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repelsteeltje  
#1 Posted : Monday, September 7, 2015 8:47:22 AM(UTC)
repelsteeltje

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Hi all,

Luckily I solved the problems with the current on the right channel of the Legato. So everything seemed ok. SE is indeed working fine. However, the balanced output gives me a clicking noise when adjusting the volume on the pre-amp. At higher volumes these get pretty loud. One time my power amp turned into some kind of safety mode due to this.

It seems to be some kind of ground problem. I tried disconnecting the ground of the XLR connectors. No luck there although they seemed somewhat less loud. Are there any alternative set ups I could try? For example place capacitors between output of the legato and the connectors just on the GND? Obviously I want to avoid placing capacitors between output and the connectors because that's one of the main reasons I bought the new Legato board in the first place.

When further info is needed please let me know. Many thanks in advance!

repelsteeltje  
#2 Posted : Friday, September 25, 2015 12:10:13 PM(UTC)
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Anybody any ideas for a different set up (grounding-wise)? Would be much appreciated !
Brian Donegan  
#3 Posted : Monday, September 28, 2015 3:07:49 AM(UTC)
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Originally Posted by: repelsteeltje Go to Quoted Post
Anybody any ideas for a different set up (grounding-wise)? Would be much appreciated !


My first guess is that it's the DC-offset to GND on the balanced outputs.

What kind of preamp is it? Ideally you can just remove the signal ground connection between the Legato and the preamp. Worst case, you will need some coupling capacitors.
repelsteeltje  
#4 Posted : Friday, October 9, 2015 12:46:51 PM(UTC)
repelsteeltje

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Hi Brian,

Thank you for you reaction. The GND is already disconnected between legato and the XLR connector in the dac. So I measured GND (XLR) to GND (Legato) which was 0,1mV. Was this what you meant by DC-ofsett to GND?

The pre-amp is a primare PRE30 going into an A30.2 power amp.

Thank you once more
Brian Donegan  
#5 Posted : Friday, October 9, 2015 10:10:31 PM(UTC)
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Confirming, when you use the SE output, there is no clicking?

Also, check the continuity between the XLR output ground and the chassis. You want that to have no conductivity.

I suspect the DC-offset because it can cause clicking in relay-based or digipot-based volume controls. Some digital volume controls have zero-crossing detection to make interval switches when the AC voltage goes through 0V to prevent this.

The next test will be another balanced source using the balanced inputs of the preamp to confirm there is no popping.
Brian Donegan  
#6 Posted : Friday, October 9, 2015 10:28:05 PM(UTC)
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This is the datasheet for the DS1666 digital pot used in the preamp.

It does not mention anything about zero-crossing detection, nor DC-offset. So, we need to make sure there is none.
repelsteeltje  
#7 Posted : Tuesday, December 1, 2015 3:22:46 PM(UTC)
repelsteeltje

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Hi Brian,

It has been some time since your last message. We have been running some additional tests and connected a second buffalo dac with Legato 3.1 which created the same popping issue (no such issues on another amp). So it must be primare related. Not sure if the popping when flicking the volume knob or switching channels can cause any serious damage but opted for some coupling caps which will be installed shortly. Assume the problem will be solved with them.

Thank you for your help so far!!
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