Impedance Matching


2001-11-08 11:05 am
Can anyone help me on the following please,

I have a SONY Mini Disk player the MZR700 which does not have a line out. It does of course have headphone out which drives 32 ohm impedence earphones.
What circuitry do I need to change the earphone out (32 ohm) to a standard line output signal to drive my main amplifier.

I have constructional and soldering experience its the circuit I need!

Thanks in advance for any help,

Most likely none.

I asssume you can take the signal as is and connect it to your amplifier.
I'm not a ear-phone specialist but if I remember right the top is left channel, the midsection right and the section closest to the cable are ground. You better check this first.

Take the signal and split it into normal RCA connectors on the amps side.

Just in case the output of the MD is sensitive to capacative loads in might be a good idea to put 100 ohms in series with each channel as early as possible in the phone-plug.

100 Ohms series resistors seems sufficient for me, mostly you will not need any circuit for matching. I tried both with different headphone outputs. Just remember the output volume setting.
As far as I know this output is intended to work also as a line output - the Sony is a small machine with not much space. Isn't there the mic input also working as a line input ?

Hedlund is right with the connection schema - there is no difference to a "normal" line stereo 3.5 jack (Tip-L, Ring-R, Ground).

If the volume is too high you can make a cable with a passive attenuator (a pad).

For a -14dB cable it would look like this:

<font face=courier>
output-------------// cable //----------2k------input
output-ground------// cable //------------------input-ground
The two damping resistors per channel should be soldered in the output phono plug.

Normally any parallel resistors are not necessary, because a headphone output should not have an "open" cap at the output (to avoid the "plop" when you plug in the phones).
Cheaply constructed headphone outs (in budget CD players) sound worse than the line output because of the headphone amplifier distortions at low volumes and an increase of noise.

good luck

[Edited by Jason on 11-09-2001 at 04:00 AM]