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Hi i have a problem wit my lexicon power amp, a buzzing/hum coming from all the channels. Its only very faint when its just the power amp on and nothing is connected to it but the speakers. buzz gets louder when i connect the pre amp to the RCA inputs on the power amp. it get even louder when i switch the plasma on. which is connected to the pre amp with a component lead, if i disconnect the component the buzz is reduced. Is there a fualt with the power amp as i'v treid loads of ways to get rid of the buzz.
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You have a short. This is either from a bad cable or a faulty price of gear.
to find the problem do you want to isolate pieces of the system. Turn on just your speakers (if they're powered) or amps (if the speakers are not powered). With the mixer off, if you were getting a pause the short exists after the mixer. No buzz? Great! Turn the amps or speakers off to prevent popping. Turn on the mixer, and then turn on the speakers or amps. If you have a bus now with all channels on the mixer down it is likely your mixer. If there is no buzz, Bring the channels up one at a time. Once you find the buzz, turn the channel back down and plug unknown working microphone and cable into its channel. If the Mike buzzes when you bring the channel up it's the channel on the mixer. If it does not then the issue exists before the mixer. This is most likely and also the least expensive to resolve. Check the snake if you have one and all cables in line in a similar fashion. Most likely a snake channel has failed, you have a bad cable plugged in the snake Or you have a bad DI box or mic plugged in.
Generally the hum is one of two things. If a sensor, pickup, per-amp, or mini-amp are too close to the receiver or speaker, Feed-back may occur or a hum and buzz join the audio signal out. The usual problem is: line in port on the instrument can be defective or the male jack is not making proper contact. If a cord is tested and working, the condition is in the input on the instrument. If a terminal has a loose wire inside the instrument the problem can be intermittent ( come and go) and thus a buzz or line noise may be present.
Hum or buzz is often caused by the mains filter capacitor letting the 50hz mains hum into the system. Regardless of voltages you just need to try new capacitors. If that doesn't cure it, the problem is elsewhere. If it's a stereo amp and the buzz is on both channels then it's something common to both channels.
The thing with stereo amps is that they are actually two mono channels put together, so if one side goes you have the other side to tell you what the other side should be doing. So you can compare the good channel with the bad. For example taking voltage readings. Also you can buzz test it. Generally you can touch with an insulated tool parts of the amp to produce a buzz. So if it buzzers in the good channel it should buzz in the bad. When it doesn't you have found the bad part!
It looks as though you have ripple noise that amplifies into the output. First of all check if the mains voltage is going down to produce the low voltage hum. If not you will have to check the DC filter capacitors , couple in parallel to confirm the capacitor. IF the buzz is still coming through then you will have to isolate the preamp and wait it the fault is coming in. If not connect the preamp output to another amp to hear the same buzz to confirm the preamp to be faulty. If so you will have to trace by a voltage check when the buzz occurs to confirm if the preamp IC or the selector Ic is faulty. Some logic IC's can also produce this noise on static switching. If teh noise is appearing on both the channels, then I would still bet on the power section. So check once again on the rectifier/ regulators and capacitors. Hope this advice helps. Good day
I had the same problem on my VTX65. I noticed it would oscillate with different effects so I removed the effects module. Problem solved. Now it's dead quiet. I use a Digitech RP500 so removing the effects module was a non issue.
1-shut down all flourecent lamp and check. 2-check for your cables in a good condition and no touching of wires to the body of amp. 3-connect(ground loop isolator)code number(270-054)from radio shack near you and connect it between your audio device(like cd player and amp)
If the problem is present with ONLY the speakers connected, that is no other powered devices like subs, or input/output cables, it will be a power supply problem inside the amp. If you have electronic fault finding skills, there will probably be a capacitor in a regulated rail that has failed. If you do have a sub connected, be sure it is powered from the same mains source as the amp, or at least a GPO that is on the same phase. Different phases will induce mains hum, as will multiple earths. Try also temporarily moving the amp(whilst monitoring the hum) from where it is sitting and see if the hum is being induced into the amp by any other devices
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