FM Transmitter for Mp3 Player

[Overclocked]

Better to Buy or Better to Make my Own? Im looking for a good sounding (good sound quality) FM Transmitter for my Mp3 Player. I dont Own a Ipod, So it would have to use 3.5mm Hookups.

Or would it be easier to Open Up the Front of the Car, Find the stereo, Locate the Input and hack that?

 

[Hero999]

Haven't you searched these forums?

There are 100s of posts about this kind of thing, perhaps we should devote a whole section to it?

 

[audioguru]

We talk mostly about mono FM transmitters for kids. They drift their frequency all over the place and sound awful.

There is an FM transmitter circuit called The Micromitter that is available as a kit. It is stereo and has a quartz crystal controlled stable frequency synthesizer that has a phase-locked-loop.
I saw a small Maxell one in a store for $9.99 yesterday. I think it uses the same good circuit as The Micromitter. The kit costs a lot more.

Have you seen inside a modern car radio? It has thousands of tiny surface-mount parts and some special ICs. It would be very difficult to add a stereo input.

 

[HarveyH42]

Check Walmart or an auto parts store, sometimes even Circle K and 7-11 have them for around $10. Been a few years, but I'm sure it's still a common item at these places. My last car only had FM, and seldom anything I wanted to listen to. My Explorer came with the radio not working at all. Suspect it's not hooked up, but I can't figure out how to get at it, without taking the whole dash a part.

 

[wmmullaney]

Search eBay, (If you want to buy, that is) I bought one and it works great.

 

[eblc1388]

For a FM signal to be detected as stereo and be decoded properly by a stereo FM receiver it should at least have a stable 19KHz pilot tone in the modulation.

If one can build a stereo FM transmitter cheaper than buying one, one must be a real genius.

 

[Overclocked]

Well, Im a bit of an Audiophile, So I want good sound quality (or atleast quality as if you had headphones on). I saw one here:
https://electronics-diy.com/BH1417_PLL_Stereo_FM_Transmitter.php

It Uses PLL, but the 15khz low pass filter has got me a bit worried..Then Again You cant hear that high with Mp3's anyway.

I can probably just order all the parts from Mouser and make everything SMD.

 

[audioguru]

Well, Im a bit of an Audiophile, So I want good sound quality (or at least quality as if you had headphones on). I saw one here:
https://electronics-diy.com/BH1417_PLL_Stereo_FM_Transmitter.php

It Uses PLL, but the 15khz low pass filter has got me a bit worried..Then Again You cant hear that high with Mp3's anyway.

The BH1417 is used in The Micromitter and many FM stereo transmitter products. The BH1415 and BH1416 are also used.

An FM stereo transmitter must have a lowpass filter to reduce the interference from high frequency sounds with the 19kHz pilot tone. The lowpass filter also reduces aliasing interference from audio harmonics beating with the 38kHz subcarrier. The Micromitter project article shows that its lowpass filter cuts 15kHz about 5dB which is not much.

A half-decent MP3 player has a frequency response that is flat to 20kHz.
The Micromitter reduces only the very high frequencies.

 

[mneary]

Im a bit of an Audiophile, So I want good sound quality

Most 'Audiophiles' that I know don't listen to FM stereo. You'll definitely be making some sacrifices.

Your age and gender might be important; males over about 50 don't usually care about 15 kHz.

 

[fever]

well i don't know abt stereo thing but this circuit is quite compact.
**broken link removed**
almost all are SMD components

 

[mneary]

It's quite compact, and mono introduces a dramatic improvement in noise and frequency response (at the expense of channel separation ).

 

[audioguru]

Hi Fever,
The transmitter circuit you posted is garbage:
1) It has no quartz crystal to keep it tuned to your radio's frequency.
2) It is mono like an old AM radio, not stereo like FM stereos.
3) It doesn't have pre-emphasis (treble boost) like FM radio stations have so it will sound very muffled like a stereo with its treble control turned all the way down.

 

[fever]

yes i know thats way i said,i don't know abt its stereo thing while posting the reply.
the only ting i had in my mind is its compactness.

 

[justDIY]

overclocked,

since you're in the states, monitor a website called woot.com for fm transmitters - they come up often. Last set i bought was $14.99 for two (7.50 ea!). They're 12v powered, but opening one up, there's a tiny step-down switcher in there trickling out 3v, a TI 430 flash mcu and a digitally controlled stereo fm transmitter IC. I'd planned to hack mine to run from a cr123a, since I don't want to dedicate a 12v socket for it, but I haven't gotten around to it yet.

the sound quality is excellent provided your can find a quiet fm channel on your dial - it's easy up here in farm country, but might be harder in a metro area.

hacking your head unit and exposing a line-level input will yield the best quality. if you have a GM with onstar, you can hack into the onstar audio circuit which feeds into the head unit - a lot easier than hacking the head unit itself.

 

[audioguru]

If you don't like good FM sound then buy a garbage compactor.

People listen to FM radio because it is high fidelity and is in stereo.
The MAX260x FM transmitter IC has neither and its frequency is not stable.

 

[crusty]

just got a ramsey fm25b, if you're good at soldering, instructions are a breeze, nicely laid out pcb. Sounds awesome, output is a lil on the weak side, but they also sell a linear amp, also a linear amp mast mount. Price is high for the amount of parts it has, $140, it ain't cheap, but it's got rock solid freq. and the audio quality is awesome.

 

[audioguru]

If you live anywhere near civilization then your Ramsey FM transmitter will cause radio and TV interference. When somebody complains then the RF cops will find you, take it away from you, shoot you then chop off your head.
Before you can say, "but ....."

 

[crusty]

If you live anywhere near civilization then your Ramsey FM transmitter will cause radio and TV interference. When somebody complains then the RF cops will find you, take it away from you, shoot you then chop off your head.
Before you can say, "but ....."

Ain't nobody out here, besides the possums n coons, and the pink elephant eating my peanut butter....

 

[audioguru]

Don't you have kangaroos, wallabies and alligators in your neck of the woods?
How about lions and tigers?
Polar bears?

I wonder if your pink elephant is the same one I keep seeing.

 

[justDIY]

I dunno how many rf police the Canadians have, but the US hardly has any.

Just recently our 911 center had an entire 800 mhz tower go down due to interference from a 'rouge' radio ... now this is 800mhz, the supposedly bulletproof encrytped trunked system, more like a cell phone than a walkie talkie. It took 'em almost a week to find the culprit, and the fcc was never involved. the culprit you ask? why it was a police radio installed in a govt building as part of a silent alarm system.