Newsletter Vol 1 Issue 3

 
           

The Care and Feeding of Motorized Faders

Aug 15, 1997

  Item 1. We need more members!!!

Item 2. Suggested Improvements for Flying Faders

Item 3. The Care and Feeding of Motorized Faders - Part 1

           
 

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Item 1. We need more members!!!
Have you contacted your friends and associates to tell them about this Users’ Group? Please help us track down all of the Flying Faders systems in the U.S. so that everyone can benefit from our information.

An important function of the Flying Faders Users’ Group is to collect ideas for making Flying Faders better. We will be compiling a Wish List of your suggestions. Please drop me a note if you have any contributions to the list, either additional information on items listed or new items.

Item 2.Suggested Improvements for Flying Faders

1. (Jay Graydon 6/24/97) Allow a mode that disconnects individual selected faders totally from the system. When recording machine tracks, many times, I have the faders up full since many of these units are -10 or lower. I use the automation for mutes as to keep the noise down when track sharing and fader moves as well. Since the automation is active (faders set to not respond), after the first pass, the faders that are selected to not look at the automation go to the snapshot level which is not maxed out on the fader but is slightly pulled back.

The bottom line is a mode that will take the fader out of the automation mode completely meaning snapshots will not be recognized.

(This problem relates to the bumper zone at the end of the fader travel. We have reserved a "keep out" area to avoid hitting the end stop of the fader on fast steps. As a result, the servo cannot move the knob into the last .7 dB of the active fader track. A similar zone at the bottom of the fader limits the "pull down" at the bottom of the fader. At the bottom we are usually into the hopoff area of the fader travel, so there is not a problem, but if the fader/console use a 3-wire audio connection to the fader that has marginal kill, the pull down becomes more critical. Dale)

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  1. (Jay Graydon 6/25/97) When turning off the automation (motor supply), the faders pull back a little. Is there a way to eliminate this problem?
  • (I believe this knee jerk is caused by the shutdown sequence of the power supplies. We have never taken a detailed look at the problem. In fact we have never documented what happens on a sampling of systems when they are shut down. Since various size systems should have different voltage decay characteristics, the symptoms might vary. If you would like to help us understand this problem, drop me a line with a description of what your system does when you power down. Dale)
  • Your suggestion?

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    Item 3. Motorized fader types -The Care and Feeding of Motorized Faders - Part 1
    By Dale Manquen

    Introduction
    The first 20 years of my career was devoted to the design of professional audio tape recorders. During that time, I never paid much attention to the introduction and growth of Neve’s Necam automated fader system. I, like many others, just chuckled and shrugged when I first saw faders moving. Little did I realize what lay ahead for me!

    In 19xx I began consulting for Joe Martinson at Martinsound on the design of a virtual console. The console was to have a virtual control surface that included moving faders, and an audio rack containing all of the analog circuitry - a Euphonix-like system. We actually built a 32-channel breadboard that had some excellent scanning and display technology, but the magnitude of the tasks to develop a full-blown system were humbling.

    After surveying the market at the 1986 AES Convention in L.A., including the Trident DiAn, the Harrison Series 10 and a Calrec automated console, Joe decided to redirect our efforts to bring a stand-alone moving fader automation system to market. Necam and GML seemed to be doing well, but he envisioned a system that would surpass anything available. We spent the next two years, with the indispensable help of Morgan Martin, Shawn Micheal and David Wood, designing a next-generation moving fader automation system which was named Flying Faders. My assignments included the development of the motorized fader and servo circuits, and the design and packaging of the servo card cage and system power supply. The other team members developed the scanning hardware and the software.

    December 1988 saw the installation of the first two Beta test Flying Faders systems at Powertrax and Groovemasters studios. In March of 1989 we delivered the first system for a Neve console to Rumbo under an exclusive distribution agreement with Neve, and the rest is history. But let’s get back to the development and history of the motorized fader.

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    Fader development
    Our choices for motorized faders were meager when we started the virtual console project. Penny and Giles had a motorized fader, but the cost and complexity did not impress us. We were too conservative to accept this fader, especially since it could not be operated manually if the drive cord failed. (Unlike a normal linear fader, the knob connects to the rotary audio attenuator with only the drive cord.)

