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Audio feedback problem

Discussion in 'General Electronics Chat' started by Space Varmint, Oct 16, 2008.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Smiley button?

    I used a smiley button in this quote but it ended up in the title instead of in my text.
     
  2. Roff

    Roff Well-Known Member

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    Use the buttons just to the right of the advanced reply window.
     

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  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hi Ron,
    I can do a Quote, an ordinary Reply or a Quick Reply. In a Quick Reply there is a Go Advanced button. I never see the page that you showed.

    I use Microsoft's IE7 browser which I recently re-installed. Maybe a setting on it is wrong or a feature is missing.
     
  4. dave

    Dave New Member

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  5. Roff

    Roff Well-Known Member

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    What happens if you click the Go Advanced button? You have to use the advanced window to post schematics, etc., and I'm pretty sure you post schematics, so I can't understand why you don't see the smileys.
    Quote also takes you to the advanced window.
     
    Last edited: Oct 29, 2008
  6. Space Varmint

    Space Varmint New Member

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    You mean choking them?
     
  7. Mikebits

    Mikebits Well-Known Member

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    Choking is to block RF, you need caps for low freq hum being coupled into your audio.
     
  8. transistor495

    transistor495 Member Forum Supporter

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    I suggest you to run your radio on a 6v battery pack :).

    ..or debug using taking the audio before the power amp and connect to external amplifier and check whether hum is there or not. If hum is ther, your transistorised circuit is picking and amplifying the power supply hum, else problem is with your power amp.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The gain of his audio amplifiers is umpteen-zillion. The first few transistors have their inputs biased directly from the raw DC supply. I don't think the raw DC is regulated.

    The first few transistors need to have their bias fed from a decoupling filter. Also the bias for the opamp.
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Ron,
    Here is my "Go Advanced page":
     

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  11. Roff

    Roff Well-Known Member

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    If you want to see and use the smileys, go to User CP in the bar near the top of the page.
    On the left side, click Edit Options.
    Go to the very bottom of the page, and select Enhanced Interface - Full WYSIWYG Editing.
     
  12. Space Varmint

    Space Varmint New Member

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    You still suspect that chip don't you? Yeah, I'm sitting listening to some 80 meters guys (SSB) right now and that hum is there.

    I put this thing on battery and guess what? No hum at all. Now what does that tell ya? Yep, power supply.

    I'll worry about that later. Going into the week end will be a flurry of activity with all kinds of hams working. QRP (low power) stations and the whole gambit. So, time to do the pre-selectors. This is where the rubber meets the road as far as over all performance.
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, it tells you the circuit is badly designed, as Audioguru has repeatedly told you - each stage should by decoupled from the power supply, this is basic design 101.

    You 'may' be able to bodge it by fairly brute strength changes to the power supply, reducing ripple to far below that required.
     
  14. Space Varmint

    Space Varmint New Member

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    Every hear chirp? Listen to this guy. This is chirp. I can be cause by poor buffering which is probably what it is because you can notice drift too. So he is probably using a VFO without enough buffering to the transmitter final. But a power supply can cause this too. That's why you must have low surge impedance and sufficient power with CW.

    I changed to a more solid CW note at the end but it is weak.

    He does have nice wave shaping. I didn't hear any key-clicks.
     

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  15. Space Varmint

    Space Varmint New Member

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    What do mean? The damn thing is decoupled. He said decouple the base, so I asked him what he meant.....choke it? I got no answer.

    Anyway it is clean as a whistle, no hum on battery. So yeah, A better power supply could be in order.
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I heard Morse Code and the audio frequency was changing a little.
     
  17. Roff

    Roff Well-Known Member

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    Even if you decouple the base bias resistor(s) on a CE amplifier, you still have approximately unity gain from the power supply to the collector, because the collector is typically much higher impedance than the collector resistor. This hum, or whatever, will add to your signal, to be further amplified by the next stage.
    Op amps are small, cheap, and have excellent power supply rejection. They lend themselves to easily calculated gain and frequency response networks. Why fool with discrete transistor amplifiers?
     
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Discrete amplifiers also have extreme distortion :(.
    I activated the enhanced interface to this site :D so now I can have smileys :D all over the place.:D:D:D:D:D
    Thanks Ron.
    :D

    On another site there is a Marquee feature where you can have text or smileys running around as a chaser.:)

    :confused::confused::confused: :eek::eek::rolleyes:
    ;)
     
  19. Space Varmint

    Space Varmint New Member

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    I do not believe it!

    I do not believe it!

    I was putting in the front end filter with selector knob and everything, setting up and was checking my straight through (no filter) select position and found a short to ground on the antenna connection.

    I went into the first section and found I had shorted it to ground somehow when I put in the AM Broadcast band stop filter.

    Guess what? I just lost a whole bunch of hum!

    I think getting the antenna off of ground should help huh? Here's a recording with power supply. You will hear a little at points but very very low if any at all.
     

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  20. Space Varmint

    Space Varmint New Member

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    Are you having a good time? :D
     
  21. Mikebits

    Mikebits Well-Known Member

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    The background hiss is worse than the hum. Your audio gain distribution is still whacked. Don't blame it on A to D sampling of your PC, your audio is horrible. Follow advice given in previous threads. Have you done a signal/noise test of the radio? At any rate, building a radio that works is an accomplishment so be proud. Still love me?
     

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