[isaacrivera]

Hello fellow members! Though I have consulted this site for several months for guidance, this is my first post.

I am curious about other member's experience with tube microphonics. About 4 months ago I upgraded from a 6 years old Cambridge Audio 640A V2 SS integrated amp for a Primaluna Prologue Premium fitted with EL34s. Sound quality aside, something funny happened--I could hear a hissy hum from my listening position and on soft/low music passages, it is quite noticeable. The noise is not affected by volume or preamp input selector. My interconnects are Acoustic Zen WOW! which are shielded. The power outlet is well grounded, there are no ground loops and there is no DC contamination in the line. The power goes through a PS Audio P5 power plant which does not eliminate the noise and then to the amp and CD player. Since I could not hear the noise with the previous amp, I doubt it is caused by EMI/RMI interference either. The hiss/hum on the speakers is responds to a wave: it is grows, sustains, and goes away for some time, then it starts again. This noise wave matches audible noise on the transformer of the P5 power plant, which can be heard if one gets close to it.

The P5, the amp and the CD player are all resting on the same wooden console, as are the Epos bookshelves. The other day, while pursuing through http://herbiesaudiolab.nethttp://  and reading about tube dampers my wife suggested that perhaps the hiss/hum is caused by the vibration of the transformers being picked up by the tubes! I had not thought about that.

Does anyone have similar experiences that would support or counter this theory?

Thank you!

[JakeJ]

From your description of hiss and/or hum it sounds more likely to be a tube that is noisy.  This happens and could be just bad (if the amp is new) from the factory or if old and worn out (ie. you purchased a used amp).  Typically microphonics manifest as a ringing sound due external vibration or sometimes the internal components of the tube start to vibrate after they heat up.  Tapping on the tube with the amp on and fully warmed up with no musical signal would be heard through the speakers, volume set at normal listening levels.  Also noisy tubes are usually, but not limited to, one of the small signal or driver tubes.

Having just checked the Prima Luna website it looks like there are four 12AU7 tubes up front.  Is the noise isolated to one channel or both?  If it's one channel then swap the tubes, one at a time, from one channel to the other and see if the noise follows one tube in particular.  If so then you will know who the culprit is.  If is in both channels then it could be your source or possibly that your speakers are very sensitive and allowing you to hear the noise that is normal.  Also I noted that the website stated there is a "bad tube" indicator for the output tubes but I doubt that works on noise but is designed to show when an output tube will no longer hold bias.

One last thing I would mention is that you stated that you speakers are on the same stand that the electronics are on.  This generally bad due to vibration (mechanical feedback) from them to the electronics.  You should place them on something that isolates them from the rest of the system.

Hope this helps and continue posting as you go through the troubleshooting process.  More info helps us help you.

Jake

[isaacrivera]

Hey JakeJ, thank you for your thoughts. You make very interesting points... a bit more info below...

From your description of hiss and/or hum it sounds more likely to be a tube that is noisy.  This happens and could be just bad (if the amp is new) from the factory or if old and worn out (ie. you purchased a used amp).

Thinking that it may be the amp itself or the tube set I got, I took it back to the shop and had them audition it with me. We used my speaker cables, but they supplied the rest of the equipment. There was no noise like I experience at home there. Only by putting my ear right next to the speakers did I notice a faint hint (which was lower with my own Analysis Plus cables). I think this rules out the amps transformers or the tubes themselves as being defective.

Having just checked the Prima Luna website it looks like there are four 12AU7 tubes up front.  Is the noise isolated to one channel or both?

It's both channels, and volume independent--it does not increase or decrease with volume. It's wavy, it starts, grows and changes pitch, then halts completely for a few seconds, sometimes minutes. It also matches the same pattern of humming in the PS Audio P5 power plant. meaning if I an close to the P5 I can hear its transformer making the same noise pattern as the nearest speaker.

One last thing I would mention is that you stated that you speakers are on the same stand that the electronics are on.  This generally bad due to vibration (mechanical feedback) from them to the electronics.  You should place them on something that isolates them from the rest of the system.

Yeah, at the moment I have no other space, so I was looking into isolation options while I change the furniture to something that will give me a better set up. Doing this I came across tube microphonics and damping, which are new to me. It sounds like my set up might be inducing some vibration...

Again thanks for your observations. I need to start by isolating the components and speakers while I can make room for stands...

[jules]

From what you're saying it sounds as though the the hiss is either caused by or not eliminated by, the P5.

Does the P5 transformer still make these sounds when there's no load, or some simple constant load like a 50-100W lamp?

