The idea of the Off Grid Music Box came about during a thought process (while recovering from a severe electrical shock) of a need for high quality audio using no utility power. As an audio aficionado the unit had to drive a decent set of speakers to average sound pressure levels, provide a good sound stage, wide frequency range, and natural sound (to my family's ears at least).
Now let's move forward with a few general steps..
Step 1: Design and Operational Theory
KISS (keep it simple stupid) my first design goal: the simpler the circuitry the better. Simple uses less power, sounds better and uses less space. My second goal: use readily available parts. My third goal: Use low voltages utilizing common and cheap batteries. My fourth goal: Use a modular and tweak-able design.
1. Simple circuits and good sound: The major parts consist of a 3s4 tube preamp and a tri-path derived power amp module.
2. Utility free power: Two 12 volt batteries (25 volts) for the tri-path amplifier, four 9 volt (36 volts) and two 1.5 volt batteries for the preamp.
3. A fancy box with room for tweaking and a storage drawer!
The preamplifier feeds the small but powerful tri-path amplifier. The tweaks are more involved but not all are necessary. Additional tweaks include rechargeable 12 volt batteries, OFC wire, upgraded capacitors, custom preamplifier layout, power amplifier volume potentiometer removal, delay turn on for the preamplifier, volt meters to monitor battery power and plastic battery shield.
Step 2: Tools for the Operation
- Eye protection
- Small slotted tip screwdriver
- Small phillips screwdriver
- Needle nose pliers
- Wire cutters
- Wire stripper for small wire
- Soldering iron (not to large and around 40 watts)
- 60/40 solder
- Ohm meter
- Nice bright light
- Work matt to protect the work surface
Step 3: Laundry List
- The preamplifier is a modified layout BottleHead "Quickie". This preamp offers great sound per dollar! The layout was changed to fit the small space.
- The amplifier is a HifiMeDiy T1-M TK2050 (volume control removed). Removing the volume control was the hardest part of the project. This amp offers good output and, paired with the preamp, great sound.
- Two 12 volt 2 ah SLA battries
- Good quality "D" and 9v batteries
- A new or old jewelry box
-Rust Oleum texture paint for a new interior finish
-Time and.. patience. One step at a time and the project is not too hard to complete.
Step 4: À La Carte Tweaks
The optional board contains:
- Volt meter(s) that will track battery voltage. These can be found on eBay for a few dollars each.
- A delay circuit (made using a 555 ic) to decrease power-on thump.
- External 12 volt battery charger.