Small Amp |
Here's a project that I completed several years ago. The idea was to have an amp of 100 to 200 watts that I could put in a carry bag along with my leads, stands and other stuff, and use for rehearsals and quieter gigs (resturants, coffee shops etc.). I have a light weight monitor wedge that's on castors and with my gig bag on my back, I can easily load in with only one trip from the car. As you can see, the small amp has had plenty of use, but its been very reliable so far. |
The amp module itself is actually half of a hi-fi project that was published in "Electronics Australia" (EA) magazine in about '94 and features an output of around 180 watts into 8 ohms and over 250 watts into 4 ohms. The module is cleverly designed with the four flatpack mosfets being sandwiched between the main heatsink and a length of L-shaped aluminium extrusion which also acts as a heatsink for the driver transistors and as a mounting bracket for the main PCB. Another feature of EA's design is the hefty 300 watt toroidal transformer. These transformers are generally more compact than traditional transformers of similar electrical specs, but the main advantage is that the radiated electro-magnetic field is far smaller, which leads to much quieter performance when mounted so close to the audio circuits. |
Recently I finally found the time to design and construct a new preamp for this amp. It is a simple class A fet circuit with my version of the classic Fender "tone-stack" filter. The jack, boost switch, and tone pots were mounted to the PCB, and as you can see from the top image, I had to fill and re-drill the front panel holes, but it was well worth it as the preamp sounds great with both guitar and bass (depending on the speaker, of course). The real trick with making this project was fitting all the bits into the smallest box possible. The one that I chose was perfect in size, but as purchased, nowhere near rugged enough physically. In the interests of rigidity, the heatsink itself has become an integral part of the enclosure. Also, the mounting points for the handle and the transformer have been reinforced, plus several extra screws have been added around where the lid and tray meet. The rear connectors are simply an XLR type socket for the speaker lead, and one of those great IEC mains connectors with the itegrated fuse holder. The fuse holder is a little draw that also features a small space for a spare fuse. |
Putting this amp together presented many challenges, but all the effort was worth it because the amp has a great clear sound, and when its not saving me the hassle of lugging my main (1200 watt) rig to small gigs or rehearsals, I'm spoilt with a 180 watt practice amp! |
Small Amp |
