[ATAT]

Cue Rickr with his transformers.... =)

mmm the DRV134 sounds like it'll end up easier than buying a transformer.. eh might end up doing it.. jensens arn't cheap

 

[ATAT]

Sighs.. it says "USB device not recognized"

So far I've traced all the power pads, checks out according to schem (3.3 v & 5v to right parts)..

Looked for solder jumps, checked continuity on every pin.. No go.

The 'Scope shows something weird.. D+ jumps to high and stays at high (with some rippling it seems) once plugged in.. D- stays at low. (I think thats what it is at least..)

All the power regulation sections check out as they're outputting the right voltage.. frequency of the crystal checks out..

Any suggestions? (including how to desolder the 2704)

 

[Alf]

Quote:

Originally Posted by ATAT Sighs.. it says "USB device not recognized"

I saw this once. I re-connected the USB cable and the problem was gone. I assume you have done this already.

Quote:

Originally Posted by ATAT So far I've traced all the power pads, checks out according to schem (3.3 v & 5v to right parts).. Looked for solder jumps, checked continuity on every pin.. No go.

Can you post a few pictures of your board? Meanwhile I suggest that you check again all PCM2702 pins and the USB socket.

Quote:

Originally Posted by ATAT how to desolder the 2704

Be prepared to damage either the chip or the board. If you decide to kill the chip, I suggest using good tweezers and desoldering each pin individually.

 

[ITZBITZ]

Quote:

Originally Posted by Alf Magsy did tests with EMU0404. The best figures were when connected to a laptop. It did not matter whether it was USB or battery. Then goes PC/battery and the worst one is PC/USB. There is no information whether ITZBITZ used a laptop or a PC.

My testing was done with a 1212m on a desktop PC with the USB card hooked to the same PC, albeit a different port. Battery power was the quietest of the three options. Even on a Dell 5100 (at that time), there was a small amount of noise on the bus-powered setup.

Anybody tear down a Plantronics USB GameCom Pro 1 and see what's inside? It's a pretty basic chipset, but it's the same concept, is bus powered and I get no audible noise with the stock headset. I'm thinking of buying another one and tearing it apart to put a 3.5mm jack on it to hook up my Shure e4c's to see how they sound powered by it.

 

[Alf]

Quote:

Originally Posted by 00940 Alf : if you consider going that road, you could perhaps change the REG102 for the TPS793** serie. Those regulators are cheaper, almost as good and there's one that outputs 4.75V if you feed him with 5V. It will allow you to cope better with varying usb voltages (some usb ports don't output the full 5V). The PCM2702 can live according to the datasheet with as low as 4.5V.

Good point! The SOT23 versions of the chips seem to be pin-compatible. I will change the package to SOT23 catering for both chips.

 

[Alf]

Quote:

Originally Posted by guzzler Interesting Alf, how reproducable are the results on the cable and port? I'm tempted to think a 1dB difference is sensitive to the setup, and certainly not audible. A 7dB reduction by skipping the switching regulator is good, and definately remove it if it gives such a good improvement (although still probably not hearable )

I can reproduce the results all the time. However the results are a bit odd. If I use switching regulator with USB, the expensive cable gives slightly better results (< 1db). If I skip the switch, the printer USB cable is better (~3db).

 

[Clutz]

I'm back after being on Christmas vacation for a few weeks. My boards are ready and I'm dying to get at them. Sorry for taking so long to put them together - life has just got in the way. Anyway, I'm going to put together a parts list tonight and make my order. Any general parts recommendations? I've noticed that Alf has made a number of modifications so far- have they been c ompiled anywhere yet?

Cheers,
Clutz

 

[Alf]

Quote:

Originally Posted by Clutz Anyway, I'm going to put together a parts list tonight and make my order. Any general parts recommendations?

* Output capacitors do matter. Get the best you can find. Elna Silmic II produces better results than Panasonic FM. If your amp benefits from input coupling capacitors, then do not populate CL/CR.

* If you populate CL/CR, use a 5mm/D 2mm/P capacitor for C24. Soldering would be much easier.


Everything else as described here http://www.myexposition.com/diy/usbdac/partslist.html

Quote:

Originally Posted by Clutz I've noticed that Alf has made a number of modifications so far- have they been compiled anywhere yet?

If you mean the changes since Rev A, then have a look here

http://www.myexposition.com/diy/usbdac/overview.html

 

[Clutz]

Quote:

Originally Posted by Alf * Output capacitors do matter. Get the best you can find. Elna Silmic II produces better results than Panasonic FM. If your amp benefits from input coupling capacitors, then do not populate CL/CR.

Re: Capacitors, I was going to go with Blackgates- any particular line of black gates that are ideal in this case? Re: input coupling capacitors- I have no idea if it does or doesn't. I am going to use it with a Millet, a PPA, and (eventually) a Dynalo and a M3.

Quote:

Everything else as described here http://www.myexposition.com/diy/usbdac/partslist.html

I guess I meant more along the lines of some of the experimenting that you've done.

