Tubemeister 36 - Too Bright on all channels

My Tubemeister 36 1 x12 combo has gone too Trebbly on Clean, Crunch, Lead channels. Even with Treble in Zero, Bass on Max, Middle in Max too bright. I’ve checked the valves on my valve tester, all good. It’s not a potentiometer issues as it’s common to all channels.

I’m an amp tech and guitarist. I’m willing to have a look even without a schematic, but I can figure out how to get the chassis out of the cabinet. Don’t want to break the front panel light.

1. Anyone suffered this ultra bright / lack of bass problem?

2. Any tips on getting the chassis out without breaking the front panel? Does it just Reed brute force as it’s never been removed before? Or is there a trick to remove the clipped on front panel?

A schematic would be magic.

Thanks for your help.

Hi Mojoampguy, sorry to hear about your problem. We don't tend to get too many queries about the combos nowadays so I don't have a lot of info re their breakdown I'm afraid, I've never had one under my hands. I'm hoping someone else with experience will see this and chip in. Failing that it will just be down to loosening screws a little at a time until you can figure out what exactly needs to be removed to allow the amp block to be extracted.

Schematics are available for a few of the H&K models but, as we have a talking relationship with H&K Support here who do feed us useful data from time to time, we take a respectful view to their intellectual property. We do not allow the open sharing of schematics in the forum. remember, these schematics are their bread and butter and if they want to be protective of them then we have to support them in that. That said I can tell you that there are a couple of schematics which I have come across in my travels. The GM36 head is out in the public domain as is the TM18 head. If you can locate them then they should give you a "family feel" so you can see how complex the whole design of the H&K amps actually is. They certainly aren't anything like the Fender/Marshall type of circuit in any way shape or form. It isn't going to be an easy job to dig into your amp's guts and come up with the solution if it is anything more than an obvious component fault.

There are a lot of complex switched tonal options around almost every stage which would need to be checked out. Some selections work via miniature relays and many others work via JFET switching. As the channel selection is changed the gain structure of many stages within the circuit are also trimmed by adding in additional components through the JFET switching. It is certainly not an easy circuit to decipher and separate out.

Yes I know this is going to be a challenge But I don’t give in easy. I have messaged H K Support. As I told them I wouldn’t share anything they pass to me in confidence.

Thanks for your response. Much appreciated.

Fixed. — I was given a message bu Hughes & Kettner on their users Facebook page to try connecting FX Loop Send to another amp. I did to a Marshall head. Sounded O.K.

When I tried my Tubemeister again, Bass tones were back. So it must have been oxidation on the FX jack sockets. I cleaned them and it’s now O.K

I don’t typically use the FX Loop so did not suspect it. Always worth checking, especially if you don’t use the connections. I’ll take it to the gig tomorrow. Happy days.

Thanks for the help.

I must admit it did occur to me that we needed to check that out as a potential source of the problem but I was concentrating on getting you the background info you needed first before going into specifics. I should have eliminated the obvious first!

Glad it was so easy to tie down. Hope the gig goes well though it should from here on in.

To be honest. Just hosted a local jam night. Still sounds too bright.

Having never owed a similar amp, I’m not sure what is correct in terms of tone?? It’s still too ice picky when it’s not on the neck pickup with the tone knob middle. Aaargh. Still unsure about H & K Tubemeister.

BTW - H & K support emailed me back to say they can’t help diagnose via email. Understandable, but leaves me a little bit in limbo…..

One thing you will learn about all H&K amps is they can be very fussy about which speakers you put them with.  You shouldn't have that issue with a combo and it's built in house speaker of course but they are still very "high gain" in design and the Tubemeister series is less refined than the Grandmeister.  My first H&K was a TM36 head.  I found the same as you, it was a great amp in principle but it had that hard top end which I couldn't tame.  I moved on to a GM36 and things improved a lot.  They still weren't as I would have preferred them to be though.  It took a lot of speaker experimentation to get things right on that one score and there was so much else to learn about these unique amps which helped too.

