Can Arduino Nano board be powered with MIDI cable?

I need to minimise the cables going to my Arduino setup. I use Nano and so far I connect it to my computer with USB. I am using MIDI out only, so I have unused leads in the cable and these are not connected to anything(but extra 5V power supply) at MIDI receiver side? But where to connect the incoming 5V on the Arduino board?
Or there is better solution to this?

5v.jpg

But where to connect the incoming 5V on the Arduino board

To the 5V pin on the Arduino.

Is this the way to do it?
I kind of remember that it may damage the board if external 5V is not regulated well. Does USB 5V power pin has been connected to Arduino pin 4 without any safety?

Is this the way to do it?

Yes. I do this myself.

I kind of remember that it may damage the board if external 5V is not regulated well.

But that is up to you, if you feed too much voltage through that MIDI cable then yes you will damage your Arduino. Where is this 5V coming from? It is not in the MIDI standard so I am assuming it is a custom thing you have made, so you know if the power is regulated.

Does USB 5V power pin has been connected to Arduino pin 4 without any safety?

Sorry that is a bit mangled, what do you mean pin 4?

pin4 on Nano should be 5V.
USB could be a bit under or over 5V, so there must be some regulator on Arduino to compensate. So I worry if Arduino 5V pin will tolerate the same kind of voltage discrepancy.
I am going to use 5V adapter, most likely switching power one.
The MIDI from Arduino goes to MIDI usb box and controls the FM synth in the computer. I wonder if there is a more clever way to power my Arduino - USB has 5V that power the Midi USB Box?

The 5V that comes off a USB is normally good enough to feed straight to the 5V pin.

so there must be some regulator on Arduino to compensate.

No.

So I worry if Arduino 5V pin will tolerate the same kind of voltage discrepancy.

Yes it will.

I am going to use 5V adapter, most likely switching power one.

That will be fine, switching power supplies are naturally well regulated.

Thanks!
I worry no more.