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    Help!!! Intermittent sound loss on my clean channel

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    Rocknut88

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    Help!!! Intermittent sound loss on my clean channel

    Post by Rocknut88 on Fri Sep 18, 2015 1:52 pm

    Hey y'all got a tubemeister 36 head anniversary edition.. I have complete sound loss on my clean channel intermittently happens most when cold but does happen when hot. I've checked all my other gear with a different amp and it is ok... does anyone have any ideas? Thanks for the help
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    HwyStar
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    Re: Help!!! Intermittent sound loss on my clean channel

    Post by HwyStar on Fri Sep 18, 2015 9:51 pm

    Are all of the tubes lit up and have filament lighting?  Including the preamp tubes under the metal cover(s)?  Have another set of tubes?  If so (I don't remember this part about the TubeMeister 36) change the preamp tubes out one at a time. I don't remember if the tube change out is as easy to do as the GM 36 is.

    Other than that it is internal and off to the shop it goes, would be my best guess.  I have the GM 36 so they are somewhat similar.  Sorry I can't be more help!


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    bordonbert

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    Re: Help!!! Intermittent sound loss on my clean channel

    Post by bordonbert on Sat Sep 19, 2015 11:19 am

    I have both.  They are essentially the same setup with differences in the details.  The GM36 has midi of course and is a more refined beast in its control circuitry.  Valve swaps are exactly the same.  That won't help!  However, if you want to check it to rule it out just swap the first 2 preamp valves around.  If you have some sort of special valve setup it won't make too much difference to the work/ not work aspect.  Just swap them back once you have proved whether the problem goes into other areas or channels.  If you are using stock valves or all changed out for a new set of 12AX7s then no problem.  (You can forget valve 3 as it will be used for the Phase Splitter for the power amp in every channel.)

    I've posted this before re the GM36 and it's the same for the TM36.  If a single channel shows a problem and other channels are fine it almost CAN'T be a valve fault.  This hasn't been backed up by H&K or anyone else in the techy side, but with only 2 tubes (four amplifying elements) available for the preamp setup, if H&K follow the basic standard topology they will all have to be in use for all of the channels.  If a valve is faulty then it is almost certainly faulty for all.  If anyone can see an error in this way of thinking please post your thoughts and let me know.  (That's not a challenge in any way, it's only me wanting objective confirmation that this is sound advice I am giving).

    Do you lose all sound everywhere when it happens, i.e. Clean channel all power soak settings and all outputs such as Red Box, Effects Loop, Line Out?

    At first sight it seems like it would most likely be a switching issue internally.  The amp probably reconfigures itself in a number of subtle ways when a channel is selected.  My Vox Valvetronix does the same thing swapping from Class A to Class A/B to Class B and with different gain and tone options at each stage.  It may be that one of the switching components has gone faulty, (probably relay/reed relay types. N.B. Edited - I'm wondering about the possibility of active components like FETs or BJTs as the switching elements but can't confirm either way).  With the other 3 channels showing no signs of any problem it's not going to be any of the main elements common to all.  It shouldn't be too difficult and expensive to get diagnosed and fixed if necessary.


    Last edited by bordonbert on Sat Sep 19, 2015 11:25 am; edited 2 times in total (Reason for editing : Thought a bit more and....)

    Rocknut88

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    Re: Help!!! Intermittent sound loss on my clean channel

    Post by Rocknut88 on Sat Sep 19, 2015 11:37 am

    No it is not in the other channels I have replaced preamp tubes with a known good set granted it only has a v1 and v2 for all 3 channels the 3rd is for the fx loop I believe. It only does this on clean I do not use my redbox out. I did have a metal mounting clip break which may have shorted out on something. But it doesn't do it all the time generally only when it is cold if I leave the amp in stand by for a while when performing it's usually ok, but if I'm first start g the amp up it will do it. I've never had a tube amp do this to me yet... mainly cause they've all been over 50 watts with individual preamp tubes for each channel... sadly I forgot to send in my warranty card I've only had her bout 6 months... almost as bad as a marshall for reliability lol
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    bordonbert

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    Re: Help!!! Intermittent sound loss on my clean channel

    Post by bordonbert on Sun Sep 20, 2015 2:21 pm

    I think you may be wrong about the use of valves for the effects loop.  It has to use a phase splitter stage before the EL84s to give a positive and negative signal to feed to each (pair of) output valves.  That can be done with a single triode but is now almost always done with two, i.e. one complete 12AX7, acting as a long tailed pair.  That only leaves 2 or 2+1/2 valves for the whole preamp, only just enough even for the Clean channel if you try to cover every possibility with valves.

