Gamma-2 (γ2) DAC Thread
Jan 31, 2014 at 9:19 PM Post #2,132 of 2,154

rbc3

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I am interested in adding balanced out to the Gamma2 I'm building because I want to drive a fully balanced amp.  I'm considering a Violectric HPA V181 to go with my Hifiman HE-500.  I have a couple of questions.  It's my understanding that one of the main benefits to running balanced is that by not having a common ground between the two channels, channel crosstalk is eliminated or at least significantly reduced.  But it looks like the ground is shared for the balanced outs.
 
I'm just looking for a sanity check that I should wire the ground near the Right and Left positive and negative balanced leads to the ground pin in a 3-pin XLR.
 
My plan is to drill some holes in one of the plates and mount a pair of these mini XLR 3-pin sockets for Left and Right balanced outs, along with the serial 22uf caps and 100k resistors from the Right and Left positive and negative to ground as shown in the Twisted Pear Opus schematic.  Here are the sockets I want to use.  I'm looking for confirmation that these will fit.  The back mounting nuts are 14.2mm diameter and the hole diameter for the socket needs to be 11.2mm.  Will the nuts fit between the Gamma 1 and Gamma 2 boards?  Since I'm not done with the build I don't know the distance between the two boards.
 
http://www.rean-connectors.com/en/products/tiny-xlr-chassis-connectors/rt3mp
 
If this doesn't work, I'll run cables out of the case to some XLR 3 pin plugs.
 
Thanks for any help,
Robert
 
Feb 1, 2014 at 10:53 AM Post #2,133 of 2,154

rbc3

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Another thought I have is to sacrifice the mini stereo output socket on the front and mount a Mini 4pin XLR socket there in its place. I can then build a custom Mini 4pin XLR to 2x 3pin XLR splitter interconnect cable and solder the shield to the grounded coupler on the Mini 4pin XLR plug since the ground for each channel doesn't appear to be seperate.

I should be able to finish up my build today and take some measurements to figure out if the Mini XLR socket will fit or not.

It would be a great help to get some feedback about the ground from someone who has a better grasp of balanced signals than I do. This will help me make a decision about two separate Mini 3pin XLR sockets vs. one Mini 4pin XLR socket.

-Robert
 
Feb 12, 2014 at 5:25 AM Post #2,135 of 2,154

amb

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From the "Parts list" section of the γ1 website:

"A 5V DC regulated AC adapter ("wallwart") or external 5V DC regulated power supply may be used to provide power to any γ1 configuration equipped with U1D and the 1.3mm DC power jack.

The AC adapter or power supply's output plug should be a barrel-type with 1.3mm ID female, the polarity is center-positive. A compatible plug for the 1.3mm DC power jack is the CUI PP3-002D (Digi-Key CP3-1003-ND).

The appropriate input AC mains voltage, frequency and plug style depends on your country. The output voltage should be between 4.85V and 5.4V DC, with a minimum current capacity of 300mA.

..."
 
Feb 17, 2014 at 3:09 PM Post #2,136 of 2,154

dhp

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So sadly I am having issues with my y2 build... the y1 side works perfectly and i can hear music just fine.  When I mate with the y2 board, all the voltage checks are fine (5V pin reads out at around 4.85ish, which I think would be ok?)  Initially when I set it all up, I was getting music out of the stereo output of the y2, but then when I unplugged the usb and replugged it, the sound started dying and then just stopped altogether.
 
I would like to bypass the ASRC and see if I can test U5.  Would jumpering JP2-n as well as lifting the input pins on U4 (pins 2, 4, 5, 6) be sufficient to achieve that? 
 
Feb 17, 2014 at 3:16 PM Post #2,137 of 2,154

amb

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No, to bypass the ASRC you would also have to remove the X1 oscillator. I don't recommend that as a way to debug it. Try inspecting and reflowing the solder joints on the ASRC and DAC chips, as well as on X1.
 
Feb 17, 2014 at 3:27 PM Post #2,138 of 2,154

dhp

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No, to bypass the ASRC you would also have to remove the X1 oscillator. I don't recommend that as a way to debug it. Try inspecting and reflowing the solder joints on the ASRC and DAC chips, as well as on X1.

 
I did try reflowing all the solder joints, although those ground pins have been making life difficult even with the iron turned up to 850F.  Are there any other checks I might do?  The fact that the y2 board is mated to the y1 seems to make some debug checks difficult.  
 
Feb 17, 2014 at 3:41 PM Post #2,139 of 2,154

amb

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Inspect the solder joints with a loupe and see if there might be solder bridges or cold joints. Most problems with these builds are solder-joint related and yours is most probably no exception.
 
Jun 28, 2015 at 3:36 AM Post #2,143 of 2,154

amb

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If it's a γ1 + γ2 combo, and U1D is installed, then you can just plug in an external 5V DC regulated power supply. The DAC auto-selects the external supply when both USB power and external power are connected simultaneously. There is no need to set jumpers.
 
Jun 28, 2015 at 12:38 PM Post #2,144 of 2,154

JustinBieber

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It's a combo and U1D is installed and JP2D is open. So, I guess it has to be something else causing the noise. It isn't hum, but static and hissing. The noise goes away when my CPU is at full power when benchmarking with Prime 95. If you close P95 the noise is there again... odd.
 
Also, when I'm using a different input, like optical, when I plug in the USB cable the noise instantly comes back. 
 
Just noticed this too, should I replace that cap?
 
Thanks for the advice everyone. 
 

 
Jun 28, 2015 at 2:33 PM Post #2,145 of 2,154

amb

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Is your computer a desktop or laptop? If the latter, does this noise occur when running on battery? Also what are you using as an amp? Is it AC powered too?

I suspect a ground loop via your USB cable:
computer > USB cable > gamma2 > interconnect cable > amp > AC power cord > wall outlet > AC power cord > computer

That melted cap is likely due to a soldering iron mishap. If it looks ugly to you then replace it, but it's probably still working fine.
 

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