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tdmckellar  
#1 Posted : Tuesday, November 19, 2019 9:04:16 AM(UTC)
tdmckellar

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My build consists of a B3 DAC and IVY-III with the Placid HD and HD Bipolar power supplies. I also have an AMB Sigma11 PSB which powers a raspberry pi and arduino controller. This PSB is effectively always on. The arduino controls a cheap relay which provides an on/off switch to the Placid power supplies which turn off the audio components.

I completed my build around a year ago, but typically turn off the power to my amplifiers first then power off the DAC. The other day I turned off the DAC first and noticed a loud pop through the speakers as soon as the relay clicked off, then a strange sort of high-frequency garbled noise for half a second. This doesn't happen when powering on the Sigma11, just when the power is applied through the relay to the Placid's.

I measured for DC offset at the loudspeaker terminals. With no music playing and with the Placids off, I get a reading of around 23mV. When on, this is around 24mV. When I power off, I get a spike for half a second up to around 150mV, dropping to around -24mV then back to 24mV. These measurements were from the Right Channel, strangely, the Left Channel measured at 5mV more.

Can someone please advise what the issue is and how to fix this?

I am thinking it may be an issue caused by the relay, and perhaps a better quality one incorporating a soft start module or perhaps simply a safety capacitor across the primaries of the transformers may help?

Thank you.
tdmckellar  
#2 Posted : Wednesday, November 20, 2019 11:43:39 AM(UTC)
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Tested further...

Unplugged the XLRs to my 2 NCore amplifiers and there is no noise, silent power on and power off. This leads me to believe it may be a grounding issue (I had thought of this but assumed noise due to a ground loop would be heard constantly and not just during powering down, unless it being tied to the IVY-III signal ground was dealing with it while the unit was on - and then it discharging as it was shut down?).

Anyway, the outputs from the IVY-III are wired with the Positive, Negative and GND all connected from the output stage to the Neutrik XLR Chassis Connectors. Pin 1 is not tied to the chassis at the connector. On the NCore Amplifier side, Pin 1 is connected to the chassis. On both the amplifiers and the DAC power GND is tied to the chassis.

I tried this morning disconnecting pin 1 from the chassis but it doesn’t make any difference. I think perhaps something I overlooked is that the Neutrik XLR Chassis Connectors are connecting Pin 1 to the chassis and perhaps I need a connector with an isolated ground? The issue is only with power off. When on it’s all dead silent with music playing wonderfully.

Does this theory make sense as to the issues I am having? Next chance I get I plan to disconnect the XLR connectors from the chassis and try hooking it all up to see if that makes a difference. Other than that I am a little lost as to what to do. Any help would be appreciated!

Edited by user Sunday, November 24, 2019 12:51:01 PM(UTC)  | Reason: Not specified

tdmckellar  
#3 Posted : Sunday, November 24, 2019 1:03:11 PM(UTC)
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Can anyone help?

Tested further and think it is DC offset not a signal grounding issue.

Would a relay or suppression capacitors at the output solve the issue or would this effect the sound?
Brian Donegan  
#4 Posted : Monday, November 25, 2019 3:20:37 PM(UTC)
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Sorry for the delayed response. I have been out of town visiting family....

A couple questions:

1) Does the power relay control the AC input to the Placids, or the DC outputs?
2) Does it control power to both the DAC and the IVY?

It sounds like the IVY is staying on while the DAC powers down. There are relays on the IVY to prevent thumps, but I think you are hearing the DAC output (which has a virtual ground created from the 3.6VDC AVCC supply) collapsing before the IVY turns off.

I would try removing the GND output from the IVY to the XLR, and keeping the XLR isolated from the chassis to see of that helps.
tdmckellar  
#5 Posted : Monday, November 25, 2019 7:40:34 PM(UTC)
tdmckellar

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No problem thank you for your reply.

In reply to the above, the relay controls AC input into both the Placid HD and the Bipolar, powering them up and shutting them down at the same time.

Wondering whether it has anything to do with using a AVCC SR (which was a replacement for a broken AVCC version) while also using the V3 Tridents?

I have tried as you suggested by removing the ground connection from the IVY to the XLR connector but it does not have any effect. I tried powering the IVY on it’s own and it still produces the same noise, although a little quieter.

Is there anything I can add in the outputs on the IVY to suppress this and would it effect the sound, or would an upgrade to a Mercury solve the issue?
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