negrinflon
1 post
Apr 06, 2014
8:35 AM
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Hi
Tried unsuccessfully to build a harmonica mic. All did not work. Advised by expert to leave out volume control. This means just two wires. One from + one from - to jack. Tried wood body plastic body metal. All failed. Do I need to earth the project. Simple components and wiring advice needed badly
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lumpy wafflesquirt
766 posts
Apr 06, 2014
8:43 AM
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I just used 2 wires, one from each side of the mic cartridge, 1 to the tip and one to the sleeve of a mono 1/4" jack plug and it works fine. Are you sure the mic is not broken and you have no dry joints. Or maybe the mic impedance doesn't match the amp.
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"Come on Brackett let's get changed"
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negrinflon
2 posts
Apr 06, 2014
9:59 AM
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1.
1.5" Dia Mic insert Dual Imp 20K & 300 Ohms Racal Acoustics.
2.
Old Telephone earpiece
3.
DYNAMIC MIC ELEMENT microphone replacement insert 500 ohms cb amateur
Have a Pignose 7-100
Some of the three may not have been working. Can you test them?
Thanks for valuable advice
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Greg Heumann
2675 posts
Apr 06, 2014
10:50 AM
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You have to know whether the element works! You test it by hooking it up and plugging it in. I think you discovered your elements don't work.
The pic of the racal element on eBay LOOKS like a crystal. Does it have two sets of leads? Try both pairs. The higher impedance pair signal should be stronger.
The #3 element is definitely low impedance - it SHOULD work but very weakly unless you add an impedance matching transformer.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
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jbone
1580 posts
Apr 06, 2014
2:01 PM
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Better mention as well- a crystal element MUST BE heat sunk so it does not fry while soldering. I lost a 1955 original in a Shure 707a shell some years ago because I did not know this. A crystal is sen sitive to high heat and also to the shock of say dropping it on the floor in or out of a shell. It's possible even rough handling during shipping can ruin one.
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http://www.reverbnation.com/jawboneandjolene
https://www.facebook.com/profile.php?id=100000386839482
http://www.youtube.com/watch?v=wa7La7yYYeE
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Greg Heumann
2676 posts
Apr 06, 2014
5:48 PM
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@jbone - The way most people use heat sinks just gives a false sense of security. If you were soldering to a pigtail lead, a heat sink between it and the actual element would indeed help protect the element. If you're soldering to the element's terminals directly, all a heat sink will do is endanger the element by making it take longer to get to temp. The best method is a good temperature controlled soldering iron and good technique. Pre-tin both parts, join and heat just until the solder flows (that should take a second or so.) Those elements had solder terminals, and the mic manufacturers all safely soldered to them.
Being cautious, however - is a Good Thing!
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
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jbone
1581 posts
Apr 07, 2014
3:45 AM
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Point taken Greg.
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http://www.reverbnation.com/jawboneandjolene
https://www.facebook.com/profile.php?id=100000386839482
http://www.youtube.com/watch?v=wa7La7yYYeE
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negrinflon
3 posts
Apr 08, 2014
10:15 AM
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Hi Guys
many thanks.
I know now that I fried all the inserts to a crisp!!
Will try again
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