Place your amp or receiver on end. You'll need at least three of the smaller pool noodles, and a roll of packing plastic on a hand held spool. Cut at least pool noodles to the length of each side, and secure tightly with wrap. It's ok to split a noodle for the sides if need be, but don't do this for the more delicate face and rear panel. Place the noodles on the front panel to protect delicate switches like toggles.
Add noodles cut for the front and back, and wrap around the sides as shown. pulling the plastic wrap tight. This adds tension to the existing wrap, and keeps all the noodles in place.
Peanuts, air pillows and bubble wrap won't cut it. If your amp or receiver can move around in the box even an inch, that's bad. Wrapping plastic wrap around pool noodles is a great option. You can buy plastic wrap for shipping on a spool with a handle at Office Depot, Staple's and Wal Mart.
If any gaps remain in the box, use pieces of carboard for the sides. Styrofoam is another great option here. If there is space on top, cut the box down to size so that only enough space remains for noodles, and trim the flaps. Your item must not be able to move more than a fraction of an inch! If it does, keep adding spacers or other firm gap filler.
Another option is expanding foam. This will usually need to be done by a professional. Here is an example.
If you are shipping to our shop, be sure to include the return label.