Can somebody tell me what is up with my amp???

[Michael_DK]

I play a Hughes&Kettner Tubemeister 18. It has a built-in power soak and line-out with speaker emulation (post power tubes), and I usually play it on silent mode (no output through speaker), and listen on headphones - the curse of living in an apartment with thin walls.


Yesterday, I took my headphones off, and noticed a buzzing sound when playing. Looked for fret buzz on the guitar, but came to the realization that the sound came from the amp head. No speaker attached (which is fine when it is in silent mode). It actually sounds like there is a tiny, fuzzed out speaker in there, because basically the sound it makes is what I play on the guitar.


This is mostly evident when the gain is up. When cranking some pedals, it actually started to kind of feed back when I held the guitar up in front of the amp. This feedback pitch can actually be modulated when turning the gain knob of a pedal up and down. This is REALLY weird.


I have changed all the tubes, the problem persists. Tried another guitar, same deal.


I noticed one of the tubes has this brown stain down its side - looks burnt?

That's when I remembered that some time ago while playing around with very high gain (lead channel, some cranked pedals etc.), I noticed a rank smell like burning plastic or something. This was after playing for like two minutes at this setting. I quickly turned it off, but never did find out if the smell came from the amp or somewhere else. It hasn't occurred since, but I haven't play with that high gain since, either.


The amp is fairly new (less than two years old).

Can anybody help me find out what this is?

 

[Solocaller]

Somebody will more experience than me can jump on this question, but my bet is a bad tube.

 

[Michael_DK]

That was my thought when I saw this (the picture). But the problem persists with all tubes changed (i.e., the "phantom speaker in the head")

 

[vchizzle]

Does the noise only exist with headphones, or only thru a speaker cab, or both?

 

[BlueSky]

My first guess it's the tubes. But then you say you changed them. Not sure if the Tubemeister requires a rebias? Probably not.
Other than that it could be speaker cone cry. Try hooking the amp up with a separate speaker cab and make sure there's no impedance mismatch.
Or it could be something more dramatic like a failing capacitor or OT after the tube went south. Let's hope not.

Edit: just re-read your post more carefully. Well, the burn smell does not sound good. It could be the tube or worse, the OT.

 

[Dancing Frog]

The last time I encountered goo in one of my amps, it was leaking dielectric from a cracked coupling capacitor that was running down one of the power tubes. It looked like that. That's what I first thought when I saw the tubes, but it can't be. The Tubemeister's tubes are above the circuit boards.

 

[g.wizz]

I have a TM18 HEAD and i run it silent most of the time but since its placed in a corner i keep a little
Fan running behind it so it doesn't heat too much.i also played it with the drive fully crancked
And added pedals to that with no problems.did you try to rebias the tubes with the automatic feature by inserting your pick in the slot on the back and made sure that it behaved the same? I did that when my amp wasn't working properly once
My two cents.hope you find the solution quickly.

 

[Michael_DK]

Does the noise only exist with headphones, or only thru a speaker cab, or both?

Neither; the noise comes from the head itself - didn't notice it through the headphones. Is something inside the actual head.

 

[Michael_DK]

I have a TM18 HEAD and i run it silent most of the time but since its placed in a corner i keep a little
Fan running behind it so it doesn't heat too much.i also played it with the drive fully crancked
And added pedals to that with no problems.did you try to rebias the tubes with the automatic feature by inserting your pick in the slot on the back and made sure that it behaved the same? I did that when my amp wasn't working properly once
My two cents.hope you find the solution quickly.

Oh yeah, forgot about that. No, I haven't tried it. I have looked at the two red LEDs, they do not indicate any problems.

 

[Felix]

What type of attenuator does the head use? My first thought is that the attenuator (the power soak) is of the "speaker motor" type, such as is used in Weber attenuators.

 

[Michael_DK]

What type of attenuator does the head use? My first thought is that the attenuator (the power soak) is of the "speaker motor" type, such as is used in Weber attenuators.

The attenuator is built in.

 

[Felix]

Yes but of what type is it please?

 

[Felix]

Oh, and as for the leaking goo and burning smell... what is directly over that tube with the stain running down it? Some sort of capacitor or other component which could be leaking oil or some such? I imagine Hughes and Kettner uses PIO caps; they are nice pieces of gear.

IDK if this is relevant, but a leaky capacitor can also cause at least some types of resistors to overheat; perhaps this could be the problem you had at high gain? -The smell, not the sound.

Also, I see I may not have been clear as to what I meant by the "type" of attenuator of which the H&K Power Soak consists: there are several ways to attenuate a signal. Perhaps the most frequently encountered is of the resistor type, but reactive loads are used too. One way to do this is to send part-to-all of the signal to a speaker coil and magnet assembly, or "speaker motor", literally a speaker without a cone, which therefore would likely sound like a very muffled speaker while in use, though I am only speculating here, as I've never heard/seen one in actual use.

