Remember, these scribbles are representing only my own views on this topic. And also bear in mind we are only an unofficial site here. We owe nothing to H&K other than gratitude for their great amps which we love. We really aren't interested whether you buy a new GM40 or not, only in offering what help we can in assisting you to making a good decision. (We're really kind and compassionate like that.
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Difference in tone between the GM36 and GM40? That's a very good question. Most of us who are long term GM36 users have a different opinion to those who came direct to the GM40 by the recent route. Personally, I have always really wanted the GM series to sound as I need it to sound as I love the concept and the implementation, (they are very well designed and made beasts and don't let anyone tell you any different). But it doesn't! It is a high gain/metal amp in the first class. It does cleans superbly so can suit country well. The GM36 undeniably has a top emphasis which can be shrill and strident with the wrong speakers and which cannot be removed totally, it's in the nature of the amp's basic design. That prevents me from finding anything suitable for my classic rock, (REAL classic rock from the late 60s early 70s, not what passes for it in the 80s and 90s). It's always a bit too thin, a bit too harsh, a bit bass light. There are other amps out there which sound much better for a lot less money in my circumstances.
And I'll be honest, the GM40 is not a beast I have ever played through. I followed the roll out with interest as a fan of H&K, listening to almost everything on YouTube I could find since the first. It was always the same. There would be a few licks of sparkling ultra clean with chorus and delay to show the alternative "intellectual, soulful, emotional" sound that metal guys have to have, then the rest was high gain chugging, tapping and shredding on a weird shaped guitar with angles and corners everywhere with associated pinch harmonics and overdrive screams with a sprinkling of whammy bar bombing thrown in. Ok, I exaggerate a bit, but not much. To date I have not found one review which shows the GM40 in use playing classic rock sounds even though younger players have pointed me towards what they think is that. There have been posts here with the latest suggestions as to good reviews but none of them touches on the Zep/Free/Bad Company/Stones/Pie/Lizzy type of sound. People swear that the GM40 is radically different in its voicing to the GM36. I just don't hear it. If it is radically different then none of the reviews out there, great though they are, do it anything close to justice.
Now it sounds as though your musical taste is later than mine as you mention modern rock rather than the 60s. I would have though the GM36 alone should suit that
with the right speaker choices which are crucial, (forget valves, they are only the cherry on the icing on the cake). I also would have thought that, if it follows in the family tradition which it seems to do, the GM40 would be a good candidate for later rock. I would advise you to think it out this way. Rather than saying "why would I want to buy a GM40?", think "why would I want to get rid of my GM36?" Don't look for reasons to talk yourself into spending money just to get a new toy, look for reasons why what you already have is not doing the job and can't be made to. Is there something that the GM36 is not doing or is it that what you are reading is just making you itchy to try something new as a case of FOMO, (if you don't know that one Google it.
)? If there is no real reason why the GM36 is letting you down do the sensible thing, forget the GM40 until you actually see something with your own ears (
) which makes you feel it is definitely a much better choice. If the GM36 is definitely not doing the job then and only then think of auditioning the GM40.
But.... Keep in mind, all you are going to get from ANY of us on this matter is "SO YEAH DOOD LIKE S AWESUM GODDA GED 1" from the modern younger guys who love it for its modern sounds, or "Heavens no old chap, it really isn't what one would want if one is determined to achieve a more classic sound" from the old guard like myself. No one can listen with your ears so the opinion they give is never going to be guaranteed to match your own. It would be a very expensive mistake to just accept someone else's opinion as a reason to talk yourself into buying.