Quote:

I decided to check it out. I connected S1 to AV+. My DMM showed 4.9V at the 5V pad and perfect 3.3V at the 3V3 pad. It was close enough and the DAC was working! Then I decided the check how (bad) it performs. RMAA produced results that indeed surprised me. Bypassing both the switch and LM317 improved the performance significantly. The figures went from mere 85db up to 92-93db. I repeated my tests a few times trying different configurations but the results were consistent.

Have you done any more experimenting this way?

 

[dsavitsk]

Quote:

Originally Posted by Clutz Re: Capacitors, I was going to go with Blackgates- any particular line of black gates that are ideal in this case?

I would use blackgate N series 4.7uF 50V caps. They sound quite good -- better than a lot of film caps -- and are easy to source. It appears they will fit the board, though they might be a tad small so you'll need to bend the leads. I know that the schematic says to use 47uF, but this is really silly. 4.7uF is more then large enough for source output caps. Here are my thoughts on some other (mostly cheap, mostly film) caps as well: http://www.ecp.cc/cap-notes.html

Quote:

Re: input coupling capacitors- I have no idea if it does or doesn't. I am going to use it with a Millet, a PPA, and (eventually) a Dynalo and a M3.

The Millett has no input caps, and the others don't unless you put them there.

 

[Clutz]

Quote:

Originally Posted by dsavitsk I would use blackgate N series 4.7uF 50V caps. They sound quite good -- better than a lot of film caps -- and are easy to source. It appears they will fit the board, though they might be a tad small so you'll need to bend the leads. I know that the schematic says to use 47uF, but this is really silly. 4.7uF is more then large enough for source output caps. Here are my thoughts on some other (mostly cheap, mostly film) caps as well: http://www.ecp.cc/cap-notes.html

What do you think of Aerovox AFPS 4.7uF film caps for this position? They're axial instead of radial - but with lead bending could be made to work.

 

[dsavitsk]

Quote:

Originally Posted by Clutz What do you think of Aerovox AFPS 4.7uF film caps for this position? They're axial instead of radial - but with lead bending could be made to work.

I like them. I use them on my own DAC (with a bit of lead bending.)

 

[Alf]

Quote:

Originally Posted by dsavitsk I would use blackgate N series 4.7uF 50V caps. They sound quite good -- better than a lot of film caps -- and are easy to source. It appears they will fit the board, though they might be a tad small so you'll need to bend the leads. I know that the schematic says to use 47uF, but this is really silly. 4.7uF is more then large enough for source output caps.

Agree. Even 4.7uF is overkill. 1uF should be enough.

Quote:

Originally Posted by dsavitsk Here are my thoughts on some other (mostly cheap, mostly film) caps as well: http://www.ecp.cc/cap-notes.html

Great article!!! I wish I had ears like yours. I am doing a lot of testing now. I suspect I fail to notice a lot of obvious things.

Would you be able to review other electrolytics? Something well regarded and popular – Silmics, Muse, etc.

 

[dsavitsk]

Quote:

Originally Posted by Alf Great article!!! I wish I had ears like yours. I am doing a lot of testing now. I suspect I fail to notice a lot of obvious things.

Thanks. I'm not sure that any of the distinctions are obvious. A lot of times it is putting something in the circuit, and after a good long listen just having a sense that something is good, or amiss. Since it is so subjective and subtle, I did try to listen to each cap a couple of times and in different orders, though I really need to get someone else to do the swapping so I don't know what they are.

Quote:

Would you be able to review other electrolytics? Something well regarded and popular – Silmics, Muse, etc.

It's a good idea, and something I should try. I know that my Millett which has Muse's sounds hard, but whether this is the caps or something else is a mystery to me. It doesn't see enough use to worry much about. I do have Duorex II's, Os-Cons, BlackGate's, FM's and Muses around, so maybe when I get a free evening or two I'll try them out.

-d

 

[Alf]

Quote:

Originally Posted by Clutz Re: Capacitors, I was going to go with Blackgates- any particular line of black gates that are ideal in this case? Re: input coupling capacitors- I have no idea if it does or doesn't. I am going to use it with a Millet, a PPA, and (eventually) a Dynalo and a M3.

Yes, you need CL/CR in this case. I suggest you try different output capacitors to find the sound you like.

Quote:

Originally Posted by Clutz I guess I meant more along the lines of some of the experimenting that you've done.

If you have some time to spend, it would be interesting to see how different parts affect the performance. The output capacitors is the most important factor here. But other parts contribute as well. It is always useful to use RMAA to confirm your findings. It helped me a lot.

Quote:

Originally Posted by Clutz Have you done any more experimenting this way?

I finished the noise tests. The results are consistent. I cannot improve it further. I cannot say whether Rev B is better than Rev A. The computer does makes some difference and I do not have a working Rev A DAC to compare it with. If someone can send me a Rev A for comparison, I would greatly appreciate this.

Now I work on adding a headphone section to the DAC. Actually I am listening to a breadboard prototype while I am typing this. It sounds promising. We should be able to get a decent bus-powered USB headamp in the 1455C80x case.