Transcript
snug@’ Volume 4 Number 3
* AMS UPDATE AUTOMATIC MIXERS & SYSTEMS
OVER 2,800 AMS CHANNELS IN DISTANCE LEARNING NETWORK One of the world’s most extensive distance learning network systems is based in the eastern portion of the United States. This system of 175 sites links major universities, junior colleges, high schools and elementary schools throughout the states of Maryland, Delaware and Virginia - and there are plans for an additional 125 sites! This distance learning system was conceived and initiated by Bell Atlantic working in close cooperation with the state governments. Using fiber optic lines, the system provides fuII bandwidth transmission without the use of echo cancellation. For the actual design and installation of the audio and video systems needed for each site, Bell Atlantic turned to Washington Professional Systems (WPS) of Wheaton, Maryland. A typical site employs two AMS8000 mixers, 15 AMS22 surface microphones for the students, and one AMS28 lavalier microphone for the instructor. According to WPS, “The AMS is extremely easy to install. We do not have to worry about threshold settings, and the logic terminals provide design flexibility to meet each site’s unique requirements. The AMS produces uninterrupted, intelligible speech, provides plenty of gain, and gates reliably. We appreciate having Shure’s Applications Engineering Group ready to give support when needed, and the end user also views this support as a real benefit.” Reports from instructors using the distance learning sites have been very positive. One
One of the
Bell Atlantic Distance Learning Sites.
teacher commented, “We have found the AMS equipment to be very durable. The fact that there are very few knobs to adjust makes the system less intimidating. We simply turn the system on and
we are ready to begin class.” The Update wishes to thank Bell Atlantic, WPS, and Perry D’Angelo o f S . K . Macdonald, Shure’s regional representative, for this story.
Shure Brothers Incorporated, 222 Hartrey Ave., Evanston, IL 60202-3696 (847) 866-2200
The city council chambers of Wellington, New Zealand was the cover story of AMS Update Vol. 3 #8. This story described a microphone control system using the automatic mixer’s logic terminals. Numerous Update readers inquired about the details of this circuit. In response to these inquiries, the Update has acquired the circuit schematic and its operational description. Note that this clever circuit will work with the Shure SCM810 automatic mixer as well as the Shure AMS.
................................ . C1 = 10 µF 16 wvdc D1, D2 = 1N4148 D3 = red LED 20 mA maximum D4 = yellow LED 20 mA maximum D5 = green LED 20 mA maximum Q1, Q2 = 2N2222 Q3 = 2N2907
CIRCUIT DESCRIPTION: This is a useful circuit for any legislative council. Each council member has a panel in which the above circuit is mounted. S1, D4, and D5 are the only parts visible to the council member. Upon power up, D4 and D5 are dark indicating the microphone is muted and will not be activated by speech. When S1 is pressed and released, D4 illuminates to indicate the micro-
GATE OUT
R1, R2, R3, R4, R8 = 1 0 k , 1/4 W R5, R7, R11 = 4 7 0 , 1/4 W R6, R9, R10 = 4.7k, 1/4W S1 = momentary SPDT S2 = push on/push off SPST U1 = 74LS74 dual D-type flip flop Power Supply = +5 Vdc @ 2 A; will supply sufficient current for a system with 80 members
phone is ready to activate if the council member speaks. When the member speaks, the microphone activates and D5 also illuminates indicating microphone activation. D5 will go dark after the member stops speaking and the mixer hold time has passed. D4 will remain illuminated indicating the ready to activate state. When S1 is again pressed and released, D4 and D5 go dark indi-
cating the microphone is muted and will no longer be activated by speech. The chairman position alone includes S2, D3, and R5. When S2 is pressed, all of the council members’ microphones will be muted and D3 illuminates indicating an all council mute. This allows the chairman to speak without interruption.
AUTOMATIC MIXERS & SYSTEMS
NEW MICROFLEX LINE FEATURES LOGIC CAPABILITY
AMS UPDATE TECHNICAL Q&A
Q. What is the off-attenuation setting for the SCM810 DIRECT OUT when it is modified to become gated? Can it be changed?
Lavalier Microphone
Boundary Microphone
Overhead Microphone
Gooseneck Microphone
Shure’s new Microflex line incorporates unique design features which enhance performance and simplify installation. The line consists of gooseneck, overhead, boundary, and Iavalier microphones. Among the new features are programmable switches, locking windscreens, and interchangeable cartridges: cardioid, supercardioid, and omnidirectional. A variety of gooseneck models (MX412/418 series) are available. Options include two different lengths, an on/off switch, and various mounting methods. Each gooseneck microphone includes a shock mount, snap-fit windscreen, and locking flange mount. The overhead microphones (MX202 series) are available in black or white with either platemount or in-line preamps. Each model is equipped with a fourinch gooseneck and 30 feet of cable. Incorporating silent-operating programmable membrane
switches and LED indicators, the low profile boundary mics (MX392/393 series) are ideally suited for churches, boardrooms, and distance learning centers. The MX392 features three additional connections to interface with the SCM810 logic terminals. (See back page article.) Applications include: remote activation of the microphone’s LED; privacy or cough button; chairperson all-mute; and remote control of video camera shot selection. No bigger than a paper clip, the Microflex lava1ier mics (MX183/184/185) may be hard wired or connected to any Shure wireless transmitter. Included with each model is a single-mic tie clip, dual-mic tie clip, black snap-fit foam windscreen, belt-clip preamp, four feet of cable, and a fourpin TA4F connector. For more information about the new Microflex line, contact Shure at 847-866-2200 (voice); 847-866-2279 (fax); http:// www. shure.com (World Wide Web).
