[guzzler]

Have you measured all the voltages in the circuit, you should get almost exactly 5V and 3.3V from each the regulators. The voltage out from the MAX1722 should be pretty much 5.5V. Check connections from the PCM2702, and also the coupling capacitors.

g

 

[individual6891]

Quote:

Originally Posted by guzzler Have you measured all the voltages in the circuit, you should get almost exactly 5V and 3.3V from each the regulators. The voltage out from the MAX1722 should be pretty much 5.5V. Check connections from the PCM2702, and also the coupling capacitors. g

After replacing most of the chips (cos they fried the first time due to the +ve on the wrong pad).. I get 3.3V and 5.0V

The PCM2702 pins seem to be ok, though one of the pads came off the PCB, but it doesn't connect to anything (definitely sure on this). I used a DMM to check for continuity between pins, but i'll double check later. It fuzzes quite a bit when you turn the headphone amp's volume knob - maybe an impedance issue?

 

[guzzler]

Yep, I was going to say it might have been an impedance issue. What's the value of the pot on the headamp? Sorry about the error on the page, I've changed it now. If it's a write off, I'm happy to ship you out another for free, as it's entirely my fault in that regard....

g

 

[individual6891]

The pot is 50K, going into a standard MINT design.

The boards only slightly damaged with some (useless) pins missing, but I'm not sure if it's something underneath the chip that I can't see - really shouldn't be, cos I doubled checked most of the parts which looked abused, and they seem ok. Not sure if a new PCB is needed or not, quite difficult to desolder the PCM2702! If you have a spare PCB, I could try it again I suppose, but it's up to you

 

[dsavitsk]

For those interested, I posted a review of this DAC at http://www.ecp.cc/gud.html. It is still a bit of a rough draft, and as such may get updates at some point.

If anyone has a better picture of an assembled unit that I could use on the site, please let me know.

-d

 

[00940]

I'm curious about that problem of bit perfect output and resampling issue. Here is what the engineer of Grace replied when asked about the digital output of the pcm2902:

Quote:

I have not tried the asio4all driver yet but the tests I have done on the PCM2902 (the usb controller in the m902) with windows 2000 and xp pro as well as mac osx using the generic drivers that load automatically have all resulted in bit perfect data transfer. However, there are some situations I found in mac osx were the os does some sort of sample rate conversion and the data is not transfered error free. It is not obvious when this is happening unless you can monitor the data stream coming from the PCM2902 with a bit analyzer. As soon as I get a chance I will post all of the setup details for each os.

 

[dsavitsk]

Quote:

Originally Posted by 00940 I'm curious about that problem of bit perfect output and resampling issue. Here is what the engineer of Grace replied when asked about the digital output of the pcm2902:

I seem to remember this guy http://www.wavelengthaudio.com/Cosecant.html claiming bit perfect output over USB from a Mac with simple settings in iTunes, though I am not seeing it on the site anymore.

Interestingly, though, he is claiming that the volume should be at 50% on windows, With the guzzler usbdac, there s definitly stuff missing with the volume at 50%. Compensating by turning up the amp volume, I think it sounds flat, but maybe I am just imagining it?

-d

 

[00940]

No, you're right, turning down the volume kills the dynamic range.

Did you try to use asio4all ? It works well with the USB dac but I couldn't get a difference compared to the standard windows drivers, this with a gilmore and grado sr225.

 

[Magsy]

Hmm I've had the same problem.

I am at this moment putting my mint and dac in a box, I put a OPA2227 on the mint in place of the previous AD8620 and its now pretty much perfect...

 

[individual6891]

Hmm I'm using an AD8620 with the fuzzing during volume change, do you think it's definitely the opamp to blame?

 

[individual6891]

Hmm still not working well at all..

Guzzler, any chance you could send over a replacement PCB?

 

[guzzler]

YGPM

Quote:

Originally Posted by individual6891 Hmm still not working well at all.. Guzzler, any chance you could send over a replacement PCB?

 

[Kenny12]

how do u guys mount ur pcbs? semms very hard

 

[z2trillion]

Quote:

Originally Posted by Kenny12 how do u guys mount ur pcbs? semms very hard

Yeah, soldering the components was surprisingly easy, but i'm having trouble figuring out how to case it up. The square usb connector doesnt help.

 

[dsavitsk]

Quote:

Originally Posted by z2trillion i'm having trouble figuring out how to case it up. The square usb connector doesnt help.

I used one of these http://www.datapro.net/products/1591.html