Laptop Audio Output to 12V Amplifier

[Rick]

I want to run my laptop audio out(EAR JACK to RCA plugs) to a 12V car amplifier (around 40W x 2)and out to speakers. My laptop external speaker set-up is not adequate. There seems to be a wide range of opinions out there. IT experts differ from car audio experts thoughts. My big concern is that there is a mismatch which would blow the sound card on the laptop(which is part of the motherboard and not a separate unit). Is anyone using this set-up? Any recommendations?

 

[Tony Z]

Use line if you can

If your audio dard has line out and your amplifier has line in, Your all set.If not, you may need a matching transformer to get the impededence correct, itwill sound lousy if not....

 

[JeffC21331]

That will work fine

That will work fine. It is better to use a line out rather than a headphone out since the line out is fixed volume. Either will work though. If you use the headphone out, you may need to play with the volume a bit. Too high a volume setting on the laptop will cause distortion to the signal. I pretty much have this setup at home with my home stereo and computer. Actually the output from the sound card from my computer goes into three different stereos in different rooms in my house.

 

[Fred Ficarra]

Yep, and

because the sound-card is supplying the signal, it can't be blown by the amp which is only capable of receiving that signal.

 

[OT]

Not many older

car stereo got line-in(even not many new one). So the only solution is to use FM modulator which is easy to find in any electronic store or ebay.

 

[Bill Roosa]

impedance miss matches

would you connect a 12 volt battery to a 0.0001 ohm load?While DC current uses ohms as a measure of resistance AC circuits use impedance and similar rules apply. the impedances must match or you get currents that are too high in one unit or the other.On another note. Using your computer to drive an amp to drive a speaker sounds like a great way to suck your batteries dry. Why not just invest in a 12 v stereo? They play plenty loud. Then all you need is to burn your music files to CDs

 

[Rick]

??????

Wow......Still a wide range of theories from the community. My primary goal I wish to achieve is to have decent audio while watching DVD's from the laptop and the external flat panel. I wish to avoid adding a head unit(CD PLAYER). So from what I understand, I need to find a way to match the impedances of the laptop to that of the speakers. I assumed that if my external laptop speaker system was 4 ohms then if my marine speakers were 4 ohms then it should work. I also assumed that the built in amplifier for the external laptop speakers could be optioned with a car audio amp. My concern was that the output voltage coming out of the laptop was too high going into the car amp. I remember years ago in cars we use to use a "booster" as opposed to amps.

 

[JeffC21331]

Without a head unit

Rick,I misunderstood earlier. I didn't catch the without a head unit part. While I still contend that the output from the sound card will work fine as a input signal, you need something to control the volume. If you were planning on controlling the volume with the laptop, you are likely to be disappointed as the range of control will be very low before you experience lots of distortion.On my boat, I have a clarion m455 head unit that has an aux input. I generally just plug in my ipod there. I have plugged in the laptop directly as well, just like I do at my house to my home receivers. The volume control is always through the head unit/receiver though.

 

[OT]

Questionable question.

Anyway,1. The audio signal from line-out of laptop or PC(or any pre-amp) is high impedance, in KOhms with the voltage level in +- 2V range.2. Input of the amplifier(whatever type of amplifier; power amp, pre-amp, with or without integrated player of any type) also high impedance.3. Those high impedance signal can't drive a speaker(not even a head phone.) Not enough juice. You can short-circuit those signal to ground and not damage anything. No noticeable consequence of "impedance mismatch" as well. 4. Speaker has low impedance usually 4 or 8 or 16 ohms at 1 KHz.5 Output impedance of any amplifier's speaker output also has impedance of 4 or 8 or 16 ohms at 1 KHz.5. Speaker/amp impedance match play little role in the sound quality but more to do about power transfer efficiency from amp to speaker. You can connect a 4 ohm amp to 16 ohm speaker without damage amp or speaker.6. You certainly can't short circuit speaker wire since power amp has enough juice to destroy itself.7. Any speaker output should therefore has output impedance of 4 or 8 or 16 ohms. How many watts of it is a another question. But I would say laptop or PC speaker output is more like for earphone, not enough power to drive speakers to the sound level you wanted to.8 It's a bad idea to connecting speaker output of laptop or PC to amp. Not it will damage anything but you'll got a lot of distortion. This has not much to do with mismatch impedance but much to do with the voltage level to speaker that it's high enough to "saturate" the input stage circuit of the amp and cause the distortion.It's not easy to give a electronic clash course here, but it's fun.

 

[Monty Miller]

USB Sound Card

Creative Labs and Turtle Beach make USB sound cards that would give you volume control, equalizer, analog stereo and optical outputs for under $50. You will get much better sound with one of these compared to the sound cards found in most laptops.

 

[Rick]

Thanks to all.....

A special thanks again to all for the advice and education. Hence, I felt confident that I would not hurt my laptop and bench trialed going from the headphone jack to "line in" on amp. As you predicted, sound quality and volume control was very poor. I picked up an older Pioneer head unit at the flea market yesterday and although volume control was much better, the quality was still poor. I bought a Creative Sound Blaster off Ebay(awaiting delivery) as suggested by Monty Miller and after reading many reviews, feel that the solution is close. I will make another post to confirm the results in case this question arises again.