Heat and hiss

Hi, guys,

Last week the amp began heating up verry quickly, as in 15 minutes of playing the top is almost hot enough to fry an egg. I've owned the amp since January, using it at home and in rehearsals but it never got this hot. Any reason to be worried.

Also, on the gain channels from Crunch to Ultra, I have a hissing trebly sound coming from the amp, even if I cut the volume pot on my guitars (tried humbuckers and single coils) or set my volume pedal to full heel position. Is this normal? I never noticed it at home or at our rehearsal place, but even my bandmates hear it. It's not like feedback (I have the gate on in all my presets), but a constant, audible, white noise.

When set to the Clean channel, the amp is quiet.

Can anyone give me some ideas on this? Should I get the amp serviced?

Is the fact that I'm hearing a high pitched overtone a sign of a faulty valve, either in the preamp or in the power section.

I have the gate on on all my patches.

A bit of background info to digest if you are interested....

Heat and temperature were constant discussions during the TM36 and GM36 phase.  These amps are VERY well designed in that area and under normal conditions it is not a problem despite what you may feel when you touch the top.  Your hand is absolutely no judge of temperature!  The metal case is used as a heatsink carrying heat away from the interior and distributing it out to the air.  That is a far better system than having a large thick insulating box covered with insulating tolex material relying on convection currents through a few slots.  When you touch it your hand will insist that a metal surface is hotter than a wood/tolex one at the same temperature as the heat cannot conduct into your hand as quickly from the latter.  And doing this job partially by conduction, the metal GM case must get hot to transfer heat through it.  The upper compartment with the valves in will naturally get hot as the valves themselves are very hot.  This does no damage at all to the valves and it is no indication of how hot the lower compartment is with the circuit boards in it.

The following are lifted from a Safety At Work site which makes recommendtions as to what temps are safe:

1st Degree Burn (minor burn):

• Non-metallic 85°C brief contact
  
• Metal 60°C brief contact
  
• Metal 50°C hold
  

2nd Degree Burn (damage to underlying tissue):

• Metal 100°C for 15 seconds contact
  
• 82°C for 30 seconds contact
  
• 71°C for 60 seconds contact
  

You can see that metal and non-metal surfaces are different just as I said. You can also see that around the 50-60deg C mark we feel very uncomfortable and that is about the upper limit of what we will experience with our amps. Despite what some may insist, that temperature is absolutely nothing for electronic components to cope with! I guarantee that!!! And in the links below I offer some tech info which puts it in perspective. The power soak is also pretty much a non-issue. It dissipates a maximum of 18W at its lowest setting into a number of high wattage resistors. The signal which is heating them up is a music signal with very little low frequency energy so it is dynamic and low power. That's nothing to worry about either.

Here are a few threads which you may find useful:

I designed and built a unit for my TM36 to stand on which was incredibly cheap to make and which did a really good job of keeping heat travelling out of the amp away from the PCBs:  Fan Cooling Stand  It also locked over the handle of my cab and the TM/GM feet were held in recesses in teh stand therefore locking it in place and making the whole mini-stack much more stable ampwise.  There is also some info in Post No 4 as to why it isn't a problem for PCBs and their components too.  There is another barrow load of crap talked about that side in music circles!

VoodooJeff did a much simpler job and also did some measurements on it: Cooling - No Fabrication.

If your amp has started to heat up much more than it did it could certainly by be a sign of a valve problem. Have you tested it with the TSC switch on the back? If not, you should do that and count the number of flashes for each output valve. Then you could try using the amp at 18W setting to see how hot it gets, then swap the outer pair with the inner pair and see if it is the same again at 18W. It would be unusual to have all four valves go at the same time.

As to the high pitched overtone, that could be a valve but it could also be a number of other things.

Thanks again on your input, Bordonbert!

I did the TSC test, with Standby OFF, and I get all valves flashing continuously for 12 times, and then one more flash for the second valve on the left (staring at the back panel).

With Standy By on, all power valves are lit.

Do the proper amount of LED's light up for each power soak setting? My GM36 combo had a bit of a high-pitched whine, and one LED wouldn't light up when I selected full 36W output even though all tubes were glowing. Turned out the TSC circuitry had some glitch that luckily for me was easily fixable. YMMV as they say....

Thanks, Billgwx! Will do that later this week, only did it in the 40w setting. Probaly the same glitch as your, I hope.

BTW, did you work it out yourself, or did you send the amp back for repair?

I sent it to a local tech, who was able to fix the problem since it didn't require HK-specific parts or expertise.

Thanks for your quick reply. I'll do the TSC check on the various power settings, and let's see how it goes... Wish me luck!

