first post here, complete newbie to DIY in general.

I was wondering, is it possible to get the ODAC PCB board fabricated? I live in a part of the world where quality audio is something no one has even heard of yet and I want to start off by introducing people to the ODAC and O2. While the O2 amp can be DIY'd, the ODAC can't and I was hoping there's a solution to this. The US$99 preassembled boards are too expensive regionally, and there are no PCB schematics that you can use to fabricate the boards with.

Can anyone advise me on what to do? If I cannot get the schematics, then some OEM solutions or bulk sales would be nice. George if you're reading this, would love some guidance here.


There are some obstacles to producing your own version of the ODAC and the main one is access to the Tenor USB audio engine. The supplier does not deal with individuals and businesses need to sign a NDA (non-disclosure agreement) to have access to the chips and data sheets.

I have made the schematics available for those who wish to hack their own ODAC but they are not to be used commercially to make clones. To be called an ODAC it must use the layout NwAvGuy and I created *and* the component selection.

It you wish to purchase a quantity of the ODAC you can contact me and we may be able to work something out.

FYI: I have no more stock and will not be manufacturing any more until January of 2013 or later. As far as I know the distributors are still selling ODAC cards at a steady clip.

Regards,
George Boudreau
 
Dear Stefan, you have a big fault in your guide on how to connect the O2 to the ODAC.
Components

In the last picture at page three you have shown that the black wires go to the upper holes and the white to the lower ones. This is reversed and if you do it like the way in the guide you'll en up with mono sound because so have I.

Looking at this picture here
odac%252520to%252520o2%252520wiring_thumb%25255B2%25255D.jpg

It show the right way of doing it. If you want I can supply you with a new picture for your guide if you're not okay with "stealing" it from NwAvGuy's blog.

I have somehow blown out my odac. It looks like the part labeled fb102 has burnt out. Could someone tell me what this piece is?

Fraggler did you find a fix?
 
I have somehow blown out my odac. It looks like the part labeled fb102 has burnt out. Could someone tell me what this piece is?

That looks like either a chip fuse, or more likely chip fusible resistor, on the #5 ground pin coming from the USB port, according to the schematic on George's site. You most likely had a ground loop going on between your computer and the ground of whatever was plugged into the audio out jack or connectors. Try measuring ac and dc voltage between pin 5 of your PC usb connector and the audio ground.

Should be easy enough to replace that chip fuse with the help of some de-solder braid if George can supply the part number.
 
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...another thought - if the ODAC is being used in an O2, then the O2's AC transformer may have excessive leakage between the secondary and primary windings. Since one end of the secondary is ground in the O2, that could complete a power line short through FB102 if the PC being used for USB happens to be 3rd wire grounded.
 
That looks like either a chip fuse, or more likely chip fusible resistor, on the #5 ground pin coming from the USB port, according to the schematic on George's site. You most likely had a ground loop going on between your computer and the ground of whatever was plugged into the audio out jack or connectors. Try measuring ac and dc voltage between pin 5 of your PC usb connector and the audio ground.

Should be easy enough to replace that chip fuse with the help of some de-solder braid if George can supply the part number.


FB102 is a ferrite bead -Digikey number 240-2399-1-ND
If you smoked the ferrite bead there is a 99% chance you have taken a lot more.
 
FB102 is a ferrite bead -Digikey number 240-2399-1-ND
If you smoked the ferrite bead there is a 99% chance you have taken a lot more.

May be worth ordering some 0.5A pico fuses too, digikey F5521CT-ND, and tack-solder one over the old bead after the ground loop is believed to be cleared to see if the ODAC is still with the living. :)
 
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