Grandmeister 40 Deluxe, volume differences/weird behaviour

Hello all,

this is my first posting here, I’m glad I found this great forum about a year ago when I was going through potential options for my next guitar amp.
Last December I bought my first ever tube amp, a brand-new unit of GrandMeister 40 Deluxe. I’ve been exploring the vast number of features and possibilities within the GM40D and the FSM 432 mk. IV MIDI controller and TM212 cab I ended up choosing along with amp itself.

I really like the tone, versatility, saving and recalling presets with MIDI etc, but I can’t shake the feeling there’s something weird with the performance, namely involving the channels & power soak section.

I’ve read many posts in this forum describing similar behaviour and I’ve tried some solutions (such as performing a factory reset) given by the experts in here, but I think the situation is a bit unique with my amp.
Here I’ll describe two anomalies I came across during past months:

1) The sound pressure level difference between channels. The clean and crunch channels are equally loud when having identical volume/EQ/gain pot adjustments with each other, with any power soak setting. It’s easy to dial in identical settings in desktop editor (created by a member on this forum, I believe) between two presets, differing only by the channel setting.
Also, the lead and ultra channels are equally loud with each other having identical volume/EQ/gain pot adjustments with each other.
The problem is the huge volume jump from clean/crunch to lead/ultra channels. The volume difference is probably at least 10 dB in perceived volume in the playing room. Interestingly, it’s somewhat challenging to capture the phenomenon on recorded waveform.

2) Absence of the sound pressure level difference between 20W vs. 40W setting, in clean channel only. In any of the other three channels, there’s very noticeable volume difference between 1W -> 5W -> 20W -> 40W setting, both in perceived acoustic sound pressure level from the cab and 20W -> 40W setting in recorded waveform. Going from the 20W setting to 40W in clean channel however has almost no volume increase at all (about 2 dB, compared to about 6dB for any other channel. The perceived difference is greater than the numbers indicate).


Last time I tried, the TSC LEDs flash eleven to fourteen times when performing the test. It’s been roughly like that from the beginning and should be within acceptable limits (under four flashes difference between any of the LEDs).

Probably worth a mention that the volume difference described in 1) or the absence of difference described in 2) do not depend on the boost setting being ON/OFF. Neither make the channel volume/EQ/gain pot positions any difference to the phenomenon, as long as the settings are identical between the two channels compared. Guitar volume is obviously kept constant while performing the tests. Master volume being low or high doesn’t make a difference, as long as it’s kept constant while performing each test.

So, any advice is greatly appreciated. I love the amp and want to continue researching the endless features of it, but I’d really like to shed a light to these issues first.
Attached a couple of images showing the issue #2. The issue exists with regular guitar output signal of course, but is more visible here when I ran a simple sine wave input through the amp.


Thanks
-vin

Hi Vinnemon.  Glad you like your GM40D.  Paired with the FSM432 it is so flexible you shouldn't really need too much other gear to get anything you want in terms of sound.

Let's start with the basics of this area.  You have four channels here.  Each of them has its own signal path through a differing number of valves with components changed on the fly to suit the tonal characteristics of that particular channel.  When you set up a preset as you want it you are effectively changing gains and signal levels across the frequency spectrum with signals clipped and distorted to achieve your desired tone.  This inevitably leads to differences in level at the end point of the chain between presets.  This is where we must get straight the relationship between the Volume and Master Volume controls.  You may have this at your fingertips already, apologies if you do, but it should be explained as a starting point.

The setting of the Volume control is remembered as a part of a preset, the setting of the Master is not.  So if you record identical settings to two presets differing only by the level of the Volume control you should get the same tone but at different levels of drive from the preamp section.  Now, if you adjust the Master Volume you should increase the level of both of those presets by the same amount, and they should remain different by about the same relative amount because of their still differing Volume control settings.  In circuit, the Volume and Master Volume control are just two pots directly connected one to the other in that order.  The Volume is actually a digipot while the Master is a normal standard pot.

