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    Tone Caps for TMeister18

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    CSG

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    Tone Caps for TMeister18

    Post by CSG on Wed Nov 11, 2015 6:12 pm

    I recently acquired a TM18 head and it lacks bottom end. Even through a 4x12 cab it is bass shy compared to my other amps.

    1. Does anyone know if C16 is the capacitor that controls the bass EQ? The value is listed as 22nf 400 volts.

    2. If C16 is not the bass cap, which one is?

    3. Also, is the V1 preamp tube on the far right near input jack (from front of amp head)?

    Thanks.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Thu Nov 12, 2015 7:58 am

    V1 preamp valve is the covered one nearest the input jack.

    You won't get any advice about component values as H&K are very protective of their schematics and keep them close to their chest, (as they would of course).  As far as I have seen no one has reverse engineered the H&K circuitry yet. Unless you're maybe in the process of doing that? Cool

    I would suggest you stop thinking of it as just a "change out the bass eq cap" type of problem, it generally isn't that simple.  No one knows even what circuit configuration H&K have chosen for their tone section.  It certainly doesn't seem to sound or respond like a standard tone stack approach to me.  It seems to have a central neutral point and work with boost and cut.  There are other configurations than the simple cut types out there, (just Google James or Baxendall), and these have more complex interactions.  They may even have made it active in a feedback loop involving solid state components  What a Face .  You won't sort out the tonal characteristics by just changing one cap as it is created by a combination of the effects of every bypass cap, coupling cap, and filter cap in the amp.  Most of these are generally chosen to be reasonably outside the range of frequencies we want, but not all!

    If you're interested, here is a useful piece of free software which shows the workings and plots the pictures for a number of different tone control types.  Free Tone Control Calculator

    CSG

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    Re: Tone Caps for TMeister18

    Post by CSG on Thu Nov 12, 2015 12:40 pm

    There is nothing mysterious about EQ tone circuits, they follow basic electronic principles. Your better sounding EQs have for the most part originated from England with regard to both recording consoles (Trident, Neve, SSL) and guitar amp EQs (Marshall, Vox, Laney). Same goes for vintage American amp circuits. H&K need look no further than those classic circuits.

    I just downloaded the schematic on the TM18. The cramped design of this amp head and stuffing the smallest and least expensive components doesn't exactly make this a home run hitter in the EQ department. All of the tone caps can be upgraded to better quality high voltage caps with different values for experimentation. I received this amp in on trade, so I am not worried about putting it on the work bench and modifying the circuit.

    For musicians looking for an equivalent amp that has musical sounding EQs, terrific bottom and a warm midrange, try a Bad Cat Cougar (also made in China).

    These TM18s are are bass shy with an overemphasize of the treble frequency range.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Thu Nov 12, 2015 1:05 pm

    Absolutely agree with you on the mysterious tone control circuits, of course they follow correct electronic principles and are subject to the same analysis as any other circuitry.  The trouble is that you can't make random amendments to single components and expect to get predictable results unless you know which form they are taking as you work.  And I agree that H&K needed to look no further than standard stuff.  Unfortunately they don't always seem to stick with that same standard stuff in other departments so there was no guarantee that that is what they will have done in the eq.  However...

    You say you have just downloaded the schematic for the TM18!  At last you've managed to crack that aspect and it's a great step forward if it is now available.  Can you share with us where you got it from?  I've been searching for any H&K schematic to use as a starting point for a year or two now and they are thin enough on the ground as to be totally invisible.  They're significant by their total absence.

    I think you've nailed the general H&K amp issue, "bass light and potential stingy at the top".  But with thoughtful speaker selection and valve swapping they do become lovely balanced beasts.  But the tone controls do remain very restricted.  I do hope you can improve things in that area, my main worry was that you were just assuming that a change to a single cap would turn it on its head.



    Edit: The penny's just dropped! If you had mentioned you are a dealer with workshop facilities in the first post I wouldn't have assumed you "may not know of what you do". Smile That explains the schematic and of course you wouldn't be able to share that with us, please ignore my request. Any info you would be allowed to offer based on what you find would be most welcome.

    CSG

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    Re: Tone Caps for TMeister18

    Post by CSG on Thu Nov 12, 2015 2:20 pm

    Bingo, Bert - my background is recording and repair work. My main criticism of the TMs is the EQs, but I think some tasteful changes in the selection of caps and values can fatten the sound up, while toning down some of the overly treble character this head seems to exhibit.

