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arvema  
#1 Posted : Monday, December 17, 2012 4:45:31 PM(UTC)
arvema

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Due to the DC on the balanced output of Legato, the Hypex Ncore NC400 is not playing properly when connected directly to the balanced outputs. When I connect Ncore to SE with the hot to + and the cold, the ground, as well as nAMPON cable to the ground, the Ncores play apparently fine.

But the balanced output should be sonically to prefer, and I need some advice here. What would be the best solution?
1.) To use the SE as described.
2.) To buy an IVY III insted, if there is no DC on the output.
3.) To use coupling caps to remove DC and in this way connect to the balanced out from Legato.

Regarding coupling caps, I do not have the technical knowledge to fully understand how to make the right choices. And I have not found a recommended value for the coupling caps between Legato and Ncore. Therefore two more questions:

a.) On the Ncore datasheet (http://www.hypex.nl/docs/NC400_datasheet.pdf) the DM Input Impedance is given as 104 kOhm. This calculator (http://www.v-cap.com/coupling-capacitor-calculator.php) provides a value 0.77uF for -3db Frequency of 2Hz. Is this a good choice?

b.) My last question regards the kind of capacitor to select. Has anyone something to recommend? What about the expensive ‘high end’ ones as evaluated here: http://diy.ecpaudio.com/...oupling-capacitors.html?

Sorry for my lack of knowledge. Hope to get some help.

Edited by user Monday, December 17, 2012 4:46:36 PM(UTC)  | Reason: Not specified

Russ White  
#2 Posted : Monday, December 17, 2012 6:21:34 PM(UTC)
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Any good quality 2uf film cap would be fine (25V or more rating) . You will pot those in series with the +/- outputs to the XLR then connect GND on the XLR directly to power GND as usual.
LeonvB  
#3 Posted : Monday, December 17, 2012 6:37:03 PM(UTC)
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If you were to build it, I would suggest using the IVY III's. In this case, I would suggest comparing SE and balanced using fairly simple coupling caps. If you like the latter, then it's time to look for upgrades.
arvema  
#4 Posted : Monday, December 17, 2012 7:29:04 PM(UTC)
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Thanks Russ and LeonvB for good advice. I have ordered some good 2.2uF capacitors and will try it out.
niekos  
#5 Posted : Monday, May 27, 2013 9:16:49 PM(UTC)
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Do you have a picture on how you installed these? if so could you post this please? Could not find any example on the forum (yet).
I was also wondering which caps you ordered?
How does it sound?

Edited by user Monday, May 27, 2013 9:29:52 PM(UTC)  | Reason: Not specified

SCompRacer  
#6 Posted : Wednesday, May 29, 2013 6:45:50 AM(UTC)
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In series with pos and neg of balanced to XLR out.

EDIT: That resistor between pos and neg is in a dual mono BIII with single Legato build. You don't use a resistor with a single BIII and Legato.

Edited by user Wednesday, May 29, 2013 7:08:18 AM(UTC)  | Reason: Not specified

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niekos on 5/29/2013(UTC)
niekos  
#7 Posted : Wednesday, May 29, 2013 7:41:21 AM(UTC)
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Thanks for your picture, very helpful.
I did it like this, which is the same (no resistor). I used 10uF capacitors (blackgate non polar), see picture.

The only strange thing is that I still meazure +/-9,5 V from GND of XLR to hot or cold lead (so after the caps at XLR side).
Am I measuring the right voltage? Or can I not meazure the effect of the capacitors on the voltage like this?
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Brian Donegan  
#8 Posted : Wednesday, May 29, 2013 3:27:56 PM(UTC)
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You should not have measurable DC.
Russ White  
#9 Posted : Wednesday, May 29, 2013 11:42:01 PM(UTC)
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if you have no load connected you could be measuring the effect of leakage current of the caps. With a load connected this should never be an issue. You could simulate the load by putting 100K resistors from the XLR phases to GND.
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niekos on 5/30/2013(UTC)
SCompRacer  
#10 Posted : Thursday, May 30, 2013 4:20:23 AM(UTC)
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With music playing I'll tickle the thousands on my Fluke (three decimals over) between pos and gnd, neg and gnd on the output side of coupling caps. Never measured it without music playing, have to try that. With the dual mono/single Legato common mode is a bit over 10.0vdc.

