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HELLO i have a problem with fm receiver

michael1978

Mar 17, 2012
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Hello to everyvone

can somebdody tell me, what for i mistake i did, i build this circuit, i dont know of antena problem but i hear nothing, when i connect the speaker, there is no sound, nothing
small-fm-radio-receiver.jpg
 

Audioguru

Sep 24, 2016
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The website with that "FM receiver" is full of errors and the author has very poor Engrish.
It says it uses SEX transistors, not ordinary transistors. Maybe the arrow on each transistor says if it is male or female.

The article says how to make the coils. Since it operates at high VHF frequencies then it must be built compactly on a pcb because the stray capacitance on a solderless breadboard will cause it to not work.

It is a horrible and simple circuit that is far from being a real radio receiver.
 

kellys_eye

Jun 25, 2010
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Plus we don't know for sure that you built it correctly (i.e. no mistakes).
 

Audioguru

Sep 24, 2016
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I do not think it is an awful "regenerative" circuit. Instead I think it is a simple "crystal radio" with an RF amplifier and an AM detector. When it is tuned to one side of an FM station then the AM detector will "slope detect" the FM and add lots of amplitude clicks and pops.
 

duke37

Jan 9, 2011
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Q5 and Q6 do not do anything.
R9 and R10 are connected in parallel to ground. R9 should be connected tp base of Q5.
C6 will give a lot of top cut.
 

michael1978

Mar 17, 2012
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Q5 and Q6 do not do anything.
R9 and R10 are connected in parallel to ground. R9 should be connected tp base of Q5.
C6 will give a lot of top cut.
you mean that is the error?
if is that no problem i can fix diret, but you think i cant i build in bredeboard
 

michael1978

Mar 17, 2012
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Guess what? It drives a power amplifier, not a speaker. Then the power amplifier drives the speaker.
The poor Engrish should have said it is an FM tuner, not an FM receiver.
are you sure the i need ic power amplifier
 

Audioguru

Sep 24, 2016
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you mean that is the error?
Almost everything in that lousy circuit is an error.

are you sure the i need ic power amplifier
Yes.
1) If the output transistor was biased correctly (it is not) then its emitter will have about 2.5V on it and its current will be 2.5V/1.2k ohms= 2.1mA. Then its peak output current is 2.1mA. If you connect an 8 ohm speaker then its peak power will be only 2.1mA x 8 ohms= 0.017W and its RMS power will be only 0.008W which is almost nothing.
1W into 8 ohms is made with a peak current of 350mA (167 times the output current of this lousy circuit).
I agree that the 47k resistor is in the wrong location, it should connect to the base of Q5, not ground but then Q6 is still biased wrong.

2) The value of its output capacitor is only 4.7uF then all frequencies below 4260Hz will be cutoff into an 8 ohm speaker. FM stations play frequencies down to 50Hz or less.
 

michael1978

Mar 17, 2012
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Almost everything in that lousy circuit is an error.


Yes.
1) If the output transistor was biased correctly (it is not) then its emitter will have about 2.5V on it and its current will be 2.5V/1.2k ohms= 2.1mA. Then its peak output current is 2.1mA. If you connect an 8 ohm speaker then its peak power will be only 2.1mA x 8 ohms= 0.017W and its RMS power will be only 0.008W which is almost nothing.
1W into 8 ohms is made with a peak current of 350mA (167 times the output current of this lousy circuit).
I agree that the 47k resistor is in the wrong location, it should connect to the base of Q5, not ground but then Q6 is still biased wrong.

2) The value of its output capacitor is only 4.7uF then all frequencies below 4260Hz will be cutoff into an 8 ohm speaker. FM stations play frequencies down to 50Hz or less.
thnx, so R9 must be connected to the base of Q5, but what do you think how to bias good Q6
 

michael1978

Mar 17, 2012
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Q5 and Q6 are a 2 transistors preamp. Here is how Philips did it 50 years ago when I worked for them:
Man you are a specialist, me i am beginner, i dont undertand thinks like you,, but i make mistake, i just gjange 47K, I al ready finish soldering
 

michael1978

Mar 17, 2012
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Man you are a specialist, me i am beginner, i dont undertand thinks like you,, but i make mistake, i just gjange 47K, I al ready finish soldering
i will send you circuits, i hope dont smile, is my second time soldering ;-)
 

Audioguru

Sep 24, 2016
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I simulated the audio preamp Q5 and Q6 of the simple FM receiver but it did not work.
I fixed the circuit and simulated it but my resistors, capacitors and transistor numbers are different.
 

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michael1978

Mar 17, 2012
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I simulated the audio preamp Q5 and Q6 of the simple FM receiver but it did not work.
I fixed the circuit and simulated it but my resistors, capacitors and transistor numbers are different.
Tthanks man very much, pfff i solderit already
 

michael1978

Mar 17, 2012
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I simulated the audio preamp Q5 and Q6 of the simple FM receiver but it did not work.
I fixed the circuit and simulated it but my resistors, capacitors and transistor numbers are different.
THANKYOU I UNDERSTAND? HAVE A NICE WEKEND ;-)
 
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