roveydoveygrovey Posted May 2, 2010 Report Share Posted May 2, 2010 I was looking at the Infrared cordless Headphone Amplifier project to build, from this page - http://www.electronics-lab.com/projects/audio/016/index.htmlThe only part of the circuit that I couldn't make sense of is the audio input in Fig 1. There's something that looks like a transformer, but there are no values given for windings or inputs/outputs. Can anyone explain what's going on here?Also has anyone built this? did it work?I really appreciate any help,Thanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 2, 2010 Report Share Posted May 2, 2010 Nope.It is a hopeless circuit designed by somebody who knows nothing about electronics. The first transistor in the transmitter is not even biased! It rectifies instead of amplifying.Have you ever heard a rectified audio signal? It has more than severe distortion.The red LED in the transmitter clamps the modulating signal so it is almost nothing.The IR receiver is a good choice if you want to hear mains hum from incandescent light bulbs.It causes DC current in the headphones which is bad because it might destroy them.Most IR communications use an FM modulated ultrasonic carrier.I have seen this circuit before on a website in India where no circuits work. Quote Link to comment Share on other sites More sharing options...
roveydoveygrovey Posted May 2, 2010 Author Report Share Posted May 2, 2010 nice one thanks for the reply. glad i asked, probably would have spent ages trying to get it to work.Im pretty new to this, so you're saying i should look for a circuit that uses FM modulated ultrasonic carrier? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 3, 2010 Report Share Posted May 3, 2010 I looked in Google for Infrared FM Headphones Circuit and found many circuits.Most use AM instead of FM and some are similar to the one you found that won't work.For the FM transmitter, the VCO of a CD4046 phase-locked-loop IC is used and another CD4046 is used as an FM detector. Quote Link to comment Share on other sites More sharing options...
Hero999 Posted May 3, 2010 Report Share Posted May 3, 2010 The only receiver circuit I could find uses the obsolete MC3237.The transmitter is on a separate site, I don't know if it works on the same frequency, I haven't done any calculations. Quote Link to comment Share on other sites More sharing options...
roveydoveygrovey Posted May 3, 2010 Author Report Share Posted May 3, 2010 ok thanks for the help and suggestions very much appreciated , if i ever get one working i'll let you know. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 3, 2010 Report Share Posted May 3, 2010 It is mono. If you want stereo then use two different carrier frequencies like 100kHz and 180kHz. Quote Link to comment Share on other sites More sharing options...
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