GM 40 Noise

Hi guys, I'm new here. I just bought the GM 40 today. I turned it on and there's a buzz sound. It's not coming out of the speakers, which is fortunate. The amp sounds awesome, tubes seem to be great. I will admit that I haven't checked the tubes either using the LEDs. But, it seems like the sound is coming from within the amp itself, on the left side where the transformer is. It isn't constant. It gets louder, sometimes lower, sometimes it disappears altogether for a while. I've only played it for about 2 hours and it seems to get a litter better when it's warmed up, definitely worse when I first turn it on. Anyone else have this issue?

Hi Dan, welcome to the forum.

Transformer buzz is a fact of life with all transformers and is not unknown in our amps. It usually doesn't cause any problems in use but that really depends on the severity. Your transformer core is really just a block of flat sheets of steel isolated from each other with an ultra thin layer of insulating varnish in order to carry the magnetic field without Eddy current losses. With a pulsing current going through it producing a pulsing magnetic field, the bits are made to attract each other and pull together when current is high, then relax back to normal when the current is low. That is happening 100 or 120 times a second depending on where you are in the world.

This simply makes the transformer hum by what is called magnetostriction. Transformers are made to not hum as much as possible but it depends on how well the core plates have bonded together in your own, that is a bit random. It usually isn't a problem, all transformers hum gently to a degree if you get them in a very quite environment. The level of the hum is also affected by the "cleanliness" of your mains supply. If you have say a heavy industrial plant nearby there can be a lot of noise and hash on your mains and this is seen by the transformer as unwanted harmonics in the mains supply. That changes the nature of the hum from a soft 100/120Hz hum into a noise which contains the overtones of the noise on the mains. As you say the level is variable and seems to almost go away at times I would suspect this is a likely factor. Try the amp in a different location on a different mains supply and see if it does this to the same extent then. In the UK, in severe cases of mains poollution you can ask to be put on a different phase of your local supply in order to try to get away from the interference. That used to be common amongst my hifi buddies years ago.

If it really is loud and is a constant harsh rattly buzz rather than a smoother hum, that could mean the core laminations are really loose and haven't bonded well but that would be very rare for any electrical device nowadays. If it is to a worrying level I would maybe think of checking up on it. It can increase Eddy current levels in the transformer core and that increases the amount of heat it has to dissipate. If you bought the amp new from a dealer just take it back and ask him to listen to it. Even if he doesn't think it needs replacement as it may even not do it in the shop and it probably won't have any problems through this anyway, you will have registered the situation and you have grounds for an "but I told you so" argument if it should have a problem.

Just how bad is the noise in general use? Do you live in a particularly noisy mains area?

Thanks for the info Bordon. I really don't know if I live in a noisy main area or not. But I've been living at my home for 3 years, and, I have two other tube amps, Egnater Tour master and a Mesa Boogie Mini Rectifier 25, neither of which make this sound. They're both pretty quite. As I said, I just got it and have only played it for a couple of hours. I have a gig tomorrow night and intend on using the GM 40. I'm just curious how loud this buzz will be on stage between songs. I'm hoping the buzz won't seem quite as loud on stage. I purchased the amp from Sweetwater, and call me cheap, but I opted for the demo version to save a few dollars. That being said, being a demo version I'm sure they fired it up several times and should have known about it. Maybe that's why they decided to sell it lol. Either way, I'm gonna contact the sales rep as you suggested.

As far as how bad it is, I can deal with it if it's not very noticeable on stage. I don't normally play loud at home and I intentionally played at a low volume and can't hear it as I'm playing. But when the amp is on and I'm not playing the sound is very noticeable at times.

I can say for certain that this doesn't happen with my GM40.

I'll also add that I've been playing guitar for over 30 years and have been in several bands over the years. I've never heard this sound coming from a fellow band mate's amp either.

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Definitely go back to Sweetwater. Sounds like a dodgy one and even an ex-demo product should not have noticeable faults.

I actually bought an ex-demo H&K cab, you would never have guessed it had even been out of the box.

I agree Jonny. I'm gonna call the sales rep today and see where that gets me. I certainly don't want to go with something else, I'm digging the tones on this amp!

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I promise you it really does exist and it's common enough to meet from time to time.  Google "Magnetostriction" and just look at the Wikipedia entry, for one.

Wikipedia wrote:This effect causes energy loss due to frictional heating in susceptible ferromagnetic cores. The effect is also responsible for the low-pitched humming sound that can be heard coming from transformers, where oscillating AC currents produce a changing magnetic field

Magnetostriction is the effect within the core of the material but there is also the effect of the laminations physically buzzing in the transformer core if they are not stuck tight and pinched up enough.  That sounds more likely to me. Many years ago I worked in a company that actually had its own transformer room pushed up in the roof space.  It was a nasty smelly place with autoclaves and ovens and vats of varnish and coughing trolls! We R&D guys hated having to go up there to deal with them. There was always an occasional one which did not pass quality because of this buzzing problem.  Reliability in general has got a lot better in the years since then but one or two will always get through which develop rattles in a short while.