The intention of that was to give you a way of setting your presets for tone, adjusting their relative levels with the Volume control for each and readjusting the other controls to suit if necessary, then storing.  Then you adjust the overall level you play all of your presets at with the Master Volume.  Is that how you have been using it?

The Power Soak is a simple device which just adds in a carefully calculated set of resistors to the speaker line which will drop the signal level by a preset amount while keeping the overall load impedance constant at the output transformer terminals.  There are a number of factors at work in our use of this.  Firstly, the differences from level to level are significantly different.  We have 1W x5 -> 5W x4 -> 20W x2 -> 40W.  The steps are reducing as we increase power and this leads to us hearing less difference between them.  A doubling of power is not particularly significant to our ears and was chosen as taking one pair of output valves out of circuit was an easy and convenient way to reduce power without changing the level to which the remaining pair are driven.

Next there is speaker response.  Speaker drivers do not have a linear response curve in any way.  If you double the input power you do not double the sound output power.  For an example, this is very noticeable if you try to drive a high powered speaker, say a 100W 4x12", from a smaller guitar style amp, say 5W.  Even if the amp gives its best tonal contribution at the 5W level the speakers are not even being driven to a point where they will "light up" and the sound will be flat.  One of the parameters in speaker design is "maximum linear excursion".  This is how far the cone can move forwards or backwards before the surround is stretched to its limit and restricts it preventing any further movement and "flattening off" the signal peaks.  It isn't a strict "no restriction up to this point then absolutely no more excursion" brick wall effect of course, it kicks in gently at a point in travel then gradually tightens its grip as we drive beyond that point. Hifi speakers are designed to be always held inside that linear limit while guitar speakers are designed to be driven outside of it.  Speakers make their own contribution to the overall richness of a guitar sound and if that is missing it usually sounds flat.  (This effect is not relevant in today's all in one digital speaker cabinet compensated units of course which need flat hifi type speakers to sound at their best.)  The increased restriction with increased power will also alter the perceived differences in relative sound levels.  That may be part of what you are hearing with your own 2x12" H&K cab not being driven near that limiting excursion when driven by the low power levels.  So greater perceived aural level differences are then permitted by the surround.  When the level is raised to the point where the speakers become restricted, maybe at around 20W, then the drive is changed to 40W, the differences are not so apparent as 20W is enough to drive them close to or into excursion limiting so there is little more increase left in forwards or backwards excursion even with increased input.  Usually the character of the distortion changes slightly from that point on, (either for the better or the worse depending on the speakers).

These are just a few ideas that I have come up with based on my years of designing, building and using amps and speakers.  Does that whole last paragraph make any sense?

I've run into the same problem, which made designing presets of equal perceived volume impossible except at "stage volume," using 20W as a compromise between 40W and the lower power soak settings, so I could still have usable settings when practicing at lower volumes at home. (Playing that loud at home didn't go over so well but told my wife it was a "professional necessity" and wouldn't last long!!) Meanwhile bordonbert I guess you're saying the amp at lower power soak settings isn't driving the speakers as hard unless you turn up the master volume, so the sound pressure will be flatter? Which also means there are hard limits to what power soak can do.

"Professional Necessity"!!!     Thanks for that one Bill, it's now sitting on top of my arsenal for future skirmishes with my own "trouble and strife".

Yes, it's a problem that is not understood and acknowledged by many, and is absolutely real and is a factor in every system.  In the band I play with I have always had this problem no matter what amp I have used, (GM36, '60s SL100, JCM800, SC20H).  It was when trying to use external power soaks that the penny dropped.  You actually make this problem worse if you add a power soak as it increases the drive the amp can supply for the good, but it reduces the speaker's drive which is bad.  I have an original late '60s Marshall 4x12" which is still utterly awesome, (yes, original Hendrix model G12Hs with original cones), but I simply can't use it nowadays as it is just too blisteringly loud when it comes on song.  Playing at below that "light up" level for the speakers with any amp may get the best out of the amp but leaves the overall sound thin and weak and the feel under my fingers very flat and dead.

