Just talked with a clubmember who is interested in this modules to. He had a UCD amp once with exactly the same problem as this.
Yikes! That sounds like it is actually being pulled down, to signal that you have a large DC voltage on the output. The amp is probably turning itself off automatically.
But there is no DC at the output . Now I will try 250 ohm in the RC for the input supply. I guess the voltage is to high. ( 22,3 V )
Only 150 mv over 250 ohm this indicates that the input section do not work . When I shut it of it plays for 2 seconds.
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Not even temporarily when turning it on?
This is for the signal stage, pins 6, 12 and ground? 22.3 V should be OK. Just to check again, you don't have anything connected to pins 11 or 5?
No dc when I turn it on. Pin 11 and 5 is not used for anything.
Yes 22,3 v is for signal stage an it do not use any current.
But if you get 0.4V on nFATAL then the nc400 definitely thinks something really bad is going on.
It should be 40 mA.
Why does it play for few seconds and it sounds really good. Than nothing can be very wrong ?
So when you turn the amp on, you first get the normal 2 s delay, and then a few seconds of music, and then it turns off?
And how do you turn it off? By cutting the power supply, or by releasing nAMPON (pin 3 of J9)?
Erlend, I haven't read your problem in detail, but it reminds me of the first time I checked my UcD180 modules at the bench.
Here's the story. I checked the modules with a CD with huge DC bias on it's output. After only few seconds the modules cut out. The huge DC was enough to get the modules to pump the supply ending up with an large asymmetric supply, finally trigging the over-voltage protection.
Perhaps the Legato's common mode DC offset is irritating the nCore input ?? Try measure the supply (2 DMMs, one at each rail) and see what's happens.
If above has nothing to do with your problem, forget I've ever been here 😀
Here's the story. I checked the modules with a CD with huge DC bias on it's output. After only few seconds the modules cut out. The huge DC was enough to get the modules to pump the supply ending up with an large asymmetric supply, finally trigging the over-voltage protection.
Perhaps the Legato's common mode DC offset is irritating the nCore input ?? Try measure the supply (2 DMMs, one at each rail) and see what's happens.
If above has nothing to do with your problem, forget I've ever been here 😀
Have you tried switching nAMPON? And avr300 has a point, you could have enough of a DC offset on the input that it is making the nc400 switch off. There won't be any DC on the output when it is switched off... Maybe try with an input capacitor?
Well is not the 2,2 uf input capacitors ? My Legato 3.1 has Russian PEPT 22 uf output capacitors.
As far as I know, the nc400 doesn't have input caps, it is DC coupled. Have you added the output caps to the Legato yourself - it's schematic does not show any output caps.
I added the caps . And I have the same problem with another pre . I will try with an tubepre tomorrow.
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