Hum on Tube Amp - Can't find source

I’ve had a number of tube amps over the years, both integrated and headphone. By design, they all produced some amount of hum. Even though I love the sound tubes produce (which in stereo mode, rarely ever 100% correctly sum to mono in headphones), I couldn’t tolerate the hum (and I’m not referring to the physical or mechanical transformer hum) the amps produced. I no longer have the patience for tubes. I personally now prefer the low distortion and low noise floors solid state provides. I believe what you’re hearing @ervikingo is hum produced by the amps, and it has no relation to the quality of AC power you’re supplying it.

@ervikingo There’s been no mention yet of biasing. Have you checked it for all tubes? From the Manley Snapper manual, this is the rated Noise Floor spec: Typically 105µV = -77dBu A-WGT Typically 388µV = -66dBu unweighted. Depending upon how close your ear is to the speaker (inches away?), with that type of noise floor spec, my ears would probably hear some hum too (especially at -66 dBu).

Manley; The Snapper manual

@jaytor

My amps have no audible hum with my ear up against the speakers.

I’m glad to hear that.

All tube amps don’t have hum problems, and all solid state amps are not hum free.

I would agree with you. All of the tube amps I’ve ever owned, did (have a certain amount of hum). I prefer my noise floors to be in the -95 dBu area (exceptions being vinyl playback). With that in mind, I could never find a tube amp that approached that. I’m not saying they’re not out there, I just however gave up my quest trying to find one. When it comes to tube headphone amps, I also don’t like the fact that rarely have I ever heard one that sums to mono, correctly (like SS does) 100%. This matters when listening to any audio mix, as the mixing engineer many times will pan certain sources to center (mono). Many wouldn’t notice this, or care about it, but I do.

@larry5729

I read an article and they said tube amps hum. That would drive me nuts.

Lucky you’ve never been there. The sound produced by tubes is many times euphoric, but that hum can drive some nuts (like me). IMO, sometimes there’s a trade-off with tubes. To get that liquidity, you sometimes have to also tolerate (ignore) the hum that sometimes goes along with it, or, if it is present, some don't even notice it.

@ervikingo 

I'd love to look at the videos you posted, but I don't have Dropbox, and don't want to sign up for even a trial membership. Can you think of any other way to post them? 

After powering up the amps, how long before the hum appears? Does the hum then remain constant for the rest of the time after it first surfaces, or does it come and go? 

the changing glow on the tubes. 

...on all tubes at the same time?

Once the noise starts you can't bias them as the voltage cycles.

I'm not 100% sure, but I don't think that's normal. Of the one stereo tube amp I've had in the past with adjustable bias, I never witnessed anything like that when biasing the tubes. Once the tubes warmed up, the bias values were stable. I've worked on many high power FM transmitters with tubes in the past, and never saw tube bias fluctuate very much there either. Once set, it remained there for a lengthy period of time.

I'd like to thank you @ervikingo for staying engaged in the conversation. Many come to this board, throw out a question or problem they're experiencing, and never show any interest, or offer any feedback after that.  

For those interested in monitoring their AC power quality, this is a cool little logger, which can also read some real-time values.

Simple Logger® II Model L261

@ervikingo

I’m going to upload to youtube and post a link

Cool! Thanks!

I have asked the power company to come test their system.

They’ll possibly pull the meter (if they do it quick enough, your generator won’t kick on), check some connections, and they *might* put a logging device on your feed (to monitor your power for a period of time). If you’re around when they get there, they may ask you some questions as to the problem(s) you’re experiencing. Some power companies are also more concerned for their customers needs than others (so be aware). If I remember correctly, most electric companies shoot for 120/240 volts +/- 5 volts. If your voltage fluctuations are within that tolerance, they might ask you then to call an electrician, and have your internal wiring checked out. Technically your local power company is typically not responsible for anything past the meter, so most times they won’t want to enter the property if they don’t have to.

Unfortunately, the link you provided above does not work. I’m guessing it’s for a surge protector you’re using.

I notice that you have an ATS, but yet the SS amps are quiet with it. Would I be correct in stating that the hum is in sync with when the amp puts through audio (ie, the hum starts at the exact time the amp has warmed up, and is now passing audio)?

I have to ask this question. To hear this hum, are you putting your ear against your speaker, or can you hear it from 3’ away?

I’ve been at this for weeks.

Hum drives many audiophiles a little crazy, because many of us spend thousands of dollars on equipment, expecting after hooking it all up, to have dead quiet backgrounds. As frustrating as it can be, that unfortunately is not always the case.

and a projector

Does unplugging the projector have any effect?

If your amp has them, make sure to run the rear impedance selector switches in the 15K position (it looks like not all Snapper models have them).

It’ll be interesting to see if installing 12AT7 tubes has any effect on the hum. I think it will.

I just stumbled upon a review of the amp:

Soundstage.com Home Audio Equipment Review

Here’s a few opinions on substituting 12AX7’s for 12AT7’s:

Can I substitute a 12AX7 tube for a 12AT7?

@hiend2 

Try a solid state unit...

ervinkingo has tried that already, and the solid state amps don't hum. Please look back at some of the past comments.

@donavabdear 

I love tube amps but I'm thinking they are such a pain. 

I agree with you, and that's one of the reasons why I no longer incorporate them into my systems.  

@hiend2 

Try using an extension cord and plugging them in on other circuits

ervikingo has tried that already.

