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Microphone pre-amp

 

Hello,
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Has anybody tried this microphone preamp :
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Evaluation boards can be found for about 5€ looks good to me but I am no expert !
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73,
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Yannig - F4IUJ
 

Yannig, good idea. But the QMX delivers 3.3 V via 2.2 kOhm. To have 2.5 V for the IC the current must be not higher than 0.36 mA for the IC and the mic. Unfortunately the IC requires 2.3 ... 5 mA in working state. To use this IC you need an external supply (but blocked towards the QMX).
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73 Ludwig
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Thanks Ludwig,
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I didn't realise that the 3.3V was just for high impedance. You saved me 5€ !
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73,
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Yannig F4IUJ

 

Hi Yanning,
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If it helps, I use a MAX9814 Arduino mic amplifier module powered by two AA batteries.
The module come with a mic capsule on board. I removed the mic capsule and wired it to my gaming headset with built in mic. I also added a foot-switch for PTT for hands free operation.
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Cheers.
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Mel. M0KMD.
 

Hi Mehmet,
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I am sure that it helps but I am trying to minimise the number of potential points of failure as I sometimes operate portable. Aborting an outing because I forgot to check the microphone battery (I can see myself doing this :-o ) would be a disappointment so I will try to find an electret microphone better than what I have now!
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I started with the Baofeng one, it was useless, then one from the local shop, it kind of work if you don't mind shouting and turns the AGC off, and now I think that I will mail order one with a proper tech spec!!!
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73,
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Yannig - F4IUJ
 

Yeah, thats fair enough. I keep forgetting to switch of the external preamp, although the battery drain in minimal.
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I have the QMX+ so i have plenty of room in the case to install the preamp inside. I need to devise some sort of switch to rout the mic signal to the premap or not when the input is used as a CW key... But thats for another day...
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Cheers.
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Mel. M0KMD.
 

Yannig,

If You have issues reaching the limit for free shipping from Digikey(and mouser), I usually add some Fair-rite ferrites to the order as they tend to find use :-)
I recommend this one for portable current baluns:??.? 7?+ 7 turns of RG-316 or as many of RG58 that You can fit work fine for dipoles.?
(maybe also include some BS170, BSS123 for spares :-) )
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Regards , Jonas - SM4VEY


Den tis 20 maj 2025 kl 10:20 skrev Yannig - F4IUJ via <F4IUJ=[email protected]>:

Hi Mehmet,
?
I am sure that it helps but I am trying to minimise the number of potential points of failure as I sometimes operate portable. Aborting an outing because I forgot to check the microphone battery (I can see myself doing this :-o ) would be a disappointment so I will try to find an electret microphone better than what I have now!
?
I started with the Baofeng one, it was useless, then one from the local shop, it kind of work if you don't mind shouting and turns the AGC off, and now I think that I will mail order one with a proper tech spec!!!
?
73,
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Yannig - F4IUJ

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