The main idea I think which would help yourself at this stage is in learning how the H&K gain structure works and in teaching yourself to not overdo things, less is definitely more in the case of H&K.  Nowadays I reckon most top end harshness comes from people trying to hit their distortion in too many ways at the same time.  The H&K TM/GM amps are all following a similar gain structure though with different levels of sophistication of course.  They all have a solid state input buffer stage.  This is in circuit for all selections and is controlled almost entirely by the signal level you feed it from your guitar or pedals.  It has built in a Tubescreamer type action which starts completely non-effective and serving as only a safety input limiter.  As signal increases it first gently clips on one side of the signal, and as level increases more then on both.  That represents mistake 1.  Most people hit it without knowing with a massive signal from either their own choice of distortion pedal(s!) or from "hot " pickups, driving their already distorted signal into massive overkill and sounding rough and harsh, then that goes on to the main gain stages which they have cranked up to overdrive those and on to the output stages which they have also massively distorting, and an awful cacophony of distortion on distortion on distortion ensues.  Have a look here at this thread I created to try to get people to think about that approach and to back off drastically with the signals they feed into the front end.  There is massive gain available inside the amp in a number of places.  That front end gain with additional pedals is really not needed to get the most varied distortion sounds out of the amp and, once you back off and select just one or two distortion components the top end can smooth off a lot.

Input Buffer Thread

Have a look at that and try to have a play with what it says there.  It may help.

Thanks for that. Interesting. In this case, I’m using the Tubemeister for a jam I host I typically go straight into the amp, using a P90 based Les Paul. Most of what a play in on the Clean channel, some on the Crunch. Never on the Lead channel. On the Clean channel I have the gain around 11 O’Clock, Master  around 12 O’clock. Sounds very bright on middle and treble pick up selections. Also quite Bright on the Neck pickup.  Based upon your post, I might experiment turning the gain down a little and Master up. Unless you have a better suggestion?

It’s at the venue so I’ll  have to wait until next week. This is not my main gigging amp. I have not spent much time experimenting with settings. The tone controls don’t appear to have much range.

Yes, the tone control situation is odd.  They often don't seem to have as full a range as other amp makes.  I have simulated every part of the amp in Spice, (electronic modelling software), and the tone controls have as broad a range as in any other amp.  There is nothing wrong with the circuit design and there is no sense in trying to "mod" this area, that isn't where the problem lies.  I think the adjustment of the tone controls somehow conflicts with the tonal changes made when selecting between channels.  The amps have a lot of additional components which are brought in when you select a higher gain channel and these are often to do with aspects like cutting bass or adjusting mid range peaks.  The tone controls get lost in amongst those multiple frequency tweaks.

With a lot of fiddling over a long period of time I eventually found that, when I had the amp working with what were pretty sharp speakers, a pair of cheap Harley Benton 1x12"s with V30s in which were my originals, I had the problem of no real range in the bass and middle controls.  I put this down to the cabinets' lack of bass and the speakers' overly strong mid range peak.  When I eventually hooked up to a cabinet with a better bottom end and a more balanced overall response with a slight recessed mid range, Marshall 4x12" with 1960s G12Hs, the tone controls became much more effective.  I do wonder if many high gain/metal guitarists who believe the mantra that "bass is muddy so get rid of it" aren't almost causing this problem as they try to restrict their bottom ends and hump the mid to "cut through the mix", (another weird mantra which so many guitarists think they have to repeat regularly nowdays).  If you do that and don't get it matching the tone control turnover frequencies the effects could be odd.

I can just say that with the right speaker combination the tone controls do extend to being normal.  All except the Presence control which many people seem to simply turn down very low to remove a lot of  the top end harshness.

My amp already has a different speaker. Still too trebly. I hooked up an external Celestion Creamback. Same.
This is not my main gigging amp, I use it for a jam that I host. I never use the High gain channel. I’m just going to live with it.

I feel like this bright trebly character is the one drawback of H&K amps. I mean they have some great technology in them but the bright aspects are a little hard to dial down, and much of it depends on a darker speaker that fits just right for the amps to work and sound good. I think many people have amps with speakers/ cabs that are doing the opposite for other brands by giving more bright frequencies, so when people hook up a Kettner amp they don't sound as good by being too bright with that other cabs speakers.

I have a similar issue with my Coreblade being too bright with the ET90 speaker which seems to work perfectly fine with my switchblade amp which I found that the amp was much darker, and there is much more bass in it as well. I currently have been using Electroharmonics EL34 EH in the Coreblade, which is what the official H&K repair center in New York fitted it with when it needed a new tube set. It is an interesting set the rounds off the top end a bit and scoops the mids. I've also been using the TAD 7025 in the v3 position which I find does also rounds off the H&K top end a bit too.

