Grandmeister40 Issue

Hey guys, need some help here. So, I bought a new/other Grandmeister 40 Saturday. I say used/other because the guy said it was a floor demo model. I has all the warranty cards etc. Still has the protective plastic on the plexiglass. Thought I was getting a good deal at $850 as he wanted $950. I don't have the footswitch or midi dongle yet but they are coming from Sweetwater this week. My nephew has one and it is awesome.

Ok so here is the deal...

1: This thing isn't loud at all, especially in "clean" mode. The nephews is OMG loud as he had it over a few weeks ago. This one, not so much. I can literally turn the master and the volume up to 11 (sorry had to do it, actually to about 2 or 3 o'clock) and it is loud but not nearly as loud as it should be. The clean channel (except where noted below) sounds good, the rest sound fizzy and well, shallow.

2: The tone knobs have minimal impact on the sound. If I turn the treble for instance all the way CCW there is a bit of a roll-off. From there to about 9 o'clock a bit of change, from there al the way CW barely discernible. Same with mids and bass. The effects work ok so I know the knobs work.

3: The noise gate even at it's lowest setting cuts off the sound after a few seconds. So if you hit a chord and hold, it only rings for about 5 seconds and there is plenty enough sound for the gate to stay open. CCW and you can't even get the gate to open.

4: Plugged my pedal board into the front (yes I know I should use the effects loop) and the clean channel had a disturbingly dark hum. The Lead channel sounded like a white noise generator. Unplugged the pedal board and back to normal. Nephew has no problems plugging his into the front jack. (all boxes were off btw)

TSC lights are all normal (out at 40w). Don't think its the power tubes. I have an entire new set of JJ's coming. Anyone have any idea what the heck the problem might be? I think I screwed myself. Should have bought new from Sweetwater. UGH! Preamp tube bad? I'm open to suggestions.

Damn, that sounds awful. Definitely not normal GM40 behaviour.

I'm sure bordenbert will be along with a better answer soon, but you could try a factory reset? There was a guy a little while back on here that had some similar symptoms, and doing a factory reset of the settings fixed it.

Hey Jonny, yeah I read that post and have tried it several times to no avail. I've read elsewhere that the tone pots not responding etc., are an indication of a bad preamp tube. I work in Avionics so it kind of irritates me that there are no schematics on this beast. The JJ's should be in today or tomorrow. I've got my fingers crossed that changing them works. My Nephews amp sounds incredible and is the reason I bought this one. Not crazy about the thought of sending it out to HK and the charges that would incur. Hove to wonder how long HK hold those schematics up before releasing them...
Thanks so much for taking the time to try and help. Much appreciated.

No worries, hope your JJs fix it. Just be very careful when changing them. As you have probably seen in other threads, you can invalidate your warranty if you don't change the tubes in the correct way.

Ahh the old, don't remove the bottom four screws. Yep, I saw that as well. As for warranty, even though this thing is new, it was being sold by a guy who sells gear over the internet and said it was a floor demo unit. Not sure HK would honor the warranty even though I have a receipt and all the warranty cards, etc.. Definitely not an authorized HK retailer.

I'm not sure how it works, but they might still honour it. Best to play it safe just in case, IMO!

Good advice for sure. What irks me is that HK don't release the schematics. If they did, I would fix it myself (if it isn't the tubes). That being said, if they won't release the schematics, got to wonder if they would sell replacement boards to non authorized techs.

So my TM112 cabs, foot-switch and WMI-1 came from Sweetwater today. Hooked everything up and...everything seems fine now! WTF? Don’t get me wrong, I’m happy but that’s just weird. Even the noise gate works normally now. Tone controls are much better (still not what I am used to as far as tonal shaping but a vast improvement over what it was). Scratching my head here for sure. Tomorrow the JJ’s should be here and I’ll put them in. Would love to hear somebody’s take on this because I’m baffled by it.

That's weird. I'm guessing it was something to do with the control system, rather than the tubes. Anyway, enjoy!

Thanks, Jonny. I'll keep you posted on how it acts with the new tubes. It really is weird. Software glitch perhaps? Thanks again for your input and suggestions.

Put in the New JJ's last night and wow...this thing is now a beast! So it would seem I had a software glitch and a weak/bad tube. Whew!

Glad it worked out! The GM40 is a hell of a good amp, I'm sure it will serve you well.

