Here is how to put a CMoy headphone amplifier inside an iPod Nano package.

Credit for this build goes to the following:
https://www.instructables.com/id/Headphone_Amp_Chu_Moy/
http://tangentsoft.net/audio/cmoy-tutorial/
http://www.headwize.com/projects/cmoy2_prj.htm

The difficulty level of this build is medium level. What makes it medium level is some of the aesthetic design elements such as exposing internal circuity and the Apple "white-wash" theme. This build would be considered easy if some of these design elements were skipped.

Tools:
Drill
Saw
File
Sandpaper
Plastic Polish
6-32 tap
Hot Glue Gun
Stepped Drill Bit
Tin Snips
Computer
Scanner
Photoshop-like Software
Printer

Parts:
iPod Nano Package
CMoy Parts - See Parts List at http://tangentsoft.net/audio/cmoy-tutorial/
This build used all Digi-Key parts except:
- In/Out Stereo Mini Jacks, Radio Shack Part No. 274-0246
- Volume and On/Off Pot, Alps Part No. RK097, Buy here - http://tangentsoft.net/shop/
- Power Indicator LED (D1), used blue LED instead of red
- Diode Resistor (RLED), Radio Shack 680 ohm value for RLED
- Note: Capacitor (C1), Digi-Key Part No. P3104 is too large, requires drilling of new holes in PWB
Matte Photo Paper
White Paint
Acrylic Glue - Tap Plastics
1/8 Sheet Acrylic - Tap Plastics
3/32 Sheet Acrylic - Tap Plastics
1/4 Sheet Acrylic - Tap Plastics
Two 9V Batteries
White plastic knob or drawer handle pull
Self Adhesive White Velcro
Two 3/4 Clear plastic bolts 6-32 - Tap Plastics
Battery clips from two old used 9V batteries
https://www.instructables.com/id/Salvage-9V-battery-clips-from-dead-batteries/
White 26AWG wire
Two 3/8" long spacers 1/4" O.D.

Step 1: MAKE the CMoy Headphone Amp

This Instructable doesn't cover the CMoy headphone amp build because it has been well documented elsewhere. Follow the steps here
https://www.instructables.com/id/Headphone_Amp_Chu_Moy/
or here
http://tangentsoft.net/audio/cmoy-tutorial/

As noted in the parts list above, there are a few exceptions to the CMoy build. The one small but main difference is the power LED. A blue LED was used which required a different value RLED resistor, 680 ohms. Both the components were then mounted on the PWB instead of the enclosure. A couple of extra holes must be drilled on the PWB to accommodate both the LED and resistor. C1 capacitor was larger than expected so extra holes were drilled and minor changes to the trace layout need to be made to accommodate them.

Solder all the lead wires, using white 26AWG wire. The leads should be 6 inches long.
For this build the lead wires were soldered onto the parts side of the circuit board. For ease of final assembly and for aesthetics, it would be better if the wires were soldered on the trace side of the circuit board.

Step 2: Fabricate the Back Cover Assembly

The Back Cover Assembly consists of two parts: the Back Cover and the Battery Wall.

To make the Back Cover, cut out a rectangular shape from 3/32" acrylic sheet, 4 1/32" by 2 3/32".
Hint: The iPod packaging came with a plastic iPod holder. Use this as a template. Fit the Back Cover to the back of the iPod package by filing the edges for a tight fit. Polish the edges of the Back Cover by using finer and finer sandpaper. Finish off with 600 grit wet sanding. Polish the edges with plastic polish to get a glossy smooth finish.

The next piece to fabricate is the Battery Wall. To make the Battery Wall cut out a 5/8" by 1 3/4" piece from 1/16" acrylic sheet. These dimensions are approximate. The Battery Wall is not a structural component so it doesn't have to be sized perfectly. The Battery Wall is needed simply to keep the batteries from sliding around.

Use acrylic glue to attach the Battery Wall to the Back Cover. Glue the Battery Wall 1 3/8" from the bottom edge of the Back Cover. Reinforce the Battery Wall with a small piece of 1/8" acrylic sheet.
Glue the joint as shown in the diagram.

Step 3: Fabricate the Battery Cover

The Battery Cover is simply a design printed on matte photo paper that is folded into a type of box. The inspiration of the Battery Cover came from the original iPod packaging. The iPod packaging has an elegantly designed cardboard box. The box contains the earbuds, docking adapter, etc. This box was used as a type of template for the Battery Cover.

First carefully unfold the cardboard box without damaging it. Scan the unfolded box. Using Photoshop-like software, "shrink" the overall length to a size that fits the batteries. At this point, customize the Apple logo, etc.

