Klark Teknik KT-2a making crackly noise after not being used for a few months?

[dickiefunk]

Hi,

I've got a Klark Teknik KT-2a compressor which I really like. However, it has started to make a lot of crackly noise after not being used over the past few months?

Here is an audio clip of the noise I mention :-

https://drive.google.com/file/d/1WRhF5g ... sp=sharing

I'm wondering if this noise is condensation on the tubes or something else?

[Wonks]

I don't think you'll get any condensation forming in this weather, unless you keep it in the bathroom. And moisture doesn't affect valves like that.

It sounds to me like it could be a valve itself that's on the way out. But it could also be corrosion on the valve pins/valve base, or a loose ribbon cable (if there is one) or even a dirty pot.

But probably a valve. You've got 12AX7, 12BH7 and EL84 valves in there. (I think the EL84 is probably used to replace the 6AQ5A valve that was in the original). Any of them could have lost vacuum. Sometimes it happens. You could look for signs of overheating (the valve lettering is normally red and goes white if it gets too hot) or a white residue inside the valve itself (lost vacuum). But leave the unit disconnected for a full day before opening it up as it's got big capacitors (a couple of 40 uF caps in the power supply circuit if its like the original) and I think runs at around 350v DC internally.

Unfortunately with 3 different valve types and 3 valves you can't swap them around to see if things improve. You could try removing and reseating each valve in turn.

I'd also exercise all the pots and switches for a few turns/operations each, which should clear any light dirt away.

Web reports seem to indicate that these things run quite hot, so is it in a well ventilated space in your rack, ideally with nothing directly above and below to allow for ventilation? Running too hot will reduce valve life.

Unfortunately valves are rather scarce at the moment and have shot up in price as a result, so it won't be a particularly cheap job to get a replacement valve of each type to try out. At least EL84s are some of the least expensive power valves around.

[Wonks]

What's the warranty on them? I've seen 10 years mentioned in some places but that could vary from country to country. If still under warranty, you may be able to get it checked out free of charge, but valves will be probably regarded as consumables with no minimum life expectancy (though an immediate failure should be dealt with).

[dickiefunk]

Thanks for the suggestion. I upgraded the valves in the KT-2a to Harma Retro tubes from Watford Valves. They are only around 18months old hand have had light use. I still have the original Bugera tubes so I’ll be able to swap the tubes out to see if that’s the problem.

[Wonks]

That’s good. One at a time would be ideal but I don’t know what the internal construction is like and whether you can change a valve without risk of touching any of the circuitry. It’s often possible to on valve amps, but with more compact equipment, there isn’t always the space for protective barriers.

[resistorman]

First thing I always try with valves is cleaning the pins. Sometimes even just pulling then reseating will fix spurious noise. I use a pen dispenser of deoxit on the individual pins, or you can use a bit of spray on a lint-free cloth. You don't want an excess of liquid!

[dickiefunk]

Hi guys. Sorry for the late reply. I tried swapping all the valves and am still getting the same noise issue!? Any more suggestions?

[Hugh Robjohns]

Sounds like reforming capacitors to me.

I'd certainly clean the valve pins and wiggle them all around a bit, just in case there's tarnishing on the pins or sockets. A bit of D5 (or similar) wouldn't go amiss.

With that done. I'd leave it powered up for 48 hours or more, keeping an eye on it just in case, and see if it's any better after that. If not... it's a warranty job.

[dickiefunk]

Thanks Hugh. I upgraded the valves as soon as I bought it so I was able to swap all the tubes for the original Bugera tubes which were practically brand new.
I will get some De-Oxit 5 and clean the tube sockets.

[dickiefunk]

There has been some development regarding this issue with the KT-2a.
I tried turning the Output Gain pot and when I touched it the noise shot up momentarily. When I finished, the noise had disappeared. I am now only getting this noise spiking when I turn the pot and then it disappears after I have finished turning (instead of being constant as before).

Could this issue be down to dirt in the output pot?

[Hugh Robjohns]

Yes it certainly could.

