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Need help in 88-108MHz preamp circuit!!

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by rahulan999, Aug 25, 2008.

  1. rahulan999

    rahulan999 New Member

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    Recently I came across with a new super-regen. More chance of working than Patrick's project if the output is done using LM386. A nice description is provided about working.
     

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  2. radiomate

    radiomate New Member

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    it does not have regeneration. there are better circuits on the net. there is a mistake in the first circuit (top), there should be a 10K resistor from base of 1st transistor to ground, like in the other circuits.
     
    Last edited: Oct 2, 2008
  3. rahulan999

    rahulan999 New Member

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    Yea, I also noticed that one. But the thing is its simplicity with a single cheap BF494 transistor. It will be a tryable,workable little receiver when built using LM386 my mind says like that :)
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The TEA5711 radio IC was not hi-fi.
    1) It typically needs an FM signal strength of 200uV for only 50dB of quieting in stereo. Its max quieting is only 58dB in stereo with full 75kHz modulation.
    2) Its typical distortion is 0.5% in stereo with full 75kHz modulation. It is 1% max.
    3) Its typical stereo separation is only 30dB.

    It is like my cheap Sony Walkman FM stereo radio.
    It is a little better than my cheap clock radio.
     
  6. radiomate

    radiomate New Member

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    You can add a regeneration control: remove the two 10K resistors biasing the transistor, connect a 20K or 50K linear potentiometer, cursor to transistor base, and the ends to the lines where the resistors are connected. Keep the 10nF from base to ground.

    If you connect the LM386 directly to the first transistor, you will not have enough output to drive the 386, so you will need to connect a capacitor between pins 1 and 8 of the 386 to get enough volume, and you will have hiss when listening to a station, I don't mean the superregen rushing sound, but a hiss from the 386. A much better solution is to have a transistor preamplifier ahead of the 386, and leave pins 1 and 8 open.

    I made a 2 transistor-1 IC superregen a few months ago, I'll put it on my website in a few days.
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Doesn't a super-regen cause high distortion when its AM detector "slope-detects" an FM station?
    Doesn't it produce the sounds from many FM stations (at a low level) all at the same time?
    Doesn't it cause interference to other FM radios?
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    And it's totally crap - yes all of those, and many more bad things as well :D
     
  9. radiomate

    radiomate New Member

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    yes no and yes and it overloads with strong signals like any radio without AVC/AGC, and it produces birdies when it receives stereo stations... did i miss anything? ;)
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Its AM detector picks up all kinds of static interference. A good FM radio doesn't.
     
  11. valve

    valve New Member

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    Audioguru suggests this chip for a home-experimenter. Not too difficult :rolleyes:
     

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  12. rahulan999

    rahulan999 New Member

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    Even we can't talk abt these qualities in front of such a receiver, I agree. But its still exciting in terms of minimum parts and we can hear to an fm station with out complicated circuitry. Patrick's radio is designed considering minimum component requirement. A lot of people wants this kind of simple receiver circuits if we check on net. Quality is not at all considered. They want it to be worked. thats all as a nice achievement.
    My upper-quality TEA5711 AM/FM stereo receiver can be expected after some time. Planning is going on now.
    TEA5711 is great...Philips semi is too great for introducing such a versatile design :D
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Haven't you heard about the lousy old TDA7000 FM receiver IC that was also made by Philips?
    Then they made the TDA7088 that "scans" for a station. They were horrible. I got two radios for free and they are sold for only $1.00 in the Dollar Store.

    I think the 80-pins TDA7513 is in my excellent car radio.
     
    Last edited: Oct 3, 2008
  14. rahulan999

    rahulan999 New Member

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    May be Philips thought that its enough for competing with ur lower-quality clock radios and cheap walkman type radios!
    Generation gap is there in between all these IC's.
     
    Last edited: Oct 3, 2008
  15. radiomate

    radiomate New Member

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    Someone is starting to sound like a broken record... :D
     
    Last edited: Oct 4, 2008
  16. rahulan999

    rahulan999 New Member

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    Hi radiomate,
    A little change on design!
    There will be a TEA5711 AM/FM receiver followed by TDA1524A stereo audio processor.All necessary controls will be there and probably inside a tuner-box.An audio amp is not necessary because I have good ones! A well processed Line-out is enough.TEA5711 will be powered by two rechargeable cells and other one with 12V regulated supply. re-charge/receiver mode will be there for built-in charger section so no need to open the box :)
    N.B: What is that 'contour' in 1524?
     
  17. radiomate

    radiomate New Member

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    Nice arrangement. Where do you see contour?
    Ahh.. I saw it in the spec. sheet, to tell you the truth, I have no clue what it is.. You should ask the audio guys, I am a radio guy :D
     
    Last edited: Oct 6, 2008
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The "contour" is the loudness compensation that boosts the bass up to 12dB when the volume control is turned down because our hearing is not sensitive to bass frequencies at low volume. The contour can be switched off if you don't want it.
     
  19. rahulan999

    rahulan999 New Member

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    Thanks. That one seems to be a good control. I really need it.
    'Contour' ON/OFF :rolleyes:
     
  20. radiomate

    radiomate New Member

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    The "contour" switch in the TEA1524 application circuit connects a 2.2K resistor in parralel with the bass, treble, balance and volume potentiometers, when the resistor is connected, it is in "linear" mode, and when it's not it is in "contour" mode... with my modest audio knowledge :D I would say the switch affects more than just the bass...
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Connecting a resistor in parallel with all the pots saves adding another pin to switch the contour on and off. The datasheet shows that the contour boosts only the bass at low levels. The LM1036 boosts the lows and highs which is better because it is the way our hearing works.
    The LM1036 has an adjustable amount of loudness contour.

    The LM1036 has much less noise and distortion than the TDA1524A.
     

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