Archive for the ‘Audio’ Category:

2018-12-14 Voice Filter For Telecom And Radio Comm

from FB group Building Transistor Radios 2018-12-14 A voice band filter for telecomm or radio comm. The .068 or .0068 uF caps can be made by putting a 0.1 and 0.22 or .01 and .022 uF capacitors in series. The opamp can be a 1458 ‘dual 741’ opamp.

2018-11-29 Fixing Badly Worn Volume Controls

from FB group Building Transistor Radios 2018-11-30 I’ve done some experimenting on volume controls that are badly worn and noisy. The idea is to substitute some resistance for the badly worn spot. The loud crackling will be reduced and the normal volume point will be moved to a higher point on the control. For a

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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 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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2013-07-05 Phase Shift Oscillator Using a Regular Transistor

First off, I must state that the PSO is not the best solution for an audio oscillator.  It uses only a single transistor, but it has a limitation that makes it put out a poor quality sine wave.    As typical of the PSO, the sine wave becomes distorted because the loop gain is greater

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