How-To:Getting a pre amp signal from OEM midline 6-CD stereo - Page 2

Flush · 03-17-2006, 12:00 AM

When I said I was getting voltage out of the rca's that was with a line out converter. If you have a LOC and have a voltmeter try and check . I bet you will have several volts at your rca/line level out. This will be at almost all times even at a low or muted volume. As far as the mod goes mine is working flawlessly since it was done at least a year ago. I been away from the forums and just checked back recently. As far as adding a capacitor wouldn't that cause a loss at low frequencies? Regardless I'm happy with mine however if it were to go out I would pick up one of the newer double din DVD players. I like the idea of being able to hook up a reverse cam to it. And frankly the FM radio is not bright enough along with the lack of mp3 on my oem.
Since we got some brains in the house I have a question. I have a dirt bike that has a 12v ac power supply for the tail and brake lights. I just converted my rear fender/brake/tail lights to a compact LED light/fender set up. I need to convert the AC to DC (for the led's)so I will be making a bridge rectifier. Do you know what value diodes I need for the LEDs? I think it was a total of 10 LED's so the draw should be minimum. Its a led so I think "dirty" DC will work. Any ideas? I was going to solder the four diodes and the cap and make a small mold and fill it with resin or silicone to keep it waterproof and insulated. I figure it will be a total of 2 cu inch or smaller. Send me a email if you can recommend a wattage diode. dhr@hawaii.rr.com Thanks and sorry for the off topic.

QWIKWHIP · 03-17-2006, 05:25 AM

Ok, so what I'm getting from all this is that these are basically just safety precautions and not "really" needed as far as the function goes? Now from my years of installing stereo's it's always been a well known fact that you can damage any stereo by letting the positive of an RCA cable touch ground when the power on. So does this mean that even high end aftermarket stereo's don't even have this protection? And I checked my meter, and it will only read the voltage in which it's set at. So if I put the meter on A/C then test my 12v battery I get 0. So this means that I am in fact getting an A/C voltage at the preamps. Also, Flush brings up a good point. Won't a capacitor limit the frequency range? Sorry to be so dense with all this.

thajjar · 03-17-2006, 11:03 AM

The cap is absolutely needed if you cannot guarantee that the amp you are going to connect the HU to has a DC blocking cap on it's input. All amps "should" have caps on their line level inputs. Certainly the speaker level inputs of an amp usually do not, but the pre-amp would not drive such a low impedance anyway. If someone was to accidently connect the IC pin to a speaker level input of an amp it could be bye-bye IC.

Adding a cap will hurt the low frequncy response, IF the capacitor value chosen is too low. If the cap value is large enough, the low frequncy roll off will be below 1 Hz. The cap value is chosen based on the input impedance of the load, in this case an amplifier.

If you want to measure an AC voltage riding on top of a DC one for THIS specific case of an audio IC, measure the signal twice with the DVM to DC and then AC settings.

All car HUs, PCMs ...etc.. have some form of surge suppression on ALL the wires connected to them. Cars are nasty sopurces of transients and it is easy to pop electronics if they are not protected.

thajjar · 03-17-2006, 11:15 AM

You telling me your dirt bike dynamo + rectifier/regulator + battery is putting out AC? I need more info on what you setup is.

Where is your battery? Normally a battery is the big capacitor "filtering" the AC output of the dynamo + rectifier/regulator. A 3 phase dynamo on a bike will generate lower "ripple" on the output of the rectifier versus "home" single phase AC.

Do you have a rectifier?

Do you have a regulator?

Flush · 03-17-2006, 10:03 PM

On the OEM line level out put I'm all good. Before the mod I had the constant voltage out of the LOC line side.
As for the bike project the bike I have is a dual ac, dc type set up. It has a charge coil/generator(100watts), regulator(12v) and a rectifier(dc). As weird as it sounds it works like this. One side sends 20w to the regulator then to the rectifier. This is the charging circuit for the battery for starting, horn and turn signal and flasher. The other side, 80w goes to the regulator then to power all other lights headlight 35w, marker 5w, tail and brake light.

ohiodish · 03-18-2006, 07:33 AM

OK, thanks for the diagram.... I will run it by my friend NEO, he can read the Matrix and what not he should have no problem!!!

I have no idea what all that means!!

Quote:

Originally Posted by thajjar

IC means integrated circuit.

In the typical HU, when you need to connect two audios ICs together, you need a coupling capacitor to block the DC biasing voltages from one IC from bothering the other. The main reason for this is due to the fact that you usually only have a single supply voltage like 5-12 volts to power the IC. The ICs audio pins will have 1/2 the power voltage on them. The same goes for when you want to feed an audio signal from an IC to the outside world. There will be say 2.5-6 volts DC offset on the input/output pins of the IC. The audio signal "rides" on top of this DC offset voltage unless you block it with a capacitor. In your case the amp you are sending the signal to probably has input coupling caps blocking this DC voltage. Be careful not to drop your RCA connectors on a ground point. You might pop your HU.

