How to get Line Out from a Wireless FM Modulator - diyAudio
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Old 27th November 2010, 07:48 AM   #1
Sajjt is offline Sajjt  India
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Default How to get Line Out from a Wireless FM Modulator

Hello Experts,

I am using a wireless FM transmitter with BlueTooth for playing music from my pen drive. I am in lookout for a line out from wireless FM transmitter as the modulator is not providing quality transmission and sometimes even other interferences are making the music almost crap quality. Is it possible to get LINE OUT from this? so that it can be easily connected to the aux socket on the HU.
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Old 27th November 2010, 08:12 AM   #2
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I'm confused by your question.

Are you saying you have [Pen Drive] -> bluetooth -> [some device] -> FM -> [Head Unit]?

Describe the system; be specific.

Last edited by Johnny2Bad; 27th November 2010 at 08:30 AM.
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Old 27th November 2010, 10:14 AM   #3
Sajjt is offline Sajjt  India
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Quote:
Originally Posted by Johnny2Bad View Post
I'm confused by your question.

Are you saying you have [Pen Drive] -> bluetooth -> [some device] -> FM -> [Head Unit]?

Describe the system; be specific.
Its a FM modulator with Bluetooth hands free option for the mobile. I used to play Mp3 songs from Pendrive connected to the FM modulator. While playing from Pendrive or SDHC, transmission is getting distorted due to interferences and the quality is low because of this. Is it possible to take a line out from the processor before the FM transmitter?

Here's the pic:

Click the image to open in full size.

The Bluetooth FM transmitter can play music of MP3 format from USB pen drive, SD Card, Mini SD Card, Micro SD Card, MMC Card, and MP3.

It supports a2dp function. So you can play music on your headset with the Bluetooth function. Or you play music from your headset from the 3.5MM socket (a 2.5MM to 3.5MM audio adapter may be needed)

What¡¯s more important, it can be used as mobile phone hands-free car kit. You firstly pair the player to your handset via Bluetooth function. Press the ¡°phone sign¡± button on the player and it can change to phone dialog when a call comes in. It returns to play music after the call end, by which you can drive much safer & more comfortably.

Hope this clears.
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Old 27th November 2010, 11:57 AM   #4
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Oh, I see.

A: No.
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Old 27th November 2010, 04:04 PM   #5
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Have you considered a new head unit with bluetooth and a USB port? I know you're not in the US but THIS search is an example of what's available. Similar head units may be available in India.
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Old 27th November 2010, 04:22 PM   #6
pjp is offline pjp  India
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Does it have a socket for external audio in for the FM transmitter ?
I have an el-cheapo FM car transmitter that has a line-in socket, and the socket is wired to the output of the mp3 decoder and the input of the FM transmitter chip. (So you could use it as a line out, perhaps with a bit of rewiring.)
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Old 28th November 2010, 05:10 AM   #7
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Quote:
Originally Posted by pjp View Post
Does it have a socket for external audio in for the FM transmitter ?
I have an el-cheapo FM car transmitter that has a line-in socket, and the socket is wired to the output of the mp3 decoder and the input of the FM transmitter chip. (So you could use it as a line out, perhaps with a bit of rewiring.)
It's hard to say. The basic problem is twofold: one, the manufacturer's description displays a poor understanding of the English language, so we have to guess what they "really" meant by it. Guessing often leads to bad results.

For example, it states:
" ... It supports a2dp function. ..."

Maybe by "a2dp" they mean 'analog to digital processor'. Or maybe not, because they follow that with " ... So you can play music on your headset with the Bluetooth function. ..."

Do they mean it will transmit from pen drive to a Bluetooth headset?


Secondly, going back to the OP, it might be useful to avoid the question completely and look at the problem itself: poor quality. Bluetooth is not likely to send good quality audio from anything to anything. 'Adequate' might be over-achieving. This brings up the question of exactly what level of quality the unit is capable of in the first place; certainly they are willing to tout an inherently poor quality option as a feature.

FM has the ability to transmit and receive good quality, but there is plenty of opportunity to do it badly as well. We don't know the performance of the D/A converter. Is it 16-bit? If so, in line with typical 16-bit consumer/computer grade D/A processors, it's probably not capable of resolving more than perhaps 12 bits.

