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SteveMiller929  
#1 Posted : Monday, June 4, 2018 3:33:21 PM(UTC)
SteveMiller929

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HI All.

I have assembled a few of the Opus Dac's and SPDIF Rx's now and the sound freakin awesome!

I am using in my system as follows: Cambridge CXC transport ->spdif rx->Opus (Volumite) -> XLR input to Amplifier

The Opus and Spdif are powered by a LCDPS and the trafo is switched on/off at the IEC filtered inlet.

When I shut down the LCDPS that feeds the dac/spdif I get an extremely! loud Pop. Its full scale gunshot loud regardless of the Volumite position. (400W amps into 102Db speakers)

If I shut the amps off first, then its ok...but I'd rather let them sleep-mode themselves, and just shut down the Dac.

Also, If the transport sleeps, when it wakes I get a loud static thats alarming but maybe not as explosive.

1) Is there some other method I should use to power off the Dac? Commercial Dac's dont have this problem in my system... ( But MiniDSP NanoSharc did also )

2) Is there not a provision for the SPDIF rx to recognize the transport is not sending AudioData and to mute until its valid? (My LED is ALWAYS green for AudioData, the rest go red when trnasport shuts off)

3) Has someone implemented a MUTE relay or something reasonably simple that works for power on/off's ?

( I AM using the Opus with the output caps in place so I was very surprised that this power off shot occurs?!)
Brian Donegan  
#2 Posted : Monday, June 4, 2018 3:44:11 PM(UTC)
Brian Donegan

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This is a classic symptom of DC offset on the signal lines. The amps deal with it while playing, but when it collapses, you get a sudden spike, as the reference ground shifts.

The solution is to either add inline capacitors, or an output stage between the Opus and the amp.
SteveMiller929  
#3 Posted : Monday, June 4, 2018 3:48:40 PM(UTC)
SteveMiller929

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Thanks Brian for the quick reply!

I agree. Seems Like a DC thing to me also...

I am using the Opus WITH the Elna's installed at the output...(C5-C8) Is this not the "inline capacitors" you mean?

Sorry if I'm dense. I haven't tried without these caps bc I was worried it could be this or worse.






SteveMiller929  
#4 Posted : Monday, June 4, 2018 3:52:36 PM(UTC)
SteveMiller929

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I have been looking at "Muting relay" circuits but without opamps in the signal path, the relay would effectively just short the Dac to ground. That seems like a bad idea to me.


If possible I'd like to avoid the output stage additional components, because while playing, I have the absolute best sound and most direct emotional connection I've ever experienced in 2 channel audio...ever -at ANY price.

could my relatively short (6') XLR's be at fault here somehow? Wondering if I could measure for this issue by some means.

Brian Donegan  
#5 Posted : Tuesday, June 5, 2018 6:53:27 PM(UTC)
Brian Donegan

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I don; think your XLR cables will have any impact on this.

One thing you can try: eliminate the GND connection in your XLR connectors, so that you are sending just + and - signals.
SteveMiller929  
#6 Posted : Tuesday, June 5, 2018 7:23:57 PM(UTC)
SteveMiller929

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Thanks Brian. Will try that for sure.

I have to figure a way to "measure" this so that I can test for the POP without subjecting my amps and speakers to it.

If the amplifier is marketed as DC Coupled, would you expect I could simply remove the caps from the Opus output?
Possum  
#7 Posted : Saturday, June 9, 2018 4:15:04 AM(UTC)
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On the subject of connecting up balanced inputs/outputs in general, isn't it advisable to never connect ground so as to prevent ground loops and isolate muck?

I never connect ground between the DAC and Legato, or Legato and Symphony for example. Works fine...
Brian Donegan  
#8 Posted : Thursday, June 21, 2018 11:56:39 AM(UTC)
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Never say "never." It really depends on the situation, but often is can be left out.
SteveMiller929  
#9 Posted : Friday, March 15, 2019 1:34:58 AM(UTC)
SteveMiller929

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In returning to this issue... I lifted the grounds and had no joy. still LOUD pop.

I've also noticed a static/surf type noise at times when no music playing.

My question now becomes, what is the method to trigger MUTE on the Opus from the SPDIF TX module?

Is there an output from the SPDIF that could mute the Opus?

Thanks in advance !!
Brian Donegan  
#10 Posted : Friday, March 15, 2019 3:15:09 PM(UTC)
Brian Donegan

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Try measuring the DC on the analog outputs of the DAC (Multimeter set to DC voltage, between + and -, + and GND, and - and GND.

The best solution would be an output stage after the DAC, as it will also filter out digital noise.
SteveMiller929  
#11 Posted : Sunday, March 17, 2019 3:01:53 AM(UTC)
SteveMiller929

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Thanks Brian

I am looking at the options on your site for just that.... I agree an output stage should resolve the DC.

......... but still with the muting... can one of the triggers from Spdif ( maybe CSB ) be used to engage the MUTE function of Opus when the data is no good?

Ie; I had a Volumio scare recently where the data rate didn't match and squealed like crazy.
SteveMiller929  
#12 Posted : Sunday, March 17, 2019 3:12:23 AM(UTC)
SteveMiller929

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Actually. Embarrassed. I just figured out how to search the lengthy development thread.... Post #1790 indicates that connecting GEN_FLAG to the Opus board will serve this'll purpose.

Thanks as always.

Still a happy customer and user and listener !!
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