    George Massenberg had solved the problem by buying only the resistive element from Penny and Giles, and then building the rest of the fader himself.

    We sought a compromise by motorizing an existing P & G linear fader with our own drive components. My first design utilized a motor at one end of the fader with a drive cord that passed through holes in the end plates of the fader. Although this design worked well, the attachment of the string to the fader slider was buried inside the fader, making servicing difficult. This design used only one pulley, with the motor capstan providing the other turn-around. I even developed a simple adjustable pulley mount that simplified tension adjustments for the drive cord.

    (This same basic layout is now becoming popular in low-cost faders that utilize toothed belts. These designs attach to the shank of the slider for convenience, rather than at the center of mass where I first attached.)

    One of the design weakness of the motor-at-one-end design is that the tensions in the two sections of the drive cord - call them the driving and returning strands - both pull on the motor in the same direction. This results from using the motor as the turn-around device and the drive device. The load on the motor bearings is much higher than a design that separates the turn-around and drive functions. The little motor that we were using, which is identical to the motor used on the newer toothed belt designs, has a very thin shaft and a bushing for a bearing. This creates very high loading and rapid wear.

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    We were concerned about the length of our first version of motorized since we had a pulley sticking out on one end and the motor on the other end. This required an extra inch in fader length, which in some consoles was hard to come by. So I went back to the drawing board….

    The second version placed the motor at the center of the fader. This allowed us to move up in motor size, so we selected a motor with a larger shaft and a ball bearing rather than a bushing. This just about doubled the cost of the motor, but we felt the improvements were necessary.

    (I am reminded of a trip I took to P & G a few years later to discuss ways of saving money on our faders. Their primary suggestion was that we drop the ball bearing and use a bushing as they did. After a half hour tour that included a long stop in their durability testing lab where I saw many motorized faders on life test, I asked what the primary source of failure was on their faders. It was the bushing!)

    Our side-saddle design puts all of the drive components out in the open for easy maintenance. Each of these components include the two pulleys, the motor and drive capstan, the drive cord and the string attachment, will be covered in detail below. In addition, the slider bushings and lubrication, the slider spring fingers, and the slider touch sensor wiring will be covered. The numerous variations of each component will be described in detail so that you can determine which versions comprise your batch of faders, and the proper inspection and maintenance for each type.

    The first Flying Faders systems were shipped in December of 1988 using P&G 40461 faders. This initial version, which we will call Type I here, is characterized by 3 features:

    The slider bushings are PTFE (similar to TeflonR) impregnated with graphite.

    The drive cord is attached to the slider via a collar and screw that mate to a threaded hole tapped directly into the slider frame metalwork.

    The Touch Sense connection from the slider frame to the wiping finger consists of a jumper wire attached with conductive epoxy.

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    Our work with P&G on improvements resulted in several enhancements that were incorporated into the 40xxx fader which we will call Type II:

    The slider bushing was changed to a green plastic named Tercite.

    The wire brushes were modified to have more strands of a smaller gauge wire to reduce wear on the fader tracks

    The drive cord attachment was changed to a threaded fastener pressed into the slider frame. The collar was replaced by an assortment of metal and nylon washers. The screw size dropped from 2-56 to 0-80.

    The Touch Sense connection became a strand of brush wire that was bent backward to pass through a hole in the slider frame. The wire was held in the hole by conductive epoxy.

    Somewhere along the way P&G learned that they could use solder to attach the touch wire to the zinc slider frame.

    The next major revision was the introduction of lubricant containment. This Type III fader utilizes rods, rubber bumper washers and sliders that are treated with a substance that repels the Silicone lubricant, keeping the lubricant from migrating away from the rod and bushings. The improved lubrication permitted a return to the original pure PTFE bushing which we used during our original development work, but found to be prone to lubrication loss.

    This configuration presents a minor problem with compatibility since:

    Putting old rods or sliders into a Type III fader will defeat the lubricant containment.

    Putting new sliders into an earlier type fader will not stop lubrication loss at the ends of the old rods.

    (To be continued…)

    Bye for now!

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