Lexus IS Forum banner

1 - 20 of 36 Posts

·
Registered
Joined
·
210 Posts
Discussion Starter #1
I just did the Aux input mod described here on the forums. The stereo is not as loud as before. With the volume turned all the way up it's apx at 50% of what it was before. Is this normal?
 

·
Registered
Joined
·
1,194 Posts
AppStar said:
I just did the Aux input mod described here on the forums. The stereo is not as loud as before. With the volume turned all the way up it's apx at 50% than what it was before. Is this normal?
This is exactly what I was expecting and afraid of when I was writing a response to this post:
http://www.is300.net/modules.php?name=Forums&file=viewtopic&t=13358202
If you read my replies to the above thread, it might give you an idea of what's going on. Basically, I think the root cause of the degrade in sound volume is connecting the SGND (Yellow) wire to the NEGATIVE wires (Red and Black) of the left and right channels. You see, the NEGATIVE wires for the left and right channels aren't really at 0volts like a typical negative lead, but if you connect them to the SGND, which is really at 0volts, they become 0volts which effectively reduces the voltage going through each channel in half. What I think is going through each pair of wires for each channel are signals that are inverse of one another. If you have 2 inverted signals and use it as a reference to each other, you get double the voltage of each signal individually. So what's going through say the Left (+) White wire is 1V and going through the Left (-) Red wire is -1V, what you get at the other end is 2V. But if you decide to connect the SGND wire to the Left (-) Red wire, then what you get at the other end is only 1V.

Anyway, this is all still somewhat speculation, but from your observations, I'm beginning to think it's correct. Any comments anyone?
 

·
Moderator
Joined
·
8,880 Posts
I was afraid that was going to happen.
Well, worse come to worst,
2 of Bridging Input Transformers may do the trick.

The RCA switcher will be the tricky part since 2 wires (+/-) for each channel would need to be switched.
 

·
Registered
Joined
·
1,194 Posts
vlad_a said:
I was afraid that was going to happen.
Well, worse come to worst,
2 of Bridging Input Transformers may do the trick.

The RCA switcher will be the tricky part since 2 wires (+/-) for each channel would need to be switched.
So I assume this bridging transformer will perform a similar task as bridging the output of an amp to combine 2 channels into 1? But, in this case, the 2 channels are really just 1 channel and the input + and - leads are inverse of one another, so the output of this bridging transformer would effectivlely be double of the input voltage of one of the input leads. Sound right?

And if what I said above it right, then you could just tie the GND and (-) leads of the output of this transformer together and then you'll still have only 2 wires going into your RCA switcher.
 

·
Moderator
Joined
·
8,880 Posts
No, it's not the same as the amp.
I think I found the right part I was looking for.
The idea is to isolate each channel from the AUX device. There might be an isolation device already available for the aftermarket audio.

Ignore the ground connector. It is for interferance issues.

What would need to be done is to connect (-) on the input of the transformer to the ground. (+) to the RCA output for each channel. That's why 2 transformers would be needed.
Now, the output +/- would go to the +/- wires for each channel on the OEM AMP input. A 4 wire switcher would need to be used to disconnect the stock stereo and connect the trasformer as the input device.
From AUX ----------- OEM AMP
(+)--->|<---- (+)
........>|<
........>|<
........>|<
(G)--->|<---- (-)


I hope that makes sence.

People, feel free to chime in. I'm just building theories here.

[edit]
It occured to me that the transformer I linked will not work. What we need is Unbalanced to Balanced converter.
 

·
Registered
Joined
·
1,194 Posts
vlad_a said:
No, it's not the same as the amp.
I think I found the right part I was looking for.
The idea is to isolate each channel from the AUX device. There might be an isolation device already available for the aftermarket audio.

Ignore the ground connector. It is for interferance issues.

