Application Note 25 - Plastic Element Pot's
- While plastic element potentiometers and faders have major advantages over the step type units, they do require some lubrication to extend their trouble-free life. Problems associated with malfunctioning or dirty elements include noise microphonics, miss-tracking of dual controls, and even dropouts. And almost totally neglected has been the effect of thin film contamination on the total harmonic distortion of the audio signal, including the tendency of this distortion to lie in the more easily audible high-order harmonics.
- APPARENT ACTION OF THIN-FILM CONTAMINANTS
- As an alternating current signal voltage passes through the zero voltage state, cu rent ceases to flow (we're assuming a purely resistive load here); if a thin film of contamination is present, current may not start to flow again until sufficient voltage has built up across the contaminant so as to break it down. The result is a small notch in the signal which in sound is not dissimilar to the notch distortion of a class B power amplifier. The characteristic sound ranges from a "grainy" quality up to a harsh "glassy brilliance" overlaying the music.
- THE USE OF Stabilant 22/22A/22E
- By applying a thin coating of water-diluted Stabilant 22 to the plastic element, the noise, dropouts, miss-tracking and these thin film distortion effects can be eliminated. While Stabilant 22A is thin enough to do the job, it is thinned with Isopropyl alcohol, (Stabilant 22E is diluted with ethanol) and many plastic elements are adversely affected by these diluants. Therefore, a suitable lubricant can be prepared by adding three parts of hot water to one part of Stabilant 22 (the concentrated form). Allow to cool before use. When applying, use only a small amount, perhaps one drop at the most, and vigorously cycle the fader to distribute the film the entire length of the track! If the film thickness is too great a phenomenon called hydroplaning could occur. This is where the contacts push a film of the lubricant ahead of them, causing it to increase in thickness until immediate contact is lost between the very-low pressure of the wiper fingers and the plastic element. This is a case where more is NOT better!.
- A SIMPLE VERIFICATION THAT AUDIBLE DISTORTION HAS BEEN REDUCED
- If you want to do a comparison of the distortion effects of thin film-contamination, it is suggested that only one input channel be treated (including all the IC's, switches and connectors which should be treated with Stabilant 22a), and then and compared with an untreated channel. The difference us usually audible as a smoother, more musical sound, on the treated channel.
- Again, keep the film thickness to a minimum. don't use Stabilant 22A or Stabilant 22E on plastic element faders unless their manufacturer OK's the use of isopropyl alcohol (commonly called isopropanol)., or in the case of Stabilant 22E, with ethanol.
- Reference is made to Technical Note Number 24 - "Effects of Stabilant 22 on Harmonic Distortion in Connectors', Application Note 4, "Microphone Connectors", Application Note 3, 'Schadow Switches', Application Note 11, "Recording Studios", and Application Note 12, "Broadcast Equipment".
Stabilants™ are a product of Dayton Wright research & development and are made in Canada
NATO Supply Code 38948
15 ml of S22A has NATO Part # 5999-21-900-6937