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Russ White  
#21 Posted : Wednesday, August 26, 2015 8:52:02 PM(UTC)
Russ White

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When you measure the output of the regs while in the whole system you can't help but observe the whole system.
Russ White  
#22 Posted : Wednesday, August 26, 2015 8:55:50 PM(UTC)
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What is especially telling is the freq of the peaks - very low. This seems induced. Any chance for pics of the rig under test?
igy137  
#23 Posted : Wednesday, August 26, 2015 9:27:19 PM(UTC)
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Russ, I very much appreciate your help :)
The thingy is pretty much disassembled now, I quickly took a photo as it's now, just buffalo and ps. It's basically as / or very similar as when I measured the tridents and placid.

(Tomorrow I can hook it up with the amp/ps and make another pic, but actually is the same "style", for example dac directly connected to the NC400 amp (with it's standard SMPS600 PS), all stock cabling.)

Edited by user Wednesday, August 26, 2015 9:32:27 PM(UTC)  | Reason: Not specified

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igy137  
#24 Posted : Wednesday, August 26, 2015 9:53:09 PM(UTC)
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I quickly put it up on my desk as I wired up for initial tests (the dsp board still not there, comes behind the dac, i2s lines isolated).
2nd pic showing the (once planned) final arrangement (dac inside the copper box, placid hd bp under the ivys).

(I tried also moving cables here and there and around with no influence heard at all, at least the output stuttering stayed for sure always).
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igy137  
#25 Posted : Thursday, August 27, 2015 5:21:21 AM(UTC)
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This morning the smallest one in the family got me up early, and I could not sleep back, of course, so... I hooked up the rig as shown in the above picture (on the table), and started doing some tests.

I verified that all is correct and there's no stutter at the output of the amp.
Then, I removed the added cap from DVCC. Started up, still no noise at the output.
Then, I removed the added cap from VDD_XO. Started up, and voila, the good old stutter could be heard from the speaker.

I guess this is a bit strange, but isn't it possible that that 12.5MHz oscillation I showed in the other thread here is really there, causing some issues, possibly HF oscillations on the output, driving the amp crazy, or similar? (So far I did not check the DAC output on scope, just with a soundcard and there it's reasonably clear).
greggtt  
#26 Posted : Monday, January 11, 2016 2:47:58 AM(UTC)
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Please revive this thread!

I've followed this with interest as I too experienced a noise coming from my current-release Buffalo-III, similar to what 'igy137' described. Based solely on information posted by 'igy137' and 'peteo' (thank you!), I completely eliminated the noise by placing a 4.7uF (tantalum) cap on the output of the VDD_XO Trident reg only. What I lose sleep over, and what both Igy and Peter have alluded to, is this a good fix or merely covering up an underlying problem that should be diagnosed?

My current configuration is:
TPA Toslink module -> coax wire -> miniSHARC -> I2S [1.5"] ribbon cable ->B-III/Tridents [purchased 3/15] 6-channel mode, volume control pot -> (6) shielded twisted pair cable ->(3) IVY-3 -> balanced amps. A single 5.0v linear reg feeds the TOSLINK board, miniSHARC and B-III/Tridents. I believe my layout conforms to general recommendations, and wiring/soldering to be of the highest quality. The noise was sufficiently loud to be heard 1-2' from a medium efficiency tweeter fed by a 27db gain amp, the same from all outputs and did not vary with the B-III's volume or miniSHARC setting. As Igy experienced, putting a cap only on the VCC_XO reg made it dead quiet.

Since I don't have a scope, my diagnosis is by listening what comes out of the speakers, which is why I've followed this thread so intently. Russ...Brian...someone(?), please continue it. Thanks.

Edited by user Monday, January 11, 2016 3:07:39 AM(UTC)  | Reason: Not specified

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