Internal Mic gain for Yaesu FT7800 2m/440 FM moble

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Internal Mic gain for Yaesu FT7800 2m/440 FM moble	Reply
by K1WJ on June 18, 2007	Mail this to a friend!
Does anyone know if or where there is an internal Mic gain pot for a Yaesu FT-7800? I'm trying to run a lower impedence desk mic 300 to 600 ohms, the stock mic is 2k which is still considered a Low impedence mic. With the desk mics the audio is very low when compared to the stock mic. This is a audio level issue. If there is no internal Mic gain ajustment to be made on the FT-7800 an EQ setup may indeed be required. In Addition: Where can I find the Service Manual for this radio: FT-7800? I looked at UK.mods:did not see. Thanks, Dave K1WJ

RE: Internal Mic gain for Yaesu FT7800 2m/440 FM m	Reply
by W6VPS on June 18, 2007	Mail this to a friend!
Dave: Sorry no direct answer to your query...but you might check the Yaesu FT-7800 or FT-8800 groups on Yahoo. There's a bunch of very savy folks over there. Perhaps they can help. Paul/W6VPS

RE: Internal Mic gain for Yaesu FT7800 2m/440 FM m	Reply
by K4JJL on June 18, 2007	Mail this to a friend!
It the FT-7800 is like the FT-8500, you won't find adjustment pots inside the radio. Yaesu has made secret menus the way to change radio parameters such as mic gain, output power, oscillator warp, etc.

RE: Internal Mic gain for Yaesu FT7800 2m/440 FM m	Reply
by KE3WD on June 18, 2007	Mail this to a friend!
>>"lower impedence desk mic 300 to 600 ohms, the stock mic is 2k which is still considered a Low impedence mic."<< In audio, the lower impedence driving the higher impedence is FB situation, especially considering that very slight difference. Yes, it is very slight when talking microphone level impedence. The gain would only be changed by the impedence if the mic was HIGHER than the input, thus the input impedence would be loading it down. That is not the case here, what is likely the case is that the mic you have chosen simply does not have the gain of the mic you are replacing. A mic level preamp, adjustable, would be the answer then. Even a very simple single transisotr common emitter circuit amplifier would be able to do the job here, although you are likely to find more cookbook circuits out there using a single IC chip. Another way to get there might be to replace the new mic's element, depending upon what it is. More info on the mic may get more answers from the OF here. .

RE: Internal Mic gain for Yaesu FT7800 2m/440 FM m	Reply
by N1TI on June 19, 2007	Mail this to a friend!
Another way around it is to use an impedance matching transformer. There are several economical choices (less than $10) that will give you a closer match. For instance, the SPT-404 from Premagnetics (see http://www.premmagnetics.com/EconAudio.htm) will give you an impedance match of 500 ohms to 1.5K ohms. I'm sure with a little help from Google that you can find an ideal match. Just mount the transformer in a little Bud box (or shrink wrap the whole thing as part of the mic cable) to make a better match. 73, Tim N1TI

RE: Internal Mic gain for Yaesu FT7800 2m/440 FM m	Reply
by K1WJ on July 7, 2007	Mail this to a friend!
Thanks to all, I put an ART mic pre-amp inline, now I have enough audio with my Shure SM58 studio mic set into a Heil desk mic stand. All Set. Reports have been fine. 73 K1WJ

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