API 7600 noise debug (soundsample)

[12afael]

I`m debugging an API 7600 of a friend, it have a strange intermitent noise. I was able to record the noise (I reduced the volume in the second 11) beware it could be loud, turn down the vol of your speaker.

http://www.soundclick.com/bands/page_songInfo.cfm?bandID=1116685&songID=9817738

here is the block diagram of the API7600
http://www.apiaudio.com/block7600.pdf

I test the controls and what I found is the noise is not in the preamp I move the gain and the noise didn`t change, also it have a preamp out the signal here is also clean. I can eq the noise so the problem is between the preamp output and the eq output or in the power supply(but why, if it is the PS the preamp should be afected :-\) the fx1 output is the eq output and the noise is present.

I`m trying to find a small allen key to remove the knobs and PCB to take a look.
I suspect of humidity, maybe a cold solder or a bad connector. If anyone have any other idea I would like to hear it.

best regards
Rafael

 

[jsteiger]

Sounds like an opamp taking a shit to me. If the preamp is fine, locate the (2) 2520's in the eq circuit. Change one out and listen, then the other. You will find the bad one. Never been inside a 7600 but hopefully those opamps are in sockets. You could always mark the opamp from the preamp as good and use that in the swaps. Is the unit under warranty? If so, they should give you another 2520 if they get the bad one back.

Best, Jeff

 

[12afael]

my friend buy this unit at Mercenary audio, the shiping cost is too high. I will swap some op amps, thanks for the advice.
I will try to take some pictures.

best regards
Rafael

 

[3nity]

Jeff is right ive seen or better heard those sounds on op-amps.

 

[outoftune]

probably a 2520 opamp.

im a tech at an API dealer and ive taken a few of these apart. The units are amazing and sound great but are difficult to take apart, its two pcbs sandwiched together. go very slowly and take extra care with rgards to the leds, i snapped one off when i worked on my first one. be sure to set aside like an hour to take it apart and put it back together!!

 

[12afael]

yes, the hard part was find a 1mm allen key for the knobs.
the problem was a 2520 in the eq circuit I swap it with one of the compressor for the moment, my friend don`t use the compressor a lot, he now is contacting api or mercenary for a replacement and for the warranty.

thanks for the help guys

Best Regards
Rafael