Amplifier Hum

[CTX]

I have an old QSC model 1400 amplifier, actually a few of them. When I have a speaker connected to them there is a hum. It seems to be worse with some of them, but present in all. This is with no inputs connected and with the gains turned all the way down. Turning up the gain seems to have no effect on the hum.

Any suggestions?
Chuck

 

[David Ashton]

they have faults and need repairing by a competent service person.There is no easy answer.

 

[Derrick]

Contact the guys at QSC tech support. They are extremely helpful. They'll let you know exactly whats going on. If it is a common failure or....... feature, of the amp, they will be honest with you in whats needed to correct it. Check on their website QSC Audio Products and follow the links to tech support. They will respond, in a rather timely fashion!

 

[Chris15]

You say these are old... it's probably age related decline. They probably need their caps replaced (these dry out with age) and the offsets tweaked. The nil effect of the attentuator would suggest the fault is downstream of this, so it's on the PCB somewhere. Send em in for a service and they ought to come right...