encoding php postgres json_encode

I have a problem with my encoding...

Everything is UTF-8 configured, namely my database (postgres) and my php files.

when I execute this script:

$eleves = $serviceManager->getAll('Eleve');
echo "<pre>";
print_r($eleves);
echo "</pre>";

I get this:

 [0] => Model_Eleve Object
    (
        [idEleve:Model_Eleve:private] => 28206
        [numeroscolaire:Model_Eleve:private] => ABE290999JOËL
        [nom:Model_Eleve:private] => Abedinpour
        [prenom:Model_Eleve:private] => Joël
        [dateNaissance:Model_Eleve:private] => 1999-09-29
        [sexe:Model_Eleve:private] => masculin
        [statusCourant:Model_Eleve:private] =>
        [statusSuivant:Model_Eleve:private] =>
        [adresses:Model_Eleve:private] => Array
            (
                [0] => Model_Adresse Object
                    (
                        [idAdresse:Model_Adresse:private] => 6176
                        [rue:Model_Adresse:private] => La Delèze
                        [numero:Model_Adresse:private] => 37
                        [codePostal:Model_Adresse:private] => 1164
                        [localite:Model_Adresse:private] => Buchillon
                        [emplacement:Model_Adresse:private] =>
                    )

            )

Here everything's ok. But if I want JSON:

$eleves = $serviceManager->getAll('Eleve');
echo "<pre>";
echo json_encode($eleves, JSON_PRETTY_PRINT);
echo "</pre>";

I get this:

{
    "nom": "Abedinpour",
    "prenom": "Jo\u00ebl",
    "adresse": [
        {
            "rue": "La Del\u00e8ze",
            "numero": "37",
            "localite": "Buchillon"
        }
    ],
    "classe": [
        "7VSG\/1"
    ]
},

I have no idea why it works with array and doesn't work with json_encode... I've tried to transform everything in utf8 (with htmlentities) but it tells me that he can't convert 'ASCII'

When I try to show the encoding of my files with this command in the terminal:

file -I myfile.php

it returns this:

myfile.php: text/x-php; charset=us-ascii

but i can't convert it to utf8:

iconv -f us-ascii -t utf-8 myfile.php > myfile2.php
file -I myfile2.php
myfile2.php: text/x-php; charset=us-ascii

thanks in advance for your help