y1 gamma-1 DAC

[K3cT]

Quote:

Originally Posted by amb /img/forum/go_quote.gif It is not surprising that the volume might be very loud with sensitive, low impedance 'phones due to the strong output. If the software volume control doesn't give you enough control range, then you should either use an impedance adapter for your headphones, or better yet, a low-gain headphone amp with a proper analog volume control. Btw, those of you who want to use a y1 to drive low impedance headphones directly should use the WM8759 DAC chip rather than WM8501. The two are identical except the former has lower output voltage.

Sorry for bringing up a rather old post but I'm just curious, is there any problem driving headphones straight with the WM8501 and its higher output voltage?

 

[MisterX]

No.

 

[particleman14]

ok, so after having remounted and reflown u1u like 3 times i have now managed to break 2 pins on the sucker.. soo i guess for sure its U1 lol... however 2707s are out of stock for a while... so am I s.o.l? i tried to order 2 u1 from amb in case this exact thing happened, but he only allows 1 per y1 board.. do i have to buy another y1 board to get another 2707? because ill do it if i have to, i just wanna finish this thing. starting to get frustrating cuz i thought i was getting good at smd lol

 

[ShinyFalcon]

Which pins did you break? (with respect to the dot)

Good thing is, you probably won't have to worry about desoldering U1U if you buy another y1 board.

You only need to populate a new USB board.

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Edit: I populated a left over y1 DAC board, and have set it up for DC input only. I omitted the 4.5V regulator and hard wired pin 2 of J4D to the 4.5V test point. I also omitted C10D, but should I populate it?

Is there a reason a resistor network is chosen besides convenience? I used individual 75 ohm resistors since Mouser did not have the 68 ohm Bourns resistor network in stock, and tried my best to keep the leads the same length. Should have gone SMD here...

 

[particleman14]

they would be pins 28-29.. looks like my y1 project is on hold as 2707 and 2706s seem very scarce at the moment..

 

[ShinyFalcon]

Those pins are not used in the y1.

 

[particleman14]

I know, and it still doesnt work.. here are some pics with a better camera.. but not better cameraman..Image upload, up to 2 Mb - Free image upload and image hosting - image upload @ filetac.com

 

[ujamerstand]

I've got a pcm2707 lying around for a grubDAC that probably won't be built in a while. My problem with y1 doesn't seem to be related to pcm2707 either. So if you don't mind international shipping, I can get it in the mail for you. PM me.

 

[particleman14]

so im checking all of the circuits and I may have narrowed it down a bit.. I am getting good voltage (3.3) on pins 24,21,15,10. good voltage on all the other u1 pins (3.3v pin2) (5v pin 3) (1.45v pin 12 1.575v pin13) However on pins 22,23 what measurements should i be getting there?
so if those readings are correct on my U1 so far then would it be something connected to the J1U circuit that is being funky?

 

[ujamerstand]

Quote:

Originally Posted by ujamerstand /img/forum/go_quote.gif The low resistance reading disappeared overnight. It is now over 1M ohm at both U1D and U6D. It was probably because of a short created after I cleaned the board with some alcohol. Thank god I did not plug it in for testing after that. The voltage readings at 4.75V point is a constant 4.74V as of now. The voltage drop on the 3.3V point stabilizes at around 2.93V. Neither chips gets hot during operation.

Well, I've decided to replace the 3.3V regulator and see what happens. Does anyone know what might cause this type of weird behaviour? A short somewhere? The strange thing is, the voltage "spikes up" to 4V sometimes at 3.3V position, then returns to 2.92V; which suggests a cold joint. But I've already reflowed all the joints on the same path as the 3.3V regulator; and it does not explain the initial 4.85V reading at the 3.3V test point when I plug y1 in. Which is why it's so strange...

 

[particleman14]

quick update: after reflowing many parts, my pins 22, 23 d+ d- pins on u1 are reading 3.11V and like 11mv. I know d+ has to be brought up to to 3.3v so is 3.11v within tolerance? also when measuring again i am getting 3.0v on pin 12 which is in the crystal circuit but on the other pin 13 i get 3.3v perfect.. are my voltages in the ballpark?

 

[ujamerstand]

My y1 stops singing at around 3.02V. That's on the DAC side. After you ohmed out everything and made sure there's no shorts, why not give it a try?

 

[particleman14]

ive tried but i still keep getting the usb not recognized.. i am suspecting the crystal circuit as pin 12 gets 3.3v and pin 13 3.0v. perhaps this 3v pin13 is the problem? still unsure but i feel im close..

 

[amb]

particleman14, measuring DC voltage with a DMM on "signal" pins is not very useful. To see whether the crystal is working you'd need an oscilloscope.

 

[ujamerstand]

I have determined that the u5d is not the device at fault. After replacing the chip with a new one, the voltage readings is still elevated at 4V. It then slowly decreases just as the original chip behaved. I must add that this did not happen when gamma-2 module is non-functional. I will proceed to test by bypassing the gamma-2 module with wires.

Edit: Well, gamma-2 is not at fault here either. (Why would it, anyways? Oh well.) So something must've happened when I was reflowing the solder at the DAC section. Arg. Now I have no idea what to do. Help?