Remember to try testing on 40W and 20W then swap the output valve outer and inner pairs around and test again on 40W and 20W simnply to see if either using the power soak or swapping the valve pairs removes the problem. There is a fair bit of info that simple test will give you. It will rule out a single faulty output valve, also a faulty pair of output valves, it will also tell you whether there is a likely fault in the support circuitry of any single valve slot on the PCB.

With the power soak on any setting other than full 40W one pair of the output valves is switched off and the TSC LEDs on the back should show this. At 20W, if the outer LEDs are lit then the active pair of valves is the inner ones. I think that is the correct pair to remain active but I could be wrong. Check that out first. Everything I say from here depends on knowing that.

If, at 20W, it whistles only with a particular pair of valves in the active slots but not with the other valve pair in their place, then it shows a valve fault and the first pair of valves has at least one duff member. It is possible that you could have a faulty valve in each pair causing the problem for both but that is very unlikely.

If it whistles on 40W but doesn't on 20W no matter which valves are placed in the inner and outer sockets, then it suggests it is down to one of the inactive output valve's supporting circuitry on the boards as it happens only when the inactive slots are in use at full power and it doesn't matter which valves are in there.

We have to assume your TSC test is being truthful when it suggests no problems with any valve. If it doesn't make any difference which valve pair is where at either 20W or 40W it suggests a problem with an active valve support circuitry as it happens all the time and with any valve.

That may seem complicated but it isn't really. follow the first paragraph and see when it happens and when it doesn't.

Of course, it might not be output valve related at all! You say it doesn't seem to be noisy on the Clean channel. Have you tried swapping the 3 preamp valves around to see if the problem changes in any way? The Clean channel doesn't use all of the available triodes so if you have a noisy preamp valve it would start to happen in the Clean channel when you put it into a position where that channel uses it. It is better to use a known good 12AX7 and swap it out one at a time but moving your existing ones around and listening for a change in the problem is almost as good.

Thanks agains for your input, BordonBert.

I haven't opened the GM40D, since I'm still on warranty, and was advised by the seller not to do it on my own, because it would void the warranty (in Portugal such goods are legally protected by a two-year warranty).

I'll try at least to do the TSC check in 20w, 5w and 1w mode. If anything happens, I'll check it out with the seller (a renowned store here in Portugal, and licensed H&K sellers).

Will back up my MIDI programs, just in case.

It is perfectly feasible to open the amp and change the valves without in any way voiding the warranty.  This info is already readily available here in a number of posts if you search for it to confirm.

Simply take out fully the two top screws on both end caps.  Remove the rear screw from the silver handle but leave the front screw alone, it only holds the handle onto the end cap.  Now the crucial bit....  SLACKEN the bottom 2 screws on each end cap only a couple of turns, DO NOT remove them fully.  You only need enough slack in them to allow the end caps to be folded outwards slightly to remove the top panel without affecting the warranty sticker on those screws in the bottom compartment.

That's how people can swap out their valves the moment they get their new amp because they "know" the ageing "vintage" replacements they bought for £20 each on ebay sound better.

Well, turns out I'm having an issue with the outboard pedals, since plugged straight into the amp there's no hiss at all.

I'm using a Godlyke Powerall to juice a Korg Pitchblack Poly tuner and a MXR CAE MC404 wah. Chain goes Guitar-Passive Fender Volume Pedal- MXR Wah-amp.

The volume pedal has a tuner out going only into the Pitchblack.

The tuner can receive power and send it to other pedals.

Could be the cables, will have to try other ones, but the problem is probably a ground loop, since I'm plugged to different outlets. Should I daisychain the Powerall to both the tuner and the wah, instead of plugging into the tuner and use its DC Out?

Still gotta buy batteries to se if it goes away, but at least it's an amp issue, since I tried the TSC test on different power levels, and valves seem to be fine.

Doesn't sound like a ground loop issue to me.  That's generally another reason to sell you highly expensive power supplies which are generally unnecessary.

Have a look here, you may believe them: PedalSnake Noise Ground Issues  Go down a little to "Isolation and Grounding".  A high pitched "whine"?  Sounds a bit like what you describe.




EDIT: And here is more on what they say about Digital Noise: PedalSnake Curing Digital Whine  Half way down to "Corrupting Our Chains" and there it is on the nose!

PedalSnake wrote:This is probably the most popular reason that expensive power supplies get sold. The good ones have all outputs isolated from one another. But this is an expensive and cumbersome solution to a simple problem.