    Unfortunately, I cannot share the Service Documents for the HU0910 TM18 Head with you, since it is for technicians who repair amps and guitars.

    The TM looks like an excellent platform to tweak the EQs and fatten the bottom end up.



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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Thu Nov 12, 2015 7:10 pm

    Hahaha!  Yes, I do appreciate from my own background you are absolutely not in a position to be able to share any of the info in there.  Good to hear that it is a tweaking possibility.  If there is anything useful you come up with in your "tinkering" which you would be able to share then please let us know.  It's going to take some reverse engineering to get a start on that for the rest of us.  In reality my interest is really with the GM36.  I started with a TM, (which I still have as backup), but moved up because of the broader tonal possibilities and the MIDI control.  While there are big areas of difference, I do think there is going to be a lot of shared ground schematically between the two.

    What amazes me is that H&K use Vintage 30s in their cabs, (which some users absolutely love), while the general opinion seems to be that they only emphasise that upper roughness.  I started with 2 x V30s but quickly swapped them out for G12M Greenbacks and that brought in some bottom end and took off some of that upper glass.  I still maintain that H&K voice their gear with an ear for German metal.

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    Re: Tone Caps for TMeister18

    Post by CSG on Thu Nov 12, 2015 9:06 pm

    I took the amp apart this afternoon and frankly, there is no room to upgrade the caps over the tiny ones already in there in an overly cramped space. Not exactly high quality components to be found in this amp Shocked I did upgrade the tubes (T1 and T2 on the schematic) for a 5751 in that has increased the headroom because of its lower gain stage. For T2 I dropped in an EI ECC83. Overall, fuller sounding and not as much breakup in the clean channel.

    I also ran the head through a single V30 cab and found it a little harsh and lacking in low end. By contrast, it sounds much better through a Greenbacks or G12Hs in a 4x12 configuration. In effect, it adds some much needed bottom and smooths out the treble character of this amp. The lead channel without the boost is actually decent and its midrange is reminiscent of the JCM 800s, but not exactly. The major hurdle with the TM18 is the EQs (treble, middle and bass) not being musical. If there was more room, I would upgrade the tone caps with some Sprague. but they are just too big for the PCB.

    Really should be renamed the TinyMeister!
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Fri Nov 13, 2015 5:15 am

    It doesn't surprise me to find there is very little space in there.  And they deplore the use of solid state!  It's not a problem in itself as long as there has been some thought as to paths of ventilation.  Hence my "forced ventilation" solution elsewhere.  Probably not necessary but it shouldn't hurt!

    I'm afraid I'm a sceptic who doesn't believe the way to Nirvana is paved with magic caps. Wink  You'll see my moaning about this piece of audio accepted wisdom in the site elsewhere.  There are differences in cap types and they can be measured but they don't kick in until way above the frequencies we are using.  In the context of hifi class amps with ultra low distortion levels and wide bandwidths there are a few places where they can be heard, feedback loop, RIAA equalisation etc., but only very subtly!  I wouldn't say a guitar amp has to build a 3D soundstage in space or that intermodulation distortion from above the working bandwidth will be a huge issue.  And in the context of 2% clean distortion on a good day and 10%+ by design....  Blind listening tests show it just isn't the issue it's made out to be in a realistic context.  But I digress, (as usual).  That's a separate issue so let's save the discussion for a different thread.  Smile

    It's interesting to hear you say you used a 5751.  I'm not a valve man by history, I work solid state usually.  I can go with valves without too much of a problem but the real lifelong valve guys have an at the fingers depth I lack.  But I have recently been propounding here the use of the 5751 rather than the 12AT7 which is everyone's "goto" replacement.  Everyone just "knows" that 12AT7 is a good replacement because they have been told so by others who "know".  Basically, way back someone tried it, it didn't pour out magic smoke, it sounded different, so it's a good idea.  Yet no one has ever questioned it and looked at the aspects of design and sound it alters.  If you compare the spec sheets with a questioning pair of eyes it's a no-brainer regarding the closer match.  The 12AT7 upsets so many other features of good design it's untrue!

    My guess is, (not expecting any comment from yourself), they have used some aspects of solid state in the signal path of at least a couple of the channels and in areas like the Boost.  Unlike those who reckon they are a bunch of lying toads for doing so then add in their own worn out solid state kit immediately where the H&K stuff is placed, Razz , I have absolutely no problem with that.  The sound is all I judge on while the technology is irrelevant other than for reliability or maintenance purposes.  If it can sound good and it stays sounding good it's a great amp!  I still rate my Vox AD120VT Blueface modeller as better than most similarly priced valve amps on the market in a live context, and it blows them away for flexibility.  If the job is done right then the results speak for themselves.