    It is very possible there are solid state stages inside to take care of things like the effects loop, reverb, input buffer/boost etc.  And no, even if that is the case that will have absolutely no impact on sound quality or reliability in any way!  Competently designed solid state stages are much cleaner than valves and neither add nor remove any "tone" or "dynamics", (I won't use the wonderful bulls**t term "mojo" which means only "something you can't convince me doesn't exist cause you can't measure it"), in any way unless they are set up to do so.  It should make those stages even more neutral than a valve one would be, so the effects loop, input clean boost, or similar will have no impact on sound, they just help the later valve stages to take on that responsibility and give only their "tubey" contribution.

    Don't be disappointed with the amp overall yet.  Your having this problem is a drag but you don't know what is behind it yet.  Your problem does not imply that it is a bad design in any way.  The number of problems reported must be seen in relation to the number in use and the amount of use each one gets and it's really the luck of the draw with ANY amp you buy.  There are no magic makes which have no problems, just some which are better at keeping the problems quiet!  And the overall power of the amp is not relevant to having problems in any way.  A preamp doesn't know if you have a 10W or a 500W power amp following it. There is technically no issue with sharing tubes across channels either, most multi channel amps do it to some degree.  Keep your chin up and we'll see if between us all we can get to the bottom of it.

    You say that you had a metal mounting clip break.  That sounds ominous!  What do you mean by that?

    As a last bit of advice, I would also approach H&K about your warranty.  Have you proof that you bought the amp only 6 months ago?  Could the place you bought it from confirm the date?  In that case you may even be able to register it now with the correct purchase date in place.  It's not like you are trying to buyu extra time and con H&K in any way, and they are very reasonable guys. Go onto their Facebook site and talk to them in the Guest area there.  Ask them about it and see what they say.

    Rocknut88

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    Re: Help!!! Intermittent sound loss on my clean channel

    Post by Rocknut88 on Sun Sep 20, 2015 4:29 pm

    Ok i have not run across a solid state effects loop but it's definitely a good possibility specialy given its size... and I'm in no way upset about this amp. It's been fabulous and love it the marshall quipped was a joke... I traded in a marshall tsl 60w head for this on for a reason lol. As for the clip there are little metal mounting clips inside that I believe are on the plexiglass face one of them broke and I found it bouncing around inside.. I may just invest in a completely brand new set of preamp tubes to make sure none of the ones I installed weren't shorted inside.
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    bordonbert

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    Re: Help!!! Intermittent sound loss on my clean channel

    Post by bordonbert on Sun Sep 20, 2015 10:03 pm

    Things like the effects loop or a spring delay section are nothing more than buffer amps at the send and the return, via switched sockets between which pass the signal either straight across or out through your effects units.  They don't usually offer significant gain, they are there more to make sure that the signal is not affected by the impedance matching at any point.  Any old opamp will do for the effects loop as it isn't ridiculously low impedances we're working with.  That's within reason of course!  I wouldn't use an ancient 741 but I would have no problem with a basic TL071, and neither do Marshall and many others.  They do extensive listening tests on their designs under correctly performed blind listening conditions so if there is any difference they will know it.  And if there is no difference they will not pretend there is and use an exotic component where it is not needed!  I would NOT pay silly money for a grotty old "classic" NOS MC1458 or an expensive modern Burr Brown specialist opamp for example which only offers a minute fraction of a % "acoustic signature" difference reduced even further within the circuit with negative feedback!  In amongst a good number of % distortion which we are deliberately creating?  And then in a live band setting?  Naaahhh!  The world gives me far better problems to worry about.  Razz

    To keep a sense of perspective, the lowly TL071, criticised as crap and "tone sucking" in all guitar circuits all over the internet, has a distortion level of 0.003% at 1kHz, a gain of x1, loaded with 2kOhms and driven with 6V input!  So you can single out that level of distortion from that component in a guitar amp?  Nope, to anyone's ears it's a totally neutral gain stage and can't be differentiated from other "better" opamps out there at all.  How low do you need to go before you can't hear it any more?  And it is a much better neutral gain stage than a valve for many positions in the amp.

    If you're still using the stock valves then you can get a real change in tone with new ones.  It's always subjective of course, but you can expect to get a smoothing off of some of the harshness that can be over the top end.  As an obvious doubter of "mojo", even I have to admit that the differences valves offer are significant.  JJs are very popular on here, (I use them myself), but most reasonable members reckon any good quality valves will give an improvement and some are definitely to personal taste.  If it is something you were considering anyway and you plan to keep the amp then it might be a good time to do it.  (Though I have to say I would be surprised if it fixed your problem. Wink   )

    I wouldn't worry about the clip.  I know what you mean now, they sit along the top of the plexi face and hold down the wiring for the blue LEDs.  If your valves have been inserted fully it's very unlikely they will have shorted out anything significant.  You'd see signs if it had!

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