Stock HU Now Has RCA Pre-Outs! This is no Joke...
- Thread starter tschanrm
- Start date
chuyler1 said:
i actually have my rcas first going to a crossover with 1:2 output voltage gain and then to my amp. however, i found that i didnt need to increase my gains that much. instead, because the freq response gets better with higher volume, i wanted my normal listening level to be 1/2 volume. so i adjusted the fader to the front speakers until i got a nice front soundstage.
feelander said:
Feelander, I'm curious, what's the max input voltage for your amp?
I ask because the main determining factor for how loud you can get the hacked pre outs from the stock headunit depends on the max input voltage of the amp(s) you are using. Ok, lets create a sceneario that should help explain:
Lets say that you have a 50w/channel amp that has a max input of 8v. In order to get the full 50w/channel going to your speakers, you would need an headunit that can push 8v. Now, many headunits cannot do 8v, so what does an amp manufacturer do? They add a gain level to the amp's channels, which can increase or decrease the incoming voltage of the headunit pre-out. This way, if you have a headunit that can only do 4v max, you can increase the gain level on the amp so you can harness the full 50w/channel. Make sense so far?
However, the amp gain can only amplify the voltage by so much. For instance, if you had a headunit that could only output 1v max, the amp gain may not be able to amplify the signal enough to reach 8v. Lets say at the headunit's full volume and max amp gain level, you can only reach 6v. This means that you could never get the amp to push 50w/channel-remember, the amp needs 8v to reach the full 50w/channel. This is not a universal rule however, as amp manufacturers have different levels of max gain. So, there may be an amp with an 8v input that can amplify a 1v preout signal to 8v.
Now, lets you have an amp that can reach the full 50w/channel at a lower voltage, say a 2v signal. In this case, you could easily apply enough gain to the 1v pre-outs to reach 2v, and push 50w/channel out of the amp. In my case, I have an amp that reaches full power at 2v, so it is not a problem for the hacked pre-outs to match the stock amp level. In Chuyler's case, he may be using an amp with a 4v or 8v max input. So, to match the stock amp level, your best bet is to find an amplifier with a lower input voltage, or just try to get a line amplifier that can add gain. Does this help explain why your volume is low?
Overall, the main problem with the headunit is that I think the volume control chip is programmed for too low of an output. The MCU inside the the headunit controls the volume control chip, and while the volume control chip is capable of outputing 2v RMS at max volume, the MCU keeps the max volume at less than half that. If this scenario is not the case, (which I am pretty sure it is, considering Mazda enabled the loudness feature) than the only other explanation I can think of is that there is an impedance mismatch between the hacked pre-outs and the 10k ohm input of most amplifiers.
This was a much more in depth post than I thought, I think I'll add parts of it to the how to section to how-to for this hack, so people understand the reason behind the quiet volume.
Last edited:
I follow. My amps are high-end and will accept 0.2 - 7 V input.
What if you were to tap into the audio signal before the volume control chip. This would only give you stereo output i imagine and you would lose control of your volume knob. However, it will give you a clean signal with no loudness and if you send that to a line driver or 1/2 DIN EQ you won't need the volume control anyway.
What if you were to tap into the audio signal before the volume control chip. This would only give you stereo output i imagine and you would lose control of your volume knob. However, it will give you a clean signal with no loudness and if you send that to a line driver or 1/2 DIN EQ you won't need the volume control anyway.
chuyler1 said:
Good question, and if possible would make for an interesting volume control. Yes, you are correct in that you would only get 2 channel output, left and right only. I am not entirely sure that would work, because there are two inputs on the volume chip: a differential input, and a mixing input. I'll have to look at the pcb traces again and see if Panasonic uses both the differential input and mixing input.
While you are poking around, there is a guy over at DIYmobileaudio that is going to make some digital output boards to be used on head units that don't have digital out...
Digital Output Board Sign-up (approximately $30)
Any idea where the DAC is on our unit? Would I be able to get the radio signal in digital form or will I only get the signal from the CD player/changer? Just some ideas to throw out there. Of course, this would further complicate the volume control issue but I would most likely add some sort of Processor to the mix instead of your basic 1/2 DIN EQ.
Digital Output Board Sign-up (approximately $30)
Any idea where the DAC is on our unit? Would I be able to get the radio signal in digital form or will I only get the signal from the CD player/changer? Just some ideas to throw out there. Of course, this would further complicate the volume control issue but I would most likely add some sort of Processor to the mix instead of your basic 1/2 DIN EQ.