    Thanks for the responses, it's great to gossip with someone who has actually worked in an informed way on one of these little monkeys.  I'm going to have to get in there with sleeves rolled up and look into that tone section.  From what you say I will have to use the same cap types but I have no problem with that until I'm educated further.  But there must be slight changes that can be made which maybe will give us more effective control on the outer ends.  Now if only you would move up to the extra subtlety of the GM36 and explore there I would be a very contented man.

    CSG

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    Re: Tone Caps for TMeister18

    Post by CSG on Fri Nov 13, 2015 4:38 pm

    bordonbert wrote: I'm afraid I'm a sceptic who doesn't believe the way to Nirvana is paved with magic caps. Wink

    That's a straw man argument and nobody is suggesting magic caps exist. What does exist, however, is the noticeable difference between the difference types of caps manufactured, along with the resonant peak that effects tone, especially when the value is inconsistent, inferior materials are used in its construction and tolerances are factored in. Mylar caps are a generally a good replacement over many of the cheap caps found in audio circuits today, most notably those circuits coming out of Asia. You aren't going to find Nichicon or Panasonic caps in those circuits, much less top of the line PTs and OTs.

    If it can sound good and it stays sounding good it's a great amp!  I still rate my Vox AD120VT Blueface modeller as better than most similarly priced valve amps on the market in a live context, and it blows them away for flexibility."

    I grew up playing Marshall Plexis, Laneys, Traynor, Vox, and an array of Fender Blackfaces. They remain the standard, not just in tone, but in durability, as many of them are still up in running because of their bulletproof P2P construction and simple circuits. I have played through many of the Line 6, Vox, Peavey and other digital modeling amps on the market. The only one that comes close to nailing the tube sound is the Fender Mustang series, but like all of these modeling amps where buyers have likely never played or gigged through a vintage tube amp, they just don't match the sonic qualities of a vintage all tube amp, especially when you start cranking them up. In my view, Marshall Valvestate (the AVT series) is the only hybrid, albeit not a modeling amp, that comes close to an all tube sound.

    Another major factor for an all tube amp has to do with the transformers that color and fatten up the sound. The same goes for vintage recording boxes, which use quality input and output transformers in the circuit, even without tubes. In effect, you are going to get coloration and a fatter sound, similar to the vintage Neve pres using transformers that set the standard on audio pres and recording.

    Now if only you would move up to the extra subtlety of the GM36 and explore there I would be a very contented man.

    If someone asked me for a recommendation on an amp running a quad of EL84s, I would suggest they look no further than a Dr. Z Max 38, as few amps measure up to it. For the budget minded, I would suggest an American made Peavey Classic 50 head, which is one of the most reliable PCB amps ever built along with the Classic 30 combo.. Not surprising that the Bad Cad Cougar Chinese made amps are also designed by James Brown, which has some of the most musical sounding EQs on the market. Although the Cougar 15 combo only uses a duet of EL84s, it has some serious mojo, reminiscent of some of the old Laneys I played through.

    Lastly, I don't think you have to worry about the TM18 overheating, since the metal chassis on which the PT and OT are mounted to have a 1/2 inch gap between the chassis and PCB where the tube sockets extend into, therefore, this air gap won't transfer heat directly to the PCB. But insofar as the low quality components and transformers, no telling how long they will last.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Sat Nov 14, 2015 8:34 am

    Sorry, this will be a long one but when I've finished I'll try to stick to answering any questions which may arise and not continue with another "tome".   Very Happy  I also try to keep myself from getting too serious by applying my childish sense of humour, this is not an attempt to mock in any way!   jocolor

    When we are in the great Cap type debate it's important to differentiate at outset between the facts that make caps genuinely different and those which do not.  The capacitance value and tolerance is not a factor in this debate in any way, as the starting point of any comparison has to be to find cap examples of each type which are of exactly the same value so as to remove any differences caused purely by the amount of capacitance.  We are comparing differences in sound due to materials and construction here, not value.  I agree there are people who can hear the difference caused by having a different value in some applications.  But you can select any specific value you want by simply applying a meter and selecting your choice from batches of any type.  If it sounds wrong because to you of that then you could just get a different value of the same type.

