What do I need to know to interface headphones into my system? How do I figure out the resisters I need to match up the Ohms, volts and amps? Any info would bring many thanks. savoo

 

It would depend a lot on the kind of headphone you're planning on using if you just want to hardwire them. Headphone power handling and resistance varries greatly from one pair to the next.

Are you trying to drive them off your head unit or another source?

 

What stereo do you have?

 

Here in MN, it's illegal to drive with headphones on; you should check this in your state to see if its legal first. But, if you have 2 or 3 sets of RCA outs in you HU, you can use one (not the sub one) with an RCA -> headphone jack converter.

 

I have no idea how the watts/volts conversion works, but be careful in doing this because it might be a little on the loud side.

Also, a good point was made by jovial. Even if it's not illeagle, you will defantly run into problems if you can't hear what's going on around you, not to mention a weird nose your car might make for whatever reason. Say a firetruck is about to pull onto your road but is blocked by trees. It has its siens on and what not, but you can't hear it. Next thing you know, you're t-boned. That would not be a happy situation.

 

I'm replacing everything. I'll be getting a head unit and four speakers. I want the headphone jacks to shut off the speakers when they're pluged in. I'll be putting one jack on the fr. speakers and one on the back. That way with fader adjusting each person can have the volume they want. This being a t-top I need them to block out wind noise. I know I have to put some sort of risister on the jacks so the resistance of the headphones and resister = the speakers. I think in my state (Maine) deaf people can drive. I had them on a convertable I owned and there's nothing like them. Just hearing the music while you drive is surrealistic. Well thanks for the info. It's always good to get others opinions. savoo

 

FYI, It is illegal in ALL 50 states (last time I check, couple for years, can't see it changing) to drive with head phones on. You can only have ONE ear obstructed (like hands free cell phone kits).
I STRONGLY recommend against this. Not just from a legal stand point, but from a technical stand point. It will be vary easy to damage the HUs internal amp. It will take a lot more then you think to keep the internal amp happy. Not just keeping the load right.

 

you need them to block out windnoise? hrm... I think that's why they invented the following for 2 different scenarios:

1. A volume ****. Turn it up, then you can hear your music.... a no-brainer

2. Weatherstripping... if you are getting loud windnoise with the tops on/windows up... there's your answer.

Everytime I see someone wearing headphones while driving, I can't help but wish to see them get arrested or in some sort of horrible accident.

I'd say go for the headphones, but sometimes people who win the Darwin award also hurt innocent people in the process... and that's more than likely what would happen.

sorry if that was harsh but if you sit down and think about this for a second, you'll see how foolish it is to even consider headphones while driving.

 

I feel bad for your ears. Headphones + loud volumes are bad news. People think its not bad becuase they are relatively quiet, but anything that close to your ear that is needed to drown out wind noise with the windows down is going to do serious damage. With that said, check out an "L Pad attenuator". Basically a huge voltage divider (made of 2 high powered resistors).

 

NEEDAZ, If the load is the same as speakers, how will the amp know what it is driving?

SCRAP MAKER I'm getting CLOSED headphones with foam all around the ears. That stops the wind noise, so I won't have to turn the headphones up LOUD.

Even when NOT listening to music, I wear earplugs cause after a day on the interstate the windnoise causes my tinnitus to get worse. I happy for all you well hearing people, but I have to do what's right for me. Thanks for the info. savoo

 

Changing (from 4 ohm speakers to the 4 ohm load and HPs when you plug the HPs in) the load will not be instant. That's where you're going to run into problems. It my work for a time, but it's asking for problems.

 

That's not going to matter. As long as:
1. it doesn't short when switching he'll be fine.
2. it's not excessive power and cranked (20WRMS +)
3. it's a somewhat decent design.

I've had piece of crap radios run without any load at all and they weren't damaged so why would no load for a fraction of a second cause any damage.

 

Just because it's never happen to you doesn't mean it doesn't happen. That's like saying 'I do heroin and I haven't ODed'. Horribly flawed logic, or lack there of. And there are a couple of things that 'COULD' happen. One would be the development of standing waves on the output, altho almost all (note the use of almost) have protection against this. This is why we can run the RCAs back to the amp and have no load on the outputs. The second, and most likely with an intermittent load is bias instability. Pioneer has this as the cause of as much of 90% of there amp IC failures. It can cause a rather complex chain of events that would cause secondary failure of the output junction in the amp IC. Long story short, one of the output junctions will short. Secondary failure is when the junction temp go up so fast the that the junction temps vary over the junction it self. That is to say one point of the junction get hotter then the rest and the on-resistance at that point is lower then the rest of the junction. This means more current flows at this point. More current flow at this point, more heat at this point, more heat at this point low resistance at this point. This localized thermal runaway is secondary failure. What starts it is a varying of current to the amp IC and subsequent varying voltage drop. When this happens to fast, the internal bias stabilization can't keep up with the varying supply voltage, and varying voltage drop IN the amp IC. If I get allot of time I'll try and remember all the steps, type them up, and save them. I get this question allot so it would be nice to have saved. I'll warn you, it WILL be vary LONG and take some pictures. I'll see if I can find it on-line and post link first. But believe me, it happens every day. This is also why twist-and-tape jobs are a BAD thing. Just because you don't know why a HU died a year or two after you put it in, doesn't mean it didn't happen because of something you did.