Some designs use very few coupling capacitors, but the ICs are specifically designed to use the DC offset on the output of one IC to bias the input of the attached IC. Other designs use very tiny ceramic chip capacitors for coupling. GM HUs do this everywhere. You can only use a small value coupling capacitor if the input impedance of the following stage is very high.

As far as measuring AC, if you use a cheapy voltmeter set to the AC scale, it blocks DC when measuring AC. If you use a True RMS voltmeter, it will measure the DC offset as well as the AC signal. You will see a "signal" voltage even with the volume muted.

Another BIG thing to mention is that you have exposed an internal IC to a world of hurt by not putting some form of transient protection on each out put. As a minimum I would add two diodes and a 100 ohm resistor plus the blocking cap.

The schematic would be like below:

IC +
_|_
/\ 1N4002
+ |
IC Output ---| |-------+---\/\/\/\/-----o Pre-Amp Out
10 UF | 100 ohm
_|_
/\ 1N4002
|
IC Gnd

thajjar · 03-19-2006, 08:31 AM

What engine is used on the bike? It would be nice to know if you have a dynamo which is used on the majority of bikes or an alternator that is used in cars.

I am going to assume that the regulator is controlling the output of your dynamo. This means the peak AC output voltage is fixed. An LED or a lightbulb will work on AC or DC. You can use a bridge rectifier if you want, but you will need a 3 phase bridge or one with 6 diodes and 3 inputs and 2 outputs.

For an LED, you must use a series resistor. You need to keep the max current through the LED below say .04 amps. An LED "running" voltage when on will be approx 2 volts. Assuming a single LED, the resistor will be R=(Vpeak-2 volts)/.04. Wattage of the resistor will be (.04*.04)R minimum.

If you use a bunch of LEDs in a series/parallel array, you will need to calculate the voltage drop of the array and the amount of current you want to drive each LED with. In general it is beeter to use multiple resistors to feed each series array.

Flush · 03-21-2006, 12:22 AM

So LED's can work with AC any hz. Ok I will try that instead of converting the ac to dc.
Thanks

thajjar · 03-21-2006, 05:51 PM

Yes a LED will work with AC or DC, BUT the typical LED cannot handle more than 5 volts negative voltage across it. You must connect a protection diode across the LED to shunt the negative output of the dynamo.

LED
o---/\/\/\/--o---|>|-----o--------0
| |
----|<|-----
1N4002

johnszcz · 03-24-2006, 04:02 AM

This is great if one is a qualified electronic tech that is is experienced with pcboard repair or reworking but the average guy would do better just to get a "blackbox" like the one from jl electronics or for that matter have a qualified shop do it.

I have noticed that many owners pride themselves on saving money performing modifications and additions themselves but pc board soldering seems a bit over the top.

John

bestatchess · 03-24-2006, 05:58 AM

Quote:

Originally Posted by thajjar

Yes a LED will work with AC or DC, BUT the typical LED cannot handle more than 5 volts negative voltage across it. You must connect a protection diode across the LED to shunt the negative output of the dynamo.

LED
o---/\/\/\/--o---|>|-----o--------0
| |
----|<|-----
1N4002

Hey thajjar, it seems like you actually know what you are talking about. Can you recommend a decent book covering practical electronic circuits like this? I am talking about a practical applications book with descriptions on circuit operations, like the ones that you provide here. I have already taken a few basic undergrad EE classes, so I have had the basic theoretical mumbo jumbo, but it is not from an applications approach.

QWIKWHIP · 03-24-2006, 10:55 AM

Quote:

Originally Posted by johnszcz

This is great if one is a qualified electronic tech that is is experienced with pcboard repair or reworking but the average guy would do better just to get a "blackbox" like the one from jl electronics or for that matter have a qualified shop do it.

I have noticed that many owners pride themselves on saving money performing modifications and additions themselves but pc board soldering seems a bit over the top.

John

Well, I guess it all depends on a persons confidence and ambition. I have never once touched a PC board before this. I consider myself to be nothing more than "the average guy".

bigwilltitan · 03-26-2006, 12:29 PM

Can this be done on a 04 RF radio? I pulled my radio to try it but my board looks different and I don't have the knowledge to identify the correct points on my own.

bestatchess · 03-26-2006, 12:36 PM

Quote:

Originally Posted by bigwilltitan

Can this be done on a 04 RF radio? I pulled my radio to try it but my board looks different and I don't have the knowledge to identify the correct points on my own.

The 04 RF uses an external amp, so I don't think it would make sense to start soldering its circuit board to tap pre-amp.

bigwilltitan · 03-26-2006, 01:22 PM

I understand. I guess I should be asking is there a way to add an aftermarket amp without the use of a LOC on an RF system?