Introduction: Passive IPhone / Victrola Amp

About: Instructor at MakerspaceCT

So I’ve been thinking about how my old Victrola works by passively amplifying the vibrations from the diaphragm through a simple box and how I can control the volume (somewhat) by opening and closing the doors.  I said to myself, “Self, I bet that would work as a passive iPhone amp too.”  I was thinking about how to get the iPhone speaker at the beginning of the sound's path, thinking it was gonna be complex like removing the arm of the Victrola.  I didn’t want to damage the old girl. 
And then, Eureka! I saw that the diaphragm and needle part of the arm come right off easily, revealing a simple way to get the iPhone sound in.  After about an hour, I had this baby working.

Step 1: Materials and Tools

I used what I had laying around:
-Some PEX plumbing scrap; one piece 4.5” long and another 6” long.
-Some dowel that was just a bit too big to fit in the end of the PEX
-A bit of electrical tape

Total cost: $0

I used the tools I had, including a drill press (but I’m sure you could do it with a hand drill), a 3/8” drill bit and some smaller ones, a utility knife, and a handsaw.  Thats it.

Step 2: Made a Plan

I carefully unscrewed the end of the diaphragm mount on the arm of the Victrola (see picture).  I made some measurements and came up with a plan.
Here’s the basic design in two parts:

The lower part is to redirect the sound from the iPhone speaker (on the bottom) down through Victrola.  It has a slot cut in along it for the iPhone to fit in and a hole that will line up with the Victrola sound path.  The ends of this part are plugged up with dowel to send the sound down through the hole and not out the ends.  Check out the diagram for some dimensions.

The upper part is just to support the iPhone so it doesn’t swivel down to the turn table.  So it just needs a slot cut along one side of it for the top of the iPhone to fit in.

Step 3: Got It Together.

First, I laid out the slot for each part.  And marked the center for a 3/8” hole at each end of each slot and made a mark for the sound hole too.  Starting with smaller bits to avoid drilling in the wrong spot, I worked up to a 3/8” bit for each one.

Second I scribed a line from one hole to the other for the slot sides with my knife.  To get as straight a cut as possible, I used the molding on a door frame to mark it (see the picture).  The slots were done after carefully cutting successively deeper cuts on the scribed lines.  To finish, I just carved the ends of the slots square.

Thirdly, I whittled down the ends of the dowels slightly, just until they fit inside the ends of the lower part.  I then cut them to about 1/4” long and stuck them in either end of that lower part.

Fourth, I carved out access to the home button after marking it with the iPhone in place.  Upon testing the fit in the Victrola, I found a bit of play so I wrapped a bit of electrical tape around the end to en-snuggen it.

Step 4: Done.

In use, I find that I still have to be ginger with it as the fit can be a bit unstable.  But overall, it sounds great.  Now I can break open the doors on the Victrola when the party really gets going.

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