I recently told about the BA1404 stereo fm transmitter integrated circuit. It is the main chip that you find in most kits (I have done kits. They usually are solder by number, and don’t really teach you anything, unless you really study them, and are therefore not much fun. It is much better to do it yourself). The Griffin iTrip uses a similar chip to this. I mentioned that the quality of this chip is pretty poor. It does too much. It has the FM transmitter built inside. Everything is too close inside the chip, and there is crossover distortion. This chip is not even made anymore.
There is a much better option to the BA1404. The NJM2035 chip does not have a built in transmitter, or the FM oscillator. This chip takes the two inputs, which should be connected through a Pre-emphasis circuit. High frequencies in a FM system contribute to noise, so the pre-emphasis circuit increases the amplitude of the high frequencies before putting them into the chip. This chip takes the two inputs, and the input of a 38KHz crystal. This chip then creates a stereo composite signal and a 19KHz pilot signal. These two signals are mixed externally, and then an mono FM transmitter can be used. Check out my simple DIY FM transmitter for how-to information on building one. Check out the pdf on this chip to read more on how to use it.
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