A critical problem related to Built-in-FX of Grand Meister 36

I am a new owner of GM36 since 2 weeks ago and found this forum Yesterday, glad to see GM36 users are here.

GM36 gives me what I was thinking about, and looks an original mini head concept though, sounds like their flagship or Large head(of course it is not completely same with them, I mean it is like)
If someone loves H&K sound concept, It will makes the one satisfied in only with this small size I bet. And I am a fan of TRIAMP.

The sound is fantastic as I mentioned, but a serious problem I now encounter makes the worth of GM36 downed. If it is gone, GM36 will almost be perfect for me, at home, on a small stages, light weight, versatility... and so on... with this amp only.

However, the amp is limited to utilise by a serious problem, what I tell you guys now. It's really sad, and I don't know if it is normal condition or hardware defective.
It is generally to cause every pop noise of my GM36 and related to the built-in-FX(althouh there is an issue of popping by swithching channel). I use the amp like below;

1. My GM36 is connected to an audio interface through built-in-Red box from rear panel. No plan to use any Cabinet.
2. The amp usually has 1 or 2 effect pedals, H&K Tube Factor or MXR Dyna Comp, before input from front panel.
3. My midi pedal is FSM-432 MKIII only. No plan to have the others. No doubt because I bought that one for GM36.
4. Original tubes came with GM36 are still stuck. No plan to swap them out before confirmed that tubes stuck in are truly defective, I bought brand new!
5. And I use the amp with step-down-transformer(220v -> 100v)
(I live in South Korea and bought the amp in Japan. Unfortunately, no authorised dealer in my country. I struggled to purchase GM36 having proper voltage, but no help from Hughes & Kettner officially. Using step-down-transformer is a common way in South Korea. Many guitar kids buy amps directly from Ebay, Amazon, or in other countries when they stay or get travel there)
6. I always have the amp warmed up(Actually, without warm-up, the amp doesn't sound )

And the problem occurs like below;

1. Cyclic pop noise often happens as soon as Stand-by switch fliped on. not really intermittent.
2. The pop noise almost happen when I adjust Built-in-FX sections with knobs from front panel.
(Sorry, I am not a Ipad user, Also no plan to use I pad, I think Ipad is not necessary, fixing a preset with knobs and FSM-432 MKIII are enough for me. back-up preset? um... I should consider for that)
3. The condition of FX-Access button after pushed, which the problem is happened, shows such a freezing of GM36. When I twist knobs, The button just stops lighting in and out. I cannot monitor FX-effects directly as if it has a delay time for process.
4. According to #3, a worse thing is I can hear dry sound and cyclic pop noise only. I must wait for several seconds or at least I do not hear the pop noise with no more twisting knobs for FX, until. Otherwise, I will encounter the worst thing.
5. The worst thing is that not to change presets or switch Built-in-FX on and off by FSM-432 MKIII. Even if the foot switcher makes preset changed or FX on and off, there is loud pop noise or such a long time to finish changing. It looks like freezed, sounds with FX wrong or dry sound. If switching fails to change preset including Built-in-FX signal according to the details above, I can only do changing channels without the FX or have to turn the amp off. At this point, Stand-by switched off doesn't help to solve and pushing FX button again as well.
6. Finally, without any connection, this problem is happened. A proof that when I twist knobs, FX-Access button is freezed, also Chicken Head switch for channels has a delay simultaneously I can experience, so I should not touch FX-ACCEESS button to adjust FX-level.

I described details above are not intermittent. I now use my GM36 as if the amp has a fixed tone with a channel. It is most stable way to use the amp or only using dry channels without Built-in-FX all.
But changing channels without the FX by the foot switcher also has an intermittent problem, which is to sound loud pop noise when switched channels, especially, Ultra to clean. e.g.) Check when you hear pop noise, LED position of channel section might stay on ultra for 1~2 sec before moving to clean position, and then poped with moved to clean channel.

