grandmeister 36 mods

i found someone who makes some mods for the grandmeister.There are some sound clips showing the differences. I know that the "after modding" clips are louder kind of tricky but with a good set of headphones there are some nice improvemennts in tone.More degined? less fizzy , more marshally sounds.http://www.krusekontrol.com/hugheskettner_mods

Pretty much got what I needed with a tube swap. I'll see how I feel after the factory warranty runs out...

You can't tell whether this represents a genuine improvement at all from those clips, no matter how good your reproduction kit. The volumes are not balanced. Is that because the recording system was not set up the same in both cases, or were the GM Volumes different which would drive the output stage harder, or were the Gain settings different which would mean a major tonal change? Without knowing that the difference was from outside of the amp it is a meaningless comparison. Even if the volume change is from outside, it still affects your perception of the tone. It's a poor way to advertise your mod package and I'm surprised they would do so. Can't find any prices, do you know how much they charge?

My mod package?unless you are talking in general(so I misunderstood ) cause mate it's not mine, I was just searching for mods for this amp and bumped into this.I live in Greece and the guy lives in Usa.I wrote from the first time that there is something tricky in his clips.Anyway....i Wonder if there is someone out there who can really modify this amp.

When I said "...your reproduction kit..." I just meant the speakers/headphones you were using to listen to the clips not that it was your mod.

I wouldn't think there would be too many mods for a while until the schematic gets out into the wild. H&K are pretty tight on their schematics and we can't blame them for that. (It would be nice to get one on the desk though to see what's what.) At the moment modding means swapping out valves which they have given advice on, and applying VoodooJeff's additional Fx loop mod which H&K came up with. Even that should be treated with a pinch of "suck it and see" as we can't see what range of impedance it will comfortably accommodate.

Hope things in Greece are sorting themselves out. I know you guys have had a really hard time of it recently. Plenty of excuses to play better Blues.

bordonbert wrote:

Hope things in Greece are sorting themselves out.  I know you guys have had a really hard time of it recently.  Plenty of excuses to play better Blues.

Thanks for your support mate.I do appreciate that. NO things aren't gonna get better.Worst definitely better nope.

It seems that often, the mod community can drive sales. Also any decent electronics guy can reverse engineer a circuit. I've never opened this box (other than the top following the tube swap instructions), but I'm guessing there will be a few black boxes where the digital midi stuff is, including some digipots in the signal path. But most mods would be in the analog signal path, which could be reverse engineered. So why not release a schematic showing the analog signal path and use black boxes for the digital stuff?

In my humble opinion I think that there are some things that have to be done in oder the amp to sound more organic, warm etc.I chose this amp cause I suffer from severe pain in my back so I can't stand carrying heavy loads. It's prohibited.This amp is a great idea but there is a big compromise in some certain things soundwise.If those things can be solved then we have the best amp ever made.Till then I cross my fingers.For example here is a great sounding amp after being also modified.



https://m.youtube.com/watch?v=8KtmFL5Ba6k

Yes most every amp can be improved. But most amp designs (and mod "improvements") involve tradeoffs. But since we have four channels to work with, lots of room to play. If someone has a mod, I'd like to see it. But decades ago I was an analog hardware engineer, so I'd like at least a hint of theory, not just an audio sample.

ignantios,

just curious....what speaker(s) do you usually play thru and have you had a chance to try others? Also have you changed any tubes?

jitees wrote:ignantios,

just curious....what speaker(s) do you usually play thru and have you had a chance to try others?  Also have you changed any tubes?

sorry mate i was out of town...well i use a palmer 1x12 with either a legend 1218 or a Tonker. With both speakers the amp sounds kind of sterile and not so warm.And the most annoying is the lead channel that sounds fizzy.I have ordered the jj el84 for start but still waiting and cross my fingers.In my opinion since it's the first h&k that i own there is a specific characteristic in the sound of each h&k amp that is obvious in the upper midrange.Even the triamp or the switchblade have it.Kind of a harsh sound.This is only my opinion don't get me wrong,i like the amp a lot as a project but i have (if so)to improve some things.

The Tonker is a very clean very efficient speaker with a late breakup - I used that for years when I was modeling into a solid state amp, meaning most of my tone was modeled and I didn't want much from the speaker.  Being cheap, I'm still using the Tonker in a 1x12 for my GM. And I still using a Crate PowerBlock as my solid state power amp, with the GM in 36W mode master at noon driving an 8 ohm 100W resistor - stage volume is a fraction of what I'd have if I put the GM directly into the Tonker.  That setup is much more pleasant using JJ's throughout the GM.
I am using a smaller cab on the front of the stage facing me as a monitor - I'm trying the Lil Texas in there, I'm liking this speaker.  I may also do that in my main cab.  Note both of these speakers weigh 4 lbs, yea buddy.
Swapping tubes is a cheap easy fix for this amp, it kind of surprises me when I read that people haven't done that yet...  Tubes are mechanical devices and do sound different.  Plate size, mounting system, process to make the plate, all have affects on the tone.  With an "auto-biasing" amp like the GM, it's EASY!  If you have a thumb and 2 fingers, you can do it.  But I do recommend watching the video elsewhere on this forum.  Using the shoelace to lift the output tube spring is brilliant.

