About the design of the Monster Amp

In the summer of 1998 I decided I needed some music to give me something to do on long motorcycle trips. I also needed to be able to hear my radar detector while riding so, necessity being the mother of invention, the Monster Amp was born. I built my first prototype in June 98 and used it on a trip to Deal's Gap (Rt. 129 between Tapoco, NC and the Tennessee border) from Massachusetts. The first model ran on a 9-volt battery like the MA-1 and I went through 4 or 5 on my 7 day round-trip. This led to the MA-2 which runs on either a 9.6 volt rechargeable pack or 6 AA cells for a much longer time. I still sell MA-1's for the occasional user or person who wants it to be totally self-contained but the MA-2 is the one I use on my long trips.

The Monster Amp was designed and tested with Collett Communications Bass Monster helmet speakers mounted in a Shoei RF-800 helmet. I tried several different speakers from Radio Shack but none compared to the Bass Monsters in sound quality (they're available from Rider Wearhouse at www.aerostich.com). I also tried several amplifier designs ranging from dual LM386 Op-Amps to a 3 Watt monolithic amplifier module. I finally settled on the Samsung KA2209B integrated circuit dual low-voltage audio amplifier as a good balance of price and performance. The power output is more than adequate for use with foam earplugs even at highway speeds on an unfaired motorcycle like my Honda VFR750. This is a serious amplifier here... Not some wimpy 3 volt unit like you'll find in some catalogs. It can and will produce enough sound to hurt your ears if you accidentally turn it up too high so I must stress: Wear Earplugs!!! You've only got one set of ears and they're irreplaceable.

I worried about RF noise generated by the bike getting into the circuit so I was careful to use aluminum shielding and shielded audio cables in the design. One early prototype I made used unshielded cables and picked up all sorts of noise from the ignition system. This has been completely eliminated on the current models.

My Sony Walkman is mainly used for listening to FM radio. The shielded cables reduce the range somewhat but it is still acceptable considering the alternatives of using poorly shielded cables. Both tapes and my Sony CD Diskman sound great with the 29 dB reduction earplugs I wear. The only problem is that AM radio reception is completely obliterated by the bikes' noisy unshielded ignition and charging system (not a Monster Amp problem, you can't get AM reception even with just headphones and the Walkman).

The need for a second (or third) audio input was solved by a simple resistive mixer network combining the inputs. I experimented with using separate amplifier stages for each input but found the cost and lack of a combined volume control made it too problematic for production units. The current design uses a low-level stereo input for the Walkman and 1 or 2 high-level (0 dB gain) inputs for a radar detector or communicator.

I build all Monster Amps to your specifications in my shop at home. All amps are individually tested and usually get a final check on my way to work in the morning before shipping them out to customers.