The only DAC's on the headunit are inside the CD section and inside the Minidisc section. There are no digital parts on the main headunit board, so you would not be able to listen to the radio if you streamed a digital out from the headunit. Unfortunately, your odds of splicing into the digital signal and using it are slim to none. In order to create a digital out you need a TTL (Transistor-to-Transistor Logic) signal. Most DAC's accept an I2s signal from the CD transport, or maybe I2c signal. You would need a transcoder chip to convert the I2s/I2c lines into a useable TTL signal.
I looked at that link you provided. It seems this guy is doing just what I said above. He is streaming the I2s line off to a transcoder chip, which sends out a TTL signal to coax or optical out. Now there is one thing that worries me about what he is selling, and that's whether or not he designed the board for our cd player. This is important because, if I'm remebering correctly, the Master Clock of the I2s line and Master Clock of the transcoder chip need to match up. If they don't match up, it won't work. Now, I think transcoder chips can accept different Master Clocks, so it may be just fine. He also says it's "future proof," and that it can accept any signal, but I'm still curious why he wouldn't say what components he's using.....
Also, I think I may have solved the loudness issue, but have not modified anything yet, or tested.
I looked at that link you provided. It seems this guy is doing just what I said above. He is streaming the I2s line off to a transcoder chip, which sends out a TTL signal to coax or optical out. Now there is one thing that worries me about what he is selling, and that's whether or not he designed the board for our cd player. This is important because, if I'm remebering correctly, the Master Clock of the I2s line and Master Clock of the transcoder chip need to match up. If they don't match up, it won't work. Now, I think transcoder chips can accept different Master Clocks, so it may be just fine. He also says it's "future proof," and that it can accept any signal, but I'm still curious why he wouldn't say what components he's using.....
Also, I think I may have solved the loudness issue, but have not modified anything yet, or tested.
Hey, here's something to play around with. With the radio on, if you hold down the power button and press the SCAN button and hold both down for about a second, "AMP-On" displays on the screen. Also, with the radio on, if you hold down the power button and press AM for about a second, "ANT-On" displays on the screen. The service manual does not describe these two messages. I'm guessing they mean "amplifier on" and "antenna on." Only problem is I can't change them using any button combination. Anyone else care to try?
(first) (first) (first) (first) (first) (first) (first) (first) (first) (first)
Take a look at this:
Full volume and 1/3 volume are now exactly the same (the white and green overlap each other). No more loudness.
Don't worry about that high frequency increase, as you can see, it's my junky onbaord sound doing that:
The one thing I'm not 100% sure on is how I lost 2db at 30hz compared to my first post (post #1 graph). I think it may be from the input of the onboard sound card, I'll check with a better soundcard when I get home. Another nice thing is that the volume is now much louder! This includes the volume for the stock amp as well. Not sure how or why that happened. Once I finish some testing, and make sure nothing is broke, I'll post what do to. I will say it's not hard, you only remove a couple of smd parts.
Take a look at this:
Full volume and 1/3 volume are now exactly the same (the white and green overlap each other). No more loudness.
Don't worry about that high frequency increase, as you can see, it's my junky onbaord sound doing that:
The one thing I'm not 100% sure on is how I lost 2db at 30hz compared to my first post (post #1 graph). I think it may be from the input of the onboard sound card, I'll check with a better soundcard when I get home. Another nice thing is that the volume is now much louder! This includes the volume for the stock amp as well. Not sure how or why that happened. Once I finish some testing, and make sure nothing is broke, I'll post what do to. I will say it's not hard, you only remove a couple of smd parts.
Just a quick update,
It seems that the volume did not really increase. Instead, the volume goes to almost full volume at only the 1/2 volume mark, then gets only a bit louder until you reach full volume. Appearently, this is a grounding issue from what I removed, and I need to add a resistor to ground to fix it.
It seems that the volume did not really increase. Instead, the volume goes to almost full volume at only the 1/2 volume mark, then gets only a bit louder until you reach full volume. Appearently, this is a grounding issue from what I removed, and I need to add a resistor to ground to fix it.
Ok, another update:
Volume control is back to normal now, but without the loudness. Full volume is same level as before the mod. I'll write up how to disable the loudness feature, and hopefully get it ammended into the original how-to. So, expect a write up in a few days. (thumb)
Volume control is back to normal now, but without the loudness. Full volume is same level as before the mod. I'll write up how to disable the loudness feature, and hopefully get it ammended into the original how-to. So, expect a write up in a few days. (thumb)
Just wanted to let everyone know I added how to remove the loudness countour to the how to post:
http://www.msprotege.com/forum/showthread.php?p=2669100#post2669100
http://www.msprotege.com/forum/showthread.php?p=2669100#post2669100
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