I put on this thead probably on the wrong forum, solid state. someone advised me to try this one. I have the above power amp,and its producing a very loud hum when connected to speakers. sensativity controls make no difference to volume of the loud hum. When i connect up mixer both channels are ok,no distortion only the same loud hum. Volume is ok. I have checked for loose connections and anything that looks burn,t but things seem ok. I have not a lot of experience with solid state amps. One thing i thought of, is possibly the rectifier,as i had a vox ac30 where the rectifier valve went. It produced a very simlar hum. Changed the valve and it was ok after that. Any suggestions would be appreciated. Michael
are you using a balanced line as input?
and what mixer do you have?
do you have the hum with nothing connected to the input?
and what mixer do you have?
do you have the hum with nothing connected to the input?
Hi There,
Thanks for reply, Hum is present with or without any input, Hum is the same loud volume at all levels. Mixers used are Mackie pro fx12 or Yamaha MG 16 Balanced lines used on input. Also tried different speakers. DAS 4 ohm 2X15 and JBL 700 Series. Still the same. Hum never changes volume. No distortion on output. Both channels ok except loud hum. Michael
Thanks for reply, Hum is present with or without any input, Hum is the same loud volume at all levels. Mixers used are Mackie pro fx12 or Yamaha MG 16 Balanced lines used on input. Also tried different speakers. DAS 4 ohm 2X15 and JBL 700 Series. Still the same. Hum never changes volume. No distortion on output. Both channels ok except loud hum. Michael
just to be clear when i said nothing connected i am saying remove the xlr (or pin plug whichever your using) from the amplifier input. if the hum goes away you have a ground loop.
QSC
Hi, Still have hum weather input connected or not. Loud hum present with just speakers connected. Michael
Hi, Still have hum weather input connected or not. Loud hum present with just speakers connected. Michael
Hi Enzo, The hum is seriously loud. I have checked another power amp in my house HK 2400 No hum present just very low noise from fan. I do not think its a output problem as when signal is fed in it is not distorted in any way,just a mix with the horrible hum. Michael
This amplifier uses a switch mode power supply, so power supply ripple cannot logically be the cause. Check for 0v DC between E9 and E10 then E11 and E12. Any DC there is a problem.
Check the ground stud E1 and all connectors that go to ground.
Check the ground stud E1 and all connectors that go to ground.
QSC
Hi Jon, Can i do the tests with speakers disconnected. I have found the test points and will try and test tomorrow and let you know.
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Hi Jon, Can i do the tests with speakers disconnected. I have found the test points and will try and test tomorrow and let you know.
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must be an open ground / bad/cracked solder joint, i would inspect input connectors and look over all associated solder joints on the input board.
is this thing still under warranty?
is this thing still under warranty?
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a magnifying glass inspection of the solder joints on input connectors can be very revealing even when i was younger and my eyes where better, i can't count how many times it showed me what i wasn't seeing with the naked eye.
and at the age that your amp is i'd ensure it's free of dust and debris, moist dust can be conductive.
and at the age that your amp is i'd ensure it's free of dust and debris, moist dust can be conductive.
Still a current product and in all my installations CX series have been really reliable bulletproof amps
700W/ch at 4Ω makes it worth getting repaired, QSC has really good service at their factory and because it's a lightweight switching-PSU amp, shipping wont be that costly.
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