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big ear, fm transmitter.


steven

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:)audio guru and dazza ive had the same problems with downloading other topics to like mine that take time to dwonload at first i thought it was the speed of my cpu at processing the task of opening or downloading that was part of the problem, dazza your cool dude, good information takes time to download even in picture form , but sometimes its a niusence but at leat you dont get the page cannot be found exscuse, when you wait to see my postings there is something odd going on before i got here it was takeing to long for the page to open or download and on my 3rd try it did it faster , so what was it , im baffeled ,audio guru can i increase sensitivity of the electret mic more than that with the 10k resister you recamended what value resister can i use to do it

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:)ante was that a few beers or few cartons of beer , i took it into concideration, that some of the bug transmitters use a 47k load resister for the electret mic so i tried it and got more sensitivity even though i want to get as much as i can so much that i could hear a flea circus on a passing dog. anyhow the potentiometer i used for the actual electret mic preamplifier is strange as when i turn it fully to get the highest sound and when i press on it the sensitivity increases, even though im useing a small 250,000 candle power spotlight dish its better to use, a speaker horn cover as the sound gathering with it was good and its pritty good to

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No more whingeing from me :-\,

after my last post I was unable to get any further than the homepage, all I got was (page not found).

I hope mixos fixes the problems soon, before ante becomes an alcoholic :P.


[move] ;D ;DAnother page too load, and another beer to drink ;D ;D[/move]


Is This A Bad Thing 8)

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Hi Steven,
An electret mic draws a fairly constant current through the resistor that feeds it power. Different part numbers of mics draw different amounts of current but most are 0.5mA. An electret mic needs at least 2V across it to work properly. You could measure the voltage of yours.

Ohm's Law dictates the maximum value of the resistor that feeds power to an electret mic. You start with your 9V battery, that is actually only 6V at the end of its life. From the 6V you subtract the desired minimum mic voltage of 2V. Then Ohm's Law says the resistor is the voltage difference of 4V divided by the current and the answer is 8K. If you replace the battery when its voltage drops to 7V, the resistor can be 10K. If your mic draws less current then the resistor can be higher for more sensitivity, but causes other problems:
1) Frequently mics are used with fairly long cables. Cables have capacitance. The RC network of the mic's resistor and the cable's capacitance rolls-off high audio frequencies. The lower the value of the resistor, the less effect cable capacitance will have at high audio frequencies. But yours is probably OK with your short cable.
2) Amplifiers such as the LM386 have input noise current. The noise is higher when the source impedance (your volume control) is a high value. But the volume control loads-down the output of the electret mic and its value must at least be equal to the mic's resistor.
3) Resistors have thermal noise. The higher the value, the higher the noise.

So you must decide between having a very sensitive mic with a lot of noise because its resistor and volume control are too high, or lower sensitivity with less noise. I think that 10K for the resistor and 10K to 25K for the volume control are a good compromise.

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:)thankyou ante and audio guru at the moment i have a 47k load resister and 10k pot still in it and if i press down on the pot the sensitivity jumps a little so i want to increase it more let me geuss if i change the pot to 25k and decrease the resister to 10k will that do it, the dish is only small

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Steven, have you considered The positioning of the mic in the dish, it can make an enormous difference 8).

To find the focal point, position the dish towards the sun and use a thermometer to find the hottest spot, which of course is the focal point, be careful because you can easily destroy your thermometer :o, if you don't have a thermometer just use your finger, when you say ouch you found it ;D. Than place your mic just above this point facing in towards the dish, this you probably already know ;).


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I nearly forgot to mention, you can increase the sensitivity by placing a small dish maybe from a torch, or maybe a (flashlight) hard to come by in Australia though ::) ;D, and place it just above the mic facing inwards.

You should view the construction of your dish, the same as if you were constructing a high-performance antenna. After all this is basically what it is 8).

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:)gazza thats a good piont there, i never thought of that useing the same sunlight phocal piont to get great sound phocus into the mic but then i would have to find a good way to suspend the mic in that pposition without useing anything that could get in the way of incomeing sound waves, or block it to much,

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steven or is it gteven ;D ;D,

Just use light gauge wire, a coat hanger ;). Bend one end to an L-shape then secure it to the dish wall with sticky tape, then bend it across to the other side and do the same, I would say you would need three legs. I'm sure you get the idea. Once you're happy with the position of the mic, you can remove the tape and permanently glue it.

