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House Number; Converting a CB Radio To The 28MHz Band; Electronics & Brock's BMW Blaster; Queensland's Powerful Electric Locomotives. November 1988: 120W PA Amplifier Module (uses Mosfets); Poor Man's Plasma Display; Automotive Night Safety Light; Adding a Headset To the Speakerphone; How To Quieten the Fan In Your Computer; Screws & Screwdrivers, What You Need To Know; Diesel Electric Locomotives. February 1988: 200 Watt Stereo Power Amplifier; Deluxe Car Burglar Alarm; End of File Indicator for Modems; Door Minder Alarm; Low Ohms Adaptor for Multimeters; Line Isolation Unit for Phone Patch; Electronics In The Jaguar XJ40; Easy Tips on Headphone Repair. March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Endless Loop Tape Player; Build Your Own Light Box; New Life for Radio-Cassette Players; Old-Time Crystal Radio. April 1988: Walkaround Throttle for Model Railroads, Pt.1 ; pH Meter for Swimming Pools; Slave Flash Trigger; Headphone Amplifier for CD Players; What is Negative Feedback, Pt. 1 ; Mobile Antennas for the VHF & UHF Bands. May 1988: Optical Tachometer for Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Walkaround Throttle for Model Railroads, Pt.2; Designing and Building RF Attenuators; Motorola MC3334P High Energy Ignition IC Data. June 1988: Stereo Control Preamplifier (uses LM833), Pt.1; Breakerless Ignition For Cars Using Hall Effect Pickups; Mega-Fast Nicad Battery Charger; Automatic Light Controller Uses PIA Detector; RF Sniffer Probe & Preamplifier; What is Negative Feedback, Pt.2. July 1988: Stereo Control Preamplifier, Pt.2; Fitting a Fuel Cut-Off Solenoid; Booster for TV & FM Signals; The Discolight Light Show, Pt.1 ; Tone Burst Source for Amplifier Headroom Testing ; National Semiconductor LM833 Op Amp Data; What is Negative Feedback, Pt.3. August 1988: Building a Plasma Display; Universal Power Supply Board; Remote Chime/Doorbell; High Performance AC Millivoltmeter (uses OP-27), Pt.1; Discolight Light Show, Pt.2; Getting the Most Out of Nicad Batteries; Data on Insulated Tab Triacs. September 1988: Hands-Free Speakerphone; Switchmode Charger for 1 2V Gel Batteries; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Vader Voice; Motorola MC34018 Speakerphone IC Data; National Semiconductor LM 12 1 50W Op Amp Data & Application; What is Negative Feedback, Pt.4. October 1988: Stereo FM Transmitter (uses Rohm BA1404); High Performance FM Antenna; Matchbox Crystal Set; Electronic December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor for Shortwave Receivers; Electronics & Holden's New V6 Engine; Why Diesel Electrics Killed Off Steam; Index to Volume 1. January 1989: Line Filter for Computers; Ultrasonic Proximity Detector for Cars; Simple Computer Sound Repeater; 120W PA Amplifier (With Balanced Inputs) Pt. 1 ; How to Service Car Cassette Players; The Goalkeeper Gatling Gun; Massive Diesel Electrics In the USA. February 1989: Transistor Beta Tester; Minstrel 2-30 Loudspeaker System; LED Flasher for Model Railways (uses LM3909); Build a Simple VHF FM Monitor (uses MC3362), Pt.1; Lightning & Electronic Appliances; Using Comparators to Detect & Measure. March 1989: LED Message Board, Pt.1; 32-Band Graphic Equaliser, Pt.1; Stereo Compressor for CD Players; Map Reader for Trip Calculations; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Electronics for Everyone - Resistors. April 1989: Auxiliary Brake Light Flasher; Electronics for Everyone: What You Need to Use this handy form to order your back copies ._. I I I ---------------------------------- • -- Please send me a back issue for: □ February 1 988 □ March 1988 □ April 1 988 □ May 1 988 □ July 1 988 □ August 1 988 □ September 1 988 □ □ □ June 1988 I □ 0. November 1 988 □ I I □ March 1 989 ll April 1 989 □ May 1989 □ Ju·ne 1989 □ July 1989 □ August 1989 □ September 1 989 □ October 1989 □ November 1989 □ December 1989 I t I I I I I I I I I I October 1 988 December 1 988 January 1 989 7 February 1 989 □ January 1990 Enclosed is my cheque/money order for $ ______ or please debit my D Bankcard D Visa Card D MasterCard Card No. I ._I_.___.___,___] IL..........L___,____.___,11~~~~ Price: $A5.00 each (includes postage). Overseas orders add Signature _____________ Card expiry date _ __._ _ $A 1 .00 per issue for postage . NZ & PNG orders are sent by Name__________________________ air mail. (PLEASE PRINT) Detach and mail to: SILICON CHIP PUBLICATIONS Stree.._________________________ PO BOX 139 COLLAROY BEACH NSW 2097 Suburb/town _ _ _ _ _ _ _ _ _ _ _ _ _ _ Postcode_ _ __ OR FAX: (02) 982 9553 l.._~.....