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    Grandmeister 36 - Popping/Crackling noises when turned off standby

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    Davroz

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    Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by Davroz on Sun May 22, 2016 2:43 pm

    Hi

    I've been gigging my GM on stock tubes for about 1 year, this weekend when powering on all was normal however after switching it off standby a noise appeared after about 30 seconds, its basically a popping,crackling,interference type noise which does not go away. It happens on all 4 channels through the main speaker and the red box out,  it does not get louder when the volume is cranked and it happens when there is no guitar connected to the amp. I've tried it in 3 different locations thinking it might be just electrical interference however the same noise persists. Could this be the valves? Has anybody had this issue? I'm gigging this amp every weekend so hoping to get this fixed this week ready for next weekend . I've emailed the H&K Facebook page awaiting a response. Any advice would be greatly appreciated.  I've recorded the noise so you could hear it but it won't let the post the link on here for 7 days as i'm new to the forum.
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    bordonbert

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by bordonbert on Sun May 22, 2016 3:19 pm

    Hi Dav, welcome to the forum. Good thorough description of your problem, thanks for that, it makes advising so much easier. Are you comfortable loosening the end caps to remove the cover and pulling the valves? If so there are a couple of simple tests which may help.

    The fact that it is independent of the Master Volume suggests it is in the power amp section or maybe the power supply. For the following simple tests turn the Master Volume fully down so there is no signal from the preamp getting through at all. Check the valve condition with your "magic plectrum" test in the slot in the back. Count the flashes of the inner and outer pairs to see if they all report bias currents with good matching for each pair.

    Does this problem happen on all power soak settings, in particular with 18W against 36W? On 18W you are using only a single pair of the output valves, the other pair is effectively switched off. You could try swapping the inner pair of valves over with the outer pair to see if that sorts it out. If it does then the problem would be tied in with one of the output valves. Make sure not to mix up the pairs, keep them matched as they are and make sure to only swap both outers for both inners.

    As you say you have the original valves in there, the preamp and phase splitter valves will all be 12AX7s. You could also try swapping the V3 and V2 valves to see if the phase splitter is at fault. These two valves are the ones without the metal cover. The power amp phase splitter is the one furthest away from the metal can covered valve. If the noise clears up then the valve you have just swapped into the socket next to the 12AX7 with the cover is noisy.

    Give that a go and let us know what you find.
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    Davroz

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by Davroz on Sun May 22, 2016 4:16 pm

    Hi,

    Thank you so much for coming back to me so quickly. I have just tried everything you said.
    First I swapped over the matching pairs of output valves and although it does appear to be quieter when I reduce it to 18 watts its definitely still there.
    So then I have swapped over the pre amp and splitter valves and the problem appears to be worse, i.e. its louder and sounds a bit more crackly (if that helps).

    The current TSC reading as I look directly at the lights is: 9 9 10 11

    Should I try anything else?

    Thanks

    Dav
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    bordonbert

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by bordonbert on Mon May 23, 2016 8:44 am

    Another simple test which occurred to me after posting is to short out the fx loop with a plain jack lead.  Sometimes fx sockets can get noisy as the switches get dirty.  Putting a lead in removes those switches from the circuit.  If it does turn out to be that then they just need a clean up with maybe a contact spray.

    Assuming you did all of this with the Master Volume turned all the way down to remove the preamp as a source of noise then that's all good info.

    So we know it plain cannot be a problem with the preamp valves as it remained even when all of the preamp signal was removed with the MV set to 0.

    The TSC bias readings are all in the zone so that shows us nothing.  Incidentally you may have a better match if you put your 2 x "9"s as a pair and the "10" and "11" as the other pair.  (Now that is purely pedantic and won't be heard, just an observation. Wink )

    Swapping the inner and outer pairs of valves and running it at 18W shows that there isn't a single valve of the 4 EL84s causing it.  At 18W the inner pair alone would be producing the noise.  After swapping, at 18W it is now the original outer pair still giving the noise.

    Swapping the Phase Splitter valves shows that it probably isn't that valve at fault.  The difference in noise levels could easily be due to gain variations in the two valves.