[dickiefunk]

That would be great if it is just that.

Here is a link to the noise of the KT-2a being turned up and down :-

https://drive.google.com/file/d/1Fqy9EL ... sp=sharing

I've got some De-Oxit5 coming tomorrow so hopefully that will sort it out!

[Wonks]

It may well be that simply turning the pot a few times clears the dirt out and removes your issues. You may not need any cleaner unless the crackles don’t fully go.

As it’s a pot, you really need to use the matching fader lubricant spray F5S after the D5, otherwise the pot could wear out much faster. Servisol 10 is an all-in-one solution for pots as it also contains a lubricant (which makes it less suited for contacts/switches than D5).

[James Perrett]

It is also possible that there is DC across the pot which makes any imperfections or dirt in the pot's track far more obvious. The normal cause is a leaky coupling capacitor.

The Servisol Super 10 that Wonks mentions is now called Kontakt Super 10. It is the same stuff but with a different brand name.

[dickiefunk]

Thanks. So should I just use the Kontakt Super 10 (Servisol Super 10) instead of the De-Oxit D5 or aswell as?

[Wonks]

I'd use the D5 for switches and the tube sockets (well worth doing those), and I'd just use the Super 10 on the pots. But it won't harm anything if you use the D5 first and the Super 10 afterwards on the pots, just to be sure.

If you're spraying valve bases & pots and poking about inside, make sure the unit's been off for quite a while first, preferably overnight. And let the cleaner evaporate before powering up again.

[dickiefunk]

Will do. Thankyou for the tips!

[dickiefunk]

Hi guys. I have used both the De-Oxit 5 and Servisol cleaners and this has definitely made a big difference. I sprayed these around the pots from the outside. I am still getting a small amount of crackling/popping when I move the Output Gain pot but once I stop turning the noise disappears. IS there anywhere I should spray inside the KT-2a to clean this pot?

I've uploaded a picture of the inside behind the Output Gain pot here :-

https://drive.google.com/file/d/14N1t38 ... sp=sharing

The pot is directly parallel to the green block labelled A104

Another thing I've noticed is that after I worked the Output Gain pot after using the cleaner, the pot feels noticeably looser?

[Wonks]

It looks like the opening of the pot where you want to spray the cleaner is the side facing directly down in the picture. The A104 label is on the pot itself.

Looks like it should be relatively easy to undo the pre-emphasis pot nut and the output gain pot nut, detach the Molex connector and pull out the small daughter board so you have better access to the pots.

Also worth some switch cleaner on the Molex connections whilst you're at it.

As the Super 10 has a lubricant in it, it's not surprising the pot is easier to move., You've probably cleaned out some dirt when spraying as well.

[Wonks]

Note that you may have to pull the valves out if the pot shaft is quite long in order to give the daughter board enough space to be pulled back.

[dickiefunk]

It looks like the opening of the pot where you want to spray the cleaner is the side facing directly down in the picture. The A104 label is on the pot itself.

Looks like it should be relatively easy to undo the pre-emphasis pot nut and the output gain pot nut, detach the Molex connector and pull out the small daughter board so you have better access to the pots.

Also worth some switch cleaner on the Molex connections whilst you're at it.

As the Super 10 has a lubricant in it, it's not surprising the pot is easier to move., You've probably cleaned out some dirt when spraying as well.

Thankyou! Ah yes that makes sense regarding the pot being looser!

I'm not sure how you undo the nuts on the Output Gain pot and pre-emphasis pot? I can't find any screws? Sorry, I don't have any experience at taking gear apart.

[Wonks]

Take the knob off the output gain and there will be a nut underneath it. Depending on the size of the pot it should be 10, 11, 12 or 13mm. The knurled ring around the pre-emphasis pot is the nut holding it in place. I'd stick masking tape around it and use pliers or mole grips to loosen it.

[Wonks]

I can't see any grub screw in pictures of the unit, so I assume the knob just presses on and pulls off.

[dickiefunk]

Thankyou! Does the knob pull off?