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Hi Steven,
I've given up with booze and beer. It was fun, but now I like to always see and think clearly.

The "toy" big ears use a dish that is 60cm in diameter. Stadium horn tweeters use a horn (dish) even bigger. Maybe your dish is too small to properly reflect the long wavelengths of sound.

In a government scientific demo place they have a "whispering galley". It has a huge 4 or 5m dish at one end and another that is hundreds of metres away. Whispering into one dish can be heard clearly at the other dish, like majic! They use a video link to show each end that are so far apart you can't see.

It's freezing up here now (winter in Canada). Don't sweat too much down under!

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Hi audioguru,

It is an interesting thing wavelength, I'm trying to understand how you could explain, voice wavelength when using the old-fashioned tin can and string intercom. Maybe an resonating affect, but what of the wavelength?. Maybe it is that the energy is transformed from one state to another and then back again.

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Hi Dazza,
Are you sweating down under too while I'm freezing up here? ??? ;D
It's nearly noon and the sun is kinda low 'cause it's shining directly on you! (Except now you have night-time way around there)

The operation of a tin can and string intercom is best understood if you think the string is rigid. Vibrations at one can's bottom at one end cause the same vibrations of the can's bottom at the other end, push-pull. The only effect that wavelength would have is that the can's bottom can't flex enough at low frequencies (it is too small and stiff).
It is true that the can and its bottom resonate. So a tin can and string intercom lacks bass and resonates. That's where the phrase, "tinny sound quality" came from.

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:) hear in western australia at the wungong dam there is a cement wall near the lookout piont at one end if you whisper into it and the other end you listen ,you can hear it well so we call it the whispering wall. dazza the old tin can phone or bush phone ive her about that and seen it on tv , its wierd how sound vibrations travel down that string to the tin can you have over your ear, oh by the way the the small spotlight dish i have is got the hole where the globe came from so thats where the mic comes through, so if i was to position the mic to above the phocal piont then i still have that hole to deal with , i geuss i cant seal that hole with putty or blue tac as that may end up as a sound dampener or obsorbant thus cutting the sound reception quality down , somewhere aroung the 10kb potentiometer is a problem i still get the mics sensitivity to jum higher if i slightly press down on the potentiometer shaft, its as if the pot is makeing more contact inside where that thing contacts , thus increaseing the mic sensitivity, now with this increased sensitivity you get the sound of all those cars out there with there engines runing its hard to exsplain, but its the number one thing i hear with the higher sensitivity, and the second is barking dogs and the sound of wind blowing through the tress , as for filtering unwanted sounds i use my ears and brains for that , i dident get any hiss in the head phones , and although i dident put the resister in yet as recamended by audio guru i think, i dident get the big bang just a small click or similiar with would probably be easy to filter out as described under my old posting, pop filtering

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Hi audioguru,

You would have a similar problem as I'm having but opposite. It's that hot you have to drink your beer really fast, before it evaporates from the heat ;D.

I guess you would have to drink yours really fast before it freezes ;D.

Here's another.

Dashing through the snow, in a one horse open sleigh.

Running fast through the sand, before I burn my feet.
;D ;D ;D ;D ;D ;D ;D ;D ;D

Hi steven,

I have heard of that dam wall, I have been meaning to look it up on the net.

Why not glue a marble in the whole, just vandalis an old paint tin, they usually have a marble in them :).

I shall be absent for a couple of weeks now, I'm heading up north for Christmas, I guess it's just not hot enough here :P.
I'll be looking forward to hearing from you all, in the new year, take it easy ;) 8).

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:)merry christmass dazza, audio guru and ante. dazza its been hot here in the western part of australia the wheather in queensland is much better as i used to live there to and over the years have been back there a few times my father is moveing to cooyar a small country town , be carefull if your going up north dazza the crocs are everywhere, if you see any yowies let me know thats why im trying to get the best sensitivity of my parabolic mic so the yowie hunters over in queemsland could hear them better

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