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[SOLVED] Echo canceller Schematic

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In this schematics, no external power is required. Bridge diodes can be skipped if polarity of phone line is observed manually. Use a manual switch in series with line to work as cradle.
 
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ALERTLINKS said:


In this schematics, no external power is required. Bridge diodes can be skipped if polarity of phone line is observed manually. Use a manual switch in series with line to work as cradle.
Click to expand...

I'll test this and update now. Is that 470pf or 470uF in series with 18k?
Thanks you.
 

470pF in parallel to 18k. It is not necessary. Sometimes when there is instability. You can skip it.
 
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ALERTLINKS said:
470pF in parallel to 18k. It is not necessary. Sometimes when there is instability. You can skip it.
Click to expand...

Are you sure schematic does not short electricity. I stuck with some short circuit position. Pin 4 get +46.6 V. Transistor base has the same voltage without connecting GND to circuit.
Please have a look.
 

Pin 4 get +46.6 V.
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Measured against which reference point?

You must not short the telephone line against a local ground or connect it to a circuit that is grounded.
 
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Sorry for my mistake. Wrongly placed transistor.

You know what ALERTLINKS it works .....................:grin::grin::grin:

Audio quality superb !!!!

With certain settings echo was 100 % eliminated. Thank you very much for this and I really appreciate. WIsh you a bright future.

 
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There are two wires in in regular telephone line. It provide DC for the telephone and audio modulated on it. When you check line voltages without telephone line there you will find 48V. When phone is connected, voltages drop below 10V.
It is because There is resistance in series. Its current will not rise than 50mA even if short it. Similar is FreeTalk telephone line output. You will connect two wires to this circuit instead of telephone. The line voltage will drop to near 8V which were 48V before.

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OK that's good.
 
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