__. . . . . . ~--------------------------------------90 SILICON CHIP The Serviceman Know About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; Led Message Board, Pt.2; Fluke's New 80-Series Multimeters. May 1989: Electronic Pools/Lotto Selector; Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; Electronics for Everyone - All About Electrolytic Capacitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Radios; Universal Temperature Controller; Understanding CRO Probes; Led Message Board, Pt.3; Coherent CW - a New Low Power Transmission Technique. July 1989: Exhaust Gas Monitor (uses TGS812 Gas Sensor); Extension For the Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electrics; Facts On the PhaxSwitch - Sharing Your Phone Line With A Fax Machine. August 1989: Build A Baby Tower AT Computer; Studio Series 20-Band Stereo Equaliser, Pt.1; Garbage Reminder - A 7-day Programmable Timer; Introduction to Stepper Motors; GaAsFet Preamplifier For the 2-Metre Band; Modern 3-Phase Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector (uses LM1830N); Simple DTMF Encoder (uses Texas TMC5089); Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (uses LMC669); A Guide to Hard Disc Drives. October 1989: Introducing Remote Control; FM Radio Intercom For Motorbikes (uses BA 1404 and TDA7000) Pt.1; GaAsFet Preamplifier for Amateur TV; 1 Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc in the PC; A Look! at Australian Monorails. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY and Morse); Super Sensitive FM Bug; Build A Low Cost Analog Multimeter; FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board (Records Up To Four Separate Messages, Uses Texas TMS3477NL and 256K RAMs); UHF Remote Switch; Balanced Input & Output Stages; National Semiconductor LM831 Low Voltage Amplifier IC Data & Applications; Install a Clock Card In Your PC; Index to Volume 2. January 1990: Service Tips For Your VCR; Speeding Up Your PC; Phone Patch For Radio Amateurs; High Quality Sine/Square Oscillator; Active Antenna Kit; The Latest On High Definition TV; Speed Controller For Ceiling Fans. Note: November 1987, December 1987 & January 1 988 are now sold out. continued from page 49 drives the base more negative, turning the transistor on. In fact, the transistor was leaking internally with normal operating voltages applied, and was turned on permanently. Under these conditions, the collector voltage fell from the correct figure of 4.1 V to something like 0.1 V. I fitted a new transistor and found that the set now worked perfectly; stable sync, full colour and all. Post mortem But why had the set been dead from the tuner on? That 6.3V at the emitter of the 1st video amplifier also supplies a bias to the video IC at pin 6. So the whole IF strip was inactive when the fault was really in the video amplifier. And the tuner was inoperative because it needs an AFC voltage which is developed from a signal provided by the IF chip. Which brings me back to the point made earlier. If I had been a little more careful when replacing the board in the first place, then none of this story would have eventuated. ~ Bose noise cancelling headphones for obvious reasons, maintained a tight seal to the pilot's head. The ear surround seal in the Bose headset uses a combination of silicone gel and soft foam which follows the contours of the head to create a better seal, with only a slight amount of headband pressure. Even without the noise-cancelling electronics, the Bose headsets still boast better passive noise attenuation than many of the ordinary types on the market, especially at low frequencies. Specifications Each earpiece has its own independent noise-cancelling system, allowing for both mono and stereo use. The sound pressure servo system has been built using surface-mount technology, allowing Circuit Notebook - from page 11 it to fit inside the earcup. The impedance of the earpiece is 1500 and the system has a frequency response of 100Hz to 6kHz. The power supply required is 150mA at 11-16V or 22-32V DC. Applications A number of helicopter and aircraft manufacturers are now offering Bose ANG headsets as an optional feature but Bose see the product as having wide application in any situation where people have to work for long periods while subjected to high levels of noise. And who knows, maybe in the future your W alkman will come with noise cancelling headphones. l!t] Acknowledgement: our thanks to Bose Australia Inc, for their assistance in preparing this article. continued from page 26 represent a variable inductance. By varying dual gang pot VR1, the resonant frequency of the inductor is changed and so the circuit can vary the frequency to be boosted or cut. The filter is an LC type based on the .001µF capacitor and the variable inductance. Note that VR1 is wired so that when VR 1 a increases its resistance, VR1b reduces its resistance. As shown, the centre frequency can be tuned from around 32Hz to 17kHz and the available boost and cut is about ± 12dB. The output of the circuit is taken from pin 7 of IC1b via a 1k0 resistor and 1µF capacitor. Darren Yates, French's Forest, NSW. ($30) (Editor's note: while the circuit shown here is run from a single supply, there is no reason why it could not be modified to run with balanced positive and negative supplies). FEBRUARY1990 91