You have to take the speaker into account in the overall picture, unless you are using a modern modeller type setup where it has been factored into the digital equalisation as I said above.  I would honestly recommend that, if you are going to use the GMs on the lower power settings you should hook them up to a much smaller speaker to get the best out of the combination.  Just going for a single 12" over a pair will help somewhat.  I am actually currently using a Fender DeVille Hotrod 4x10" driving into a Fryette Power Station PS100 which loads the amp section reactively and buffers the amp's output signal back into the Fender's speakers.  This takes care of everything I need in terms of the amplifier sound in a genuinely remarkable way at all levels and I reckon is the future of using power gear in small spaces.  But it still suffers this same issue with the speakers!  It loses a definite something, a "liveliness", if the speakers are underdriven even by the Fryette.  If I drive only one of the Fender 10" the sound really opens up.  Mind you, the Fender is open back so there are no real cabinet volume issues to contend with.

It's a cheap and easy thing to test yourself if you have the multiple speaker cab to play with.  You have to be careful with impedance of course, (in my own case 4x10" -> 1x10" = same impedance), though with the H&K amps and their forgiving impedance requirements it is much easier than, say, a Marshall/Fender style design.  And what's more, there is no other way around this other than doing a Stevie Ray Vaughan and "blanketing" the speaker or smothering it in some similar way.  Maybe build a decent "speaker isolation booth"?  Damn, now we are back to Bill's "professional necessity"!

bordonbert wrote:Hi Vinnemon.  Glad you like your GM40D.  Paired with the FSM432 it is so flexible you shouldn't really need too much other gear to get anything you want in terms of sound.

Hi Bordonbert, ye ol’ reliable, and thanks for your reply! Indeed, the setup is fantastically versatile.

bordonbert wrote:Let's start with the basics of this area.  You have four channels here.  Each of them has its own signal path through a differing number of valves with components changed on the fly to suit the tonal characteristics of that particular channel.  When you set up a preset as you want it you are effectively changing gains and signal levels across the frequency spectrum with signals clipped and distorted to achieve your desired tone.  This inevitably leads to differences in level at the end point of the chain between presets.  This is where we must get straight the relationship between the Volume and Master Volume controls.  You may have this at your fingertips already, apologies if you do, but it should be explained as a starting point.

The setting of the Volume control is remembered as a part of a preset, the setting of the Master is not.  So if you record identical settings to two presets differing only by the level of the Volume control you should get the same tone but at different levels of drive from the preamp section.  Now, if you adjust the Master Volume you should increase the level of both of those presets by the same amount, and they should remain different by about the same relative amount because of their still differing Volume control settings.  In circuit, the Volume and Master Volume control are just two pots directly connected one to the other in that order.  The Volume is actually a digipot while the Master is a normal standard pot.

Yes, this is good information and makes perfect sense. I think I’m familiar with the logic behind both volume controls. The image I attached in my opening post shows the exact settings used in recording the output shown in two other images. The presence/resonance/treble/mid/bass/volume/gain are all dialed in value “127” in the desktop remote app. No effects being used. I’ll call this a “127-preset”. Now, both the waveform images attached in my last post show the recorded result from the Redbox out into PC. First clean channel with “127-preset”, power soak setting getting changed from 20W to 40W midway through. Then exactly same with lead channel. The result is that there is much smaller volume jump from 20W -> 40W in clean channel than any of the other three (crunch & ultra channel behave exactly like the lead channel). Master volume is kept the same during the recordings/test.

bordonbert wrote:The intention of that was to give you a way of setting your presets for tone, adjusting their relative levels with the Volume control for each and readjusting the other controls to suit if necessary, then storing.  Then you adjust the overall level you play all of your presets at with the Master Volume.  Is that how you have been using it?

Yes, that’s how I’ve been using the amp, when playing around with the presets and adjusting tones. The process of recording the sample images I described above.

bordonbert wrote:The Power Soak is a simple device which just adds in a carefully calculated set of resistors to the speaker line which will drop the signal level by a preset amount while keeping the overall load impedance constant at the output transformer terminals.  There are a number of factors at work in our use of this.  Firstly, the differences from level to level are significantly different.  We have 1W x5 -> 5W x4 -> 20W x2 -> 40W.  The steps are reducing as we increase power and this leads to us hearing less difference between them.  A doubling of power is not particularly significant to our ears and was chosen as taking one pair of output valves out of circuit was an easy and convenient way to reduce power without changing the level to which the remaining pair are driven.