    Let's face it, if a 0.022uF made by monks on a particular Greek island out of medieval parchment and sun kissed olive oil from a tree on the side of Mount Olympus which measures at 0.02uF is compared to a 0.022uF bog standard ceramic as used by Gibson, (booh hiss!  Evil or Very Mad ), which measures at 0.024uF, you have a 4nF difference to account for anything you may hear.  That will swamp any other effects and no reliable conclusions could be drawn from that comparison on either side.   Wink

    As to resonances, do you mean the natural resonances in the characteristics of the types themselves or the resonances set up between the pup inductance and the cap?  If it's the former, they are well above any frequencies we are working with and their effects do not translate down into the audio band in any way.  Those cheap ceramics Gibson got slammed for using in its guitars have natural resonance at above 10MHz and that's pretty much the ballpark.  As we know, they become inductive above that but who cares?  I can't see a mechanism whereby that can make a difference below 10kHz, can you?  This isn't radar technology, it's guitar amps with a bandwidth of 8kHz on a good day with the wind behind them!  If it's the pup inductance resonance you mean, yes of course that is audible.  However it's only created by the value of the capacitance at that frequency, (and associated damping resistances), the pup inductance more than swamps anything any cap would show.

    Yes, the longevity of caps is a factor in choosing them but not because of overall tone.  Electrolytics are nowadays criticised to the point of almost hatred, totally unfairly, despite the fact that at their rated temperature, voltage and ripple current they will offer 1000s of hours of reliable working.  Yes they can be improved by paralleling with higher frequency types, but once again, the effects are high frequency and will not be game breaking.  Their fault modes are well documented now and the way they work is well explained elsewhere, yet still we see people swapping out every capacitor in their amps on a regular basis as "necessary maintenance".  That's like changing every bolt on your car at a service because one might strip or snap.

    What can be heard can ultimately be measured!  You cannot hear a difference that would remain invisible to measuring technique for ever.  It is of course possible that it may be a newly identified phenomenon and the measuring technique needs to catch up but I would respectfully suggest we aren't at the cutting edge of technology here.  These issues have been done dusted and laid to rest decades ago very publicly in the hifi industry, a much more revealing, (not demanding), arena than the guitar and its amp.  The results of their findings are that it has noticeable but limited effect in a few specific places at the most demanding level.  As I said before, 0.005% is a lot more transparent to these things than 2%.  And nowadays the heavyweights like Seymour Duncan are now becoming vocal in their support of the view that cap type makes no difference to sound.

    Over the years I've set up a number of very simple blind listening tests with adamant believers in this phenomenon in the driving seat and, while everyone can hear differences when they klnow which is which, no one has ever been able to identify any repeatable differences when they don't know which is being applied.  As I said, hifi is another thing.  Differences of 0.05% distortion can be appreciated consistently but not in terms of tone which is the only criterion for our guitar amps which do not have to deal with 3D soundstage presentation.

    If I may, I'll put in a trite little anecdote to make a point here.  Early in my working life I was able to mix with a lot of classical musicians.  The talk often turned to hifi equipment they used.  I thought that they would have demanded the most accurate and transparent kit they could afford.  It turned out that most of them used gear which was very average at best, yet they still insisted it was incredibly revealing of the music they played on it.  The answer turned out to be very simple, they are the worst ones to review hifi equipment!  They know most of that music so intimately their brains were able to inject any minor nuances which were missing and to hear an almost live performance.  Even in comparison with ultra top flight kit most of them could hear virtually no differences.   The power of their imagination really was strong in that case, and that's potentially in all of us, in both directions!

    I can't see us easily agreeing on this one Wink , the debate lines are drawn as strongly as the trenches in the Somme.  Suspect I am really not just "an acolyte of the negative way", I argue over issues like from a flexible position looking to have it changed by exposure to different viewpoints which may educate my own further.  That way I understand more and become wiser!  geek So, I've put forward a few ideas which I hope are worth at least considering and will do the same with anything in return, but I really don't want to start an ongoing war here, just a swapping of technical points for and against the idea.


    EDIT: Oh and I should have added. My own systems includes my late 1960s Marshall Super Lead 100 and Marshall 4 x 12 that I bought in 1970 and still have and love today. I'm of that era too and have experience of "real amps" to draw on. They're great, but not all they're made out to be when other factors are taken into account.