    So everything seems to suggest a different source of the noise other than the valves, and if that is so and it isn't the fx loop sockets it would need equipment to track it down.  The only other simple thing I could now suggest is to swap out the valves with others you may borrow from somewhere to be absolutely sure.  There is the possibility that you have more than one noisy valve and the swaps are somewhere changing one noisy one for another.  That would be really bad luck and is pretty unlikely!  My advice would also be, don't just stqart by blindly swapping out every valve as the "revalving kits" suggest is wise.  That's unnecessarily expensive and poor engineering.  You won't understand your problem and be able to deal with it when it occurs again, perhaps in a different amp.  Swap out the single inner pair of the output valves and try out only that pair at 18W.  If the problem clears then one of those output valves was noisy.  Stepping up to 36W with that new pair in place and using the outer pair will then test them as well.  No noise with all four then tells you the second pair are fine and it was a single faulty valve, if not then replace the outer pair too.  Job done cheapest way! Swapping the phase splitter is a single valve issue which may help to rule out the slim chance that both of your 12AX7s are noisy.

    A bit more info which might be useful....

    This is technical but please bear with me, it may well be relevant for us as GM users.  Preamp valves, despite what current "common knowledge" says, are not over stressed in a guitar amp and they usually run perfectly for a lot of years barring physical damage, certainly a lot longer than the fanatic valve rollers say is good.  Power amp valves do wear out, but they also usually give years of use before they suffer badly enough to warrant changing.  Again against "common knowledge", they don't "wear out" by use.  The idea of "cathode stripping" which is often cited as a cause doesn't apply to the class of valves we use in guitar amps, that's both preamp and power amp valves, the energy levels are way too low to cause it.  They usually die by cathode poisoning creating "interface resistance".

    Interface resistance happens when a valve is left powered on at the heater but with no anode voltage applied.  With no current flowing a barrier layer slowly forms between the base metal former of the cathode and it's oxide coating which increases in resistance and gradually reduces the valve's effectiveness.  This process is irreversible.  Let's see, heaters on, anode voltage removed, errrmm, isn't that called "on standby"?  Yes, in fact the usual type of standby switch circuitry actually harms the valves it says it is protecting.

    Now worse than that, as GM users we have the power soak setting on our amps.  What does that do?  It starts by taking out of circuit one pair of the valves.  And I believe we are right in saying that it leaves the heaters on with the anode voltage removed.  So it would seem all the time we are running at less than 36W we are poisoning one pair of our output valves.  That worries me and I am intending to ask H&K what they think of it.  When not in use I now leave my amps on 36W and muted with the MV turned fully down rather than on Standby.  I can see no penalty in doing that and it may be preventing damage to my output valves.

    So the path onwards from here, assuming it isn't the fx loop sockets, depends on whether you can get your hands on a borrowed set of known good output valves and a good 12AX7.  Swapping out is the only easy way I know of to diagnose this problem.  Can anyone else come up with any other simple ideas?  scratch
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    Davroz

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by Davroz on Mon May 23, 2016 9:31 am

    Hello, Thanks again for your extremely informative reply on this subject, you obviously know your onions on this - Impressive!

    So just a thought, unless I have misunderstood you, there are 3 12AX7 pre amp valves in the front and I haven't touched the shielded one (metal can covered valve) - Can I swap this out with one of the other 2x 12AX7 valves to fault find?
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    VoodooJeff

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by VoodooJeff on Mon May 23, 2016 10:20 am

    My observation won`t be nearly as thorough as BB up there. I`ll just say "A year on stock tubes? Here`s a fiver that that`s the problem. Put a full set of JJ`s from Tube Depot in for less than a hundred bucks and call it a day".