This is all good information. I’ve read about the mechanics of power soak before here in the forums. I even did some math earlier to calculate the theoretical volume increments going from 1W -> 5W -> 20W -> 40W (see attached image). The measured volume dB increments of Lead channel (also crunch & ultra) correspond well with the theory: 1W -> 5W is about 7 dB jump, 5W -> 20W is about 6 dB jump, 20W -> 40W is about 5.5 dB jump. I suppose the 5.5 dB instead of 3 dB what the theory says is because of the two vs. four output valves, which probably makes the difference between real life and theory. I don’t pay too much attention to that, but I DO pay attention to why the volume dB increment of clean channel going from 20W to 40W differs so much from other channels

bordonbert wrote:Next there is speaker response.  Speaker drivers do not have a linear response curve in any way.  If you double the input power you do not double the sound output power.  For an example, this is very noticeable if you try to drive a high powered speaker, say a 100W 4x12", from a smaller guitar style amp, say 5W.  Even if the amp gives its best tonal contribution at the 5W level the speakers are not even being driven to a point where they will "light up" and the sound will be flat.  One of the parameters in speaker design is "maximum linear excursion".  This is how far the cone can move forwards or backwards before the surround is stretched to its limit and restricts it preventing any further movement and "flattening off" the signal peaks.  It isn't a strict "no restriction up to this point then absolutely no more excursion" brick wall effect of course, it kicks in gently at a point in travel then gradually tightens its grip as we drive beyond that point.  Hifi speakers are designed to be always held inside that linear limit while guitar speakers are designed to be driven outside of it.  Speakers make their own contribution to the overall richness of a guitar sound and if that is missing it usually sounds flat.  (This effect is not relevant in today's all in one digital speaker cabinet compensated units of course which need flat hifi type speakers to sound at their best.)  The increased restriction with increased power will also alter the perceived differences in relative sound levels.  That may be part of what you are hearing with your own 2x12" H&K cab not being driven near that limiting excursion when driven by the low power levels.  So greater perceived aural level differences are then permitted by the surround.  When the level is raised to the point where the speakers become restricted, maybe at around 20W, then the drive is changed to 40W, the differences are not so apparent as 20W is enough to drive them close to or into excursion limiting so there is little more increase left in forwards or backwards excursion even with increased input.  Usually the character of the distortion changes slightly from that point on, (either for the better or the worse depending on the speakers).

This is also extremely useful, important and interesting information. This, I believe actually explains my issue 1).
I earlier recorded the volume difference between all the channels with my “127-preset” settings with constant master volume, and ended up having proof that the recorded output signal is pretty much at the same level on all the channels, although while recording, the perceived volume was much, much louder with Lead&ultra channels vs. Clean&crunch. I figured the explanation might be something like you you described, the cabinet speaker being driven differently with different amount of gain/distortion offered by each channel, affecting the perceived sound pressure level. However, I don't think the speaker qualities can explain the issue 2), as the volume difference can be seen on the waveform recorded from redbox out.

bordonbert wrote:These are just a few ideas that I have come up with based on my years of designing, building and using amps and speakers.  Does that whole last paragraph make any sense?

Yes, everything you write makes sense, and I can’t thank you enough for helping me and always participating in the technical discussions here. I enjoy reading them as I keep learning about all the features and details about this great amp. It’s just that particularly the issue 2) I mention is troubling my mind. I keep wondering if replacing all the valves could “fix” these anomalies I’ve been writing about.
I mean, might the problem 2) suggest that there’s something wrong with the power amp valves? But how could a broken power amp valve(s) affect clean channel only? That would point more to a broken pre-amp valve, wouldn't it?
Solution for all of this could potentially be as easy as replacing some/all of the valves, but I haven’t gotten to that yet as the amp is obviously still under warranty, and I don’t want to jump to hasty conclusions because I first want to fully understand the behaviour of the amp. I do know though there’s a way to change the valves without breaking the seals...

