GM problem with random modulation

I've had my GM for about 2 months now and I am very impressed! I've been playing for over 25 years and I've owned lots of boutique amps (Mesa, VHT, Tone King, Bad Cat, etc.) but the GM is just as toneful as any of them and much more versatile. I'm very fickle when it comes to amps and I've eBayed far more amps than I've kept, but the GM is definitely a keeper...if I can solve this problem.

Currently I play in a 90's alternative cover band and I just gigged it for the first time. The amp had been on and idling for maybe a half hour and when I switched it off standby and started sound checking there was a bad modulation / chorus-y type of sound that you could hear on every patch. It sounded a bit like a chorus effect with the modulation turned too high and made everything sound slightly out of tune. Understand that many of those patches did not have ANY fx programmed into them.

I went into fx mode on a few of the patches, turned the fx intensity all the way off and saved the patches. The bad modulation sound was still there. I tried everything - turning the amp off and letting it cool for a while, creating new patches from scratch, etc. but nothing got rid of that nasty modulation sound. Unfortunately I had no choice but to play the entire gig with the amp sounding that bad. What a nightmare!

The next day when I fired up the amp at home, the modulation was gone! It sounded perfect for a week, but it came back at our next rehearsal. So it's been intermittent since then and since I don't know what's causing it or when it'll kick in, the amp is basically unusable.

I submitted a tech support request to H&K via their website, but I've heard nothing back for two weeks.

Has anyone else had this problem or ever heard of it?

I have a 1 year warranty through the company that sold it to me, so I'll be attempting to exchange it for another GM. I'm assuming I just got a bad one. I'll keep ya'll posted.

Well I'm certainly no amp tech but you definitely tried all the things that I would have done. My advice: don't spend any more time on this - if you are able to replace the amp, DO IT. Intermittent issues can be the most difficult to get a handle on... even if it gets 'fixed', you'll always wonder if it is indeed FIXED, especially with a complex amp like the GM.

I wish you the best of luck bro. Keep us posted.

PS: what wattage mode are you running it? I'm just curious - if there's any sort of correlation between the symptom and the heat that is generated by the lower wattage modes - there's probably no correlation, but I'm just wondering...

If you're looking for more input, I haven't had this issue. I agree with KebSan - back it goes. Intermittents suck...

Haven't had (or heard of) that problem either.
Had mine for over a year with no problems.
+1 on sending it back. Might be an idea to contact them via their Facebook page - they seem to respond really quickly there.
Hope you get it sorted!

Thanks for the input guys. Apparently the warranty I have through American Musical Supply only kicks in after the manufacturer's warranty - which is two years. If I had found the problem within the initial 45 days they would have exchanged it no questions asked.

So my only hope is that H&K have AMAZING customer support and will eventually replace my Grandmeister. I left a message for them at their US Tech Support number a week ago but still haven't heard back.

In the meantime I'm going to bring the GM to my next rehearsal, point a fan at the back and see if it makes any difference. Wish me luck!

All the best,

Kevin S.

Well that sucks. Sorry to hear it. I've had mine running for very long periods, including extremely hot outdoor gigs, with no problems.

Can you provide a little bit more on your signal chain, any differences between settings when it happens versus it working well? Wattage setting? Using Any fans running in the culprit locations? It sounds like you are using the foot controller, right?

Hey Egads,

The signal chain is dead simple: a Boss tuner and EH B9 Organ Machine pedal in front of the amp and nothing in the fx loop. I'm using just the fx in the GM at this point. I use my old Digital Music Corp MIDI pedal to change patches.

The funky modulation doesn't seem to be tied to a particular patch or gain range - although it's a bit more noticeable on clean settings. When it kicks in, it doesn't go away when I change patches. It just kind of fades in and out randomly. I tried to record a video of it, but you couldn't really hear it that well.

I haven't been experimenting much with wattage settings yet - all my patches are full power.

There may have been a fan running at the last gig, but there wasn't one at the last rehearsal where I heard it.

I'm tempted to do a full factory reset on it - but I spent so many hours refining my patches, I'd hate to lose all that work.

Thanks for the info. Did you try removing your pedals and plugging straight into the amp when it was freaking out? I sometimes get a pumping-type sounds from one of my power sources (a PedalTrain Volto battery power supply). If it goes away, try adding the pedals back in one at a time (and/or using 9v batteries as a test).

There also could be some odd tube malfunction happening, though I don't think this sounds like. If you have them, you could try swapping power tubes with another matched set.

If worse comes to worse and you are about to ship it out for service, you have nothing to lose by doing a factory reset. If you are using the iPad app (or can borrow one from someone), you can backup all your presets.

Good luck and keep us in the loop.

I have heard it Once or twice, I believe faintly,, but only on startup. if I turn on the fx and back off etc. it seems to disappear. Or at least soon after. So to me it seemed like a warm up issue. since I have never noticed it after it is warmed up. Would be good to know more about it f on H&K though if anyone gets an answer.

I would suggest trying another midi pedal. Just a thought that this old midi pedal of yours, sends out modulation messages or something.
just an idea.

Well, I finally figured out what's been causing this out-of-tune modulation - and it's friggin bizarre!

I had contacted H&K US support, described the problem and they had issued me an RA number. I was one day away from packing and shipping the Grandmeister. I took my backup rig (Mesa TA-30 head, 1x12 cab w/Celestion Gold) to rehearsal. I was setting up the amp and tuning up when suddenly I heard the funky modulation again - through an entirely different amp! I yelled "what did you just do?" to our singer and he showed me he had just connected his mic to a VE-20 vocal pedal and to the PA. We did some experimenting to make sure we weren't losing our minds - and it was absolutely the connection of that pedal to our PA that was causing it!

The weird thing is it affects the amp even when the channel volume to the mic connected to the VE-20 is turned off. And the modulation sound is not coming from the PA but from my guitar speaker. It doesn't appear to affect anything else connected to the PA.

So the good news is my GrandMeister is working perfectly - and the Boss VE-20 has been exiled from our setup.

I did a quick net search but didn't find any other complaints about the VE-20 causing problems like this, so it's probably just a freak one-off thing.

Cheers,

KebSan

That is really nuts! Was it only happening in your rehearsal space? I wonder if there is a weird grounding issue? Glad you figured it out and didn't have to ship out the amp.

Our drummer sings and uses a VE-2, with the vocal key being triggered by a feed from the rhythm guitar player. We've had great luck and nary an issue. If something odd starts happening, I know where to look!