Gain structure Nexo

[Biljon]

I have been working on the gain structure and have a few problems.

I use a M7CL (+24 dBu max) and a NX242 (+28dBu max).

To match them I have a 4dB attenuation between them. When I feed the system with pink-noise (no clip from mixer) and just under clip on the input of the NX242 I get protection on my outputs, this means no clip from amps (Macro-Tech 5000VZ) with them on max. I have tried to use maximum power (5000 W) in the setup but with the same result. What am I doing wrong?

[Bobbsy]

The figures you quote mean that the M7CL will clip 4dB before the NX242...or, put another way, the Yamaha board should never drive the Nexo controller into clipping.

 

However, putting a 4dB attenuator permanently in the circuit means the the maximum level (as the mixer just hits clipping) getting to the NX242 will be +20dBu, or a full 8dB before clipping....which should explain why you can't drive things as hard as you expect to.

 

Bob

[mackerr]

As Bob pointed out, the pad is the wrong solution. The difference in maximum level before clipping is in the other direction. It may also be irrelevant. Just because the NX232 can take +28dBu before clip does not mean that with your amp and normal gain settings that your speakers can handle that full output. The NX232 is also sensing the voltage output of your amplifier, and that may be what is causing the protection to kick in. If you are making these tests without speakers connected, it is possible that your amp is delivering a higher voltage into the relatively high impedance of the NX232 sense input without the low impedance load of the speakers. Those are very high operating levels, 20dB and 24dB above a normal 0Vu (+4dB) output level.

 

Mac

[Biljon]

My mistake, ofcourse I gain the input on the NX242 4dB.

 

As Bob pointed out, the pad is the wrong solution. The difference in maximum level before clipping is in the other direction. It may also be irrelevant. Just because the NX232 can take +28dBu before clip does not mean that with your amp and normal gain settings that your speakers can handle that full output. The NX232 is also sensing the voltage output of your amplifier, and that may be what is causing the protection to kick in. If you are making these tests without speakers connected, it is possible that your amp is delivering a higher voltage into the relatively high impedance of the NX232 sense input without the low impedance load of the speakers. Those are very high operating levels, 20dB and 24dB above a normal 0Vu (+4dB) output level.

 

Mac

 

I do the tests with no speakers connected. I also have a hard time getting a amp-power reading when I am doing the full power tests. I set up the NX242 on 4 x S2 80Hz and feed the system pink-noise but "no reading yet" shows up on the display. Any clues why I don't get a reading?

[Chris Hinds]

You aren't getting a reading because there is no current swing due to the lack of a speaker to complete the circuit. The NX242 sense lines won't pick up jack because the amp is probably protecting itself due to the high levels and lack of load. Assuming your MA5000 is in 26dB gain mode as it should be for Nexo systems, you need +14dBu not +28dBu to drive it to max output on an S2. That excess level is what's causing the lack of readings. There's no power flowing so it can't detect a reading.

 

Personally with the Macros on 26dB gain (pretty low by power amp gain standards), an NX242 not a 241 and an m7CL, I'd be content to leave the NX242 on 0dB gain and accept it has 4dB more headroom through that stage. I've never had any noise issues with AlphaE, Alpha or the PS Series using NX241s, Macros and a variety of desks. In an ideal world the headroom should all be aligned, certainly, in reality when you're that far above the noise floor and have that little gain after the DSP, it doesn't make much if any audible difference.

 

Regards

 

Chris

[Biljon]

Well I finally got a reading from my amps, 2100 W. Pretty far from the specified 1300. According to the NX242 manual I should use the number I get from the test. Well I have to try how it works.