Archive for the ‘Audio’ Category:

2020-06-23 LM386 1W Mono Amplifier Input Jack Reconfig

A year or so ago I bought a few 1W mono amplifiers from a Chinese eBay seller for cheap – see the attached photos. The only marking on the PC board is YX-1667 but I’m not sure if that’s the potentiometer or the PC board itself. . I found that if I pushed the 3.5mm

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2020-06-10 Dubbing Adapter

This is an adapter to connect a source such as a smartphone stereo headphone output to the input of an MP3 recorder. The view and diagram is looking at the back of the adapter where the plugs are inserted into the jacks. The switch handles are on the far side. The switch on the right

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2020-03-29 AM Osc + Modulation + Buffer

This is from Electronics Illustrated Projects 1968. It shows crystal sockets, but instead a RF coil may be used and its value will be about 220 microhenrys. And C1 and C2 will have to be changed to bring the frequency down to the AM band. The germanium transistors are no longer available so silicon transistors

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2018-08-24 2N3904 & 2N3906 for Output Transistors

From FB group Building Transistor Radios 2018-08-24 – The discussion was about the OTL complementary symmetry audio amplifier that Mr. Barnett has posted several times to the group, which uses a 2N3904 and 2N3906. Willie Barnett Let’s talk about current. Suppose your amp has a 9V supply. When the output transistor is turned fully on,

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2018-01-31 1kHz Wien Bridge Oscillator Kit

Also photo posted to FB group Building Transistor Radios. I got several of these Wien Bridge Oscillator kits from an eBay seller in China.  They are built using the circuit from http://redcircuits.com/Page13.htm More information can be found on the wiki for this oscillator. The kits come with no instructions, so to assemble it, use this red circuits

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2017-07-14 Underwater Speaker

From a reply on FB I built a speaker for a swimming pool.  It was a large can of steel with an audio transformer mounted inside.  The ‘I’ laminations were removed so the ‘E’ laminations could be very close to the end.  I drove it with a 2N3055 on a heatsink.  The secondary winding must

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2017-06-25 Mini Audio Transformer From Goldmine Electronics 

I bought several of these miniature audio transformers  from Electronic Goldmine.  They are encapsulated so I can’t see anything, windings, core or materials.  There are 5 pins, 2 on one side and 3 on the other, but the center pin measured open, so it’s apparently there to make sure the transformer is inserted the right way. The

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2014-11-22 Ultrasonic Dog Repeller

A few weeks ago I ordered an ultrasonic dog repeller from an Asian dealer and it finally arrived this week.  It wasn’t very expensive. I think one reason why is because this product has never been scientifically tested to prove that it works. The reason I say this is that this product apparently is not

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2014-01-25 70.7 Volt PA Transformer Impedances

When you get a 70.7 Volt Public Address Transformer, you see that it has connections  for different speakers, such as 4, 8, and 16 ohms.  On the other winding are various taps for different power outputs such as .625, 1.25, 2.5, 5 and 10 Watts.  But there is nothing to tell what the impedance is

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2013-11-04 Audio Preamp, Two Transistor

This was in a schematic from the 1960s, the days of silicon transistors, before low noise op amps.  The 2SC369 is old and very likely to be no longer available.  The replacement transistors could be any low noise small signal, such as the BC550C or 2N5088.  The supply voltage shown is 34 VDC, but this

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