Transformers usually emit some sort of hum but the "growing, sustaining, disappearing" doesn't sound normal. To take a long shot I'm wondering if you've got a failed/failing capacitor somewhere though I'm ignorant of the circuitry of the P5.

[JakeJ]

Also try disconnecting the source(s) and see if you still get noise, to eliminate them as a problem.

[Austin08]

...or some simple constant load like a 50-100W lamp....

+1 my first though was exactly like that.

[isaacrivera]

The power on my apartment is not great, which is one of the reasons I have played with different power conditioners, finally settling on the P5. Prior to the P5, the same thing happened with a P3 and a BP-1 Ultra. If I bypass the conditioner and connect the amp directly to the wall, the noise is still there on the speakers. Again I have checked and the grounding is good. I have a custom DC filter too.

The P5 makes the noise when everything is disconnected from it or if I turn off all of the outlets on it. And the noise comes out of the speakers if the amp has nothing connected and regardless of input selector position.

After trying different things, the only thing that has somewhat tamed the noise down, but not eliminated it, was to connect 3 PS Audio Noise Harvesters in the same circuit as the stereo.

[rollo]

  Let's start with the speakers. If you cannot manage stands the next best thing is Auralex speaker pads. It appears to me that if both channels are experiencing the noise it is not the tubes.
   Sounds like a power issue. What is the sensitivity of your speakers ? Do you stack your gear meaning sitting on top of each other ? or extremely close to each other ? Are there any commercial stores, restaurant or supermarket in the building ? Are you getting proper voltage meaning 122V or more ?
   Do you have circuit breakers in the panel ? or old fuse type ? How old is the Bldg. ? Back to basics. If all components are off except amp still hear it ? Disconnect speaker cables does amp hum or buzz ? Reconnect one component at a time and listen.
    IMO it sounds more like a power related issue than anything else. Do you have any dedicated circuits in the Apt ? if yes try that one. Are your appliances on the same circuit as your system ?


charles

[Quiet Earth]

Man, it's so hard to troubleshoot over the Internet, but here a few things I thought really stood out :

1. Since I could not hear the noise with the previous amp, I doubt it is caused by EMI/RMI interference either.

2. The hiss/hum on the speakers is responds to a wave: it is grows, sustains, and goes away for some time, then it starts again. This noise wave matches audible noise on the transformer of the P5 power plant, which can be heard if one gets close to it.

1. Not necessarily. It just means that the first amp was immune to the local problem.

2. I think there is a serious issue going on with your power and/or the location of your current system if you have two components that are making strange noises (the amp and the P5). Is there any strange electrical activity happening on the other side of the wall? Maybe a neighbor with a big server, or a shared utility panel for the apartment? You might ask your electrical company and apartment manager to come out and inspect your power. It doesn't sound right to me.

You might also try to set the system up in a different location of the house, just to see if it changes.

Thinking that it may be the amp itself or the tube set I got, I took it back to the shop and had them audition it with me. We used my speaker cables, but they supplied the rest of the equipment. There was no noise like I experience at home there. Only by putting my ear right next to the speakers did I notice a faint hint

3. This sounds like there is indeed an issue with your amp, and that it could possibly go unnoticed under better conditions with different (less sensitive?) speakers.

[isaacrivera]

Hey Quiet Earth, thanks for your observations.

2. I think there is a serious issue going on with your power and/or the location of your current system

There is definitely something fishy going on with my power... Before the Primaluna and the P5 I used to have the SS Cambridge Audio and a PS Audio Quintet power center. The Quintet cuts power if it drops below 110 or above 130 volts. It would be cutting power every 5 minutes or so because the power went over 128 volts or so. The PS Audio power plants condition power first, then store it in batteries and you draw from its outlets continuous power at your set voltage (120v). Before the P5, if I disconnected the Quintet, I would blow a fuse or two a week. The P5 took care of all of that, plus there were some serious sound improvements. But this noise on the line became apparent. Further, changing the amp made it come all the way out to the speakers. Again, with the Noise Harvesters the noise on the speakers was cut back enough that it does not interrupt my listening experience anymore. Adding a custom, strong DC filter made by another member of this community did not have any impact on the noise. The apartment next to mine is mostly not used by the tenant, likewise the one above. The one underneath is lived by an old, handicapped doctor and I doubt he runs anything strange or powerful there. However, all apartments are fitted with multiple light dimmers (mine has 7).

Now I have at least a dozen breaker circuits on my fuse box and the stereo is connected to one of two that control the living room, 15 amps. Nothing else is connected to this circuit, just the stereo, but it also powers the dimmer-controlled light overhead and a light in the bathroom behind the wall behind the stereo. The bathroom and an adjacent closet sit between the stereo and the next-door neighbor.

