The actual source of this impression is harder to place.

However, the actual sources are other publications of the same pieces as noted below.

"And why are you so slow in finding the actual source?"

If someone ever delved down deep, he might approach the actual source of power.

The actual source of the name is not known.

It is not easy to determine the actual source of the quotation.

Did your daughter ever tell you anything about their actual source?

The actual source of the breach, however, wasn't discovered until last week.

The actual source must be what the chief picked up before.

The actual stellar source of the light detected no longer exists.