I think you get the best bang for your buck if you find the right speaker though. I'm considering trying a Celestion Redback now after hearing it with a Duotone.

https://www.youtube.com/watch?v=_THiXBIFALE

Yes I agree with a lot of what you are saying DIB.  I too find the earlier H&K amps like my GM36 to be too toppy in most setups.  While there are routes to sorting that out it is still a mystery that they should take this stance with their voicing.  In the past I have made a joke out of pointing out that they are Germans and they are permanently stuck in their "drop tuning high gain chug chugga chug" mould.  There is an element of truth in that however.  Everything else they are interested in playing seems to be melded with the limiting (to me) high gain foundation at some stage.  I find it makes their ear for voicing a little one directional.  Of course there are many players who will welcome this sort of sound and good luck to them, but a tad more versatility in the levels of coarseness would have been nice.  For example, it would have been good had it led to a greater selection of speakers that these amps work well with.  I have spoken to the H&K designers about their design decisions in the past and the amps' weakness at not being able to model, for one, classic rock tones (60s/70s) at all well.  They were, well, let's say a tad mystified that I should even think that.  We just didn't both see the problem!

I don't go into the ins and outs of valve rolling as readily as I used to.  You probably know my own feelings on that aspect from other posts.  I know the technical background in depth so I know full well the myths which continue to be propounded about their behaviour and sound.  I can assure you that all valves of the same designation in their linear design regions have exactly the same flat frequency response.  Guitarists forget that using electronics in their limited frequency range is a pretty undemanding task for the valve to perform.  Remember, the valves which the early designers decided to base their circuits around, (12AX7 which is the US designation of the original ECC83 for example), were simply the cheapest commonest ones they had to hand around them.  And they were all cheap radio receiving valves.  And radio frequencies run up to...

I won't argue about this any more as people will always believe what they want to believe and trying to shift that with evidence only causes upset.  The days of showing people factual evidence to prove that something is true are now long gone.  Everyone "knows" the truth about whatever is of interest to them, they found it on the internet or hear it for themselves, and questioning it before believing is no longer in the process of acceptance.  If information confirms what we already believe it must be true and anything which contradicts it is "fake news".  I will attach frequency curves for several makes of 12AX7 in exactly the same Fender style preamp circuit.  The shape of the curves is an indicator of the tone of the valve in that circuit.  There is absolutely no tonal difference between any of those valves at all, the only differences are slight ones in the overall gain within the circuit, and that is more down to production variations than makes.  These curves were actually produced by a company selling valves and who were producing data which they could make out proved that valves DO have different tonal characteristics.  No one with an engineering background would equate that view with the curves themselves!  You may not have seen this thread I posted where I link to their website.  As I pointed out in that thread, once they were "outed" and criticised here the curves themselves vanished from their website overnight and only the ridiculous claims were left!  That speaks volumes.  Valve Make - Frequency Response Comparison

Sorry if that steps on your toes a little, that wasn't my intention, but engineering truth is the truth when backed up by factual repeatable data.  I'm sure my saying this once again won't upset you, you will believe what you choose to believe in the end.

You are certainly right about getting the best out of these amps.  Find that golden speaker and you are set for a heavenly ride.  Getting to that stage can be a long frustrating journey with a lot of cul-de-sacs though.

I don't propose to know all the complicated factors in knowing why the tubes change the sound of the amp but they do in my opinion. All I know is that is my experience. It is a very slight change and nowhere near as drastic as changing a speaker, but know that some speakers hinder what you hear or exacerbate it. I know if I combine different brands of tubes sometimes I get big changes and sometimes I don't much change at all. Maybe these gain changes in the tubes are pushing the Power tubes or allowing certain frequencies from your guitar to through the signal chain that wouldn't ortherwise go through.

Note the frequency chart doesn't go past 10,000 Hz.

I would like to have see the FFT or a IR made using Two Notes blend of chart of the speakers and the corresponding tube chart at the same time.