I have more details for this problem though, descrtion above seems to be enough I think.
I couldn't find any information of it on every serch engine I know. There is only a praise of an extream performence of GM36 with Built-in-FX. But I cannot enjoy this features

Well, I can ask for check of mine to a good tube amp technician in my country. But, to follow the rule of H&K warranty(Mine is still new!! ), if my GM36 is defective, in order to inspect I have to go to JAPAN, because of no authorised technician, even dealer in my country. Not easy to go there again. So I should try to get more informations what points are related to it. I don't want to believe my GM36 is defective. I don't agree it is a proud German quality. Well, all H&K mini amps including GM36 get being made in China.

I reported this issue through H&K official web, but I'd not heard yet.
If someone here has some comments about it, please reply on this post.

Thank for reading to all

I have none of these problems. Excuse my ignorance of non-USA power standards, but could it be that stepping down all the way to 100v is the problem? I work in electronics, and some of the random behavior indicates a power supply issue, particularly with digital circuits.
Unless you are in Europe, their website is worthless - try their Facebook page.

Either your power is bad/dirty, or the amp is defective. Can you have the step-down transformer checked? Seems like that might be easier than getting the amp checked, in your circumstance. Make sure it is delivering clean consistent power. Or, if you have access to one, put a UPS (uninterruptible power supply, like what's used for computers/servers) between the transformer and the amp - that will help condition the electricity going to the amp. At the very least it will be a troubleshooting step.

I can attest that dirty power can cause absolutely bizarre behavior with electronic equipment. I remember a couple outdoor festivals with inconsistent stage power, mini brown-outs etc... and it wreaked havoc with a lot of our gear. Crazy stuff. Lesson learned, and we now bring our own UPS units.

I wish you the best of luck getting this sorted out. Keep us posted.

I agreed that the power might be a cause as both of you mentioned, but my step-down transformer is fine my friend simply checked last weekend
 
As gravydb suggested a way, putting UPS between the transformer and the amp. It was a good try I have never thought. However, the same occured and the result is not reliable because my UPS is the cheapest one, APC BE-700, has been used since a few years ago.

I might have some tests more for the power though, here, I should consider the electrical problem as the last possiblity because I might have a big payment for the electricity.

And, last weekend, I did check the circumstances more clearly to report Hughes & Kettner again.
- YES, namklak told me about official H&K support but I did already before the reply is posted. -
Also, Email is sent to the retailer I bought the amp in Japan.

I could make the problem obviously where it comes from and what features represent the problem.

The problem must include cyclic-pop-noise and make the amp freezed when three-built-in-FX, which are Reverb, Delay, and Modulation get being adjusted by knobs and recalled by preset patches including one of  built-in-FX signal. Also, if the problem is ingeminated, three-built-in-FX will be dead soon, and the pop-noise again with dry signal. Although the condition of the amp freezed is just a moment, all the buttons and channel switch do not react.
Therefore, if I do not utilise three-built-in-FX, the amp works fine.

I now think some of the parts are defective. I just want to know if it needs a simple solution due to some parts soldered bad or assembled wrong.
To keep warranty, I should go to the retailer that I know well, but everyone cannot always meet authorised technicians. They are hidden when we need to find them even online.

I will leave what I got from H&K or the retailer, here.

I got an answer from official Hughes & Kettner today. It was faster than I expected!
I paste a part of the answer below;

-----------
the failure you describe looks like the Micro-Controller does not work properly. This can be caused by undercurrent or a hardware defect. Please check the output of your step down transformer. Is is really stable 100 volts? If the internal voltage of the controller drops below 5 volts, then the amp trys to reboot until the voltage is correct, and this can cause a cycling pop noise and a “frozen” user iterface like you describe.
If the transformer is ok, please return the unit to the to get it checked (warranty!)
-----------

My step-down-transformer is OK - already checked -
Being rebooted by dropping 5 volts is involved with the cyclic-pop-noise and frozen.
- It is hard to understand what the amp try to reboot and what the internal voltage of the controller is. Is it inside GM36? I think some parts are much sensitive to use for guitar amplifires -

As the support team suggests, my amp should be returned to Japan in order to check more because my amp keeps WARRANTY!! However, Going to Japan is not a peice of cake.

