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I have a question concerning biasing the pa. Seems like the goal is to get it to draw 1amp when you give a big hallllooooo. I used a tone signal generator app set to 1000hz with the volume all the was up with the mic a inch away from speaker as a standard.? It says you can turn it up past 100 ma with out speaking into mic if it doesent reach 1 amp. but my question is is there a danger of going to much? I had to set mine to 350ma to get 1amp.
-- Barrett K5SSO |
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Gordon Gibby
¿ªÔÆÌåÓýYes, if you set it to .35A at idle, that will be about 4 watts dissipation at idle.....
100 mA is a better idle current!!!?? ?(1.2 watts dissipation)
Perhaps you could just unbalance the diode balanced mixer with a 10K to get plenty of signal, or else inject audio into the input amp?? ??
In my case I found that a bit of pre-amp on the microphone (X5 amp or so) made it more pleasant for me.
Gordon
From: [email protected] <[email protected]> on behalf of Barrett O <ogebarrett@...>
Sent: Tuesday, November 14, 2017 9:25 PM To: [email protected] Subject: [BITX20] PA Bias question ?
I have a question concerning biasing the pa. Seems like the goal is to get it to draw 1amp when you give a big hallllooooo. I used a tone signal generator app set to 1000hz with the volume all the was up with the mic a inch away from speaker as a standard.?
It says you can turn it up past 100 ma with out speaking into mic if it doesent reach 1 amp. but my question is is there a danger of going to much? I had to set mine to 350ma to get 1amp.
-- Barrett K5SSO |
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Gordon Gibby
¿ªÔÆÌåÓý?I agree that if you replace the 100 ohm emitter resistor with a 10 ohm you will get 10x more gain roughly;? I didn't need quite that much but the little preamp I built about 5X was sufficient.? ?I haven't studied the other circuits presented on that page.
Gordon
From: [email protected] <[email protected]> on behalf of Karl Heinz Kremer, K5KHK <khk@...>
Sent: Wednesday, November 15, 2017 1:24 PM To: [email protected] Subject: Re: [BITX20] PA Bias question ?
You may not need a preamp. Take a look at mod #1 here:??
I don't have any first hand experience with this (yet).? |
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Trent Trent
Just do what ai did and put a relay on the PA power On 15 Nov. 2017 1:25 pm, "Barrett O" <ogebarrett@...> wrote: I have a question concerning biasing the pa. Seems like the goal is to get it to draw 1amp when you give a big hallllooooo. I used a tone signal generator app set to 1000hz with the volume all the was up with the mic a inch away from speaker as a standard.? It says you can turn it up past 100 ma with out speaking into mic if it doesent reach 1 amp. but my question is is there a danger of going to much? I had to set mine to 350ma to get 1amp. |
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Barrett,
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Try reducing the value of R123 by putting a lower value in parallel. Start with 47 or 33 and go down to 10 Ohms. The gain will increase for the mic. Raj At 15/11/2017, you wrote:
I went ahead and set it back to 100 ma. Is there a link that can show me how to make or buy a preamp for the mic? |
Raj vu2zap