How much hum is normal from a new tube amp

I just bought a great sounding Lab12 Suara KT120 tube amp. The issue I am having is a hum that is coming from the transformers. I can hear it with no music playing faintly from my listening position 12 ft. away. The question is, should I return it, or is this normal acceptable. 

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I have a few friends who tolerate 'some' hum. I tell them, something is wrong, find it or fix it. 

Years of 'some' hum later, they get it fixed, zero hum.


That amp says KT150 (you have a different version?)

does maker approve using KT120? (don't assume, I would verify)

old post here:

"daveyf OP

2,658 posts


The varying opinions of the KT150 tube seems to be primarily dependent on whether the amp was designed to utilize the KT150 in the first place. Since the KT150 needs a more stout transformer and has to run on a higher voltage,"


Return is work and money, be thorough, MAKE SURE it's the amp. Get your Sherlock Holmes hat out of the closet.

Switch tubes 1 at a time left to right, any changes?

VERIFY it is not something else, i.e. only one device with it's own volume control, directly into amp to speakers (check speaker wires at speaker ends). One pair of previously silent interconnect cables with tight connections. Single device thru volume control (preamp if needed).

Power from your normal (dedicated I presume) outlet. Change power to an outlet on a different circuit.

No matter what: always hum, do you have an alternate amp to put in to verify the hum is definitely caused by the new amp before you pack it up?

Same hum, I would return it!

I have 3 tube integrated amps , a Line Magnetic 518IA, a Finale Audio 7189Mk2 as part of my main system, and an Ayon Audio Spirit 2 in my second system none of them have ever had any transformer hum

@elliottbnewcombjr  Yes I meant to say KT150, that's what I have.

I have rebiased all the tubes.The hum is present with the preamp off. I used the DB meter from my phone and tracked the loudest reading and it is coming from the back of the amp. I have also changed the power cable, and I just tried plugging it into a different socket. I checked the speaker cables. I have used all this equipment setup with different amps and they are dead silent. 

@blue-magoo You could try a DC blocker. Ensure it's on a flat surface. Any loose bolts on the power transformer?

Any loose bolts on the power transformer?

That's the low hanging fruit.  If you press on the transformer, does the hum stop?

Is hum from the transformer or from the speakers?  Speaker hum is generally from AC heaters and low level is often considered acceptable.

Hum from transformers is a different story.  power transformer, not output transformer.  There are many threads chasing transfoermer hum.  many chase  "dc offset" but I find that highly unlikely--maybe I've just been lucky.

It is generally caused by either poor design or an unbalanced load.  Some designers put fuses in the outpot of the voltage rectifier tube.  there are 2 legs to this tube and if one leg blows a fuse the amp will still play fine but the transformer will hum.  I've found this once in an amp I owned and helped others find it twice.





In time you might get a hum from a transformer, but you should never get a hum from the amplifier itself.

Know that I think of it I had a hum that was intermitant and it turned out to be a loose wire on a Cap. BE CAREFUL investigating that one.

Mechanical hum is mostly from a poor grounding layout. Sometimes it's caused by heater wiring and sometimes by bad transformer construction. I have solved a couple of tube amp buzzing problems by simply moving wires with a wooden chopstick. You shouldn't have to. I agree it should be returned because it's either a factory lemon or, worse yet, a poor design or construction -- which will definitely impact sound quality. 

Transformer connected to the AC line with the wrong polarity. Send it back to the builder.

Might be a lemon set.

i have Lab12 Integre4 MKII, zero hum.

The demo set I auditioned had a slight hum when using XLR input, but none when using RCA input. My brand new set has no hum though at all. Perhaps try switching the inputs first? If it still bothers you just exchange a new one. 

Now that I listen to it more, I think the sound is coming from the inside. I'm not very technical and I don't know what the implications of that are. The hum is consistent. It starts within 8 seconds and never wavers. I suppose sending it back is the best course. 

The humming is most commonly caused by the magnetic field from the coils causing the iron core of the transformer to change dimensions--as it does so, it is vibrating, hence the noise.  To some extent, all power transformers vibrate this way, although most are designed so that the vibration is minimized and sufficiently damped.  If the noise is not too objectionable, you should just ignore it--there is probably not anything wrong with the transformer such that it will get worse.  In any case contact the manufacturer if you can about this issue to see if it really is a manufacturing defect that they will address.

Someone above mentioned checking the bolts that hold the transformer down to the chassis.  This is a very good first step.  If they are loose, the vibration from the transformer might be made worse by the poor coupling to the chassis.  If you are not experienced with tube gear, have someone who is experienced go under the hood because there may be high voltage stored in the capacitors that you don't want discharged through your body (amps can shock even when unplugged).  

Good luck.

The amp costs $5K+. You appear to have a return window. why settle on living with something that will continually be, at a minimum , an annoyance.


Have you tried a cheater cord? Or perhaps a different outlet on a different circuit?


Yes a different chord and outlet. I have a Furman R8 strip. I haven't had any hum on previous tube amp.


They will take it back but, I Love the amp. I guess my question should be if I get a replacement with the same amp will I have the same problem.

It has been suggested that this a an issue with KT150 amps in general.

I think I should pose the question on a new post. "How many have had hum issues with KT150 tube amps".

