Line Magnetic 216IA Integrated Amp - Sudden Hum Coming From Speakers

I recently purchased a Line Magnetic 216IA integrated amplifier through Craigslist. I've had the amp for a few weeks and it's been fantastic. I've listened for maybe 10 hours, with the amp turned on for at least 30-40 hours during this time.

Today I spent almost all day listening to music, and just about an hour ago my speakers started to hum. I haven't touched anything, and my turntable is off. The hum is coming through both channels and stays the same regardless of the volume. It also isn't affected if I switch modes from triode to ultra-linear, or if I activate the mute circuitry.

Is there any way for me to tell if this is a tube issue? I've never owned a tube amplifier before. The KT88 power tubes are the originals from Line Magnetic, and I was thinking about upgrading these anyway. I'd just hate to spend money on new tubes if there is a major issue with the amp. Any thoughts or suggestions would be appreciated.

 

If it helps, the hum isn’t present when the amp is first turned on. It starts as soon as the tubes get warm, increasing in volume for 30-40 seconds.

 

Have you biased the tube amplifier according to the instructions?

 

I have, but just the first couple of days. When I checked at the end of the day, it was way off. How often is it recommended to check?

Unfortunately, even with the bias corrected the hum is still present.

 

If you turn the volume off, do you hear hum coming off the amp itself?

It could be a tube problem. Defective tubes do happen, though not very often in my experience. One member here described a tube with a bias that fluctuated quite a bit. Eventually, it was deemed defective. Getting another tube addressed the problems.

Last possibility (and I hope it's not that) is that the CL seller knew the problem was intermittent and sold it to you fully knowing it wouldn't start acting up until after you had left with it. Is it still under warranty? Do you have the original bill of sale? Maybe LM can help either way, assuming it's not a tube issue.

I've always made it a habit to have an extra set of tubes purely for testing purposes. Because of that, I just buy the very cheapest. If such a symptoms shows up, I can switch tubes and see right away if the problem goes away. If it does, I can get then replace the tubes one at a time until the symptom comes back and therefore know exactly which tube is problematic and order a replacement of the good type I enjoy the sound of.

 

Thanks for your reply... Yes, the hum is present when the volume is off and when the mute circuitry is active. I appreciate the suggestion of swapping out tubes for cheap ones. That would help diagnose the issue I think. Hopefully that's all it is, but we'll see I guess.

 

Transformer hum can occur with tube amps. I hope it isn't a defective transformer.

 

It sounds to me more like the transformer as the hum is in both channels. I am having the same problem from my Line Magnetic 215 CD player. The drive failed 4 years in and the new drive and everything was fine for a few months and now it too hums.

 

Thanks for the replies... I really appreciate it. When I turned on the amp this morning, the noise was still present but better than it was last night. I probably just never noticed because I can only hear it when my ear is up to the speaker. By the end of the day yeasterday i could hear it from the listening position. Also, it's more of a "buzz" than a hum. I just want to mention that although I'm guessing it doesn't make a difference.

 

Could it be a grounding issue? Is it under warranty? Have you contacted LM?

 

It's not under warranty from what I understand. Bought secondhand from someone who wasn't the original owner. I'll see if I can troubleshoot any grounding or EMI issues.

 

Some manufacturers will honor the warranty period regardless of who owns the device. If you can't fix it yourself, there's nothing to be lost by contacting them.

 

So, it turns out that the Line Magnetic amp is probably not the issue. I realized that the hum gets worse when we turn on a light fixture with a dimmer switch on the same circuit as my stereo. As soon as the lights go on, the hum becomes noticeable. I also have an issue with another piece of equipment causing some noise, because if I unplug everything the amp gets nice and quiet. I'm assuming I have a ground loop somewhere that I'll have to try to isolate. I've been researching how to diagnose/fix the issue. Anyway, thanks again for the suggestions here. Much appreciated.

- jp

 

Don't drive yourself crazy with that. Either remove the dimmer switch or pay an electrician to have a direct isolated circuit to your breaker panel... the latter being a sure-fire way of eliminating the problem. Shouldn't cost much and would save you lots of troubleshooting time.

 

A cheap fix is to plug your LM power cord into a USA to European converter ans then plug that into a European to USA converter and into wall. It looks a bit ugly but is dirt cheap as those converters are like $2 each. This grounds the amp.

In fact I might take my own advice and try this for my lm 215 tonight and see how it goes.