@ervikingo

When it comes to AC power, audio gear, or electronics or electricity in general, I have never seen or heard anything like that ever before. Thanks for sharing the video! Wow, WHAT is going on here? And both amps do this?! Plugging one of these in at a completely different location should also tell us something. Has that been tried yet?

@jea48

did you start up the generator and transfer the load of the ATS to generator? You would be off line of the Utility Power Co...

Great suggestion! Since you can’t just pull the electric company meter to simulate a power outage, the ATS would need to have a special function switch to power up and transfer the load. Not all ATS’ have this switch and function, but it’s worth a look. Many generators and ATS’ have test switches, but don’t always transfer the load.

@stevencason

I had this issue for years. Turned out to be my Rel subwoofer. I grounded it to the preamp and it disappeared.

Crazy.

@jea48

Are you sure that is the whole house SPD, (Surge Protection Device) you have?

Good call! Let’s see. Hopefully it’s the TPS3A11 version, if the service drop is single phase.

Siemens TPS3 External or Wall Mounted SPDs

@jea48 

speaker wire it was it was causing an impedance mismatch for the output transformers for the amp.

Wow, these tube amps are more sensitive then I thought. Come to think of it, I was really into tube headphone amps for a while. I discovered that they too were very sensitive to headphone impedance, when it came to low level hum produced by the amp. I weighted the issue, and concluded that the headache just wasn't worth it. I was also many times hearing sporadic plinks, plunks, and noise bursts with tubes, and that drove me a little crazy too.  

@ervikingo

The unit was biased and received a complete test. Unit passed all factory specs.

I’m assuming you sent it in, because of this problem? If it came back with a clean bill of health from Manley, it sounds like this problem was not taking place when they had it on the bench, otherwise I’m quite sure Manley would have contacted you about it (yes, no, maybe?).

@builder3

ervikingo reports: "there is no mechanical hum on the amps; I have noise on speakers."

@ervikingo 

they had non OEM inline fuse holders

Curious as to how they got that way in the first place (I'm sure we'll never know)?

@imhififan @ervikingo

Have you tried connect a different pair of speakers on your Manley Snappers?

Another good point. The manual states: Recommended Speaker Load: Optimized for 5 ohms

Do you know what impedance your speakers are rated ervikingo?

Once the noise starts you can’t bias them as the voltage cycles.

To me, this is the most concerning factor in this whole scenario.

Here’s a few other tidbits from the manual:

-For the power tubes in our amplifiers, after a few years if you notice a small revolt going on where several of the output tubes are misbehaving or getting hard to bias, you might consider doing a full re-tube.

-Three tube types that are electrically and plug-socket compatible with the 12AT7A dual triode include the 6021, 6679, and the ECC81 (I find it a little interesting that they made no mention of a 12AX7 here).

-Never operate the amplifier without a speaker load, or suddenly disconnect the speaker load while the amplifier is producing a signal. This risks punch-through of the enamel insulation covering the transformer’s internal magnet wire. Permanent damage to the output transformer may result 

-Additionally, it is best to cut power to the Snapper when not in use rather then leaving the power on indefinitely. This will enhance tube and system life.

@ervikingo 

I wonder if sending the tubes out to be tested might not be a bad idea?

TC Tubes

Desert Amplifier Repair

@jea48 

"Manley Snappers Blowing Tubes (over and over)"

Great catch (although at the same time, possibly a red flag)!

@ervikingo 

I did try with my other speakers (Aerial 8b) and noise is present. 

Good to know. OK, can cross that off the list. 

Here’s some highlights from the jea48 linked Tubes Asylum discussion:

-check the bias as they power up, and let them settle in for a bit (like 20 mins) for a final check.

-do not buy new tubes for hi-fi amps from guitar tube suppliers. Buy them from hi-fi tube dealers. Tubes (even matched quartets) sold by most guitar outlets are specially selected to distort early (low transcoductance tubes), therefore they run out of bias adjustment pretty quickly on a HI-Fi amp and there goes another tube!

-Manley has checked out the amps (one of them twice) and says there isn’t anything wrong with them.

-I have one Snapper that has been back to the shop once. It seems to be holding its own ok in terms of not blowing tubes. The other amp is a different story. It just came home from its second trip to the shop and after two hours of use, blew its B+ fuse and two of the tubes, separating the center post of the two tubes from the tubes themselves.

-Try plugging the monoblocks directly into the wall outlet and check the bias to see if you have better bias stability (bypassing any power conditioners).

-When you pull output tubes in and out on a regular basis, we have a tendency to stretch out the tube pins and even can cause tiny stress cracks on circuit board..Now this leaves you with low bias or intermittent bias or no bias voltage many times therefore causing tubes to burn up. I don’t know how much technical knowledge you have on this kind of stuff, but I would re-solder the tube socket connections and tighten the pins inside the sockets or even replace the sockets with better ones

-Manley’s have not-so-good sockets in them.

-yanking tubes in and out of both amps, he could very well have bad sockets in both or loose solder connections at the very least

-We are rebiasing the amps each time we replace the tubes. We recheck the bias every few hours and the amps have never held bias well. We are terrified of damaging the output transformers, power supplies, speakers, and everything else. My husband and I have been audio enthusiasts for almost 30 years and the hobby is becoming more stressful than fun with the problems we have had with these amps. We have spent many thousands of dollars (money we don’t have) replacing tubes by the octet since we bought the amps, not to mention the shipping back to Manley.