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    Re: Tone Caps for TMeister18

    Post by CSG on Sat Nov 14, 2015 12:09 pm

    You have now morphed the discussion from a straw man argument around "magic caps" into claims based on Duncan and anecdotal accounts you have read on the internet or in books. For someone who cannot obtain a schematic on the TM18, perhaps you should spend some time as an amp technician and builder, rather than lecture those of us who actually work in this field?

    In any event, if you believe cap values don't affect amp tone, knock yourself out, as I am sure not here to convince you otherwise.

    Regarding your tenuous claims about overheating, this can easily be dismissed by looking underneath the hood of any automobile engine that uses "electrical" components located in hot engine compartments, which are exposed to significantly higher temperatures on any given summer day than any guitar amp you or I will play through. That's where the rubber hits the road.

    You can add ALL the ventilation you want, but if the amp has incorrectly soldered joints, uses low quality components or the transformer windings are made from budget insulated wire or the incorrect gauge, your amp will fail or fry at some point, irrespective of what fan is added. That's why most of these budget Chinese tube amps fail and adding a fan is not going change those underlying factors.

    Thanks for the low down on circuits and amps.

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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Sat Nov 14, 2015 2:22 pm

    Despite my attempts to keep the tone of the discussion light and with an air of swapping both facts and opinions between two interested equals I seem to have ruffled a few feathers.  For that I am sorry.  I did hint as to my having some background in this area but, unlike my assessment of your own position, you appear to have missed that by an arrogant country mile.  I have been a designer of electronics equipment in the audio and then the seismic fields for over 40 years.  Not a technician with their specialist area of knowledge of a wide range of units and their maintenance and repair, but a design engineer with an in depth knowledge of just such topics as we are discussing.  The two roles require different expertise and both should have a healthy respect for the tasks and skills of the other.  You seem to believe you have it all rolled into one.  So to answer your points...

    NO MORPHING:  I don't see how the discussion has been morphed at all!  You first mentioned "Sprague" caps at the very end of your first post with the suggestion that changing the "tone caps" to that type would be an "upgrade", (your words).  I did not introduce the subject of magic caps just the term as a joke, in response to your own assertion that Sprague caps have some inherent capability to sound better than other lesser types. You opened it up to discussion.  I simply replied to that.

    CAP VALUES DO NOT AFFECT TONE:  You must have skimmed over my longer post so quickly that you missed the part where I clearly refer to the fact that CAPACITANCE VALUE is the ONLY factor that affects capacitor action in this field.  Did you catch my points about starting with caps of exactly the same value before comparing to rule out changes introduced by differing values? That has been my main point all along.  If you haven't the wit or you just plain can't be bothered to properly read and consider the point that the other person in a discussion presents to you then, just as you said, "I am sure not here to convince you otherwise".

    OVERHEATING, THE TENUOUS CLAIMS:  Regarding my tenuous claims as to overheating, I make none.  I have stated previously that I have faith that the H&K designers will have taken into account all of the factors they need to.  I have stated before that I believe it won't be an issue, design ideas like the metallic case acting as a heatsink have made it a non-issue.  And when you crunch the numbers properly you will see that there is plain not the energy going into the unit that people believe. However, I have also said that it cannot hurt to take steps to reduce the working temperature inside.  Is that wrong?  Most components benefit from this, (as I said), and I used the electrolytic merely as an example to show how precise this is.  (Maybe look up Arrhenius' Law?)  My little fan unit was a fun attempt to explore this and improve reliability (which it will), not tone (which it won't).

    If you knew about your automotive electronics you would know that the under a car bonnet is exactly the last place any high grade electronic unit should be put!  Note I used the term "electronic", not "electrical".  With its constant vibration, humidity and wet conditions, corrosive fumes and its extremes of temperature of both directions it is most unsuitable.  Which is why all sensitive automotive electronics is placed in the cockpit wherever that is possible.

    BUILD QUALITY:  I have made no comment about the build quality of the H&K, in truth I have yet to open it up and have a look see.  I do not know what the standards of soldering are like, I have never said or implied that I did.  I don't know what the internal quality of the transformers is, do you?  Have you opened one up to see?  If so then I will certainly accept your implication that they are cheap.  I do know about the quality of many other units though and, as you now know, have a background of high grade demanding work so I can recognise good quality soldering, and it isn't as immediately easy to spot as is widely believed.

    I was under the impression that I was swapping interesting info on a level playing field with another person who shared my interest in things electronic.  Sadly I see now that I was talking to someone who believes he has nothing to learn so you advice is sound, I'll stop trying.  You didn't answer a single point that I raised in my previous post, despite the fact that they were based on sound technical info not just opinion and they were precise to avoid unnecessary confusion.  I think I can guess why!