Hahaha! Sounds like I came too late to the party! Sorry I missed you for a while, I've had a couple of days of work being done in the house and it's been chaos here.

It does sound odd doesn't it. The idea of a software glitch is very real and I think we may get more problems of that sort than we realise. The digi-pots are very good, probably better than normal analogue ones in many ways as they are built on separate switched fixed resistors which is a hifi concept. They are under the influence of the control software though. And of course the valves may have been the culprit. It isn't unusual for a valve to have a burn in issue like this with either minute swarf particles (why is that not in the dictionary, it's a real word!) or low levels of gas which then get swept up and cleared. My guess is that your new valve will remove this as an issue. It's a good idea to get your hands on a new replacement set for the Orientals when you can and most of us here would have probably advised the JJ route as practical and sensibly cheap. You most likely know my thoughts on that if you have been reading around and no one ever produces any evidence to the contrary, (no, I said "evidence" ).

Having done the factory reset there is not much else to say except welcome to the forum, it's a great amp, and to advise you to keep an eye on it and get back to us if it occurs again. Oh, and you're not alone with the tone control thing. I have always been amazed at how weak the tone controls are on the H&K amps. It definitely improves with better speaker choice but it's still anything other than monumental, highly - errm - "underwhelming" to my mind!

Hey, great to hear from you. Ahh yes the tube thing. I have read a lot of your posts besides the ones on tubes and while not an expert on them by any means , I did think it was just a tad bit insane people spending hundreds of dollars for say, a NOS Telefunken. Now I can see the 12AX7 variants making a difference with the lower gain/higher current but I was never convinced that the NOS tubes were all that. Made better, possibly?
Well, I’m glad the amp is normal now and indeed, the tone controls are better but not what I am used to. Curious if there will be someone out there who comes up with a mod to improve that aspect. For speakers I went with the TM112’s, so I’m now the proud papa of a mini stack. I also have a Fractal AXE-FX II so those 1x12’s can be hooked into the Matrix amp I have if need be. They sound pretty darn good for their size.
Your input is much appreciated and always welcome. Have a great weekend!

Let me put my usual (long winded but necessary) advice in here just to dispel one of the worst guitar amp myths once again.  Beware the "variants" word in the valve arena!  It may not be what you meant of course but, if you mean the 12AT7, 12AU7, 12AY7 etc, then they are NOT variants of the 12AX7 even though some techs seem to swap them around as perfect matches.  They are totally different valves with totally different characteristics designed for totally different tasks.

The idea of "Gain" in the quoted parameters of a valve does not really exist.  The gain in a real life circuit depends on a group of connected parameters.  There is a parameter called "Amplification Factor" or "μ" (that's myu) which is what is usually misquoted as Gain.  It isn't!  It is the ratio of the anode voltage to grid voltage, (seems to be gainlike), but for a FIXED ANODE CURRENT.  This is definitely not what we have in a working valve setup.  The anode current varies greatly in use due to our signal and the anode load resistor converts that current change into a voltage for us, so that parameter is not anything to do with the real gain of the valve in that stage.  There is also "Internal Anode Resistance" which is a parasitic resistance in parallel with the load resistor and is hugely different between them and varies massively with current.  Because of this if you swap in one of those "equivalents" you change wildly almost every other carefully designed aspect of the stage.  It's a "bad thing" to do to your amp despite what "gurus" will tell you.  Most can cope with it without damage but they are no longer the same amp in any way and reliability is one aspect which may even be compromised.

The only good swap is a 5751 which has all parameters very close to the original 12AX7.  That is your only "low gain" equivalent and is definitely safe to use in almost all circuits designed for the 12AX7, (which is really an ECC83 ).

Now you may not have actually meant that originally I realise but it never hurts to put the truth out there one more time.

Good to know. I’m an Avionics tech by day, and at night, well, that’s questionable ...lol. My tube theory is basic at best and I have only just recently started brushing up on it. Been well over 30 years since tech school and even then they barely brushed on tubes. I’ve often wondered about people swapping tubes. I’ve even seen videos of people hot swapping them on YouTube! That’s not even remotely smart IMO. I’ve looked at the 5751 and I may purchase one just to see if it makes any noticeable difference, and if it’s a positive thing.
As for your responses being long winded...nah. I like tech nerdy stuff.
Again, thanks for your input!