Of course there is always the possibility that it may not actually be the transformer itself.  In which case it would need to be opened up and explored a bit more closely.  Sweetwater should be able to diagnose where it is coming from, (you would hope! )

Thanks Bordon. I'm not an electronics expert by any means, but I get the concept. As you said, it may not be the transformer at all, the sound only seems to be coming from that area. As I said, I haven't opened it up yet, I'm gonna go through the proper channels or procedure before attempting that. You asked earlier how loud the buzz was. Not extremely loud, although it seems loud in a quite bedroom when not playing. I'm hoping ambient crowd noise will drown it out between songs. And, although the amp has its own DI, I think the buzz is loud enough to be picked up by a mic should I choose to mic the speaker.

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Good description of the level of the sound. If it's loud enough to even consider whether the crowd could hear it or whether it could be picked up by a close mic on your cab then it's loud enough to need dealing with. The level you should expect is a soft hum only heard when not playing in a quiet environment. Getting in touch withe the supplier to hear what they have to say is the next sensible stage to take. If you need any further help as in maybe needing to open it up for a look see then get back here, there is a proper procedure to do that without voiding the warranty. And make sure to let us know how it goes with Sweetwater. What you find out can easily help others who may have similar problems in the future. Good luck.

Ok, I called Sweetwater and the sale's man's exact words were "not cool" (that I'm having the issue). He transfered me to the support department, I explained my problem to them. They're sending me a brand new amp and I send the defective amp to them after receiving the new one. That's pretty good customer service. The best part is I paid a discounted price for a demo amp and I'm getting a brand new one instead. Can't beat that! Thanks for the help anyway.

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Sweet!!! ( babbaddaboom - tssshhh! ) That's the sort of service you would expect isn't it? And it makes you go back to them in the future.

No problem with the advice, that's what we are all here for. It's always good to hear and talk about problems like this, you never know when someone will come up with some info you didn't know before. We all go forward through it. Keep in touch and let us know how you get on with the new amp.

I certainly will. I'm gonna play it at a gig tomorrow night. I have a Mesa Boogie Mini Rectifier 25 head that I'm gonna bring along as back up just in case I run into problems. Our gig is 4 hours, I'd rather play it safe!

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Good luck!

So,CajunDan.How did the Gig go with the GM40? ,4 hrs.playing time  ,still when you pick up your $500,it'll seam worth it

The gig went well for the most part. There was an awful hum in the PA. It was the house PA, not ours. But, it was something locally because everyone with an amplifier (including me) had a terrible hum. So, that hum trumped the buzz my amp was giving me lol. The Grandmeister performed well, but I did have one issue. I'm sure I can search the topics here and maybe find some help. We don't normally mic our amps, but we did mic our amps for this gig. Our sound man used the Red Box DI on the Grandmeister. It sounded good coming out in the PA speakers, but this venue was short on monitor speakers. I couldn't get my guitar sound through the monitor speakers without disrupting our singer who was using the monitor. I tried turning my amp up so I could hear my amp in the stage volume. When I did the sound man asked me to turn down my volume because the signal to the sound board was too hot. I don't have any mic cables or any way of testing the Red Box DI at home. Is there a way to control the volume coming from the speaker out differently than the volume going out of the Red Box DI?

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No, I don't believe there is. You can stop sound coming out of the speaker altogether, but that's it.
As good as the RedBox is, micing the speaker itself is always going to sound better IMO. Just use the RedBox when you really have to.

Yeah, I knew you can stop sound coming out of the speaker, but that's the opposite of what I was needing. I even put my ear to the speaker while playing (with the band) and couldn't hear anything coming out. I spent about 75% of that gig literally not hearing a single note I was playing. I use a wireless system, and by getting out in front of the speakers was the only way I could hear myself. It would have been doable if I would've had my own monitor. And, I agree with you Johnny. The Red Box is convenient, but I prefer a mic as well.

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Maybe your speaker just wasn't plugged in properly?! Nightmare trying to play a 4 hour gig like that anyway.

No, it was plugged in properly, i could hear myself if I made a little noise between songs. During our last break I did grab some bungee cords and braced the amp to the speaker cabinet. I tilted the cabinet back, facing more towards my ears, turned the volume up some (pissed off the sound guy) and I was able to hear myself the last set. The bungee thing actually worked great. I'm gonna invest in an amp stand, bungee the amp to the cab and tilt it up for future gigs. I'm not the typical head banger that just needs to be loud, but I do like to hear myself, if at least to make sure I'm playing in the proper key lol. I bought this amp because it sounds great at low volumes. My other amp is a Mesa Boogie mini Rectifier 25W. It doesn't sound good until the volume level hits 4, and that's way too loud. I can barely put it at 1 on stage, without being mic'd, before the sound man says I'm too loud out in the audience. I don't need to be louder than anyone else, but I do like to hear myself.

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I agree it sounds great at low volumes. The GM40 sounds slightly better loud, but it is generally very consistent across different volume levels.

Right, and I noticed that with the Tubemeister 18 I test drove as well. My mine rectifier has 2 channels. Each can be switched independently to 10w or 25w. There's a huge difference in tone between those two. The 10w has virtually no low end, it sounded like I was playing inside a beer can lol. The H&K has Mesa beat hands down in that respect

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Agreed. I also have a Mesa Road King, which is capable of some great sounds, but I don't know when I'll use it again. It really needs to be turned up loud and just isn't anywhere near as practical as the GM40. And I prefer most of the sounds from the GM40 - it's much easer to get a good tone from.