Thanks for your reply JLMRNEO, the sound if it is clear when using headphones, the problem is that I can not find the diagram to see which is the amp. of output.
Colleague commented that I found the manual of the mixer, there were 2 amp in short, obviously I changed them, and now this is great, when I changed it I noticed that when the volume increased, I heard choppy and also change the potentiometer fader of the master, thanks for your suggestion.
Greetings.