3. This sounds like there is indeed an issue with your amp, and that it could possibly go unnoticed under better conditions with different (less sensitive?) speakers.

The faint hiss I made reference too I have found to be normal of most amps on most speaker systems. It is also not wavy, like my issue, but just a constant hiss. I have read this is normal and trying to eliminate it would seriously affect sound quality. This is not noticeable at all unless you actually place your ear against the speakers' drivers.

[Ericus Rex]

The wavy in-and-out quality of the noise makes me think something else in your apartment, or in a neighbor's apt is injecting noise into your power line.  In my experience, tube hiss is constant, i.e. non-variable.  Either it's there or it's not.  Think about what might be in your apt that cycles; like ACs, furnaces, fridges, etc.  You'll figure it out.

[raindance]

Get a shorting plug & short the active input. All you should hear is the amp's own noise.

Tubes generally make some noise (tube rush) and are never as quiet as solid state. Changing tubes may help. It is the small signal ones that make the noise usually.

[Captainhemo]

Get a shorting plug & short the active input. All you should hear is the amp's own noise.

Tubes generally make some noise (tube rush) and are never as quiet as solid state. Changing tubes may help. It is the small signal ones that make the noise usually.

Would/could a tube cause the noise to cycle like he is  experiecing ? 

I know it may be a PITA but    unplugging everything else on that circuit and trying it. might be a good idea.  Might even be worth   unplugging everything in the apartment  and going from there ....

-jay

[isaacrivera]

Get a shorting plug & short the active input. All you should hear is the amp's own noise.

Tubes generally make some noise (tube rush) and are never as quiet as solid state. Changing tubes may help. It is the small signal ones that make the noise usually.

If you mean one of those plugs without grounding post, I have tried that. Sounds incredible, but no difference. I also used a volt meter to check grounding. It tests fine. Additionally, I plugged one of those line trouble detectors that will light different diodes depending of different issues. It lights green. Again a strong, custom made DC filter has no effect either. I took the P5 around the apartment, plugging it into other circuits... same type of noise could be heard on its transformers.

Some have suggested there is some noise backwash from all the apartments sharing the ground, but again there is no difference when disconnecting the ground post from the wall. Another suggestion from my hifi dealer was that the boiler of the house is electrical and those send DC contamination into the line. But again there is no effect at all from DC filtration.

All these plus the effect of the Noise Harvesters leads me to believe that there is noise on the lines. Probably the dimmers. Likely more noise harvesters would be the best bet.

Anyhow, my thought at the top of this topic was that the speakers temporarily sharing the counter top with the other components (all sitting side by side about 2 inches apart on a solid pine with metal frame buffet) and all the vibration from the noise on the transformers, maybe, was producing microphonic effects on the tubes.

[raindance]

I was not referring to a fancy connector. Just a pair of RCA shorting plugs. Plug them in, select the input, see what the noise level is. Nothing connected except speakers.

What most folks don't realize is that tubes are very high impedance devices and are susceptible to all sorts of interference.

Also try moving the amp physically away from any component that may have a switching power supply. The noise you describe is not low frequency transformer noise, more likely high frequency interference.

[raindance]

PS: in all my years of having audio gear, mostly tubes, I have never had noise issues except when I placed a tube component directly on top of another component. You need separation.

[isaacrivera]

I see. I'll have to get a pair of short plugs, but other than the cd player 2 inches away, and the P5 3 feet away there is nothing powered near it. If the P5 and cd player are off the noise is still on. Still is curious that the P5's transformer and the speaker noise is the same and not affected by volume levels on the amp.

[raindance]

On second thoughts I don't think the shorting plug will get you anywhere. Here's a question: Is the noise about the same in both speakers?

If yes, it is not a bad tube.

Take your amp and speakers to a friends house and see what happens.

If the problem goes away then you know it is your environment.

[Quiet Earth]

He already did that. Go back and re-read how his AC power is so bad that even a power conditioner cannot tolerate the situation. It shuts down due to improper AC operating conditions.

I would not waste anymore time and money focused on the amplifier. I would make the power company come out and test their power. I would also tell the apartment manager about it too. It could be a sign of something really bad going on, like a failing power service transformer, or something not wired correctly in the apartment.

You're paying good money for utilities and rent,  they should provide good service.

[isaacrivera]

Con Edison? In the NYC area? I will give it a try, but I am not holding my breadth. Monopolies on high demand areas don't feel like they actually need to serve you at all. However, I have assumed they would not do anything based on previous experience and have not actually complained about this.