[quote=

I wouldn't think there would be too many mods for a while until the schematic gets out into the wild.  H&K are pretty tight on their schematics and we can't blame them for that.  (It would be nice to get one on the desk though to see what's what.)  At the moment modding means swapping out valves which they have given advice on, and applying VoodooJeff's additional Fx loop mod which H&K came up with.  Even that should be treated with a pinch of "suck it and see" as we can't see what range of impedance it will comfortably accommodate.

[/quote]

I was looking at the mod for the post FX return, and there should not be any impedance issues at all.
The new "send" is the line out. It is a line driver. Nominal level -10dBV, max of +10dBV. It does spec the output impedance, but it would be being used as it was designed to do, not not as some kind of band aid.
The only possible issue would be in the return. I am going to do the mod in the next week or so and will find out what the input impedance is at that node. I would be willing to bet the designer of the amp that created this modification chose that insert point for a reason.

Thanks for the heads up Si, it's good to have confirmation of what that little hack is based on. A wise man once said:

Namklak wrote:....so I'd like at least a hint of theory, not just an audio sample.

He's on the button for my money.  A mod without background factual info is a double edged sword.  It could sound awful in which case it kills itself off, it could sound great but be basically unreliable in some way and a "bad thing".  You've confirmed that this should be no problem.

If it's the Line out then it quotes 220R impedance, happily low, and it certainly is a line driver which takes case of the first issue of output impedance.  As long as the new mod is used as an Fx loop with sensible pedals we should also have a decently low output impedance to drive the return which should be considerably higher than the 220R as you said.  It needs confirming in practice but I'm sure you've cracked it now Simon.

And your comment on the designers being canny is spot on by my experience.  The GM36 is a really good solution all round within its design parameters.  And they have always been helpful with technical questions within sensible limits, (gotta use Facebook though).  It's great to see them willing to come up with a mod like this after the fact and release it to us.  I can't think of another manufacturer who has done anything similar.  I'm sure there must be a few but I've never heard of it.

Can't see clearly from Jeff's picture of the internals but I wonder if the Line Out is actually a stereo jack masquerading as a mono one?  That is sometimes done. If so there is a really neat solution involving a Dremel, a grinding wheel, a stereo to 2xmono splitter cable and the PCB......

Hello,
I looked at the schematic and got an idea. If C39 swaps 1uF for ELKO 10uF or 22uF, you get more bass and overall sound gets warm
er.

Yes, that a standard type of mod to apply and seems very simple when it is talked about on guitar forums for more basic "classic" amp designs.  Opening up the bottom end rather than lifting it more broadly might not be the best route to choose, though we can't be absolutely sure of that without trying it and listening of course.  You are not changing the overall balance across the frequency spectrum with this mod, only allowing lower frequencies to come through which may not help in any real way.  That value was chosen carefully to match the guitar signals it is having to deal with.

With that in mind I would suggest that 10uF is too much , more than necessary, and 22uF is way too much.  The trick with this is to only open the door as far as you need for what you want to get in.  The original 1uF/1k8 has a breakpoint there of 88Hz.  Increasing to 10uF moves that down to 8.8Hz and 22uF means 4Hz.  I'm sure any musical whales would love that!  That is a lot of potential for other slush to get in.  If you want to do something like this I would recommend no more than 2.2uF.  That moves the breakpoint down to 40Hz and means that any further increase is not going to affect any guitar pitch signals in the path.  This is not a bass guitar rig, bear in mind that your guitar only goes down to about 82Hz on the lower E string.  And the fact that the breakpoint is a little over that is not as significant as you might think.  As things stand the signal will be 3dB down at 88Hz and your ear cannot really distinguish that in music.

I do think that the edginess in the GM36 is not coming from a lack of bottom end, if anything it's from a peaking of the upper middle or top end.  Taming that is not so easy as just opening up the bass further.  It would need rebalancing across the frequency spectrum and that is an impossible job taking into account the channel interaction.  Believe me I've looked into it and gave up on the idea.  That said you may like that mod of course, but don't go overboard and introduce low frequency rumble and mush in doing it.  I modelled the whole GM36 circuitry stage by stage quite deeply using Spice and saw first hand how complex the interweaving of the channels is.  Some mods may change one channel for the better but another channel will most likely suffer.  Unfortunately the H&K amps are nothing like simple Fender Tweeds.

And then there is the problem of working manually with surface mount devices in a lot of places, (though not here)...

One other not commonly considered factor which is usually applied here is to stagger the lower breakpoints of each stage to minimise the possibility of detrimental peaking at any frequency due to the phase shifts that are introduced.  If stages have the same lower breakpoint it can lead to a peaking at that frequency with ringing and that is to be avoided as much as possible.  There are a lot, and I mean a lot, of low frequency high pass filters like this in the signal path of this amp.