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70WATT
I've always just wanted the power amplifier part of a stereo system to make my own stuff, so many years ago I decided to make my own. So, roughly five years later and an associates degree (I'm still paying for) in digital/analogue circuits and who knows how much in devices that blew up in my face I finally have something to show for it. I've built a variety of flavors based around this amplifier model and have come up with what I believe sounds best for the lowest price.
If you would like to build this module yourself I have provided some info on this here.
I have done a fair amount of research and analysis on this module over the past few months and believe it's ready for the public. The module is very stable and has all the features of an amplifier costing much more like: short circuit protection, over temperature protection, 2 ohms stable, and the use of high current output devices as well as being built on FR4 glass epoxy boards that are fire retardant and very durable, are just few of the highlights.
The high power output devices used, which were just recently released by Fairchild semiconductor, are the FJL4215 and FJL4315 which are capable of continuous output (not RMS) at 4.4 amps into an 8 ohm load at over 35 volts realizing there stated 150w continuous capabilties, not to mention there 30A peak out current and repetetiveve peak power levels at 100ms and 10ms are 300w and 700w respectivley.
The 70WSP power amplifier is conservatively rated at 70w RMS into an 8-ohm load but can easily as stated before output much more. The circuit paths are clean providing smooth electron flow, dual side traced PCB's provide shorter trace length over single sided boards. The artwork on these modules is laid out nice and clean. Here is a picture of the output devices power transistors.I have tried to use the best components on a budget and a good example is the transistor insulators (between heat sink and transistor). I'm using new technology from Bergquist, there Silpad 900s, which is a step up from generic transistor insulators, conducting more heat away from the transistors then any material before providing a safe operating area for any range of power levels required.
These amplifiers are only power modules and do not include any pre-amplifier or signal conditioning.
Care must be taken to provide the heat sink with an unobstructed flow of air or the device may fail prematurely or shut off due to excessive heat. If used in a speaker enclosure such as a subwoofer a 6" x 4" x 1/4" or larger aluminum rectangle can be adopted to seal the enclosure and provide a mating surface for the module and heat sink. Here is a sample Appnote1-03.jpg. Don't forget to use thermal compound between the sink and plate also you must reinstall the transistor isolators between the transistors and aluminum plate or you will short the supplies together through the collectors of the output devices and destroy the amp or at least blow some fuses.
Always replace fuses with same type and rating if same rating fuse is unavailable use a lower rating fuse until you can replace with original rating. Never replace with a larger amp rating fuse, there is a serious risk of fire if the amp were to fail and more then likely it would destroy your speakers as well.
A transformer with a rating above 200VA is recommended for a pair of 70WSP's. Best performance will come from a transformer with a rating of 30v @ 5A (approx. 84v d.c. +/-) each center tapped winding. Of course it would be good to get a toroid or at least a copper wrapped IE laminated, but these are not always available or cost effective so if a standard transformer is used the further away from the power module, and especially any high impedance signal source, the better. The supplied rectifier unit should be used and placed midway between the transformer and module but this is not that important.
While these amplifiers do have over temperature and short circuit safety mechanisms do not get a false since of security. Being that these amplifier modules are sold in this manner I leave it up to you to provide an acceptable working environment for the modules. Electronic manufactures like the big names have tailored environments for there equipment (they case them) but this is where the money starts to come in.
These modules are not designed for use in public address system like clubs, bars, or concert halls and the like. I'm also providing a schematic shortly for the 200WSP model, which will be intended for this application. The 70wsp's are for home or car applications only. If you believe you will be using this modules at a continuous power output of over 50watts you will need a larger heat sink and possibly extra paralleled output transistors to increase the thermal conducting area .
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