Wired fm modulator help

[rbf1138]

Today I had a wired fm modulator installed in my 2003 Lexus ES300. The one used was the "Farenheit Phase Lock Loop FM Modulator (EFM-01 / EFM01)." My issue seems to be that when the music is quiet/not busy, it comes through clear, but when the sounds pick up I get some seriously bad buzzing/distortion.

The shop I had it installed at is extremely reputable, and they assured me it'd sound better than my cassette adapter. However, if there is going to be this buzzing, it certainly isn't better. I have an on/off switch to disable the radio when i use the modulator, and there is also some little knob i can turn, though im not sure what that does. The station they have it using is apparently a good one (88.9).

The best example of the problem I can give is that during the opening of Radiohead's Airbag, it's smooth until vocals come in, at which point they distort, seemingly primarily on the vocals themselves.

I'm wondering what may be wrong here, or what I can do to fix/improve the issue. I'll probably call the shop tomorrow, but I'm interested in what you guys have to say.

I should add, it's definitely not like clipping from being played too loud. I've tried it with a Cowon player with a dedicated line-out, and even when the volume is turned down on my car's stereo, it still distorts. It's like a certain frequency in the music is screwing with the system.

Click to read more...

 

[Saint211 10+ year member]

Im assuming you are using this to play an I-pod or something like it through your factory stereo. They are just like the ones we install. FM modulators are better solutions than fm transmitters and in most cases cassette adaptors, but they aren't perfect. What these modules do is introduce the audio over a wired connection. It is wired in line with the antenna of the radio, sometimes using 2 antenna adaptors. What confused me is that you said you had an on/off switch for the radio when you use the FM modulator. This isnt possible because the factory radio need to be on and tuned to the frequency you have the fm mod set to in order to work. When we do sat. radios the fm mods rarely give us an issue. We see issues more frequently when people use these generic fm mods for I-pods and such. Honestly, its hard for me to help you without looking at the vehicle, but heres issues I ran into before.

• problem with the 3.5mm to RCA cable
  
• problem with the antenna adaptors
  
• problem with the bitrate of the mp3 audio being played through
  
• noisy power and ground source for the fm modulator
  

If I did the install, and you brought it back to me with this issue I would start eliminating the obvious. Fisrt, I would see if ther issue happens on normal radio/cd. If not, then I would try a different cable. If that didnt change it I would try different adaptors/make sure they are connected. Also make sure you dont have a powered antenna in the vehicle that they may have fudged with. Make sure the connections are firm. If the problem persists I would try a different power and ground source for the modulator. If it still persisted I would then try a different module.

IF they eliminate all these options its likely a bitrate/compression issue.

It reminds me of this gentleman I encountered with an FM mod in his BMW. The problem he had was at certain points in each song, there would be this strange clicking noise. It wasnt the same point in every song, but it would always happen at the same point if you replayed a certain song over and over. I went through a lot of crap to verify everything was sound and secure and the problem persisted. We ended up finding out that ith was an issue with how the audio he had was compressed.

 

[rbf1138]

Thanks for the detailed reply. A couple points of clarification:

By on/off switch, I just meant, I can flip it so that when I'm tuned to 89.1 it uses the modular signal, or I can flip it so that it functions normally with the radio frequency.

I'm sure it is not an audio issue, as I've tried it with a player I have with lossless files and a direct line-out. Fortunately, I know enough about audio to know that this isn't an issue of bitrate, or even distortion from clipping due to volume levels.

It really seems that I can isolate the distortion to certain parts or sounds in the various tracks I've tried. Like I said, with Radiohead, sometimes the distortion seems focused right on the vocals, no matter how loud the volume is turned up or down. It'll be totally clear and then a new instrument will come in, or new sound, and then I'll get crackling that seems isolated to that particular voice/instrument.

I have had a Sirius radio installed for several years, and I do not have a problem with it. It also uses a wired fm mod.

It sounds like it's probably an issue with the ground noise, or that the mod doesnt have enough power to handle the input and gets overwhelmed when the music gets more complex, in a sense?

 

[Saint211 10+ year member]

Well, tbh with what you just provided it seems narrowed down to either an issue with the FM mod itself or perhaps the power and ground source for the FM mod. So your on/off switch is actually in line with the FM modulators power line?

First thing I would try here would make sure there is a direct ground to the chassis or atleast a solid metal support under the dash. Then try different power sources for the FM mod. Lastly I would try running the power line direct without the switch just to be thorough.

I would guess its likely that they installed the FM mod and tapped power and ground behind the radio in the radio harness, which isnt a truly direct source. Something to look into.