I came across and article in an old electronics magazine on how to make a directional microphone with a cardboard horn. I decided to copy the horn part. The horn consists of four triangle shaped pieced of cardboard cut from boxes. Each of the four pieces is 1 inch (25.4mm) at the small end, 12
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I have a lot of these 600 ohm telephone hybrid transformers that came out of a PBX (see here for much more info). They’re sturdy and well built, and make great audio transformers. Last week someone posted a video to Youtube of some Joule Thiefs that used an audio transformer and the frequency of oscillation
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I got an email from QS saying that he posted a Joule Thief Beeper to his web page, about 2/3 of the way down. I think it might make a metronome if the speed was adjustable. basically it’s a two transistor circuit with a single coil made from the voice coil of an 8 ohm
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I tack soldered this phase shift oscillator together and used a 2N7000 MOSFET for the PSO. The second transistor in the upper right is a 2N4401 being used as an emitter follower to drive the LED. The LED would draw too much current and load down the oscillator – the PSO has to have a
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This amplifier has been around for awhile, however the date code on the Altoids tin is “Use by 22 Aug 06”, so it had to be made sometime not long before that date or later, most likely later. I used a high gain, low noise Japanese transistor (looks like a 2SD636) for the preamplifier, and
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In this Youtube video, the experimenter connects the Joule Thief to the audio output of an amplifier, and lights a string of LEDs. About the only thing new about this is the source of power: the amplifier. I would say that it’s less than desirable to use the amplifier for power for the obvious reason
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This picture was dated Oct 2002 so I had already built it and put it into service by then. I took the handset of an old phone, and sawed off the handle and microphone, leaving just the part that holds the earphone. I built the circuit on a piece of perfboard and installed it
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I came across this column in talkingelectronics.com where the author discusses small signal and medium signal amplifiers. This medium signal term is one that I’ve never heard used before, and I’ve read a lot of literature that uses the small and large signal terms. I’ve heard the small signal term applied when an incremental term
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I was perusing this circuit on Redcircuits.com when I noticed the capacitor C4 seemed to be backwards – the plus should be on the left. I contacted the author and he said that he would correct it. The idea of talking and listening at the same time “full duplex”, which is technically a communications term,
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I found this circuit that uses an opamp with a pair of diodes in antiparallel in the feedback loop to reduce the opamp gain when the signal rises to a certain level. I would think that this is more of a limiter than a compressor, since it cuts in at 0.6V and stays that way
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