I can think of my case as no luck but Hughes and Kettner seems to know the cause of the some problems very well. It means they got simailr reports for the noise and the frozen condtion. I began to be skeptical about H&K Q.C. of the amps getting made in PRC.

If anyone doesn't have an authorised dealer, shouldn't try to purchase GM36 in other ways or must bring the one who knows how the functions of GM36 are operated well, because anyone cannot have proper tests without helps. Staffs in a shop might not know about the features of all the amps very well and they might not have tests for the possibility of the defects instead of the customers.

I need a time to think a bit what I should do of it.
There might be a few way more to make the amp work properly, the easier way than going to Japan.

How was your step-down transformer tested? Are you absolutely positive that it is delivering consistent power? Is there a different step-down transformer that you could try? Maybe a friend's? And/or try your existing transformer at another location, a friend's house? Again, more troubleshooting

It is possible you are just unlucky and have a defective amp but my gut says it's the electricity. I could be wrong. I'm simply connecting the dots between the wacky symptoms and the transformer (I've never heard of such crazy symptoms, and, you're the first person I've encountered that's using a step-down transformer with the GM). I'm not suggesting it's a bad idea, I know of other folks who use a step-down with traditional amps. I'm simply saying I don't know of anyone else who is using one with this specific amp. The GM is more complex than a traditional amp and perhaps is more sensitive to non-ideal power. Your transformer is suspect #1 unless it's been thoroughly and technically checked.

I'm not an EE, in fact I don't know squat about electricity. I just hope this gets figured out asap so that you can enjoy this amazing amp!

Thank gravydb for your interest keeping of it and you let me know what I might miss the possibilities of the power issue to check.

I don't ignore the power issue but I got common tests for the power issue. Nevertheless, I cannot make the results 100% sure because there is still number of cases. So I left the power issue as a suspectible cause and I will try to check that whenever possible.

My friend, who is a technician to repair machine tools, used a AC/DC tester how accurate voltage the tranformer supplies. He said that no need to warry about this and the transformer is well designed for stepdown but is influenced by original output. In addition, the transformer is the one highly recomended by the users from retro, HIFI and Guitar player in my country. However, there might be an unexpected point of the transformer. So I said it was simply checked.

If the cause is truly the power, it will be my pleasure. The simplest way that 100v transformer and main fuse inside GM36 can be replaced with 220/230v ones. Hughes & Kettner supplies proper ones for their users. However, even if Hughes & Kettner suspects the power, they seem not to be able to conclude it is the power problem.

As gravydb said, GM36 might be more complex than the traditions, but I don't agree that GM36 might be more sensitive. I heard German PCB designs is highly reputed by tube amp technicians. So I'm skeptical about the Q.C. of PRC

Anyway, I will meet a tube amp technician to check the possibilities of the problem in my country once. I think it is a easier way to decide what I should do for the amp or keeping warranty and then report here.

To clarify, I believe what H&K is saying that if the input AC voltage gets too low, the 5V regulator for the microprocessor will drop too low, and the microprocessor will reboot. This will not blow the fuse, but will produce erratic behavior.
The transformer must be tested under load. I'm sure your friend did that though...
If you turn the master volume almost all the way down, and put the soak in 18W mode, does the amp still do this? If that alleviates the problem, the 220 to 100V transformer is not capable of supplying adequate current for the GM36.

I now understood what H&K said to me, thank namklak.
I got a test in 18W mode namklak suggested and saw the same symptom.
But it was a good try and will be double-checked with the technician as I planned to meet him in this week or last week.

