Bill Firebaugh: The Well-Tempered Innovator Page 3
Firebaugh: Yes, it is. So I asked myself, "What would happen if I just put a certain kind of grease in there?" I happened to have some saltwater wheelbearing grease, which is quite heavy and doesn't get runny when it gets hot. And I squirted that in there, and gosh, that worked great. I mean, it made a difference you could really hear.
Holt: Doesn't it creep up the sides when it's spinning?
Firebaugh: Well, I had to experiment a lot with the viscosity of that grease, but, no, it doesn't. It's too thick.
Holt: Then it wouldn't leak out if someone shipped the turntable back for repair.
Firebaugh: No. The motor grease isn't thin enough to flow. The platter lubricant does, but in that case, the bearing just comes right out and you could just pour that out. It's a completely nontoxic silicone fluid.
Holt: And now that we've found out how to clean it off things, spillage is no problem. I suppose you know that lighter fluid will do it, too.
Firebaugh: Yeah. Gasoline is one of the better solvents for silicone fluid. The Dow-Corning brochure for their silicone grease lists all the solvents for it. Rubbing alcohol is one of them. It isn't the most effective solvent, but it's very safe, and that's what I always recommend. Lighter fluid of course is gasoline, and that can be dangerous.
Holt: Yeah, but if you use it very sparingly, like on the end of a Q-tip, it would hardly be hazardous. With lighter fluid, you just squeeze it out of the dispenser onto the Q-tip. The worst you can do is set the Q-tip alight, and it would be hard to do that unintentionally.
Firebaugh: Trichloroethane works really well too, and is commonly available. It's used in the electronic industry for cleaning circuit boards. And it's the same kind of stuff Kodak sells as film cleaner for slides and home movies. Camera stores sell it.
Actually, the turntable is much easier to prepare for shipping than the tonearm, because all you have to do is pour the fluid out of the platter spindle into a Ziploc bag, which you hang on to. Then ship the 'table back.
Holt: What about shipping your tonearm? A number of people have asked me how they could prevent that sticky goo from getting all over everything when they ship a viscous-damped arm.
Firebaugh: Well, of course, you don't ship the viscous damping goo. To ship my arm, first you cut the strings, then you remove the damping paddle, then...
Holt: Whoa, now! You cut the pivot strings?
Firebaugh: Yeah, just cut 'em. They're very easy to restring. At least by anybody with some manual dexterity. Then you pry the damping cup off...
Holt: Pry the cup off?
Firebaugh: Yeah. It's held on with double-backed tape. The secret to separating something held on with that tape is a slow, steady pressure. You put a prying instrument under it and apply slow, steady pressure, and it separates. But if you try to do it fast, boy, that stuff sticks like crazy!
Holt: So you dump the goo into a Ziploc bag . . .
Firebaugh: Yes. Scrape off as much as you can from the paddle and well, let them stand overnight over the bag to drain off the rest, then wrap them in grease paper and pack them with the rest of the arm for shipping. Keep the goo until the arm comes back.
Holt: Bill, going back in time a little bit, whatever gave you the idea originally that you could design a tonearm that would be accepted by the high-end audiophile community?
Firebaugh: I didn't plan to sell it. Originally, I just thought I'd try making an arm for myself. Sort of as an intellectual exercise. At the time, I had not the slightest idea of what was going on in a tonearm. But in 1977 a guy named Poul Ladegaard from the Brüel & Kjaer Company in Denmark wrote what I think is a landmark article entitled "The Audible Effects of Mechanical Resonances in Turntables." B&K had this fabulous instrumentation system using Fast Fourier Transform analysis and parallel processing and all that kind of stuff. Actually, I think the main reason they published the paper was to show off the capability of their test instruments, but they were obviously also interested in doing basic research about audio.
I read that paper, and I had the feeling I thoroughly understood what the fundamental issue in a tonearm and a turntable is—stability. It started me wondering about the stability of the arm I was using then.
Holt: Which was?
Firebaugh: I had one of the original AR 'tables, which I had bought back in the dark ages. So I hooked up a high-gain wideband amplifier to my 'scope, and tried to figure out a way of measuring how stable the arm was.
