4 watt fm transmitter help

[Damo666]

Hi guys, great forum.I've just bought a couple of "Smartkit 1028" transmitter kits.I've assembled both and they're working fine apart from some poor audio issues.One uses a 2n3553 and gives out almost almost 3 watts, the other uses a 2sc1947 and boots out just over 4 watts.I think i've found a mistake on the supplied schematic in the preamp stage but want some assistance to confirm it(see if you can spot it).Anyway, on this note - the audio is either quiet or very distorted while being fed from a personal cd player in mono regardless of spending ages playing about with vr1 and varying the audio from the cd player.Please have a look at this link 4 Watt FM Transmitter ..I hope i'm allowed to post this link by the way.I'm ripping my hair out here, please help me and see if you can see the mistake in the preamp stage.If it is a mistake that is.Cheers in advance guys.

 

[transistor495]

Why need 4Watt. Just add a 2N3866 on the output of an ordinary single stage fm oscillator circuit. You will get good signal strength something upto 1km with a tiny wire antenna. Search for Rod Elliott's fm music transmitter.

 

[blueroomelectronics]

Plus a 4 Watt AM transmitter probably requires a license to use / build. Big FCC fines if you're caught.

 

[audioguru]

Like I said on the other website, the volume control is shown connected backwards. It shorts a dynamic microphone which doesn't care if it is shorted. Your sound source probably has a signal level that is much higher than a microphone and shorting it might cause poor sound.

The transmitter is missing pre-emphasis (treble boost) that all FM radio stations have. The de-emphasis (treble cut) in all FM radios will make the sound from this transmitter muffled like your stereo with its treble tone control turned all the way down.

 

[Damo666]

..

Hi Audioguru.I've managed to get the audio sounding half decent now by removing and amending some components in the preamp stage.I just need to eliminate the fan noise that's superimposed on the carrier without using a seperate power source now.

 

[audioguru]

The audio preamp transistor is powered directly from the supply. If decoupling was used then it would not amplify noise from the fan.

 

[mneary]

the volume control is shown connected backwards.

Although it is shown incorrectly on the schematic, the actual SmartKit circuit board shown on the website is correct.