If it's worth another opinion at this late stage, I reckon Namklak is right on the ball.  This smells absolutely of the CPU rebooting from poor line regulation.  I've designed multi-processor equipment for industry and experienced this first hand with both poor supply regulation (on boats) and with poor PCB power line routing (minute voltage drops across restrictions on PCBs).  All of the symptoms you mention can be caused by a sudden increase in current load causing it to drop for an instant to just below the threshold level for the digital circuitry.

I can think of my case as no luck but Hughes and Kettner seems to know the cause of the some problems very well. It means they got similar reports for the noise and the frozen condition. I began to be skeptical about H&K Q.C. of the amps getting made in PRC.

That's a little unfair!  Sure, H&K will know about this problem, you can expect a problem like this to rear it's head at some time in the life of an amp model and people will of course report it to them.  But you have to accept, if Namklak and H&K are correct, it is not a fault in the GM36 caused by a weakness in the amp, it's a probable weakness in the supply that you are hooking it up to.  There is a limit to how much you can protect against this type of issue in any design!  In UK the supply is regulated as 230V +10% −6%.  In other words the supply cannot drop below 216V.  We can design our equipment to cope with that minimum, (minus a little headroom).  If our equipment has problems at say 220V then it is poor design, but how low can it go before we can say it is not our fault?

If you are in South Korea you must be dropping 220V @ 60Hz to Japan's 100V @ 50/60Hz.  The H&K GM36 Manual states that the Mains Voltage Tolerance Range is +-10%.  Your mains voltage from the SDTx must stay above 90V.  It also states that the Max. Power Consumption is 200W!  You may be working in silent mode but you could technically still be drawing maybe 150W at times.  Can your transformer supply a guaranteed 90V at 150W under conditions of varying load including sharp switching, (as in coming out of standby hooking up the supplies again)?

That said...  Another cause could maybe be that something is raising the ground level of at least the digital circuitry section a tad due to bad connections within the amp.  If the PSU has a good ground and the circuitry a poor high resistance one then this will drop the DC voltage the processor section actually sees even though the line voltage is not dropping at the PSU.  Something like that, poor ground connection, is not so good in a high voltage amp! Mind you, it's only an unlikely suggestion.

It might be the last mention by me for the power issue.

The results, the mains output shows the voltage range, min 217v ~ max 221v.
                  , the converted output shows, min 100.7v ~ max 102.3v.
                  , the concern about the load effect. At least, not me.

I now make sure that the results are 99% right and I lost an easier way, 100v transformer and mainfuse are replaced with 220/230 ones.

I won't describe what I checked in detail.
If I excuse, frankly, not easy to explain in English well, particularly to choose proper words as native speakers, but I bet I didn't have any disregard for the comments above.

For 2 days, I made some people annoyed, who are an engineer from the maker of my step-down-transformer, my friend who I mentioned above, a tube amp technician, even my apartment manager. They kindly gave me helps and answers, except for my friend , and I shouldn't spend a time for the power more I thought. Especially, I didn't know when my friend got a test of my step-down-transformer, he had used a digital voltage regulator to check mine. And, last night, after all the suspectible things were checked by him in my home, he attempted to throw my amp out I should've trusted his opinion.  

What 1% is, the tube amp technician experienced a 100v amp + step-down-transformer didn't work properly and couldn't find out the cause. - Sorry I don't remember the maker, becuase I was shocked. He denies checking GM36, unless he obtains the circuit diagram. -
Futhermore, he guessed if the problem is truly digital section, my GM36 might be replaced with a refurbished one by the retailer in Japan.

H&K gave me 2nd Email and said, if my step-down-transformer is double-checked as it works fine, there are 2 options, anyway I should try to contact with the retailer to return my amp OR an unauthorised tube amp technician, who I find in South Korea, will be officially supported to fix my GM36. So I gave my opinions and questions again to them.

Also the retailer in Japan told me what the retailer did through Email and I replied, but we still have a difficulty to communicate. Maybe, the response from the retailer will be late.
I will keep to post anything I discover or know.