Printing the Battery Cover can be tricky. To get the exact size, play around with the overall image size in the Photoshop-like software. First print on plain paper, cut it out, test fit, resize, reprint, repeat. When the size is perfect print it on matte photo paper. Then cut it out with a ruler and Exacto knife and fold it up. To ease the folding, score the fold joints first.

Step 4: Modify the IPod Package

This step includes adding tabs to the iPod package and drilling holes for the In/Out jack and volume knob.

First drill the holes for the volume knob and the In/Out jacks. Use the diagram for measurements. Care must be taken during drilling, the iPod package is thin and brittle so it is easy to crack the plastic while drilling. Use water as a lubricant to keep the plastic from melting while drilling.

Next fabricate the tabs. The tabs have two functions, one to hold the CMoy circuit board and the other to attach the back cover assembly. Fabricate the tabs from 1/4" acrylic sheet. Cut out a 3/8" x 9/16" piece. Shape the tabs with a file. Sand the edges with sandpaper using finer and finer grit.
Wet sand with 600 grit then polish. Use acrylic glue to permanently attach the tabs to the package.
Use the diagram to position.

Using a drill press, drill holes into in each tab. First use the CMoy circuit board to mark the center of the holes. After drilling use a 6-32 tap to thread the holes.

Next, drill corresponding holes into the Back Cover Assembly. To do this, temporarily screw in the plastic bolts so that the heads are just underneath the inside surface of the Back Cover Assembly. Fit the Back Cover Assembly noting the correct position. Careful, it is easy to mistake the top from the bottom. Next mark the Back Cover Assembly where the bolt heads touch the inside surface. This is simply to mark where to drill the holes. Carefully drill the holes in the Back Cover Assembly. Use water as a lubricant.

Step 5: Apple White-Wash Theme

For that Apple white-wash flavor, start by painting both jacks and pot (volume knob) bodies and CMoy circuit board. Mask off the parts you don't want painted first such as the lead wires on the circuit board and the threaded shafts on the jacks and pot.Start with a light coat of gray primer and finish off with white paint.

To continue with the white-wash theme, create a CMoy Circuit Board Cover using the same method used to create the Battery Cover. Scan the circuit board, use Photoshop-like software to create a mask. Provide cut outs for the circuit board components. Include component labels if desired. Test with paper, print, cut, test fit, resize and repeat. When perfect, print it out on matte photo paper and cut it out.

Next design and print up some labels for the "In, Out, On Off Vol" jacks and pot. To save matte photo paper, include these labels on the same page as the above Circuit Board Cover. Cut these out and glue them to their respective components. Make sure the "In" and "Out" labels are correctly marked, it is easy to mislabel the jacks.

One final step in the Apple white-wash theme is to paint the inside of the Back Cover Assembly (Step 2). Simply spray paint it white and avoid getting any paint on the edges.

Step 6: Fabricating the On/Off Vol Knob

Fabricate the volume knob using a 3/4" long, 5/8" diameter plastic rod. These can be found at your local hardware store in the form of a U-shaped white drawer handle pull. Cut the plastic rod to length, round off the edges with a file. Using a 1/4" drill bit, drill the center of one end for the knob shaft.Then use sandpaper with finer and finer grit to get a smooth surface. Wet sand with 600 grit, then use plastic polish.

Step 7: Final Assembly

The funnest part is the final assembly.

Install the "In, Out, On Off Vol" jacks and pot. Temporarily install the CMoy Circuit Board. Using the attached schematic solder up all the lead wires. Tricky parts are remembering which jacks are In and Out and also the Ground on the Volume knob.

Next connect the battery clips. Start by harvesting 9V battery clips from this Instructable. https://www.instructables.com/id/Salvage-9V-battery-clips-from-dead-batteries/
The batteries are a tight fit.Cutting down the batteries clips help. Using tin snips, reduce the overall size of the battery clips. Solder per the schematics.

Slide in the Circuit Board Cover, this isn't glued into place. It is simply held in place with friction.

Next, fabricate some spacers that fit in between the Circuit board and the inside of the Back Cover Assembly. The spacer should be a tube that is 1/4" O.D. and about 3/8" long. It should have a hole large enough to freely fit the plastic bolts.

Finally, using a hot glue gun, glue the knob (Step 6) on the volume shaft.

Step 8: Attach IPod

The iPod packaging includes a piece of plastic that holds the iPod. This holder is used to attach the headphone amp to the iPod. Simply place the iPod in the holder and mark the location of the headphone jack. Remove the iPod and drill a hole using a stepped drill bit.

Lastly, add Velcro to the holder and Back Cover Assembly. Insert your 9V batteries, plug in a 1/8" stereo patch cord and your headphones. Enjoy!