 

I love when people try to use analogies and fail miserably. A better comparison would be you saying "I didn't OD using X amount of heroin, so I probably won't OD using a fraction of that amount". No even remotely decent amp will blowup without a load for a fraction of a second.

 

it's a bad idea to have the RCAs hooked up with no load, for any amount of time...

also, if windnoise is that bad in your car, you obviously need better weatherstripping.

 

At this point I'm almost positive he means with his windows down.

 

NEEDAZ, I'm not sure what you mean by RCAs to an amp. I won't be using an amp. I'll be hooking the HP jacks inline on the speaker wires. I own TVs and radios that have HP jacks that shut off the speakers when pluged in. How do they get around the problem you mentioned?
I've picked up two 1/4" stereo normally closed jacks with 5 terminals each. That way I won't be using a common ground for either speaker. I believe I'll have to turn down the power before plugging and unplugging the HP, because any resister I use to balance out the load would have to be ON the HP wire.

Yes I'm talking about windows down and top off.

I thank all the people here, who are burning up their gray cells on my Q? savoo

 

he means the internal amp, the one inside the HU.

 

Hey champ, it's not the amount of time that's going to/could be the problem. It's the fact that load change will not be seamless. As the HP are plugged in, the load will change in an unpredictable manner as the in-speakers are cut off and the HP become the load. And I love it when people suggest things that can damage someone else's equipment because they don't under stand all the details.

 

NEEDAZ, If I turn the unit off before plugging and unpluging the HP will that solve the problem? How do home TVs and radios solve the problem. This load difference must be able to be solved. I'm 54 and I'm not into loud super bass getto blasters. What I am trying to make is a system with crisp highs and mellow mid ranges that aren't harsh. Because of my hearing loss ( Too much gunfire and sirens. Thankfully not at the same time.) any backround noise puts me off the net. Thanks savoo

 

I under stand you don't what to use an amp in this system. That was to show that most car amps use protection for a no-load condition. This is usually just a high resistance load on the output in parallel with the load. I want to say something like 470-1.5K ohms. High enough not to be much of a load at all.

Now on to your TVs and radios. They use a total different amp IC configuration. For one, your TVs and radios use amp IC that uses bi-polar transistor junctions as the output device. Most car radio amp ICs use FETs for the output device. You also need to under stand that each output channel of the HUs amp is basically 2 single ended amps in bridge mode operation. So that 4 channel amp has 8 little amps inside. Both of these things are VARY important. Why? If the amp IC loses bias stability it is possible for both outputs to saturate at the same time. This means the TWICE the MAX current is passing through the each output device’s junctions. A bi-polar transistor can take some abuse before they dump. This gives more then enough time for the amp IC to regain stability. A FET on the other hand CAN’T take it for more then an instant, and by instant I MEAN instant. If you go through the service info for the ‘digital’ (I hate that this is what they call it) Class-D amps you will see a dead-time circuit. This usually consists of a 7400 IC setup as a buffer on the push or pull side path. This gives just a fraction of a second delay and makes it impossible of both to be ‘ON’ as the same time and the output FETs stay happy. Note to that newer TVs that use HPs AND use FETs as there outputs don’t interrupt the speakers, they MUTE the speaker amp IC and use something like an LM386 as the HP amp (some cheaper set use the LM386 as a pre drive, take the HP off of that, then mute the amp). Also note the frequent use of ‘can’ and ‘could’. You can F’ around with the load 1,000 time and not setup just the right conditions to lead to secondary failure of the amp IC. But by the same token you could do it 1,001 times and have a problem.
If you are SET on doing this (I still say VARY bad idea) the RIGHT way would be to MUTE the amp IC when the HPs plugged in and use an LM386 as an HP amp off of the RCA outs. Need more coffee now.

 

You just really need the turn the volume ALL the way down and you'll be safe. You wouldn't set things up with little to no signal. One of the things that need to be just right is having is having the signal at or close to peek. Other wise the amp IC isn't pulling enough current to develop a significant voltage drop, and stability is unaffected. Also bad connections at ground and B+ exacerbate the possibility of this condition (again, more potential for voltage drop).

 

With your windows down and your top off, hopefully you won't get a ticket, since you will be really noticeable wearing those GIGANTIC headphones... they would need to be really big otherwise their wind noise blocking ability would be worthless.

let us know how that goes.

can you not use earplugs and just turn up the speakers to compensate or is the sound quality too poor and you cannot adjust the eq for the plugs?

 

Come to think of it, I think you can get a permit to drive with headphones on if there is a legit medical reason. People here who have sensitive eyes can get thier front windshield tinted to a degree, something that is otherwise illegal.

 

if it were me, and wind noise caused ringing in my ears... I wouldn't drive with the t-tops off... but that's just me.