B&K had used impulse testing, but I had to figure out what to use to induce impulses to the arm. The technique I eventually came up with is to straighten out a paper clip and use it to tap on the arm at various places.
Holt: That's a technique I've been using for years, except that I listen to what happens instead of watching it on a 'scope! Put the stylus in a stationary groove and tap on the arm. A poor one will go CLICK; a good one will go CLUNK.
Firebaugh: I used it because it's very easy to generate a pulse that way, and it's very easy to analyze the output and to understand what you've got. I was tapping on those things and looking at waveforms and getting what I thought were pretty good results, but the sound...Well, that needed work.
It was very clear to me that the AR arm had a lot of friction in its pivots. You could see it in the erratic tracking-force measurements you got, and the way the stylus deflected from side to side when tracking an off-center disc. So I thought, "What kind of pivot might give the least amount of friction possible?" Then I remembered what I had read about Henry Cavendish, the 18th-century English physicist, and his experiments into the nature of gravity.
Physicists have known for hundreds of years that the lowest-friction "pivot" you could get is a single long cord fastened to the ceiling. Cavendish used this arrangement to test for gravitational attraction between a suspended bar and stationary objects of known mass, and his results enabled him to determine, for the first time, the mass of the Earth. And Gauss used this type of device when he was investigating very weak magnetic phenomena. I just used the same idea to make a frictionless pivot for my AR tonearm.
Holt: You used a single thread?
Firebaugh: I started out that way, using the AR arm, but it was a complete disaster, of course. It flopped all over the place. It wasn't too bad in the vertical plane because the stylus is resting on the record, so it can't go very far up or down. But torsional movement is completely uncontrolled. It was obvious that I would have to use two cords to prevent the arm from twisting. So I drilled a hole in the arm and fastened a rod across it, and attached the cords to the ends of the rod. That was an improvement, but that thing was still tremendously unstable. That was when I started thinking about viscous damping.
Maybe I've told you that when I was working on this tonearm, I made 81 different very distinct prototypes of it. And one of the early ones had a little tab sticking down in a bowl of STP, the oil additive. I used that because it had fairly high viscosity and I could buy a can of it locally for 50 cents. That did make a noticeable improvement in the sound, but it still had a long way to go. By using these impulse techniques, I tried different amounts of damping. I couldn't change the STP's viscosity, but I could change the damping coefficient by using different-sized paddles.
The more I got into it, the more problems I found. According to my pulse tests, I should have been getting pretty good sound, but I wasn't. Even designs that looked as if they were behaving themselves sounded bad. I had to start questioning my instrumentation.
Then I made a rather important discovery. I had been overlooking an important characteristic of magnetic cartridges: They're rate sensors. That is, you get so many mV of output per cm per second of stylus motion.
Holt: Yeah, they're velocity-responsive.
Firebaugh: They're not amplitude-sensitive. So you can fool yourself into thinking you have a stable system by observing the output from a cartridge, because all the worst instabilities are at low frequencies, where stylus velocities are low. What you have to do is to transform that velocity signal into an amplitude signal. And that's done electronically by what's called an integrator.
Holt: Which is essentially a device that introduces a 6dB/octave treble rolloff across the whole audio band. An equalizer.
Firebaugh: Yeah. You need something that will double the voltage output each time the frequency is halved. So I fed the cartridge through an integrator and gave the arm a tap, and man, that thing jumped all over creation. It was tremendously unstable. And, of course, that causes scrubbing.
Holt: From the vertical tracking angle of the stylus.
Firebaugh: Laterally, too. It just happens at a different place (footnote 1). And scrubbing is the fundamental evil when an arm is unstable, because it doesn't generate orderly harmonics. It generates nasty little sidebands which aren't harmonically related to the signal at all. The unstable motions of the arm may be subsonic in frequency, so you can't hear them directly, but they powerfully affect the rest of the sound.
Footnote 1: Scrubbing occurs when LF motions of the headshell move the armature pivot away from its normal point relative to the average groove path, effectively changing the length of the armature and thus varying the speed with which its tip scans groove modulations. For a given amplitude of headshell vibration, vertical scrubbing produces much more flutter than does horizontal scrubbing, because the armature's at-rest position is at a 15° angle to the groove path.