Question about Amplifiers & Preamps
I have an ancient Peavey KB100 (a solid-state, 75watt w/1-15" + piezo amp) which I've used for years (typical Peavey). Lately, after playing for a while, the amp starts to emit a loud hum. The instrument signal can be heard faintly in the background. Disconnecting everything and turning all the pots to 0 doesn't alleviate the problem. The hum remains, even with nothing in or on.
Any ideas on what the prob is, or a possible fix?
I realise this is a very old thread, but somebody may still be looking for a solution for this amp. There is a very common problem with the original 3-channel, 3 phone-jack version of this amp. ( and indeed, with a lot of amps that hold the main circuit board in place by using the front jacks and controls). over time, the connections to the input jacks fracture as the unit is moved around and subjected to different temperatures. You need to remove the head from the amp, disconnect the speaker wires and the reverb send-return cable, remove the main circuit board by unfastening all the front-panel jacks and controls and removing the 2 screws that hold the left side of the main board in place and the 2 screws that fasten the long aluminum heat-sink to the bottom of the chassis. Then you can pull the board free of the chassis ( if you are careful, you can do this without removing any more wires) ,and re-solder all the jack and pot connections along the front edge of the circuit board. This will last for a while, but does not permanently fix the problem. To fix it permanently, you should replace the 3 board-mounted input jacks with jacks that mount to the front chassis plate instead. They will have to be connected to the main board using shielded wire to keep noise out.
Posted on Apr 18, 2013
Hum can come from all sorts of places in an audio amp system......
The shielding on the input cables may be broken.
An earth somewhere can be broken....which then allows "ground loops" to form and unbalances the earthing...causing HUM....
Your note about reducing the controls to zero and the hum is still there leads me to believe that the power filter capacitors or some other filter capacitor in the DC supplies have dried out.
Capacitors can also go "open" which can cause low level sound and HUM.
The motto is "Capacitors get "old" and cause hums"....
It looks like its time for a full service....the amp has done you very well over the years and its like anything else needs a service now and then to maintian the quality of sound expected...If there is one capacitor showing you its getting "HUMMY" then there will be others in there as well needing replacement....
High heat can kill an amplifier so while its getting a check over there will be checks for other problems in there as well..Hot running resistors which can dry out adjacent Capacitors...
Cheers for now YUBEUT
Posted on Nov 03, 2007
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