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repelsteeltje  
#1 Posted : Monday, July 6, 2015 7:19:09 AM(UTC)
repelsteeltje

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Hi All,

Recently bought myself a new Legato 3.1.0 board to replace the older version in my dac. Installed all the proposed parts except for the SE buffer IC2 & IC3. I only use balanced outputs for now anyway.

So installed everything. Placids are doing well around 14.8-15V. Tuned both VR1 and VR2 to get 0VDC on both right and left channel. No problems so far.

Took it back home (was at my friends house) and connected the XLR cables of my system. Just for safety I did not turn on the rest of my system (pre + power amp). Measured voltage on both channels again. Left channel still around 0VDC. However, the right channel increased to around 0.138/0.139 VDC....

Switched the XLR cables. Switched the cables from legato output to XLR connector. In both cases the problem still existed on the right channel so no solution there. When disconnecting the XLR cable, right channel goes back to 0VDC.

I can obviously try to adjust VR2 such that voltage for the right channel goes down to 0VDC again (if possible) but it just feels strange. No change in the left channel with or without XLR cable attached but a big increase in the right channel.

Does somebody have any idea where to look for a failure? Can it just be a bad soldered resistor so to speak or should I look elswhere?

Many thanks for your help!

Edited by user Monday, July 6, 2015 7:54:11 AM(UTC)  | Reason: Wrong VDC value

repelsteeltje  
#2 Posted : Monday, July 6, 2015 7:50:04 PM(UTC)
repelsteeltje

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Ok some additional info:

Left output:
- plus / gnd measures 9.45
- min / gnd measures 9.45

Right output:
- plus / gnd measures 9.45
- min /gnd measures 9.58 v

Right plus / min measures -0.138v

So that adds up... Something wrong there.
repelsteeltje  
#3 Posted : Tuesday, July 7, 2015 8:21:33 AM(UTC)
repelsteeltje

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Still wondering why it would make a difference being connected to XLR cables or not...

Does this give any of you any clue on where to look?
Brian Donegan  
#4 Posted : Tuesday, July 7, 2015 3:15:51 PM(UTC)
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What is the other end of the XLR cable connected to?
repelsteeltje  
#5 Posted : Tuesday, July 7, 2015 5:29:05 PM(UTC)
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Hi Brian,

Sorry for the missing info. Dac is connected to a primare pre 30 (pre amp) going in a primare a30.2 power amp.

Up till now the pre30 was connected and on standby. With cables disconnected the reading 0. With it connected -0.138v (right channel). Pre30 powered on the same reading of 0.138v.

As said switched the xlr cables so left was connected to right input on the primare. Still the right channel had the problem.

Hopefully you can use the above info. Thank you.
Brian Donegan  
#6 Posted : Wednesday, July 8, 2015 1:57:42 PM(UTC)
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Measure the voltage between cable pins when connected to the pre-amp, but not connected tot he Legato.
repelsteeltje  
#7 Posted : Wednesday, July 8, 2015 2:58:47 PM(UTC)
repelsteeltje

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Hi Brian, with the pre30 turned on all combinations (+/gnd, _/gnd) measure 0.
repelsteeltje  
#8 Posted : Wednesday, July 8, 2015 3:32:03 PM(UTC)
repelsteeltje

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Brian, I did some additional measurements. As said the SE buffers are not installed so j5 and j6 are connected with jumpers. Now without cables i have dialed everything to zero again (SE+BAL). After connecting xlr (SE not connected!), the left channel sees a slight increase +0.6mv on SE and 1mv on XLR.

Right channel both SE and BAL a measurement of -138mv approximately

Maybe this last info says something about a possible cause? So when connecting xlr cables the increased mV measurement is seen on both SE and BAL output.

Edited by user Thursday, July 9, 2015 9:38:06 AM(UTC)  | Reason: grammar!

repelsteeltje  
#9 Posted : Monday, July 13, 2015 1:57:37 PM(UTC)
repelsteeltje

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Anyone any ideas? Would (off course) be much appreciated!
repelsteeltje  
#10 Posted : Monday, July 20, 2015 1:49:48 PM(UTC)
repelsteeltje

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Brian, any further ideas or things I should/could measure to trace the problem? Pray
Thank you,
repelsteeltje  
#11 Posted : Sunday, September 6, 2015 5:30:33 PM(UTC)
repelsteeltje

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Hi all, hopefully you had a great holiday.

Did some measurements. Right balanced channel gave me a "infinite" reading on the minus. This time I opted for spikes and thus the middle three holes. There does not seem to be a link between the outer minus connection point and the point next to it (where the pin is placed). Left channel no such problems. Noticed that the left channel has two round rings when seen from the bottom of the board. Right channel has a ring and a square.. (?)

Connected the two holes with a small peace of wire.. problems gone..

Is this a known issue?

Thx

Edited by user Tuesday, September 8, 2015 10:06:56 AM(UTC)  | Reason: issue max. speaker current is solved

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