    STRAW MAN ARGUMENT:  "The Straw Man fallacy is committed when a person simply ignores a person's actual position and substitutes a distorted, exaggerated or misrepresented version of that position."  I fail to see how that applies to my responses at any point, your own however have jumped to the level where you actually accuse me of saying exactly the opposite of what I did say, what I did say clearly, very clearly, would you like me to quote examples?  (You aren't Ray Bolger are you? Wink )

    You are welcome for the previous ELECTRONICS 101.  I am glad you appreciate it, I would say you definitely need it! (Next semester LOGIC 101 in parallel with SOCIOLOGY 101.)

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    Re: Tone Caps for TMeister18

    Post by CSG on Sat Nov 14, 2015 8:10 pm

    I don't know what galaxy you studied electronics in, but I can tell you know squat about repairing amps or what a good circuit comprises. I can't speak for you, but I have repaired many amps over the years including repairing recording equipment and consoles.

    Because you heard something about amps overheating on the internet does make it gospel, because if we applied your flawed analysis to automobiles, there would be no cars on the road as a result of the electronic components overheating from being exposed to hot engine compartments and extreme cold and hot temperature fluctuations. But in the real world, electronic components are designed to handle temperature variations, and seldom malfunction when they are built from quality materials and conform to spec.

    Regarding your question about internal quality of transformers. If you are a designer of electronic equipment, you should already know this. But it all comes down to the wire and insulation used, and I have a lot more confidence in wire that conforms to AWG standards, than I do with the wire being used in most of your budget Asian amps. I mostly use Temco for rewinds and have not experienced any failures or shorts.

    There is nothing further to discuss here, since you have not looked at the TM 18 circuit and don't repair amps, but apparently are an expert in telling those of us who actually do this what it is all about.

    Really, go spend some time on a work bench instead of lecturing on a forum.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Sat Nov 14, 2015 8:59 pm

    Ooh! Ouch! Woe is me! tongue I am undone! Sad In truth a mortal withering reply!!! Very Happy

    So it is still "nyaah nyaah you know nothing I know everything". It's very sad that the 100yards of your real experience should be lost because you simply cannot stop yourself from trying to make it stretch over a mile beyond anyone else's. I see I have nothing left to learn from you. In truth the only thing I could have learned is how little you do know and how much you want to be seen as in the know! And that is a disappointment, I had hoped for more but "You are not the One". (Despite what you think.) Wink

    Have a good rest of your day. cheers

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    Re: Tone Caps for TMeister18

    Post by CSG on Sat Nov 14, 2015 9:40 pm

    Instead of relying on long winded rants and parroting information you heard about electronic circuits, go learn about it and you too will have access to schematics Wink

    I am not here to refute your "magic cap" fallacies and anecdotal claims about it. Hot air seems to fit right in with your silly claims of overheating.

    I seriously doubt you have even pulled apart a transformer much less rewound one, maybe in some fantasy setting, but not in reality.

    Get off the message board pulpit.

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    Re: Tone Caps for TMeister18

    Post by HwyStar on Sun Nov 15, 2015 12:57 am

    Guys...  Play nice or else...  This forum has been live now for over a year and not once have I had to get involved in a discussion...  Please re-read the FAQ page, Rules of Conduct about the proper etiquette on this forum.   Thanks!


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    namklak

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    Re: Tone Caps for TMeister18

    Post by namklak on Mon Nov 16, 2015 5:28 pm

    It's too bad this thread devolved, I was hoping for some valid mod info. We are all players seeking better tone, so we are the same team. Ideas will differ, but we are all still brothers. (sorry a bit maudlin, I just lost a bro to leukemia).

    If H&K are using cheap caps, they are using cheap "consumer" grade semiconductors, which do not have the heat range of automotive grade chips. But the air gap mentioned helps. I use small pc fans to cool my rig at home, no biggie.

    If you don't like the tone control voicing, suggest value changes (which you started to discuss) - I'll live with the same family of caps that physically fit. I do believe there are subtle differences in cap types, but I think those differences are trivial in this application. Also, you can't publish the schematic, but you could hint at tone stack topology maybe.

