Help me develop a car music system

[xibalban]

Hello fellas,

This is my first post, and my first electronic project endeavour. Let me put my project details as follows:

The Project

I have a Maruti Gypsy, an Indian version of Suzuki Samurai, with a fabric hood. I would like to install a music system on this vehicle:

An AM (Shortwave/Mediumwave) tuner
An MP3 player

Say, a 10 W + 10 W rms two speaker system



Why build a project, why not buy it?


Firstly, theft is an issue. My vehicle is always parked in the open, and anyone could unzip/un-button the soft fabric hood and lay a dirty hand on the system. Hence, I need to keep it concealed and discreet.
It is difficult to lay hands on an AM receiver anymore, with most systems preferring FM instead. Besides, these systems are a tad too expensive and come with redundant features like CD player, equaliser, remote, etc.
I wish to build the system out of salvaged parts, most of which I have access to.
Lastly, for the pride that I could gain from being able to build a novel music system customised to my vehicle's need.



What do I have in mind?


I have a LA4445 (**broken link removed**) salvaged out from an old tape-deck.
I also have a TA2003P (http://pdf1.alldatasheet.com/datashe...A/TA2003P.html)
I would assemble the circuit on a general purpose PCB and fix it under the bonnet; I have located a suitable spot near the battery to bolt the PCB through the heat-sink screw-holes.
...and I have the following plan in mind:
To feed the output from my cellphone (HTC Legend) through its 3.5 mm stereo jack to the stereo inputs of LA4445 based amplifier. My cellphone also works as FM radio, just in case.
To feed the output from TA2003P to the above cited amplifier using a toggle switch, placed suitably on the dashboard.
To embed a sliding-type potentiometer somewhere along/attached-with the 3.5 mm input cable to act as volume controller.
A common power on/off switch.




So, where do I seek help?

I request feedback on my design/block-diagram, please.
Which is the best way to regulate 12 V from car battery to 3.3 V rated for the TA2003P?
How do I feed mono output from the AM radio section to stereo inputs of amplifier section?
What is the best way to design the radio-antenna or ferrite coil, etc?
Anything else that I need to consider?

I thank you all for reading through this post. Cheers!!

 

[D.A.(Tony)Stewart]

AM chip runs from 1.2 to 7V so 78L05 is simple choice for 5V
AM is very sensitive to ignition noise, so test with a radio 1st, Many choices with large loop coil or ferrite but directional or whip antenna with preamp.

 

[xibalban]

AM chip runs from 1.2 to 7V so 78L05 is simple choice for 5V
AM is very sensitive to ignition noise, so test with a radio 1st, Many choices with large loop coil or ferrite but directional or whip antenna with preamp.

Thanks, but is it really required? How about a voltage divider using a pair of resistors? I believe that the variation in current (at least in the pre-amp section i.e. AM section) is very minute.
And, is it okay to bridge the stereo inputs of the power amp section to feed mono input?

 

[BradtheRad]

Thanks, but is it really required? How about a voltage divider using a pair of resistors? I believe that the variation in current (at least in the pre-amp section i.e. AM section) is very minute.

What you suggest can work.
However you may get louder or softer volume from the radio depending on whether the engine is on (typically 13.5V from the alternator), or off (typically 12.8 V from the battery).

Regulating the supply may reduce hash on the supply wire.

Located in the engine compartment where there is sparking, do not be surprised if the AM radio only produces buzz.

And, is it okay to bridge the stereo inputs of the power amp section to feed mono input?

Yes. Notice that for stereo you will need a dual ganged volume control.
Screenshot:

 

[xibalban]

Thank you for the valuable inputs, and for the circuit diagram. I have noted your comment on the ideal placement for the kit. I had chosen, a priori, under-the-bonnet location for two reasons:
1. Safe from thieves
2. Closer to the battery, lesser length and lower gauge cable required.

Could anyone suggest the best antenna/loop for the system?
A digital station tuner would be great, by the way.

 

[Audioguru]

The output from the LA4445 amplifier is only 2.2W per channel into 8 ohms or 4W per channel into 4 ohms.
They spec 5.5W when it produces horrible 10% clipping distortion (square-waves).

 

[tpetar]

See this maybe you will find as useful :



TDA1554 2x22W Stereo Amplifier

TBA3810 Mono to Stereo
https://www.aaroncake.net/circuits/stereosynth.asp

12 to 3,3V for TA2003P

Why you whant 3,3V for TA2003P ? This IC have voltage range from 1,8V to 7V, I think 5V will be fine. But if you insist you can use any regulator with fixed 3,3V.

What is the best way to design the radio-antenna or ferrite coil, etc?

Buy fabricated external antenna this is not expensive.

Anything else that I need to consider?

Consider buying of fabricated stereo device. Your design needed budget is over cheapest device in market. You can buy nice device for small money.




Better invest some money in SoundRacer V8 and impress some girl:
https://www.youtube.com/watch?v=b9XAC-BvUyo

 

[Audioguru]

The TDA1554 amplifier is not made anymore. Philips stopped making many amplifiers when they changed to NXP.
When it was available its output was only 12W at 0.5% distortion into 4 ohms when the battery was 13.2V.
When the battery was over-charging at 14.4V and the distortion was horrible at 10% then its output was 22W square-waves.

- - - Updated - - -

The TDA1554 amplifier is not made anymore. Philips stopped making many amplifiers when they changed to NXP.
When it was available its output was only 12W at 0.5% distortion into 4 ohms when the battery was 13.2V.
When the battery was over-charging at 14.4V and the distortion was horrible at 10% then its output was 22W square-waves.

 

[D.A.(Tony)Stewart]

Apparently the TDA1554 is replaced by the TDA1554Q 0.1% THD @1W

Power bandwidth THD = 0.5% Po=−1 dB w.r.t. 15 W Bw 20Hz to 15kHz
Max Output Power x Channels @ Load 22W x 2 @ 4 Ohm in bridge mode; or 11W x 4 @ 2 Ohm
Voltage - Supply 6 V ~ 18 V
Features Depop, Mute, Short-Circuit and Thermal Protection, Standby

It's a great solution.