https://i.servimg.com/u/f75/20/52/64/91/clean_11.png
Clean channel 1W - 5W - 20W - 40W

https://i.servimg.com/u/f75/20/52/64/91/lead_c10.png
Lead channel 1W - 5W - 20W - 40W

This makes clear that you are pretty well up on aspects of this sort of tech stuff.  That does my old engineer's heart good to hear that!  Too many guitarists are intimidated by the technical side of what we do, particularly anything which involves a bit of maths which is universally hated, and that restricts their understanding and eventually their creativity enormously.  It leads them to reject any technical info concerning things "tonal" and straight into the arms of the snake oil peddlers.

In truth, there is nothing that should be beyond virtually anyone who is prepared to put in a little time reading through, dissecting, questioning, and taking on board anything which engineering types like myself may explain.  That should not be without solid factual based proof of course but that applies to both sides of any argument.  The problem is in the old adage:  "In order to learn something new you must be prepared to give up what you already know".  Once we realised the Earth was round we had to give up the idea that it was flat despite the fact that we had definitely and unquestionably "known" that was so for a long time.  In our case I would actually describe that as: ...what you already "know" in inverted commas with pairs of fingers hooking downwards by my cheeks!  Most of what guitarists "know" of the tech side of their field is given to them by other guitarists who plain "don't know" but who talk as though it is indisputable fact.  Engineering types like me don't know anything because we don't have "guru status", "that magic touch" or "golden ears".  We prefer the results of measurement by unemotional test gear to being guru minded.  Back down the line so many ideas have started from someone who plain knew nothing but, when they are passed on to others as though from an expert, they stick and become "common knowledge".  It's now established and unquestionable "common knowledge" that valve brands all sound massively different, that "tone capacitors" (no such thing) sound better than simple ceramics, that the 12A*7 "family" are all interchangeable.  None of those are true and can easily be demonstrated on a workbench with top quality objective test gear to an unbelievable degree of accuracy but the myths still proliferate and become fact against all the evidence.  Anyway, I ramble once again, my apologies...

I would say that this issue is almost certainly not related to your output valve condition, don't worry about them.  As long as the amp sounds as it should and is generally giving you the power it should without obvious issues then they will be fine.  I do think it is just down to inevitable design compromises which many amps have to make, and external factors like the speakers.  Think of this, the amp stores up to 128 presets.  For me, the approach to take with this is to store everything as a separate preset with the levels adjusted to balance.  Don't try setting the amp up as you want it then kick between the channels with that setup, it won't work like that.  I'll explain that point a little later.  Many people seem to be loathe to make everything into separate presets, and to even duplicate presets into different banks for convenience.  That "bank of 4" approach is a great one and the FSM432 is designed to use that.  I used to set up a few generic banks of up to four presets, (sometimes less but I have presets to burn so the excess could be ignored), which I used for general numbers.  Then I would set up a unique bank of presets for any specialist number which needed it.  Often I would duplicate presets into more than one bank if it made "tap dancing" between presets easier for some numbers.  That way I am never more than one tap away from the next voicing I need.  Many people here have said they use that approach.

Back to just working with channel selection.  I don't know if you are aware of this but if you adopt a "play as you go" approach with amp settings and just swap between channels on the fly rather than selecting discrete presets, each channel remembers its own settings without needing to store them in any way.  When you change between channels all of the other settings also change to the last values that they had when that channel was last used.  Being digipots you don't see this in any way but the background value of each digipot may well have changed.  That is why you sometimes get that "LED blink when adjusting a pot".  It tells you where the pot was set before you twiddled it to a new value.  So if your Clean and Lead each require the same tonal setup but with different levels to balance, just follow these steps.  Select the Clean channel, set it up as you want with its own Volume setting, then select the Lead channel, reset the controls off until the LED blinks and back to exactly the same as for Clean, (you WILL need to do this even though their positions have not changed, they are digipots remember), then adjust the Volume until it balances the Clean channel the way you want.  Now when you select the Clean or the Lead channel the settings will genuinely be exactly the same except for the Volume levels which should now balance as you want.

