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haha!! unexpected behaviour that unfortunately i dont want

 
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gelo
HG Junior


Joined: 01 Feb 2007
Posts: 20

PostPosted: Thu Jun 14, 2007 1:26 pm    Post subject: haha!! unexpected behaviour that unfortunately i dont want Reply with quote

i eventually got my amplifier working but now while it does amplify it also amazingly is receiving radio!!! i thought it was the protection device on the input but it isnt the input of the chip is acting as the aerial. So how do i overcome this problem? it DOES amplify the input thats the important thing.

And another thing. How the hell is it recieving radio without an osc?!
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Nginuity
HG Ruler


Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Thu Jun 14, 2007 5:39 pm    Post subject: Re: haha!! unexpected behaviour that unfortunately i dont wa Reply with quote

gelo wrote:
And another thing. How the hell is it recieving radio without an osc?!


You don't need an oscillator to receive radio (I have actually picked up signals with a 50 ohm resistor shorting the antenna connector)....in fact, you really only need a frequency discriminator, which would be as simple as adding a diode to the circuit.....You just have something resonating. And, after that, your amplifier is handling the amplification of it....

One probably place you are getting the signal is in the input wires.....You can put something to the effect of a 10 pf capacitor (I think) in parallel with the inputs, and it will act as a low pass for your audio.

What frequencies would you say you are picking up?
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Thu Jun 14, 2007 8:52 pm    Post subject: Reply with quote

Funny how cool stuff like that just happens... If you were shooting for that result nothing would have happened. Smile

A few things to try.
* Keep all of your connections (wires/traces) as short as possible, this is especially true for the pre-amplified sections.
* Use shielding over sensitive areas, this can be tinfoil or a metal box.
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gelo
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Joined: 01 Feb 2007
Posts: 20

PostPosted: Fri Jun 15, 2007 2:09 am    Post subject: Re: haha!! unexpected behaviour that unfortunately i dont wa Reply with quote

Nginuity wrote:
What frequencies would you say you are picking up?


its definately AM for sure i dunno what freq exact but it sounds like is from the LW area
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Nginuity
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Joined: 13 Nov 2006
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Location: Dallas, Texas

PostPosted: Fri Jun 15, 2007 12:17 pm    Post subject: Re: haha!! unexpected behaviour that unfortunately i dont wa Reply with quote

gelo wrote:
Nginuity wrote:
What frequencies would you say you are picking up?


its definately AM for sure i dunno what freq exact but it sounds like is from the LW area

Try the filter cap across the inputs before you make any changes to your wiring.
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gelo
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PostPosted: Fri Jun 15, 2007 12:42 pm    Post subject: Reply with quote

i replaced the 220uF's with 100uF's and it has lowered the hum a bit but not enough and the higher freqs of the hum are still audible plus there is ecence of radio still heard but it has improved a lil.
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