To promote the sale of expensive power supplies, sales info tells us our power chains are the problem. We are told they cause “ground loops”, “differences in potential”, etc., and the only way to fix digital noise and have quiet power is to spend big, and isolate every pedal.

Wrong.

Thanks, Bordonbert. That's exactly the issue I'm facing, since I have an extra DC power supply, will try to power the wah and the tuner separately, and see if the high pitch whine persists.

Your input is definitely a lifesaver! Thanks again!

Did someone say HEAT?

Check this out - it's hot as ballz here (108 °F / 42 °C) in this photo.
The amp was in direct sunlight (from behind) and ran all evening fine.
Pedals running on the front end.

Excellent post Ravensha.  Just as we've always said, the design works.  The fact that the top gets hot is irrelevant, it's doing its job.  Does anyone feel the bottom to see if it's the same?


(On the other hand, PRS + Mesa, no wonder you love this amp!    Where is the Les Paul and Marshall cab? )

Update: turns out the link Bordonbert provided, concerning "Isolation and grounding" provided the answer to the high pitched whine. I connected the wah to its own 9V DC power supply, the Godlyke Powerall (1Spot "clone") just powering the Korg Pitchblack and bam! absolutely no noise.

Since I had a shorter 5-pin MIDI cable than the 7-pin provided (way too long for my needs, and seemingly that aren't any shorter 7-pin MIDI cables for sale anywhere), I took the chance to power the FSM MKIII from the DC Out on the Pitchblack, to see if the noise would be present again, and bam! absolutely no noise.

In short, I will consider buying a power supply with isolated and regulated 9V DC Outs, since carrying two power supply means more weight and cables, and I want to keep the board simple and tidy. But the main issue is now solved, so I thank all, especially bordonbert, for your input and advice.

Concerning the heat, Portugal is having the strangest weather, with heat waves lasting a few days, on which probably the heat dissipation was not as apparent. In truth, the heat didn't cause any malfunction, only a hot sensation when handling the amp after use. As stated before, it's probably in the nature of the beast, and I guess german engineering was top notch when designing the amp, and its shortcomings (if heat can be considered such) were all accounted for.

To be honest these expensive power supply modules are really unnecessary if everything else is done right, and of course that is where the fudge factor comes in that they live on, it rarely can be guaranteed to be.  I often go on about ridiculously expensive pedals on this forum and elsewhere.  £120 for a diecast box with about £1.50 worth of components on a £2.50 PCB doesn't justify the price for my wallet.  I don't want the kudos and bragging rights of having something with a flashy decal on it and a name which makes other guitarists faint when you speak it in hushed tones.  For that sort of price you have an absolute right to expect something special electronically. They VERY rarely are anything other than another version of a standard existing configuration brought about with everyday bland components often with weaknesses designed in and even errors. And you should at least expect that the cheap simple details like PSU noise immunity and lack of PSU pollution will be implemented in a rock solid way.  It costs nothing to do so and it is bog standard electronics to anyone who knows the game properly and cares.

95% of problems which make people fork out £100+ for a bloody 9V PSU are down to badly designed pedals and the other 5% are down to not knowing the basics of how to wire them up.  The term "ground loop" is tossed around by all guitarists now as a sign of membership of the club but so few actually understand what a ground loop is, how it causes a problem and how to solve that simply.  I do use a multi supply PSU myself for convenience.  It originated in China and cost me £16.99 including p&p!  Here is the up to date version still on sale: Cheap Pedal PSU  I'm not advertising it, only suggesting that units at this cheap level are perfectly adequate to do the job if the more expensive elements in your rig justify their ridiculous price. My original has outputs in pairs, each pair separately regulated and provide all the isolation you should need.  As soon as you start getting into the realms of exotic stuff you think you are getting value for money but, as I keep on boringly trotting out, most of what goes around in musical circles today as "the PROPER way to do it" is snake oil and it's priced accordingly!

Good luck with the rig Syn, I'm glad you got to the bottom of your problem.

Well, I've found that Thomann (webstore based in Germany), via it's own Harley Benton brand a clone of the T-Rex Fuel Tank Jr. (priced around €120) for € 33. Some reviews online state that it sports 5 isolated 9vDC/120mA outputs. Will probably check it out, since I'm only powering two pedals.

Probably something built around the specs Bordonbert related on the previous comment, priced higher mainly for Thomann branding reasons.

So far, all is well, and I've been very happy exploring the amount of coverage this amp gives for many genres. It may not be perfect, but unlike many, I like the "jack of all trades, master of none" aspect of the amp.

You can remove the top and access the tubes without disturbing the warranty seals. How video on YouTube easy to find

Errm, isn't the procedure in post 11 of this thread?