If the hum level changes from time to time, it may be from  DC offset in your power line caused by other things in your home contaminating your power.  You can try powering the amp from a different circuit using extension cords, or turning off each circuit until the hum stops.  Depending on when the offending equipment is in use, the hum level will change which may be an indication that the cause is in your power delivery to the amp.  Some transforms are more susceptible to this problem than others, which may account for why this is only happening to this amp.  Toroidal (round shaped) power transformers are more apt to hum from less than ideal power feed.  The problem with DC offset is that one cannot easily measure it to get a definitive diagnosis and most power conditioners don't deal with it. 

Another possibility is that the power transformer is overheating because of a problem in your amp or because the manufacturer put in one that is not up to the task.  Is the transformer hot to the touch or merely slightly warm?  If it is fairly hot, you should talk with the manufacturer even if you had decided you could live with the slight hum because there could be a bigger problem.    


I have decided that the sound may be coming from the inside rather that the transformers.  The hum is consistent. I have change power chords and used a different socket, though they may be connected. The transformers are slightly warm to touch and square in shape.  I do not think that this is a moderate hum. In a quiet room with only the amp on and no music, I can hear it from 25ft away. I would describe my heating to be good but not stellar.

That sounds like a fabrication defect. I would ask to exchange it for another one if you really enjoy the sound. 

@larryi @femoore12 @facten @auroravengeance  and everyone that has chimed in

Yes, I think replacing it is the best idea. It has a great sound, I would keep it if the hum was minor but I feel like this is beyond that.

This is the right thing to do, particularly if the manufacturer is not giving you grief.  You should not have to live with loud noise and doubts about your gear.

Good luck.

The whole system was fine. Only thing changed was the amp which HUMS.

Bad luck, Safest: RETURN IT, for refund, if it's a bad design the next one will hum.

If they can convince you they can fix it, or a replacement will not hum, you have to decide, make them pay for return shipping if you can.

good luck.

I had a slight hum from my speakers (not transformers) when running a LM805ia SET amp that was effectively eliminated using an Equi=Core balanced transformer. The amp has hum pots so some hum is expected. However, with proper management it can be reduced to nearly null.

If the manufacturer does not offer to eliminate the issue - and it IS an issue - or if they refuse to replace the defective amp, then return it immediately. You should hear no hum from the transformers of a new amp. I have (reluctantly) discarded products that over time have developed a pervasive and musical enjoyment-destructive hum in the transformers. As I understand it this is not something you can fix other than replace with brand new transformers. If you hear it now with brand new transformers, imagine what it will be like as those transformers age.

I have a KT150 amp. There is a very faint hum from the amp on start-up, that goes away once it's fully on and warmed up for a few minutes (it has a 2 stage power up process). Otherwise it is really quiet. 

I sometimes hear a very faint hum/clicking sound from one speaker but I have to get very close to hear it and I know that is from the modem.



The seller TMR has been great. They are going to take it back inspect and either repair , replace, or refund my choice. Which amp do you have? If I can ask.


How long have you owned the Lab12 Integre4 MKII. Im asking because i heard the the hum can develop later or if you have a slight hum it can get worse. 

Which amp do you have? If I can ask.

Of course - details in my profile but it’s a Rogers High Fidelity EHF-200 MK2. I’ve had it just over 2 months. Very happy. It replaced a Raven Audio Osprey which was fantastic but I wanted more power to drive my Harbeth’s.

Correction, sorry.

There is a very faint hum from the amp on start-up, that goes away once it’s fully on and warmed up for a few minutes

The faint hum on start up is from the speakers - fades after 10-15 seconds - the amp is dead quiet.

@blue-magoo Less than 2 months. Mine so far is dead quiet. But like I said, the demo set I auditioned had faint hum from the amp itself when using the XLR. Finger-crossed it would not happen to mine because I really like the sound of it. 


I really liked mine too, I sent it back today, I can tolerate a faint hum, but I think mine may have had a malfunction. The performance was not effected through. It still sounded fine. 

Hum should only be audible when you put your head about 6" or so from a speaker cone with volume set to your "normal" listening level.

If it's audible from normal listening distance with your volume pot set to where you usually like to listen, something is way wrong.  

Could be grounding issue among your components in the chain, or some problem with the internal electronics of the amp.

I've had two tube power amps with KT150 tubes in my system the last few days and neither had any hum whatsover. 

Lab12 is a good company and their products sound great.   The Music Room is a safe bet when you have a problem.   I just purchased a Cyrus integrated amp from them.   I had an issue that led me to believe the unit was defective.   It wasn't,  it was a simple problem but they were great to deal with.   Hopefully you get it straightened out.   

While I’ve found the KT-150 Tubes to be the least reliable power tube I’ve ever used, they never produced hum in my amp (primaluna evo 300).

Agree with the choir to return the amp for a refund or replacement. I had a similar issue with a Carver Crimson 250 amp and was lucky to work with a dealer who fully refunded the unit. Best of luck with your replacement.

I have very recent experience with this. I've had a Pass XP10 pre amp running my Pass 250.8 through a JL Audio CR1 active crossover. I have a purpose built very solid, very tight and quiet listening room. I could hear a very faint hum at 7 am when the house was totally quiet, otherwise I never heard it. I just upgraded to an Audio Research LS28 tube preamp - surprisingly it's dead quiet !  

It's down to the electromechanics of the transformer.  These things can be a bit elusive in that the amp might hum less in another installation. But it's still indicative of less than perfect design and manufacturing.

"OP, Good you sent it back.      I would not accept any hum."

                 ^^^^^ What he (et al) said! ^^^^^