What would need to be done is to connect (-) on the input of the transformer to the ground. (+) to the RCA output for each channel. That's why 2 transformers would be needed.
Now, the output +/- would go to the +/- wires for each channel on the OEM AMP input. A 4 wire switcher would need to be used to disconnect the stock stereo and connect the trasformer as the input device.

I hope that makes sence.

People, feel free to chime in. I'm just building theories here.
So this bridging transformer would actually go between the AUX device and the stock AMP. I thought it was to be used between the stock headunit and the stock amp.

So what does that do to the signal for the AUX device? Does it just split it into 2 signals, one inverse of the other?
 

·
Moderator
Joined
·
8,880 Posts
Ideally, it would produce the same signal on the output as one on the input. The reason for it, the AUX device has (-) output wire same as the ground, whereas OEM does not. The transformer would take input signal and convert it to magnetic waves, then back to the electric current. That would produce output signal not relative to the ground.

This would need to be done for both channels.
 

·
Moderator
Joined
·
8,880 Posts
I'm doing more reasearch and it seems that a "Ground Loop Isolator" may also work. The cost is around $20, so it is not expensive to give it a try. 1 device is needed for both channels. Original Sophie's instructions must be followed, where he does not recommend connecting (-) input terminals to the ground.
 

·
Registered
Joined
·
210 Posts
Discussion Starter #9
Isn't a ground loop isolator used to remove the humming noise that come out of speakers due to improper installation. I don't have any humming or other undesired noise coming out at all of my speakers.
 

·
Registered
Joined
·
1,194 Posts
AppStar said:
Anyhow I found a really cheap one if that's what we need... http://shop.store.yahoo.com/xmfanstore/grloisei.html
I'm not sure if that's what we need. If you think about it, even though the (+) and (-) lines coming out of the headunit both have signals, what matters is the voltage difference between these two lines. Just because one of them isn't constantly at 0volts, doesn't mean what the stock amp sees at its input is any different than a signal that has one of the leads constantly at 0volts.

Say we grounded the (-) lead going into the stock amp, meaning make it a constant 0volts and we doubled the voltage in the (+) lead going into the amp. I'm pretty certain you will still have the same volume as if the (+) and (-) leads were untouched.

What I think you would have to do to preserve the original volume of the stock head unit is to NOT cut the Yellow wire and NOT connect the Black and Red wires. Instead, connect the Red wire only to the LEFT neg terminal of the RCA jack, and connect the Black wire only to the RIGHT neg terminal of the other RCA jack.

Other than that, follow SophieSleeps instructions. The only other tidbit you might need is to boost up the voltage of the AUX input signal, coming from your MP3 keg or whatever, so it will match the signal volume of the headunit.
 

·
Moderator
Joined
·
8,880 Posts
Here is why the volume decreases. When one of the wires is connected to the ground, the output level (sum of 2 lines) goes down 1/2 because one of the lines is grounded, therefore canceled out.

Before:


After:


Previously, the amp was getting a "sum" of both outputs, whereas now, there is only one.

What will happen if you cut only one, let's say (+) wire on the OEM amp input and leave the other intact, is that you will have half of the feed from OEM HU and the other half from AUX. So, you will have 2 sources overlaying each other. :crazy:

Now, you could use a 4 wire switcher and connect the (-) wires to the ground when in AUX and back to (-) output from HU when not.
Why connect it to the ground in AUX mode? Because the output from AUX device uses ground as neg terminal.

I think that the grounding loop should work (if I understand correctly what is used inside).

In the article the device is called "Balanced Line Driver".
 

·
Registered
Joined
·
1,194 Posts
OK, listen you don't need any fancy $100 balanced line converter or even a $20 ground loop isolator to make your headunit signal back to the level it was before you added the AUX Input mod. Think about it, everything worked fine before you added the AUX Input mod, so why do you need extra stuff to get your head unit signal sounding at right volume?