    There has been a lot of guessing on what section of each dual triode does what - in my case particularly on the GM, as I look for less saturation in the Lead and Ultra channels. A schematic based hint on that would be worth a beer to me...
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Mon Nov 16, 2015 7:57 pm

    There are no "cheap" consumer grade semiconductors Namklak, these amps will definitely not benefit by starting a trend to roll the semiconductors.  As long as the conditions under which they will be used are within their spec there is absolutely no benefit in using higher spec military grade devices.  Higher grade devices are not different in any way from the point of view of tonal quality, their internal circuitry is identical to the standard grade devices.  They differ only in the specs which allow them to work in extremes of environment.  As you can see here, there is at least agreement that in our H&K amps temperatures are not extreme in any way.  Silicon devices are usually considered to be within "conventional" limits up to +125deg!  The Texas TL071 opamp, a very simple device scorned by most modders as sounding awful, has a quoted absolute max temperature of +150deg and that's fairly standard.

    The circuitry in which most semiconductors are usually used depends greatly on feedback, local and/or global, and one of its characteristics is that it reduces distortion drastically.  For example, if a circuit had a gain without feedback of 1000x and a distortion of 1%, then if feedback is applied to drop the gain down to 50x, the distortion is naturally reduced to around 0.05%.  That's feedback. The Texas datasheet for the humble TL071 shows that when it is used as a follower (as is often seen in say a tone stack driver) with a gain of just 1x, (i.e. you get out what voltage you put in), distortion is 0.003% up to 10kHz.  Can you hear that in amongst maybe 5%+ deliberate distortion from the valve stages? Differences in distortion figures between different opamp types for example are reduced by factors of this level to the point where the different types are indistinguishable in our application.  You have the valve technology in there to give you the tone you are looking for, the rest of the solid state stuff should just be as neutral as possible, and it is this very neutrality that is usually not liked in guitar work.  The only time differences appear between opamps is when they are forced to work outside of their maximum or minimum parameters, for example with too large a signal voltage which causes them to clip internally or by driving too low an impedance and hence try to supply too much current.  The trick of designing decent circuitry is to always make sure this cannot happen.  And that isn't hard! The H&K boys will have taken care of that.
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    namklak

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    Re: Tone Caps for TMeister18

    Post by namklak on Tue Nov 17, 2015 9:55 pm

    Well....
    http://www.ti.com/lsds/ti/audio-ic/audio-dac-product.page
    The PCM 1770 is an old reliable D/A used in cheap consumer applications.  0-70 C.  One used to be able to buy an TL-07x in the 0-70C grade.
    BTW, I mis-typed, and left out the phrase "then maybe" they are using cheap consumer grade semis.  I have not opened the GM to see what they are using, and it probably is mostly an ASIC or two - I'm not interested in op-amp rolling like a audiophile head phone amp.  I'm going to assume since there haven't been many early life failures reported on this site (only infant mortality), and H&K has a rep of good design, that they designed for the operating temps the GM will see.  That being said, I use fans - that was my only point.  Looking at FIT and MTBF charts, heat is the enemy.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Wed Nov 18, 2015 4:42 am

    Agree with you absolutely on the heat issue, there's no real signs of it being a problem but it doesn't hurt to help it along.  And like you I look to reports here and on their Facebook area for any inherent fault.  No sign that I can see!

    Regarding the cheap semiconductors, I was trying to head off a rush to swap out transistors for genuine NOS BC109s and opamps to exotic expensive hand labelled Japanese only types!  Sorry if it came across as rapping your knuckles, it really wasn't intended as that.  What a lot of people forget is that when you talk openly amongst others who actually have real experience in this area there are also inexperienced people reading along wanting to absorb what is said.  That's how the myths and legends start and they proliferate like a plague thanks to the internet.  I would guess it took you a bit of time and effort to get your knowledge of this level of thinking, but in their eyes they have read what you wrote and now understand it like you do.  Without clear info and a gentle guiding hand they can't make discerning choices, and we all know that in depth modding and then using your own ears as a measure is a tad flawed s an objective process.

    I see what you mean with your chip temperature specs and I again I agree entirely.  My main point was that internally a device like TL0x is a TL0x.  I did say "They differ only in the specs which allow them to work in extremes of environment."  My comment about silicon and +125deg wasn't meant to imply that any device can be used up to there, only that silicon itself is theoretically usable up to that temperature (intrinsic, exhaustion, extrinsic levels?).  Details of the physical circuitry implementation, connection , packaging and others will alter that downwards drastically.  My poor choice of phrasing in "silicon devices" is what I have just said, a way of potentially misleading the ordinary guy if he takes it literally.  Hands up, and my thanks for pointing it out. Wink

    Incidentally, that's why my posts are always so long.  They are an attempt to say what I am trying to as clearly and unambiguously and generally unconfrontationally as I possibly can.  (As we can see I don't always achieve that! Embarassed   ?Hey, so I'm human, so shoot me!!!  Very Happy )

    P.S. Here's a link to a really excellent PDF of tests to a range of opamps.