 

[Michael_DK]

Oh, and as for the leaking goo and burning smell... what is directly over that tube with the stain running down it? Some sort of capacitor or other component which could be leaking oil or some such? I imagine Hughes and Kettner uses PIO caps; they are nice pieces of gear.

IDK if this is relevant, but a leaky capacitor can also cause at least some types of resistors to overheat; perhaps this could be the problem you had at high gain? -The smell, not the sound.

Also, I see I may not have been clear as to what I meant by the "type" of attenuator of which the H&K Power Soak consists: there are several ways to attenuate a signal. Perhaps the most frequently encountered is of the resistor type, but reactive loads are used too. One way to do this is to send part-to-all of the signal to a speaker coil and magnet assembly, or "speaker motor", literally a speaker without a cone, which therefore would likely sound like a very muffled speaker while in use, though I am only speculating here, as I've never heard/seen one in actual use.

I haven't opened it up, but I'm sure it is just a resistive load (no speaker motor).

There is nothing above the tube, just the "lid", for lack of a better term.

 

[Felix]

I did a cursory search, and could find no info; I suspect you are right. The "speaker motor" load would be one way that your signal could be audible, though. Sorry if it was of no help.

On a related note, the phasing on the attenuated signal from the load of the built-in H&K power soak: is it a subtle thing, or is it in-your-face, as it can be with some attenuators? I understand that any load will cause a phase in the signal, but is it very noticeable?

 

[Michael_DK]

I did a cursory search, and could find no info; I suspect you are right. The "speaker motor" load would be one way that your signal could be audible, though. Sorry if it was of no help.

On a related note, the phasing on the attenuated signal from the load of the built-in H&K power soak: is it a subtle thing, or is it in-your-face, as it can be with some attenuators? I understand that any load will cause a phase in the signal, but is it very noticeable?

Hmmm... Good question. I'm not sure I understand what you mean by phasing. What I have heard told is that the high-end suffers from attenuators, generally. The direct out in the amp has a "speaker emulation" built in, but I'm not that impressed with it. This is what I have the most experience with. I actually have a second attenuator to get it down to apartment level (the Weber MiniMass, which has the aforementioned speaker motor inside) I haven't run the amp wide-open really at all, so I don't have much basis for comparison. It is also my first tube amp...

I did a segment on the Home Recording Show podcast where I compared different ways to record guitars at low volume, you can check that out if you want. It is basically a comparison of the following:

- Direct out of the amp (with the built-in speaker emulation)
- Line-out from the Weber MiniMass (with cabinet emulation from Amplitube)
- A couple of mics in different positions

All these, unfortunately, have both attenuators engaged to some degree (pretty high degree, I think).

Link: http://www.homerecordingshow.com/2013/05/10/show-213-low-volume-electric-guitar-options-and-more/

 

[Felix]

Hmmm... Good question. I'm not sure I understand what you mean by phasing. What I have heard told is that the high-end suffers from attenuators, generally. The direct out in the amp has a "speaker emulation" built in, but I'm not that impressed with it. This is what I have the most experience with. I actually have a second attenuator to get it down to apartment level (the Weber MiniMass, which has the aforementioned speaker motor inside) I haven't run the amp wide-open really at all, so I don't have much basis for comparison. It is also my first tube amp...

I did a segment on the Home Recording Show podcast where I compared different ways to record guitars at low volume, you can check that out if you want. It is basically a comparison of the following:

- Direct out of the amp (with the built-in speaker emulation)
- Line-out from the Weber MiniMass (with cabinet emulation from Amplitube)
- A couple of mics in different positions

All these, unfortunately, have both attenuators engaged to some degree (pretty high degree, I think).

Link: http://www.homerecordingshow.com/2013/05/10/show-213-low-volume-electric-guitar-options-and-more/

First off, it would have been nice to get a heads up that your clips begin some 33 minutes into the podcast, but I skimmed around and found them without too much trouble.

Next, the speaker emulator is to my ears a little too dampened out in the midrange, "flat" in the sense of "unexciting"... but that might just be me. I like tube amps and good bell-like speakers for guitar, and this sounds to my ears not so much emulated as filtered. Some nice tones come out in the later samples, though. Not the sounds I would go for, but not bad at all. Cabs (and good speakers, say Celestion Blues or Greenbacks, depending) are the way to go. Just my opinion, of course.

As far as phasing and attenuators, almost any attenuator will cause what is called a "differential phase shift", examples of which I have heard -it is like a phase effect in the signal chain, with low depth or blended low- but I can't explain the physics or electronics behind it, being at best a hobbyist.

It is not unpleasant, but there is a phasing in the signal which is reduced in some designs. I first heard it mentioned about the Weber (who make excellent pieces of hardware, however, make no mistake), but since have read -this is my understanding- that any loading, resistive or reactive, will induce phasing, though there are supposedly designs which minimize the effect to such low levels as to be unnoticeable.