HIFIdiy's mini USB DAC MK2--Also a headphone amp! - Page 7

I really don't think there is a 'buffer' part in the mk2. The 2134 deals with LPF, and the 2604 the HPA.

The problem with bipolar/fet is that bipolar opamps don't always play nice in circuits designed for fet opamps. That is something to bear in mind - the mk2 was designed around fet opamps.

I'm not clear on ways to pick up problems, but a touch test (touch the chip, if it hurts then you probably have a problem) is one I've heard some use. The safest approach is just not to use a bipolar chip.

Francis - I got the upgraded PSU from coolfungadget on eBay.

Yes, you're right, its a LPF circuit. Actually, after some further digging the circuit can be found on the pcm1793 DACs datasheet at page20. It's said there, that 5532 is recommended for the application as well, and that has bipolar input. Excessive heat is coused by oscillation, and that can happen with any high bandwidth opamp, also i couldn't find the "usual" 0.1uF bypass caps near the v+ anb v- power supply points, so i'll probably add a ceramic on the backside of the pcb if it fits there. Some friends of mine are using lt1364 there without any problem, so it should be ok.
I'm interested in this "upgraded" psu as well, however i think my next project will be a good 18v psu using lm317 voltage regulator. I don't really trust switching psus, even a good one that does the switching at very high frequency might oscillate with the lt1364(70Mhz bandwidth). Too bad the psu will be as big as the whole dac, damn toroids are too big
If you're using the amp from an analogue source, the audio signal is ac coupled by electrolytic nichion caps, it would be wise to replace them with polys or mkts if you have enough space to fit them. Everyone i talked to said the electrolytics should never be used in the signal path. I'm living at the students hostal and i have my tools at home, so i rarely have the chance to do some modding.

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Good to see so many discussions about this DAC. If you have some ability to DIY, here's a simple way to improve the sound of this DAC. The 1uF capacitor(the small 105 in the first picture) beside the PCM1793 can be changed. I've changed it with one EVOX 10uF MMK.

Mine has a bigger cap there by default:

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Don't know why but I can't see the picture. A bigger cap by default, really interesting.

Try this maybe. I rolled in the lt1364 to the lpf, its not hot or anything, i guess its fine and it sounds very good. LM4562 in the amp part, its not bad either, well better then the stock anyway, but i'll wait for the opa2111 before i decide.

Do you have the "upgraded psu" mk2+ model? On your screenshot your board is missing the whole power supply part lol, i guess there's an external +/gnd/- psu there

edit: Eugene, can i ask you to sum it up, what's happening in this thread? I've done an rmaa test today(only the dac, rca outputs at the back), and it doesn't look good.

You're right.I've used a psu which consists of a pair of 7812&7912. It was used for another headphone amp earlier.
Sorry but I don't quite understand what you want me to sum up. I feel puzzled when I see a full screen of English.

I've asked you to to tell us(translate) what has been said on that thread, because i can't speak chinese, and google translation is not good. Not the whole thread of course, but some important points. I've done another rmaa test, with lm4562 as lowpass filter, and the high thd is gone. Guess with stock psu, the 1364 is no good there.

I couldn't say what, but something isn't right with those test results. I've seen other tests done on this DAC, and - among other things - noise level and dynamic range should be in the 90s, or 80s with the headphone amp.

You should do one then Just use the rca output at the back. I don't have the stock opa2134 with me now, so i can't do one

OKOK,now I understand. I was so careless that I didn't notice "this" was a hyperlink. So sorry.
Give me some time, I'll translate some of the important points.