    Opamp_Distortion.pdf

     It clearly compares the characteristics of a range of cheap and expensive opamps, (at length I have to say, it's a dry read).  It also shows that there are less differences than are imagined by the average pedal builder (no I'm really not being scathing, only honest) when they are correctly used within their electrical spec.  Load them down or drive them into clipping and they will behave differently, but who designs a circuit which has too low an impedance load for the device or which would allow an opamp to clip in normal use?  Decent design around them should be an understood. It's a good scan for a rainy day if these things interest anyone.
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    namklak

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    Re: Tone Caps for TMeister18

    Post by namklak on Wed Nov 18, 2015 1:54 pm

    I am guilty of rolling op-amps in headphone amps... I am going to share that pdf with my hardware engineer - he is an audiophile. I used to fancy myself an audiophile, now I just say "what?" and "someone better answer that phone".

    I've never been a pedal-phile, I have a TS-808 but only rarely use it. But I'm guessing you could put an op-amp in a bad circuit (topology pushes op-amp out of any range - load, gain-bandwidth product, etc) and get "interesting" distortion.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Thu Nov 19, 2015 8:34 am

    Hahaha! Laughing  "Interesting distortion"!  Good description.  A bit like the Chinese curse "may you live in interesting times".  "May you experience interesting distortion"!  Personally, I find most inherent opamp distortion mechanisms sound really rough if you use them as a "creative" tool.  Generating distortion is easy, generating good distortion is more long winded but not hard, generating good distortion by methods which are reliably repeatable is really demanding.  For example there is a wealth of distortion pedal types out there which specify particular types and even eras of diode or transistor.  That will make a difference in their circuitry.  But only on a hit and miss basis!  If specific component parameters mean you have to choose components from a pile until you get a good sounding one then your design is seriously flawed as a design for the wider use.  You might use it personally as a one off but don't peddle (see what I did there  Smile ) it round to others as a great design.  How can many other people reproduce your results reliably?

    In hifi, as in your headphone amps, I am a bit less of a heretic sceptic in terms of sound differences.  As I've said before, you don't get massive tonal changes but imaging and soundstage representation can definitely be affected by some critical components.  But it's subtle and I STILL can't say whether it could or should be designed out or not.  Logic says a good design should be made immune to it but in the real world, maybe... Wink

    As regards your "used to be an audiophile" I'm the same.  I still fiddle with redesigning and rebuilding parts of my own system at home periodically.  Whereas I used to listen for any improvements I had made, nowadays I tend to listen to the music a bit more.  And pedals are a no-no to me too.  I know there are some musical genres which do absolutely need them but I play simple older style good time rock.  My singer, another curmudgeonly guy,  puts it best when he says about the typical pub band: "Classic guitar, classic amp, 8 foot of cable, what more should you need"?  If I can't get by with just that I'm playing the wrong song! jocolor
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    bdw

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    Re: Tone Caps for TMeister18

    Post by bdw on Mon Jan 25, 2016 12:51 pm

    I'm a little shocked that someone opened a topic asking which was the tone capacitor, and then gets self-righteous about amplifier repair & won't share the service document.
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    ignantios

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    Re: Tone Caps for TMeister18

    Post by ignantios on Mon Jan 25, 2016 3:33 pm

    Sooo the bad news are that it's impossible for this amp (tube-grand Meisters) to be modified?Even if we have the schematics?Then these are bad news.I thought that there was some room in there to let us (the experts) to experiment.But unfortunately, it seems that this is impossible.If this is true since I haven't given a try then for me the amp(grandmeister) has to go.
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    bordonbert

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    Re: Tone Caps for TMeister18

    Post by bordonbert on Mon Jan 25, 2016 6:22 pm

    No that's not really the case Ignantios. There is always the possibility of modifying any circuit, as long as you can identify the circuit configuration and you know what you are achieving by changing something. For example, once you know what tone control configuration is in the TM and you know which components on the PCB fulfill which role, you can change them knowing that what you do is a) safe and b) an improvement.

    The H&K concept of compact design does make it more difficult than traditional open build amps unless you are used to working on tightly packed circuitry. But, as I said, it's not impossible.

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