That coupling cap pic of mine was old; I went from two to one Legato one weekend and picked up some inexpensive 2.0uf Radio Shack film caps to deal with the common mode. I ordered and use 2.0uf Gen 1 Sonicaps. I have some 2.0uf Dynamicaps to try on my next build.

Edited by user Thursday, May 30, 2013 4:42:07 AM(UTC)  | Reason: Not specified

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niekos on 5/30/2013(UTC)
niekos  
#11 Posted : Saturday, June 1, 2013 10:59:21 AM(UTC)
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I preplaced the caps I had installed (10uF) by 2,2 uF Mundorfs and I am able to measure the 0V now, even when I do not connect a load (takes a while to reach 0V).

I connected my Hypex NC 400's to it, and both seem to have a problem with the sound. I hear a quite load humming sound, it sounds like a ground loop?
I connected ground/earth of mains to the GND of the XLR, but it does not remove the hum I hear unfortunetely (see the yellow cable in the attached picture).

The DAC and amps are connected to the same AC outlet, I also use an APC lineR 1200 Automatic Voltage Regulator (but tested also without, no difference).

On the NC-400 I have connected XLR pin 1 to shield of xlr cable, and connected to earth/chassis (aluminium case), as recommended in instructions by Hypex (see http://www.hypex.nl/docs/NC400_datasheet.pdf page 12 preferred connection Figure 2).
The NC-400s have been tested with balanced output on Buffalo II with IVY-III without any noise/problems.

When I use the SE output of the Legato to my tube amplifier there is no hum, just music :)

Any ideas how to solve this?

Edited by user Saturday, June 1, 2013 5:41:22 PM(UTC)  | Reason: More info about NC400

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niekos  
#12 Posted : Monday, June 3, 2013 12:59:39 PM(UTC)
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Update: yesterday I removed the legato and resoldered/reflowed all joints, it did not improve anything unfortunately.
SE is still ok after reflowing.
When I compare the two these is also some other noise on the outputs of the balanced outputs next to the 50 Hz hum.
It sounds a bit distorted depending in the music I play, a bit like radio whitenoise.

I will next measure all the pads to see if somehere there is a short circuit. If I cannot find anything I will start measuring using a 1Khz tone om my scope (never used it before, so that might be a challenge).
Thanks Mfly for the tips :)

Edited by user Monday, June 3, 2013 1:03:22 PM(UTC)  | Reason: Not specified

niekos  
#13 Posted : Monday, June 17, 2013 10:28:12 PM(UTC)
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Ok, finally found what was wrong..... I switched pin 1 and 2 on the XLR, see the images I posted earlier :( Brick wall
Stupid mistake...... I corrected this and all plays well now, no noise at all Dancing

Edited by user Monday, June 17, 2013 10:30:29 PM(UTC)  | Reason: Not specified

Russ White  
#14 Posted : Tuesday, June 18, 2013 3:18:41 AM(UTC)
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Enjoy!
stringgz301  
#15 Posted : Tuesday, November 5, 2013 12:06:56 AM(UTC)
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Hey guys - similar issue here. Have Legato 3.1 + Buffalo II going out balanced to an EHHA balanced headphone amp. It was working with my IVY III but when I swap out for the Legato I get some hum on both channels. I've installed 2,2mf caps in series between the + and - output and the xlr connector, and have ground going straight to the xlr. I measure 0V at the XLR between ground and both + and - (and of course 0V between + and -). Any ideas?

Edited by user Tuesday, November 5, 2013 12:08:08 AM(UTC)  | Reason: Not specified

stringgz301  
#16 Posted : Tuesday, November 5, 2013 12:43:29 PM(UTC)
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So after doing a little more analysis, I think this is RF. I measured for any DC offset at the amplifier inputs and there is none. What I'm hearing is a low hum along with a random soft crackling. I had the caps attached directly to the Legato and then with a short wire run to the XLR connector. I guess I'll try soldering the caps directly to the XLR connector and see if that makes a difference.
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