    While I do agree without question that quality tubes don`t really have the life expectancy that some of the hoity toity tube folk would have you believe, I do hold the opinion that the stock tubes, in particular the cheapo chinese tubes ours come with, do have a shorter service life and a year of steady use is about it. My "B" amp is the one from the NAMM show, and it sat mainly untouched and on, all day long for four days straight. The tubes did exactly what you`re describing the day I took possession of it and new tubes stopped it.
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    bordonbert

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by bordonbert on Mon May 23, 2016 11:44 am

    You could swap the V1 covered valve with the others just to test Davros but there is really no point. It is more or less ruled out as causing this by testing the amp with the MV at 0. It cannot get any noise through to the power amp under those conditions so all your noise is coming from the power amp or PSU. In the circumstances Jeff's advice should be followed here. I can often give you good background theory which often is the thing to follow. But in cases like this an ounce of well considered first hand practical knowledge is worth a pound of theory, (not that "common knowledge" I often scathingly quote which comes from someone else's sister's neighbour's pool boy's milkman who once changed a light bulb).

    That's good to have your experience Jeff. Interesting to see your thoughts on the life of the stock tubes. It is kind of at odds with the older info from the genuine days of valves, particularly with the preamp valves, but it isn't surprising now that cost cutting is the norm in production. Everyone used to make valves that were the best possible 50 years ago. This lower frequency flicker noise is generally caused by roughness in the surface of the oxide coating leading to irregular electron emission. If the coating is not as robust or as thick as it once was and gradually pits in use then I would guess this could occur early on. It's a relief too to hear someone who knows confirm that the valves are the most likely culprit. We know that H&K deliberately cut corners on the valves knowing that these will be changed out fairly early on for an owner's favourite flavour.

    Get a set of JJs in then Davros, (unless you have a different favourite type). I wouldn't take any advice on valve types from someone taking their experience from a different amp, a good match is better considered amp specific. Most of us here get on well with JJs and I haven't seen anyone post anything bad about the combination. They do seem to match well and give a smoothing of the top end.
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    Davroz

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by Davroz on Tue May 24, 2016 1:43 pm

    Hi Guys

    Great News! As a last resort I've decided to go out and buy a brand new set of TAD valves to put in the amp, 4x EL84s and 3x 12AX7s and it worked a treat!
    First I changed the EL84s which worked straight away so I guess I was unlucky and had a couple of dodgy power amp valves! No buzz, no crackles = happy Dav! Then I put in the 3 new pre amp valves for good measure. The Amp sounds lush and the main thing is its working again ready for 2 gigs this weekend... Phew!!
    Just want to thank both of you for all your help and advice, to be honest as it was my first valve amp failure i've learn't more about valves and amp testing in the last 2 days then I have in 15 years worth of playing so thank you for that!
    To be honest before joining this forum I was expecting it to be sent away and i would be without it for weeks but having found this forum its a fantastic place to learn about the kit we love and use and you helped me fix it so i'm chuffed to bits!
    So thanks again guys!
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    bordonbert

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by bordonbert on Tue May 24, 2016 2:38 pm

    That's what we like to hear. Jeff always gets down to the point and gives you the advice that is the most likely solution, (and he's always bloody well right!) I'm the pedantic one who always tries to follow a logical path through it. Hopefully along the way you get a fix and you also get a bit of reliable info to take on yourself. That seems to have happened so a good result.

    Do stick around here as we love to hear from people as to their ideas about using their kit. Have a browse through the other threads, you will find a lot of good experience posted in there. There is bound to be something that helps you get more out of the GM.
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    VoodooJeff

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    Re: Grandmeister 36 - Popping/Crackling noises when turned off standby

    Post by VoodooJeff on Wed May 25, 2016 9:58 am

    Power tubes can be a malicious b*tch when they fail, and yet another reason I love H&K so dearly for this amp. Had a power tube fail in another brand and when it went it shorted and took out the power transformer before the fuse blew. The power transformer is typically the most expensive single component in an amplifier.

    Preamp tubes really don`t ever "need" replacing, per se. They don`t see the same 500 - 700 volts that power tubes do so they don`t "wear out" (not that power tubes do, by definition, but I`ll play into the hoopla for a moment LOL). Think about this: there`s enough voltage, pushed by enough current in the power section of an amp to potentially kill a person who carelessly sparks the wrong lug. The preamp might make you swear a bit.

    Glad your amp is back to action as usual.

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