I almost forgot, 2 more things bordonbert mentioned.
Max power consumption my SDTx supports is under 1400W, recommended by the engineer from the maker.
I tried to purchse higher one than mine though, the engineer didn't recommend to replace with the higher.

Ground, sadly, my home hasn't been earthed since the aprtment is built. It was the one I was concerned about. The tube amp technician told me if ground influences the amp, the speakers I have would have made such noises before the amp shows the problem.


Sorry for adding my comments more after posted... I should be free during weekend.

Hi, guys.

I got the last comment from H&K and it says ' all the products of Hughes&Kettner can't be officially supported to fix troubles, unless an authorised dealer or technician checks in any cases '

Although I struggled to solve my problem, I couldn't even check my amp.
An only way to have official support was to submit the qualification of unauthorised technicians who I contacted, but all the unauthorised technicians denied to give the qualification to H&K. They aren't interested in my problem as much as I struggled.

So, my suggestion is not to buy Hughes&Kettner's amps, if the retailer where you bought isn't close to you. If not, 3years warrnaty extended by registration is much useless, and the amps mightn't be repaired easily.

I'm sorry for telling it to the users who are satisfied with their H&Ks, but, in my case, H&K's behavior was the one of the worst in my experiences. There were only common phrases to prevent their loss.

I'm aware of the cause of the problem that I bought Hughes&Kettner's amp in spite of no authorised dealer in my country.

I will arrange my schedule to go to the retailer and try to get refunds on my GA36 and FSM432MKIII.
A pity that I better leave H&K.



One more thing is about a bad symptom below; I found recently.

I sometime got such a long time to warm-up when my GA36 is first turned on in a day.
Even though the amp got a enough time to warm-up, the amp isn't still ready to play.
This symptom shows as no red LED position of the channels and means the amp is frozen.
I handle the symptom with switching modes of FSM432MKIII, and I doubt it is involved with defective digital section.

Sad to hear you haven't had any success in fixing this problem.  I understand your difficulties in giving us information in English, I admire your ability to even post, if this was a Korean site I would be completely stumped!  

It sounds like you have taken all of the steps that we could have hoped for to check your power supply's regulation with the step down transformer in place.  Let's assume that is not the problem.

Ground, sadly, my home hasn't been earthed since the apartment is built. It was the one I was concerned about. The tube amp technician told me if ground influences the amp, the speakers I have would have made such noises before the amp shows the problem.

No, I cannot agree with him!  It is not necessarily the case that you would experience noises of distress through your speakers if the ground situation was causing some sort of problem.  There is an amplifying area of your amp which is running on high voltages and it has been designed to do its best to reject noises from the supply.  The speakers are driven via a transformer which is in turn driven from the amplifier and will not be affected by the lack of a ground.  It is very common to find amplifiers which have power supply ground faults which are completely noise free and apparently work perfectly. They are not necessarily safe, (as I know to my cost), but that is not quite the same situation as you have.

The digital section is not so lucky.  It is powered from a much lower supply line.  Noises in the ground line caused by the lack of a true local ground may very well approach levels where the digital circuitry will see it as a signal and respond in unpredictable ways.  It is understandable that under those conditions the results may not be stable. Can you take it to someone who has a well grounded supply and try it out there to see if the problem still occurs?

It is a shame that you would have to give up on a very very good amplifier if does turn out to be only the supply which is causing the problem.

I thank for reply and keeping the interest of it to Bordonbert.

In Korea, to find a house earthed is still not easy, because government in Korea, just a few years ago, made a duty when new structures are built to be earthed. However, I will try to find the house as the last test before returing my amp to get the refunds.

The retailer didn't answer about I questioned, and I now wait for that.
I hope to get the test before going.

You know, GM36 has really wonderful tone! and I still love GM36 as I chose it instead of Mark V 25,
So I'm still upset about the official support, but I will make me calm down to finish my problem.