Protection circuit for my headphone

[Guto]

Recently I bought an etymotic ER4P and would like to build a protection circuit to be able to use with generic equipament tv,radio... Should protect against DC-offset, transients and to transform the P for S because the phone is already very sensitive. Could anybody tell if this circuit would it work? Thanks.

[bidoux]

Looks interesting but you will make your headphone's impedance really high.
Is it a single channel circuit ?

[Guto]

Only shown single channel.

At least simulating in spice it works. In the 1.7v led voltage occurs a hard clip but
this is already a lot for the ER4P then the resistor is a voltage divider.Both eletrolitics act like a single bipolar And bypass cap is a film tipe for less distortion. Thanks!

[Uncle Erik]

You might be interested in AMB's Epsilon12:

The ε12 Muting / Protect Circuit

[Guto]

Thanks Erik by the suggestion. It is one very good project but I search something simpler with the expense of losing some audio quality. Even because most equipament that I am going to connect to that are not high fidelity.

[nikongod]

I would *just* use a slightly larger cap, and a few resistors.

the LED's are connected properly, BUT 3.4vP-P will make you deaf with any ety. They wont protect you from anything with these headphones.

[Guto]

Nikongod, I changed electrolytics to 5600uF improving the phase distortion in low frequencies

Well, I did some research ...

both p and s drivers himself has impedance of 5 ohms. Added to this the cable (2 Ohms) and a resistor (20 Ohms to the p and 100 Ohms for the s).
Thus, the total impedance of the p is 27 Ohms and the s is 107 Ohms.

Through data of this link Etymotic Research, Inc. - ER-4 - Technical Specifications could do some math. Then I obtained that The driver's real sensibility ( 113.6 db/mW ) and the maxim continues voltage (140mV rms).


Using spice to simulate the circuit I obtained a voltage of 44.5mV with o.ooo% distortion at 1khz. This would give 95db spl.




With one very high entrance voltage I would have an exit maxim voltage of 58mV rms with a hard clip. This would feel well below the 140mV rms continuous that the drive support.





Here the small phase distortion




Well, I do not be any smart in electronics and know that simulation is never the real thing. Then if anybody knows about any reason for this do not work let me know.

Thanks!