Saturday, February 18, 2012

Tube Dampers

I have a Dared MC-7P preamp presently in my rig and out of the box, it was a decent but not particularly spectacular sounding piece of gear. There were a few annoying things about this particular piece of equipment that just made it fall short of being a really great little no nonsense preamp. In my investigations (I love taking off the cover off of such equipment and pouring over the PC board - I think this is fun and describes part of my inbred geekdom), I discovered that in some cases well accepted design concepts were used. However, there were a few things, like ground loops - the topic of several other blogs - that stunted its potential.

Fast forward beyond the post-surgery trace cuts and elimination of wiring redundancies, this preamp really started to sound decent. After additional tube swaps, the clarity and detail came alive and proved to me once again that an idea conceived in the R&D lab was not properly implemented by the production team. It is unfortunate that these two worlds are so far apart since the things I did to transform this gear - especially removing the ground loops - cost little if nothing to implement AND transforms how this particular piece of equipment could be priced. To me, that's like leaving money on the table in a sale and something that seems to be fundamentally wrong with high end manufacturers, Chinese made or otherwise.

So after proper tube burn in (this took a mere two weeks), one day the tonality and balance snapped to attention as if a new piece of equipment was suddenly in place. I was elated to the sound since my particular biases are in timbre and body resonances of acoustic instruments. It seems that the vast majority of loudspeaker and equipment designs ignore this all important property and on that day (let's call it B-day for short), on B-day, tears literally dripped from the corners of my eyes. I was entranced as was my wife who too heard this remarkable transformation.

Well, you get the picture that something happened and everything just settled in. I had been emailing someone who contacted me encouraging him to attempt this same modification (a free PDF document of what I did is available if you just send me your email address in a request). Long story short, he achieved similar results so much so that out of gratitude, he sent me some tube dampers.

As you may already know, everything resonates at some frequency; everything resonates. Some resonances appear within the audio band and when this happens, it is a NASTY thing.  But others when they appear out of the audio band can still impact sound quality as infrasonic and ultrasonic vibrations. On B-day, it seemed that this little preamp could not get any better. It was dynamic, detailed, quiet, and most important of all if you've been reading any of this blog, musical. After B-day, things sounded so much more realistic, playing music with which I was intimately familiar sounded like a whole new performance, there was that big of a change. On B-day I had not, however, addressed the resonances in the tubes, and one that I feared one day would need attention.

Last Friday morning, as I was finalizing my tax information, a delightful surprise appeared in my mailbox, completely unannounced. This same person - out of the kindness of his heart - sent me two pair of Levey Tubes' dampers. It was almost as if he were clairvoyant and could somehow hear my system across the miles in the frigid white north of Minnesota. Without delay, I powered down the Dared and slid them onto the rectifier (a Sylvania 5U4G) and driver (an RCA 6V6GT) tubes. What happened next took a while for me to sort out.

Tubes get hot - very hot - and when touching them with oily hands or putting something on like tube dampers, there will be a period of time when the odors that waft into the listening room become rather unpleasant and even obnoxious. Such was the case where, although the odor was not entirely unappealing, it was indeed foreign and invasive, annoying if nothing else. Struggling through this burn-in period may be much different than that of the B-day tube burn in since in that time period my nose, eyes, and throat were not inconvenienced. But I will persist and persevere after hearing what I am about to say.

In a word, they worked! So what happened? Go up to your speakers and briskly rap the side with your knuckles. What you hear is the natural resonance of the speaker cabinet.  Rasonances are unavoidable since everything resonates, tubes included. To further deomnstrate this to yourself, play something at a reasonable sound level and put your hand flat against the wall midway against its length and height (if on a stud, move 6" left or right). You will notice that the wall itself moves gently underneath your hand in response to the sounds created by your stereo. This is the natural resonance of the wall and it too is unavoidable. The resonances you feel under your hand may be excited at different tones so this natural resonance can occur at more than one frequency. So it is with the glass envelope that surrounds every tube.

As the sound level increases, so does the intensity of this resonance. During loud passages, you can imagine the glass in the tubes wiggling in and out just as the sheet rock did underneath the flat of your hand. These gyrations occur in the floor, walls, and ceiling along with anything else in your listening room (ever heard a window pane resonate, or wine glasses buzz on a glass shelf, or a picture rattle on the wall?). So it is with the glass envelope of a tube - it resonates.

Fortunately, resonances can be treated. In listening rooms, tapestries, sound absorption panels, and rugs can help tame those annoying little buzzes that interfere with what the acoustic information your speakers are trying to convey. Such buzzes and resonances are often at such a low level and so familiar that they are ignored by the ear-brain biological mechanism and disregarded as nonsense noise. BUT it is during this neural-processing step wherein the attempts to eliminate these annoyances, also loses other acoustic information.  Much like turning a tone control up or down to compensate for speaker driver inadequacies, resonances too transform what cold be into something that is just plain nasty.

The tube dampers tame resonances in the glass envelope of a tube. If you gently tap a tube with a small piece of metal like a ring on your finger, you will hear a tiny clink or tink. This sound is the natural resonance of the glass envelope. Combined with the mechanical coupling to the rod-mounted pieces inside the tube, these tiny mechanical resonances are added to the electrical signal inside the tube much like the Doppler effect changes the pitch of a car as it approaches.  One would think that such minute resonances would be imperceptible however that is not the case. Because of the gain the rest of the stereo creates, these mechanical resonances are in effect fed back into the low-level amplification stage and thus re-amplified and the resulting distortions re-amplified again and again.

If you have ever driven in a car with a tire out of balance, you know that there is a certain speed at which the tire wobbles wildly and at other speeds it seems to be just fine. But once the tire is balances properly, you feel the total impact of how this imbalance affected the feel of the car at all speeds. You realize that although not resonating wildly, it indeed changed more than this single resonance point and only until it was gone did this effect become obvious at all speeds. So it is with tube dampers and other resonance removing products.

What I heard was much like a vacuum cleaner sucking out the garbage from in between notes. Individual resonances in strings became more defined and echoes faded away in a smoother, more natural way. The best way to describe the effects is as if I were listening to the quality of the master mix itself placing the entire playback system in the recording booth, the transformation was this complete. Even watching movies, the soundtracks are tranformed into delightful melodies that even seem to improve the visual images. Impossible, yes, but the tiny distractions of these minute resonances once removed permitted my brain to be less busy process out junk information and enjoying everything else more.

So now, the level of my acoustic enjoyment has shifted once again as I hear more things from unfamiliar source material. Once identified, I hear these same revelations in all source material improving the overall quality and enjoyability of everything I play.

So the lesson is clear: do what you can to tame resonances. Take this lesson and apply it not only to your tubes, but also to the rest of your listening room, as will be the subject of the next blog.

Yours for higher fidelity,
Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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