Application Note 4 - Microphone Connectors

Application Note 4 - Microphone Connectors

Background:
Microphone connector problems of the type such as breakage at the soldered joint between the microphone cable and the pin or socket extensions have overshadowed many of the other problems inherent in any connector carrying a low-level signals. These include microphonics in the connector itself as well as degradation of the signal to noise ratio both of which are caused by erratic contacts. 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.

Some manufacturers have resorted to the use of gold-plated contact means in order to ensure reliable contacts, however this by itself has almost no effect on thin-film contamination.

Apparent action of thin-film contaminants causes distortion.
As an alternating current signal voltage passes through the zero voltage state, current ceases to flow (we're assuming a purely resistive load here); if a thin film 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 harsh 'glassy brilliant" coloration.
The use of Stabilant 22, Stabilant 22A or Stabilant 22E
By applying a thin coating of either Stabilant 22, Stabilant 22A or Stabilant 22E to the contacts in an XLR or equivalent connector, these thin film distortion effects can be eliminated along with most cases of connector microphonics and signal to noise degradation. Where fanning strips are used to pick up the signal lines from remotely locate microphone jacks, the fanning strips should also be treated with Stabilant. This also extends to any edge-card or other connectors used to connected the fanning strips and/or lines to the individual input modules.
Results that are to be expected:
It is suggested that only one mike channel be treated initially and compared with an untreated mike channel. All connections from switches to IC sockets as well as the input connector should be treated! The difference us usually audible as a smooth more musical sound on the treated channel.
Precautions:
Do not treat condenser microphone cartridges with the Stabilant materials, in such a way that any of the material gets on the insulator between the back and diaphragm electrode connections. The resistance between the back electrode and diaphragm electrode must be maintained at extremely high levels; Stabilant across the insulation would lower this. However, Stabilant may be used on the XLR or equivalent connectors without concern when it gets on the connector insulation. There the leakage resistance will stay so high as to be ignored.
Reference:
Reference is made to Technical Note Number 24 "Effects of Stabilant 22 on Harmonic Distortion in Connectors".

Revision 2

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