A. From the factory, the SCM810 DIRECT OUT feeds are not gated. They are pre-gate and pre-fader. As described in the SCM810 manual, any DIRECT OUT may be modified to become gated with an off-attenuation level of infinity, i.e., when the input is gated off, the DIRECT OUT contains no signal at all. In some circumstances, it may be desired to have a small amount of audio “bleed through” to the DIRECT OUT even when the input is gated off, for example, to maintain room ambiance in a recording. The modification described below provides any GATED DIRECT OUT with an off-attenuation level of -15dB. Part needed: one 2 O k , %W resistor with leads To modify input channel #1 of an SCM810: e Solder the 20kQ resistor from U101B pin 7 to the junction of R1143 & U108. * Repeat as necessary for other channels. The 2OkQ resistor “bleeds” audio around opto-isolator U108 which controls the signal path. * For less than 15dB of off-attenuation, decrease the value of the resistor. * For more than 15dB of off-attenuation, increase the value of the resistor. Contact Shure’s Applications Engineering Group for assistance if you have difficulty finding the locations of the SCM810 surface mount components mentioned.
AUTOMATIC MIXERS & SYSTEMS
NEW MICS COMPLEMENT SCM810 OPERATION The MX392 boundary microphone and the MX412D desktop microphone have unique features which interface to the logic terminals of the SCM810 automatic mixer. Three additional wires in the microphone cable are used for the following features. LED activation by GATE OUT: Normally, the LED on the MX392 or MX412D is controlled by the built-in membrane switch. Alternatively, the LED can be controlled by any SCM810 GATE OUT terminal. To accomplish this, change the microphone to Automatic Mixer mode as described in the User’s Guide. Connect the orange wire of the mic cable to an SCM810 GATE OUT terminal. Connect the green wire of the mic cable to the SCM810 LOGIC GROUND terminal. Now the microphone LED will illuminate whenever the selected GATE OUT terminal goes “logic low”. (Remember that the
Shure MX392 Boundary Microphone
GATE OUT terminal is “logic high” when its associated input channel is gated off, and is “logic low” when its associated input channel is gated on.) Control of MUTE IN by the mic switch: In addition to acting as an on/off control, the built-in membrane switch on the MX392 or MX412D can provide a “logic
low” signal when pressed. Based on the DIP switch settings inside the mic, the logic signal can be momentarily “logic low” or latching “logic low”. This remote indication of switch actuation could be used to call up video cameras. It could also be employed for polling meeting participants, e.g., “All those in favor, push the switch on your microphone.” Another way to use this feature is for a chairman all-mute switch. Connect the white wire of the mic cable to the MUTE IN terminal of every SCM810 input to be muted. Connect the green wire of the mic cable to the SCM810 LOGIC GROUND terminal. Whenever the mic switch is depressed, each SCM810 channel where MUTE IN is grounded will be immediately gated off. The Update suggests caution regarding to whom this feature is given as ultimate muting power corrupts ultimately.
SCM810 EMPLOYED FOR REMOTE DIGITAL RECORDING Marquardt Productions, located in Fayetteville, Arkansas, employs the SCM810 as part of a portable digital recording system. The heart of the system is a Tascam DA-88 which records eight tracks of digital audio onto a Hi8 video tape. But as the DA-88 has no microphone preamps, phantom power, equalization, or channel level controls, the SCM810 was chosen to provide these functions, as well as voice activated gating. The SCM810 was modified so that each Direct Output is postfader and post-EQ. The eight Direct Outputs feed the line inputs of the DA-88. The microphones used by Marquardt Productions, the Shure SM57, AKG Printed in U.S.A.
3OOOS, and EV RE55, connect to the Shure RKC800 XLR panel which mates to the SCM810. When used for music recording, t h e S C M810 is op erated in Manual mode, i.e., no gating. For speech recording, the SCM810 is operated in Automatic mode. This is a clever use of the exceptionally quiet preamp sections of the SCM810. Marquardt Productions tells the AMS Update that several of its customers, upon learning the function of the SCM810, have commented “Wow! I’ve never seen that done before.” Perhaps, “never heard that...” would have been a better choice of verb. Many thanks to Sol Marquardt
of Marquardt Productions for the information he provided to the Update.
Back Issues of AMS Update Available
If you missed previous issues of A M S Update, they may be obtained by contact-
ing Max Buchanan at Shure and requesting the issues you want. If in Europe, you can contact: SHURE BROTHERS EUROPE Wannenacker Str. 28 74078 HeiIbronn Germany Telefon: 49-7131-72140 Fax: 49-7131-721414 AL936-Volume 1 Compendium AL1130-Volume 2 Compendium AL1255-Volume 3 Compendium AL1263-Volume 4 No. 1 AL1282-Volume 4 No. 2
AL 1289
