What To Do?

I should clarify even further.  To my knowledge he only takes appointments to meet him at his shop. I'm sure he's there at other times, but i know he has a full-time day job. So, my chances of seeing him at the shop are very low.  And, of course, I can't make an appointment because he won't return my correspondence.

cleeds' advice is very good, I think.  Problem is, I only have the shop address, and I'm sure he receives no mail there (it's way out in the country, in a metal quonset hut). 

So, he only uses the shop to do his tech work (lots and lots of audio equipment and tvs laying around). It's not a registered business (cash only) and has no name.

The amp would probably bring up to $1,500 if sold on a site like this one.

Have you gotten your friend who recommended him involved.

Does he live any closer? Perhaps your friend could reach him, make an appointment about one of his pieces, then he takes your unit, or you go with him, take your piece.

Have a nice visit with your ex-friend while there.

property record for hut = destination of letter @cleeds advised

I am in New Jersey if I can offer any assistance.

Register/certified letter first, but be clear in the letter about the next steps, which is small claims court. It It might be a pain for you, but for him it will be a major issue with having two jobs. You can always cancel the small claims court appearance (he cannot) if he gets the amp back to you before the court date, which he will do with the thought of spending most of a business day in court, in which he will lose anyway. And make it clear the claim is for $1,500.00 plus your expenses, not just the repair cost. Most small claims go up to $5,000.00 these days, court costs, your travel and time, etc., your state may be different of course. 

I cannot image the police doing anything in this situation. He really hasn't stolen anything - yet, you gave him the amp and you don't have a specific return date. He could keep it for 5 years, and the police still wouldn't considered it stolen.