Angular 2/4 trying to get Observable with calling a javascript array object - to be subscribed to

I have a Service file that I am trying to set as an observable , with a component that i want to subscribe to it. But it's not working, what am i doing wrong?

Service: Tracker.service.ts

getAllCoins(): (Observable<string>) {   //<Response> {
    return allC
        .map(res => JSON.stringify(res))
        //.do(data => console.log('coins ' + JSON.stringify(data)))
        //.catch(this.handleError)
}

my function in which this observable of it does not like
Previously i used a REAL URL and I used http.get FYI and that worked ( coded differently though)

My JSON data:

const allC =
[{
    "BTC": {
        "USD": 3349.1
    },
    "ETH": {
        "USD": 296.3
    },
    "LTC": {
        "USD": 47.56
    },
    "EOS": {
        "USD": 1.83
    },
    "DASH": {
        "USD": 195.83
    }
}]

Next I setup component and try to subscribe to it.

Component file

coinsList = [];

constructor(
    private coinService: TrackerService
) {
  this.coinService.getAllCoins()
      .subscribe(
        (data) => {
            for (let key in data) {
                this.coinsList.push({ coinName: key, price: data[key].USD});
            }
        },
        (error) => console.log('error :' + error)

        );
}