[Last printing 2002-08-22]
J. Brown convened the meeting in the absence of Working Group Chair Ray Rayburn and Vice Chair Werner Bachmann. The agenda and the report from the previous meeting were approved as written.
J. Woodgate reported on the meeting of Task Group SC-05-02-F held on 2002-05-09.
A proposed draft, AES32-TU, has been published as a Trial-Use Publication. The current goal is to monitoring the trial use. Members present considered that a revision or amendment of the document is now necessary.
The draft specifies a high-quality connector, and there were suggestions that others should be included. It was suggested that the insistence on including only the SC connector had caused a loss of interest in the project. IEC SC 86C has standardized several new connectors and it is not known whether any of these are likely to be used for audio. R Caine mentioned a connector designated as 'ST1', recommended for use with MADI and FCDI, of interest to SC-02-02 as a connector already in use for AES3. A dual version has been adopted by an ISO committee. Caine was invited to submit a document on the subject, preferably with proposed texts for an amendment or a new document.
Gaunt considered that the type of connector was less important than the signal protocol. The chair suggested a set of tables showing which connectors, fibre types and signal protocols worked together and which did not.
It appears unacceptable to let the existing AES32-tu draft go forward to publication as a full standard; it needs to be reviewed for further improvements. It was agreed that, at the present stage of technology, the document should be a Report of what is actually being used, rather than a standard specifying what shall be used.
It was agreed that a 'user' survey should be carried out, to determine which connectors are actually in use. A form was designed (see a plain text version at the end of this report) and some responses were obtained during the Convention. Responses would be collected by the Standards Secretariat and sent to the Task Group. The closing date for the submission of responses was set at 31 July 2002. The draft was then reviewed in detail:
The following text was agreed: 'This Report mainly deals with connectors for use with IR of wavelengths 1300 nm and 850 nm. 1300 nm is most widely used, while 850 nm is occasionally used for graded-index applications.'
It is possible that more terms should be defined, if really necessary. The texts in the Glossary need not be as formal as that of a definition.
Additional connectors, ST1 and MTRJ should be mentioned, together with any others found to be in significant use according to the results of the survey. More information should be submitted on the ST1 (Caine) and the MTRJ (Gaunt) connectors.
It was stated that IEC MT 61806 looks to AES for input on professional applications of optical fiber.
AES-R3 has been issued as a project report. Current goal is review of this document with a target date of 2005-10. No action required.
The work done by members of SC-04-04D on a digital microphone connector will be used by M. Natter to develop mechanical specifications for the connector. It is our hope to have that material prepared for inclusion in the IEC XLR standard as an amendment during the next maintenance cycle (roughly three years). The Secretary of SC48B has been notified. The digital connector should include the option of a capacitor for the concentric connection of the shield to the shell. Current goal is a standard. Target date is 2003-05.
The project intent is to develop a specification for a jack that will take both international 60603-11 jacks and B-gauge plugs. The original project initiation form or a new one will be produced as soon as possible. A. Eckhart has previously indicated that such a connector exists, and volunteered to document it.
The new intent is a Performance Standard for both male and female connectors that includes performance limits, defines test fixtures and methods, and defines an objective for each generic type. The goal is a PTD. Target date is 2003-10.
At least six connector types are anticipated, as recommended in the draft X13 document. Two are cable-mounted types, both male and female, intended for the termination of both microphone and line level circuits. These connectors should contain a concentric capacitor to terminate the shield to the shell at radio frequencies. Two connector types, male and female, are intended for use within equipment, and according to the recommendations of SC05-05, should offer greatly improved contact between the shells of mating connectors, greatly improved contact between pin 1, the shell, and the outside of the chassis (or shielding enclosure), and small radio frequency bypass capacitors between pins 2 and 3 and the shell. Two connector types, male and female, are intended for use on wiring panels external to equipment.
M. Natter reported on research work on several pre-production prototypes of a male cable-mount connector incorporating a capacitor of concentric construction. B. Whitlock reported, via email, on preliminary measurements of concentric capacitors. Measurement techniques, including suitable test fixtures, were discussed. The test jig should allow determination of the impedance of the capacitor over a wide frequency range by the measurement of the voltage divider ratio when a generator of known impedance drives the capacitor.
Woodgate described a test jig he has constructed that connects the center conductor of a coaxial connector from the generator to the shield connection of the concentric capacitor. The shell of the coaxial connector is connected nearly concentrically to the shell of the connector in which the concentric connector is mounted. The cable shield also connects to pin 1 through a suitable ferrite bead. The center conductor of a coaxial feed to an rf voltmeter (spectrum analyzer, network analyzer, receiver) connects to pin 1 of a mating connector and the shell of that coaxial connector is connected to the shell of the connector holding the capacitor being tested. The test jig must be qualified (that is, its effectiveness should be determined) by replacing the capacitor with a copper disc that short circuits the generator but makes contact with pin 1 in the same manner as it would with the capacitor, and measuring at the same point as before. Under the short circuit condition a very high value of attenuation should be measured over the frequency range of interest. Brown noted the need for measurements that test for detection of radio frequency energy by a differential input stage connected when signal is injected in the same manner as in the Woodgate tests.
Natter and Woodgate will continue work on one or more prototypes of connectors that include a concentric capacitor and measurements of their performance.
Commonly used panel-mount connectors with mounting flanges that contact the outside of the chassis or panel were seen as nearly ideal for contact between the shell and the panel. Some redesign is needed to reduce the impedance (principally the inductance) of the connection between pin 1 and the chassis by shortening the signal path. This may be accomplished by connecting pin 1 to the shell within the connector.
Male and female connectors were described to meet the requirement of insulating XL connector shells from a mounting panel external to equipment. These connectors require a capacitor between pin 1 and the panel and another between the shell and the panel. Because of the way SC-05-05 intends that these connectors be used, these capacitors can be conventional types having good high frequency properties. It was noted that the capacitor between the shell and the chassis can be subjected to considerable stress from ESD, and should be of a type suitably rated for that condition.
The intent of the standard to be developed needs clarification. J. Woodgate will put a summary of IEC SC48B documents on CAT6 connectors on the reflector. Current goal is a PTD. Target date is 2003-05.
Secretariat note: at the subsequent meeting of Subcommittee SC-05, the proposed clarifications were adopted with minor amendments so the the scopes now read:
"The scope of the SC-05-02 Working Group on Audio Connections shall include, within the bounds of the scope of SC-05, new usage, description, and contact designation for connectors for audio and ancillary functions."
"The scope of the SC-05-03 Working Group on Audio Connectors shall include, within the bounds of the scope of SC-05, documentation of established connector usages for audio and ancillary functions."
The next meeting is scheduled to be held in conjunction with the AES 113th Convention in Los Angeles, CA, US.
(C) 2002, Audio Engineering Society, Inc.