There you have a method of balancing levels which should work for a "preset based" use and one for a "channel based" use.  Would either of those approaches solve your problem?


EDIT: I'll add to this on the issue of using large chunks of the presets. If you find the channel balance is different for different power soak settings then why not just set up a block of presets for each power level adjusted for Volume in each case? I do remember someone way way back suggesting this as the way he worked. He also found that things changed between a gigging environment and a home practice one. 128 presets / 2 situations = 64 presets for each = 4 x 16 banks, still a shed load of presets to play with.

bordonbert wrote:This makes clear that you are pretty well up on aspects of this sort of tech stuff.  That does my old engineer's heart good to hear that!  Too many guitarists are intimidated by the technical side of what we do, particularly anything which involves a bit of maths which is universally hated, and that restricts their understanding and eventually their creativity enormously.  It leads them to reject any technical info concerning things "tonal" and straight into the arms of the snake oil peddlers.

In truth, there is nothing that should be beyond virtually anyone who is prepared to put in a little time reading through, dissecting, questioning, and taking on board anything which engineering types like myself may explain.  That should not be without solid factual based proof of course but that applies to both sides of any argument.  The problem is in the old adage:  "In order to learn something new you must be prepared to give up what you already know".  Once we realised the Earth was round we had to give up the idea that it was flat despite the fact that we had definitely and unquestionably "known" that was so for a long time.  In our case I would actually describe that as: ...what you already "know" in inverted commas with pairs of fingers hooking downwards by my cheeks!  Most of what guitarists "know" of the tech side of their field is given to them by other guitarists who plain "don't know" but who talk as though it is indisputable fact.  Engineering types like me don't know anything because we don't have "guru status", "that magic touch" or "golden ears".  We prefer the results of measurement by unemotional test gear to being guru minded.  Back down the line so many ideas have started from someone who plain knew nothing but, when they are passed on to others as though from an expert, they stick and become "common knowledge".  It's now established and unquestionable "common knowledge" that valve brands all sound massively different, that "tone capacitors" (no such thing) sound better than simple ceramics, that the 12A*7 "family" are all interchangeable.  None of those are true and can easily be demonstrated on a workbench with top quality objective test gear to an unbelievable degree of accuracy but the myths still proliferate and become fact against all the evidence.  Anyway, I ramble once again, my apologies...

Thanks again for your reply, Bordonbert.

I now begin to realize I’m probably worrying for nothing. It’s just the mathematician /engineer in me that has a burning desire to seek answers to all questions. Anything out of ordinary automatically catches my attention and I try to clear up everything puzzling my mind.
Love your philosophical approach to guitar playing and life itself by the way. I tend to be minimalistic myself, not concentrating on building a huge rig that I cannot comprehend, but having one main unit of an amplification which performs tasks as well as possible. It's a huge bonus that the unit in question has a rich pack of features though. I’ve already half decided I’m not going to delve into having endless sea of effect pedals when the GM40D does everything I need instead. At least for the time being. I have almost no interest in modern profiling amps for example, it’ll just get too complicated. That in no way means I’m not a tech enthusiast, because I am (even modern one), but there are some things I prefer to have simple and a bit more old fashioned, and guitar rig just might be one of them.

bordonbert wrote:I would say that this issue is almost certainly not related to your output valve condition, don't worry about them.  As long as the amp sounds as it should and is generally giving you the power it should without obvious issues then they will be fine.  I do think it is just down to inevitable design compromises which many amps have to make, and external factors like the speakers.  Think of this, the amp stores up to 128 presets.  For me, the approach to take with this is to store everything as a separate preset with the levels adjusted to balance.  Don't try setting the amp up as you want it then kick between the channels with that setup, it won't work like that.  I'll explain that point a little later.  Many people seem to be loathe to make everything into separate presets, and to even duplicate presets into different banks for convenience.  That "bank of 4" approach is a great one and the FSM432 is designed to use that.  I used to set up a few generic banks of up to four presets, (sometimes less but I have presets to burn so the excess could be ignored), which I used for general numbers.  Then I would set up a unique bank of presets for any specialist number which needed it.  Often I would duplicate presets into more than one bank if it made "tap dancing" between presets easier for some numbers.  That way I am never more than one tap away from the next voicing I need.  Many people here have said they use that approach.

