A new take on an old problem

[scootcoupe91]

So I know that you can add aftermarket amps with line level converters when you keep the stock head unit. I also know that a lot of people ditch the stock head unit for aftermarket head units for all the audio features you get.

What I wanted to do was keep the stock head unit and add RCA terminals on the back of the head unit so that I could add a much better amp than what the stock head unit came with.

I started by getting a sacrificial head unit, one of the full equalizer ones, at the junk yard and tearing it apart. After some looking I found the IC that handles the amplifying side of things.

TDA7384 datasheet pdf datenblatt - STMicroelectronics - 4 x 35W QUAD BRIDGE CAR RADIO AMPLIFIER ::: ALLDATASHEET :::

That is the chip that gm uses in our stock AC delco head units. Looking at the data sheet you can see that the built in amp is good for 26 W at 10% THD running 14.4V, most decent aftermarket amps run around 0.1% THD.

After desoldering the chip I am going to take the low level inputs before the built in amp to RCA jacks on the back of the radio and run a much better amp after that WITHOUT having to use line level converters. This should let me keep down the component count down on the system and allow me to have near aftermarket sound out of the stock head unit with all of the fancy integration stuff GM included.

Right now I am waiting on the RCA chassis mounts to show up and then I'll use the o-scope at work to see how it turns out.

If it all turns out well and I like the setup I'll post a write-up if there is interest.

 

[TexasTanker19kilo20]

Subed cause this sounds interesting, will be waiting for the final product.

 

[ericspecullaas]

This is getting good. Pictures are a must for this kind of build. Also subed

 

[scootcoupe91]

A couple of things to cover before anyone starts this.

You will lose the mute function on your stereo since that is a function of the chip that you will be removing.
I highly reccommend a very bright light to work with, what you are soldering is very small wire and it is easy to bridge two solder pads and make an accidental short.

It is likely that you will burn yourself or get very frustrated at some point during this.

If you are still interested in this then read on.

You need 4 Chassis mount RCA jacks that you can pick up off of eBay.
1 ethernet cable


I've taken some photos along the way.

https://picasaweb.google.com/117231099274446631031/2013051802?authuser=0&feat=directlink

The arrows point to the screws that you need to remove to get to the main board on the radio while the circles show snap tabs that you need to pry up to get the front face off.

After you have removed the mainboard and the heatsink you will want to desolder/cut and remove the longer of the two chips. I used some small side-cutters to cut the chip off and the used the soldering iron to remove the leftovers of the pins.

I took some ethernet cable and cut it up since it is both cheap and it is a twisted pair setup, which makes it less susceptible to electronic noise. 4 or 5 inches is a good length to work with, it doesn't occupy too much space in the radio and it will allow you to assemble the mainboard back into the case without too much headache.

Open up the data sheet and scroll down to page 2/9, this is where most of the info you need is. Also be sure you take note of the orientation of the chip when you remove it so you know where to solder the wires to.

Take the ethernet cable and solder the solid colored wires onto IN1, IN2, IN3, and IN4. This is the audio coming from the mainboard to the amplifier chip.

Here comes the tricky part, the chip only needs to share one ground for all of the inputs but you have four rca jacks to ground. What you will end up doing is soldering one of the white wires with the colored tracer to the spot labeled S-GND on pg 2/9. From there you will splice the remaining white -traced wires to the one soldered to S-GND.

After you have drilled the holes in the case, go ahead and install the RCA jacks and tighten them down, you will have a hard time getting tools in there after you have soldered the wires on so it's really now or never. I installed the white insulators between the body of the radio and the jacks but if I have some floating ground issues I will probably go in and solder a wire from the radio chassis to the jacks

The solid colored wires go to the center protrusion on the RCA jack and the white/traced wires go to the rings.

After that it is a matter of reassembly and testing. Which if someone has the pin-out of the back radio connector I could go ahead and check this out before I give everyone the green light to do it to their own radios. That's what I have gotten done so far and i will clean this up when I am not so tired.