I'm certainly open to the idea that you can hear a change and I'm relieved to see you have described it as slight, that's a refreshingly honest appraisal of this phenomenon.  Most people wax lyrical about the night and day difference a valve change makes.  If it does then they had VERY badly worn out valves before that which are way way off spec.  I absolutely agree that any changes you get rolling are dwarfed by speaker changes which produce genuine big differences in tonal characteristics.  The only thing I take issue with is that these audible differences are not caused by valves from different manufacturers having different frequency responses, they simply do not.  They all produce a flat response from DC to above audio frequencies.  It is the interplay of different genuine differences in valves' characteristics which can cause a degree of tonal variation in the overall circuit.  That should be taken on board and the whole "frequency response" myth put to bed in order to stop the snake oil salesmen doing their job, just as the guys at Amplified Parts are doing.  Their individual "appraisal" charts for each graph are split into a range of 0-10.  If you look at their own frequency plots which I posted and read off the figures you will find that that 0-10 represents a real range of 2.8dB - maximum.  In the "red/grey/yellow" bargraphs of the valves tested, they show that the maximum difference for any valve between its Bass Mid and Treble is 2 steps on their scale.  That represents less than 0.6dB - maximum for any valve.  That is inaudible to all but a member of the Marvel Superheroes in any real setting.

Sadly, the whole "decide by listening tests" idea is fatally flawed for the home user right from the start.  The ear/brain simply cannot hold onto any accurate tonal information for longer than a few seconds so the only way to compare with any hope of accuracy is an instantaneous swap between valves in what must be the exact same circuit.  To listen to one valve then switch off, swap the valve out and switch on again, then wait for the new valve to warm up is far too long for the brain to retain a clear accurate memory of what it has already heard.  That is when the listener's own expectations come into play in what they hear.  This is a well documented phenomenon and is taken into account in genuine tests.  I have in the past been a part of double blind comparisons where people listen to two items swapped at random repeatedly and say which they think they were listening to.  They always show that, while people think they can identify and describe differences when they know which they are listening to, as soon as they are not aware of which is which they still think they can hear differences but, strangely, their guesses as to which is which now drop to 50% right and 50% wrong.

It takes highish repetitions to generate the number of results required to accurately analyse this statistically of course, but the results do show that there is only an absolutely statistically insignificant chance that they really can identify differences under these conditions.  As an aside, this test absolutely destroys the "super tone capacitor" idea for your tone cap in your guitar!!!  With just a simple switch for the tester to swap between the two in the player's guitar cavity and a coin to flip to either change or not change, guitarists have no idea when there is an Orange Drop or a "nasty" ceramic in there.  Gibson used to use the dreaded ceramics on a huge range of their guitars and everyone loved them - when they didn't know they were "bad things".  Then gradually the internet started reporting that techy guru types had found "unsuitable capacitors" in them and suddenly everyone could hear that their guitars now sounded - well - crap!  They still couldn't identify any differences in a blind listening test though.  That's the level some of these issues descend to.  If you question and test the King always seems to end up having no clothes!

I have always thought that there may be a semantic difference in what people are meaning by "tone" to how I use it.  Tone to me is a frequency based characteristic.  I separate it from aspects like the character of overdrive and distortion which are much more relevant to our playing.  Those are not tonal aspects which you measure with frequency response plots.  You yourself mentioned FFTs and that is a totally different ballgame to simple frequency plots, much more revealing and relevant to the real sound when playing.  You are then looking at the ever changing production of a huge range of harmonics which cannot be described by simply looking at the frequency response which only applies to steady state clean signals.

And you are of course right, the plot didn't go past 10kHz, but it isn't really relevant to us.  That is because the guitar only produces its relevant output up to about 6kHz or so before it has tailed off drastically.  Pickups, as coils with a huge number of turns and seriously magnetic cores, have very high inductance which is not at all good for high end responses.   And don't forget guitar speakers are also very limited in bandwidth too, by design.  For example, the Vintage 30 which is usually thought of as a pretty toppy sharp speaker begins a very steep drop at 4kHz and is 25-30dB down at 10kHz.  Most other types are at least that much down with some more mellow types even more.  That last octave up to 20kHz is a must for hifi but an absolute no-no for guitar to get the sound we expect nowadays.  Just as well for us they limit as they do as the tone they do produce is just right for rocking at that bandwidth.

Here is a little tickler for you.  Look at this old thread from our own forum:  Tube Swapping - for something outrageous  Look for post #122 by Voodoo Jeff and read down a few responses.  He talks about his set of Wathen CryoTone valves, (you can find them online under Wathen Audio).  The 12AX7s currently start at $93!!! while the EL84s are $95 a piece (and that is - each).  Jeff still describes the difference between these and his usual plain old JJs as "subtle at best" and he is a professional musician with demanding tastes.  It makes you think.