Yeah, I extensively use the preset banks myself. I often copy a certain preset to another slot added with an effect, for instance. The different modes of FSM-432 MK IV make the amp/MIDI controller co-operation more enjoyable of an experience, as the preset mode offers a great way to control pre-programmed presets in live or band practice situations, while the stompbox mode suits home practicing very well. Then there are the Direct7 & Bank direct modes (the MK IV has an additional mode vs. MK III I think).

bordonbert wrote:Back to just working with channel selection.  I don't know if you are aware of this but if you adopt a "play as you go" approach with amp settings and just swap between channels on the fly rather than selecting discrete presets, each channel remembers its own settings without needing to store them in any way.  When you change between channels all of the other settings also change to the last values that they had when that channel was last used.  Being digipots you don't see this in any way but the background value of each digipot may well have changed.  That is why you sometimes get that "LED blink when adjusting a pot".  It tells you where the pot was set before you twiddled it to a new value.  So if your Clean and Lead each require the same tonal setup but with different levels to balance, just follow these steps.  Select the Clean channel, set it up as you want with its own Volume setting, then select the Lead channel, reset the controls off until the LED blinks and back to exactly the same as for Clean, (you WILL need to do this even though their positions have not changed, they are digipots remember), then adjust the Volume until it balances the Clean channel the way you want.  Now when you select the Clean or the Lead channel the settings will genuinely be exactly the same except for the Volume levels which should now balance as you want.

There you have a method of balancing levels which should work for a "preset based" use and one for a "channel based" use.  Would either of those approaches solve your problem?

Yep, I’m aware of this, some modeling amps I’ve owned or played with, have similar logic. The store LED indicating the earlier saved setting of a dialing pot is a great feature, the amp manual even makes a specific mention of it. When playing at home in front of my PC, I tend to use the desktop remote app, which monitors the pot values in real time. When changing the channel/preset, the app immediately shows the real values of pots.

bordonbert wrote:EDIT:  I'll add to this on the issue of using large chunks of the presets.  If you find the channel balance is different for different power soak settings then why not just set up a block of presets for each power level adjusted for Volume in each case?  I do remember someone way way back suggesting this as the way he worked.  He also found that things changed between a gigging environment and a home practice one.  128 presets / 2 situations = 64 presets for each = 4 x 16 banks, still a shed load of presets to play with.

Yes, this is how I've balanced the volume between my presets, using different combinations of power soak settings and volume knob values, and controlling the general volume level with master volume. It's just that I've been sort of obsessing about the somewhat irregular behaviour (at least against mathematical theory) of volume/sound pressure level difference of a certain channel on different power soak settings, or even between channels. But my mind is more at ease now after your contribution

I’ll most likely use this thread in the future if more questions will raise. Until then, I thank you answering my queries and providing further information on many subjects. I’ll keep reading the forums and experimenting with the amp.

See you around, everybody,
-Vin

Good rounding off there Vin. Getting back to enjoying the amp is the best place to go now. As a fellow mathematician, (tagged on electronics in my second year at university ((many many years back)) and it took over), I understand your desire to approach things from that direction. It's clean and clinical and removes any preconceived biases. However, I often get wrapped up in making what I see fit my maths when I should be doing the opposite. And we haven't mentioned our Fletcher-Munson curves of equal loudness. They could give us an insight into how our perceptions of level based on what we are hearing is being fooled "guided" here. Changing levels of perceived loudness over a spread of SPL and frequency is exactly what they should predict. The frequency responses of the channels of the GM40D are significantly altered so as to not "flub" up the sound too much at the higher gain end. Enough already from me. Too much theory and information. Let's get out and play!!!