Is it 8-bit? Possibly, certainly Bluetooth is up against it's inherent limits with an 8-bit signal, and some of the more aggressive mp3 formats easily fit into 8 bits, but nobody's going to be fooled into thinking it's high quality. So, taking a line out, if you can, from the D/A processor's analog out and soldering an output jack might not do anything as far as solving the problem goes.

If it were me, I'd burn a few mp3 CDs and be done with it. Alternately, rather than trying to get a line out, I would see if I can find the FM transmitting antenna in the unit, and add a length of wire to it. 14.25" is 1/8 wave for broadcast FM. That should significantly increase the S/N of the FM transmitted signal.
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Last edited by Johnny2Bad; 28th November 2010 at 05:38 AM.
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Old 30th November 2010, 06:12 AM   #8
Sajjt is offline Sajjt  India
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Quote:
Originally Posted by pjp View Post
Does it have a socket for external audio in for the FM transmitter ?
I have an el-cheapo FM car transmitter that has a line-in socket, and the socket is wired to the output of the mp3 decoder and the input of the FM transmitter chip. (So you could use it as a line out, perhaps with a bit of rewiring.)
@PJP, its there and its working too, only glitch was the line out strength is too weak so I've to keep the vol to higher levels and its irritable when switching between other sources and it can spoil my speakers as the AMP may exert heavy stress on speakers too.

Quote:
Originally Posted by Johnny2Bad View Post
It's hard to say. The basic problem is twofold: one, the manufacturer's description displays a poor understanding of the English language, so we have to guess what they "really" meant by it. Guessing often leads to bad results.

For example, it states:
" ... It supports a2dp function. ..."

Maybe by "a2dp" they mean 'analog to digital processor'. Or maybe not, because they follow that with " ... So you can play music on your headset with the Bluetooth function. ..."

Do they mean it will transmit from pen drive to a Bluetooth headset?

Secondly, going back to the OP, it might be useful to avoid the question completely and look at the problem itself: poor quality. Bluetooth is not likely to send good quality audio from anything to anything. 'Adequate' might be over-achieving. This brings up the question of exactly what level of quality the unit is capable of in the first place; certainly they are willing to tout an inherently poor quality option as a feature.
@J2B, You are right, its always over highlighted with the features which may not be realistic in performance.

The Bluetooth referred here is for the hands free operation on the cell phone. Its only one way I think.Once its paired with the phone its working as a bluetooth headset. It wont transmit from any cards/USB to a bluetooth device.

Quote:
Originally Posted by Johnny2Bad View Post
FM has the ability to transmit and receive good quality, but there is plenty of opportunity to do it badly as well. We don't know the performance of the D/A converter. Is it 16-bit? If so, in line with typical 16-bit consumer/computer grade D/A processors, it's probably not capable of resolving more than perhaps 12 bits.

Is it 8-bit? Possibly, certainly Bluetooth is up against it's inherent limits with an 8-bit signal, and some of the more aggressive mp3 formats easily fit into 8 bits, but nobody's going to be fooled into thinking it's high quality. So, taking a line out, if you can, from the D/A processor's analog out and soldering an output jack might not do anything as far as solving the problem goes.
I still have hope in this mod. The 3.5 Stereo jack is providing line out but its too low but from FM transmitter the audio is much more bright.

Considering the limitations in processing and the loss of quality than the CD(I tried to play the same 320Kbps songs from the CD as well as from the transmitter, the quality difference is very much evident in CD), is there any other media player can be used for playing from USB/MMC?

Quote:
Originally Posted by Johnny2Bad View Post
If it were me, I'd burn a few mp3 CDs and be done with it. Alternately, rather than trying to get a line out, I would see if I can find the FM transmitting antenna in the unit, and add a length of wire to it. 14.25" is 1/8 wave for broadcast FM. That should significantly increase the S/N of the FM transmitted signal.
I cant carry any more CDs as my glove box is full with Mp3 CD albums and it doesn't look neat either.

Yes thats what I am going to do, its clearly marked on the PCB the antenna extensions like saw tooth layout.

Can you elaborate the highlighted portion in laymans language on the signal strength?

Also somewhere I read that disconnecting the Antenna wire from the HU will take care of the interferences and it does its job some what better, but at the cost of other radio channels

@Perry Babin, I choose a wrong HU which doesnt've a USB and its only 5 months old, so buying a new one with USB is not acceptable for the moment. Am thinking of an economical option with the available resources.
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