Do as I said in the above post. Follow SophieSleeps' instructions with these 3 modifications:

1) Don't cut the Yellow Wire
2) Don't connect the Red and Black wires together
3) Connect the Red wire to the negative terminal of the left channel RCA plug and the Black wire to the negative terminal of the right channel RCA plug

That's it! Your head unit will now be at full volume as it was before. Why? Because you didn't change any of the wiring by tieing the SGND (Yellow) wire to the negative leads of the balanced left and right outputs. It's that simple!

Now the only other thing you might want to do is convert your AUX signal, which is more than likely unbalanced, to a balanced signal with one of those fancy balanced signal converters just to keep the AUX signal consistent with the signal coming from your head unit. However, I don't think it is absolutely necessary; the stock amp seems to take in unbalanced signals as input without much problem.
 

·
Moderator
Joined
·
8,880 Posts
^^^^
You're finally getting it. :eek:
It is not the OEM HU signal that needs to be converted, but the AUX output signal from Unbalanced to Balanced.

As I stated before, you can either convert it, or use 4 wire switch to connect (-) wires on the AMP input side to the ground.

Step #3 is has a flaw because AUX device has Negative terminal same as the ground.
Why? Because it is unbalanced. That is why the either a conversion or 4 wire switch is needed.
 

·
Registered
Joined
·
1,194 Posts
vlad_a said:
^^^^
You're finally getting it. :eek:
It is not the OEM HU signal that needs to be converted, but the AUX output signal from Unbalanced to Balanced.

As I stated before, you can either convert it, or use 4 wire switch to connect (-) wires on the AMP input side to the ground.

Step #3 is erroneous because AUX device has Negative terminal same as the ground.
Why? Because it is unbalanced. That is why the either a conversion or 4 wire switch is needed.
My instructions above have NOTHING to do with the AUX source ok? It is NOT ERRONEOUS and you are an asshole for putting it in BRIGHT RED LETTERS. I'm not here to compete to see who has the biggest car audio dick, I'm just trying to save the guy some money for something that he doesn't need. The original post was to rectify the decrease in volume of the HEAD UNIT due to SophieSleeps' insturctions. My solution works FINE to fix his problem and get the orginal sound volume back from his head unit. I actually did this on my car, it works.

What you mentioned is something absolutely different. It has nothing to do with the decrease in volume of the head unit. Besides, if you read my post a bit more carefully, unlike how you've done in the past, it is NOT ABSOLUTELY NECESSARY for the AUX signal to be balanced, the stock amp seems to take an unbalanced signal as input without much of a problem. And why do I know this? Because I actually TRIED it..... no speculation here. Have you even done any of these mods to your IS? It doesn't sound like it.

Appstar, trust me, you don't really need to buy anything to get your headunit volume back to how it was, follow my 3 steps above. If you want more details or clarifications, you can PM me. I'm getting a bit tired of others baggin on my instructions when they are actually talking about something different and haven't even done the work themselves on their car.
 

·
Moderator
Joined
·
8,880 Posts
Once again, the maturity level with name calling just shines through. :roll:

I see... put it back to the way it was before the MOD is a good advice to fix the problem. :roll:

No, I did not do this mod. I might do some experimenting of my own if I have spare time.
My car is partially taken apart. The whole OEM setup will be replaced with a custom design, fully rewired.

P.S.
I changed the color and wording prior to your posting.
 

·
Registered
Joined
·
1,194 Posts
vlad_a said:
Once again, the maturity level with name calling just shines through. :roll:

I see... put it back to the way it was before the MOD is a good advice to fix the problem. :roll:

No, I did not do this mod. I might do some experimenting of my own if I have spare time.
My car is partially taken apart. The whole OEM setup will be replaced with a custom design.
Oh and the maturity level of putting stuff in bright red letters just to prove you have a bigger dick? Oh please, save it.....
 

·
Moderator
Joined
·
8,880 Posts
^^^^
Thank you for supporting my point. :roll:
 
1 - 20 of 36 Posts
Top