As with any electrical issue, you have to isolate the problem.
Is the hum in one channel or both?
I don't know what you've tried and some or all of this you may have tried by now, but regardless, here is sort of a manual that anyone can follow in trouble shooting a system hum or any other kind of noise, like popping and crackling:
Quick Check Of The System:
A. If the hum is in Both Speakers, check to make sure that none of your interconnect connectors are touching.
If that's not an issue and you don't have a line conditioner, try connecting an extension cord to another circuit (an electrical outlet on a different circuit breaker than the one supplying electricity to your audio system) in your house and first connect your speakers to that to see if it's coming from a wall outlet.
And if not, connect your system to that and see if that eliminates the hum.
This is a lot quicker than going through your entire system, only to find out, after eliminating everything, that the source of the problem is from your electrical system.
If it's in your electrical system, you could have a 60 cycle hum, also known as a ground loop.
The quick fix is lifting the grounds by using plug adapters that allow you to plug a grounded cord into a non grounded electrical receptacle.
The problem with that, is that you now have an audio system that is ungrounded and has lost it's safety feature of shutting the circuit breaker off, should a short circuit develop in a component or cord.
If the hum is happening in your electrical system, you'll need to hire an electrician to install a dedicated circuit (if you don't have one for the audio system) or find the source of the hum and fix it.
If the hum is in One Speaker, swap out the power cords to the speakers to see if that eliminates the hum in one speaker and introduces it into the other.
Also, if the speakers are not plugged into a single source, like a line conditioner, but are plugged into different wall outlets, then you need to swap speakers between the two wall outlets to see if it's a bad wall plug.
If it's not connectors touching, not the speaker power cords, not a bad wall plug and not the electrical system, then this is where you start:
The Preamp is in the middle of the signal path and a good place to eliminate almost 1/2 of the components in the system to see which direction the problem lies.
(If the hum turns out to appear to be coming from a component, you have to swap out the interconnects from that component, to isolate the problem to either the component or the interconnect.)
Hum In One Speaker:
B.
Disconnect the preamp interconnects from the amp and turn the amp back on and see if the hum is still there.
If the hum is still there, then you've eliminated everything else and isolated the problem to being either the amp, the speaker cables or the speaker as the source of the hum.
(If the hum is gone, then move to step C [or D if it's both speakers])
If this is the case, then next swap your speaker cable connections at the amp, between the L&R channels on the amp, to see if the hum moves to the other speaker. If it does, then you've eliminated the speaker and isolated the problem between the either the amp or the speaker cables (swapping in the other speaker cables with the ones that are connected to the amp will then reveal the source of the hum).
If the hum doesn't occur in the other speaker when you swap the speaker cables and stays with the same speaker, then you've eliminated the amp as a possible source and isolated the problem (hum) to your speaker or speaker cables.
Swap the speaker cables out (between the speakers and not at the amp) and see if that isolates the problem to the speaker.
If it turns out to be a speaker, then you have to contact Martin Logan. They have excellent customer support.
C. If, when you disconnect the preamp the hum is gone, then that means the problem is located either at the preamp, interconnect or other component back in the system chain.
If this is the case, disconnect everything from the preamp, connect the preamp back to the amp and turn them on. If the hum is there, the problem is either the preamp or the interconnects between the preamp and amp.
Next, swap out interconnects to see if the hum goes away. If it does, it's your interconnects causing the problem.
If the hum is still there and nothing else is connected to the preamp, then it's the preamp.
If the preamp has nothing connected to it when you connect it back to the amp and hum is gone, then it's not the preamp and the problem (hum) is occurring farther up the system chain.
If this is the case, connect the next component and turn everything back on and see if that's the source. And if not, then the next component until you find the component that introduces the hum back into the system. Once you do, you have to determine if it's the component or the interconnects.
Hum In Both Speakers:
D. If it's in both channels and you have a line conditioner, then it could be any one of your components (and) or cables and you would still follow the procedures under "C" to find the problem.
If the hum isn't coming from the amp, speaker cables or speaker, then you have to work your way back through the system, starting with the interconnects between the amp to the preamp and on down the line until you find the source.
As an example:
I had a similar situation recently, with a hum in both speakers.
Disconnecting the preamp, removed the hum. With all of my components disconnected from the preamp, I connected it back to the amp and the hum returned. It was the preamp.
Got the preamp back and a few days later, I heard a crackling / humming sound in both speakers.
Going through everything isolated that problem to being a grounding issue with the exterior antenna for the tuner. When I disconnected the tuner from the system (even though it wasn't turned on), the crackling stopped. When I reconnected the turner, but disconnected the coax to the antenna from the tuner, the crackling stopped.
I changed the coax connectors on the coax cable attached to the antenna. But that didn't fix the problem. Then I disconnected the antenna but left the coax connected to the tuner (to see if I possibly used a bad connector or had a bad coax). The hum was gone.
Taking the antenna off of the mast and connecting it back to the coax did not produce a hum. The issue was with the mast introducing some sort of ground hum into the antenna, through the cable and into my system. On the mast I wrapped the point of connection for the antenna with electrical tape in order to insulate the antenna. That fixed problem and no more crackling.
Your source of your problem can be from something obscure.
As a side note:
In the last two years, I've had issues with my preamp, a bad panel and my radio antenna grounding out on the mast.
Each time one of these problems occurred I went through my system, just as I described above. By knowing exactly where the problem is, it kept me from wasting anyone's time (at the manufacturer) and allowed me to quickly resolve the issue.
This also leaves you less vulnerable to the possibility of contacting someone at a manufacturer who is not knowledgable (and shouldn't be the one helping you) and who could mislead you and further delay the resolution of your problem.
Anyway, good luck and let us know what you found to be the cause of the hum.
