I keep getting crackling through the speakers when I use the microphones plugged in through the karaoke machine. The speakers do not crackle with just CDs or even the CDG instrumental from the karaoke machine, but the microphones make it happen. Ideas?
Checked all connections, put foam covers on the microphones
The crackling noise you are describing is usually due to a failing shielding conductor or a failing shielding conductor connection within the microphone cord. If you are getting this on both mics, there is still a chance that this is the issue, but it is much less likely. If you get the sound all the time, then you probably have a problem with your preamp. Especially if it is more pronounced when there is a stronger (ie, louder) signal going through the mic(s).
Is it prominent on both mics? Does it only happen occasionally, such as when the person holding the mic moves?
Is it only notceable when you adjust the volume on the mic? Then it could be a dirty pot (potentiometer, the volume knob is attached to it).
Are you there? It says you are standing by.
Try spraying some contact cleaner into the volume potentiometers, while moving them back and forth rapidly, with the power off. You will have to remove the knobs to do this, or better yet, get to them from the back. Let it dry for a half hour or so, then try it again. If that does not solve it, and you have KNOWN good mic cords, then you will need to take it in for repair.
Also, if you have electret condenser mics, or cordless mics, make sure they have fresh batteries, and the wireless base units, as well, if they need them. They will crackle if the batteries are going dead.
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I have done everything that you suggested. Used contact cleaner on the potentiometers, both from the front and back. But the karaoke machine has no access from the inside to the back of those areas...it is all covered with electrical rectangular components permanently in place. Shouldn't you have known that before suggesting it....are you familiar with karaoke machines? None of the mics are wireless...so no batteries.
All you said was "karaoke machine". There are MANY brands and models, hundreds, of karaoke machines. I, nor any other technician alive, can possibly know every machine, and how they are all built, however, there are things that are common to all electronics. Some equipment allows access to these parts, some doesn't. If you remove the correct screws, you can access anything in the machine. Otherwise it would be impossible to service and/or replace the switches, pots, and other front-panel-mounted items. NOTHING is PERMANENTLY in place, I assure you. If you have tested all the mics with a KNOWN good mic cord, then you will have to take it in for service, it is most likely the mic preamp that is defective. There is nothing that you can do to fix it beyond that, unless you want to get a service manual for your model and attempt the repair yourself. Sorry! I am sure you checked the cords and connections to the speakers as well. The fact that only the mics cause this and not the other inputs probably would rule out the possibility of a speaker connection problem. I can locate a service manual for you, or a link to a repair facility, if you would like.
I have built and serviced hundreds of electronic musical instruments.