Headphone to RCA

[trogadoror]

I'm looking to interface the headphone jack on my laptop with an RCA
jack on my TV. I already have a cable that goes from 1/8th inch stereo
to stereo RCA. The problem is, the volume is terribly low and loud
noises (such as explosions during a movie) cause the output to saturate
and the volume drops even more. So I figured I could build a simple
op-amp circuit. I've been looking everywhere for the electrical
characteristics of the headphone jack and the RCA jack but I can't find
anything! Apple's website lists the characteristics of their headphone
jack as having a peak output of 4.5Vp-p with a 10 ohm source impedance.
Of course, I have a Compaq laptop, but I figured mine is probably about
the same, at least with respect to the peak output voltage (which is
all that really matters with an op-amp since 10 ohms is nothing). Also
mentioned that headphones have an impedance of 32 ohms so I thought I
might make the input impendance of my little amp 32 ohms. But I can't
find anything about the RCA jack. In particular, it'd be nice to know
what the max voltage is that it expects. I wouldn't want my amp to
drive it too high. Any information or other insight would be great!

 

[Andrew Holme]

trogadoror wrote:

I'm looking to interface the headphone jack on my laptop with an RCA
jack on my TV. I already have a cable that goes from 1/8th inch stereo
to stereo RCA. The problem is, the volume is terribly low and loud
noises (such as explosions during a movie) cause the output to
saturate and the volume drops even more. So I figured I could build a
simple op-amp circuit. I've been looking everywhere for the electrical
characteristics of the headphone jack and the RCA jack but I can't
find anything! Apple's website lists the characteristics of their
headphone jack as having a peak output of 4.5Vp-p with a 10 ohm
source impedance. Of course, I have a Compaq laptop, but I figured
mine is probably about the same, at least with respect to the peak
output voltage (which is all that really matters with an op-amp since
10 ohms is nothing). Also mentioned that headphones have an impedance
of 32 ohms so I thought I might make the input impendance of my
little amp 32 ohms. But I can't find anything about the RCA jack. In
particular, it'd be nice to know what the max voltage is that it
expects. I wouldn't want my amp to drive it too high. Any information
or other insight would be great!

How is the RCA jack on your TV labelled? Ext audio? Line level? RCA line
level outputs between hi-fi seperates are usually around 200mV which doesn't
make sense if your laptop delivers volts.

 

[Dbowey]

trog posted:

I'm looking to interface the headphone jack on my laptop with an RCA
jack on my TV. I already have a cable that goes from 1/8th inch stereo
to stereo RCA. The problem is, the volume is terribly low and loud
noises (such as explosions during a movie) cause the output to saturate
and the volume drops even more. So I figured I could build a simple
op-amp circuit. I've been looking everywhere for the electrical
characteristics of the headphone jack and the RCA jack but I can't find
anything! Apple's website lists the characteristics of their headphone
jack as having a peak output of 4.5Vp-p with a 10 ohm source impedance.
Of course, I have a Compaq laptop, but I figured mine is probably about
the same, at least with respect to the peak output voltage (which is
all that really matters with an op-amp since 10 ohms is nothing). Also
mentioned that headphones have an impedance of 32 ohms so I thought I
might make the input impendance of my little amp 32 ohms. But I can't
find anything about the RCA jack. In particular, it'd be nice to know
what the max voltage is that it expects. I wouldn't want my amp to
drive it too high. Any information or other insight would be great!

--

You need to put a (approximately) 32 Ohm resistor to ground to terminate each
laptop output. Capacitively couple the stero pair of your (32 Ohm terminated)
laptop, to the TV input. This will eliminate the blasting and there may be
enough signal voltage to give you a decent level. If not, try the OP amp
again, with 100K Ohms to the - inputs and 1MegOhms in the FB path.

Don



Don