Informe De Amplificador De 60-100W

Páginas: 17 (4225 palabras) Publicado: 2 de mayo de 2012
60-100W Hi-Fi Power Amplifier

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Introduction
Update - 25 June 2009 - Although the last update highly recommended the latest OnSemi power and driver transistors, they remain hard to get in most countries. As a result, the recommended power transistors are now the much more readily available MJL21193/4. While in theory these are not quite as good as the latest versions, they are stillexcellent devices. It is extremely doubtful that anyone would ever pick any difference with test instruments, and there will be no change that is audible.
Much the same applies to the driver transistors. Although the BD139/140 devices are not considered to be the "finest" audio transistors available, they work very well indeed, and have been used in all of the P3A amps I've built for my own use or aspart of a system. Again, it is highly unlikely that there will be any meaningful measurement that will show these transistors to be inferior to "audiophile" parts.
24 Jul 2003. - OnSemi released a new range of transistors, designed specifically for audio applications. These new transistors have been tested in the P3A, and give excellent results. As a result, all previous recommendations foroutput transistors are superseded, and the new transistors should be used ... if you can get them. Six years after release, the new devices are still not readily available.
The output devices are MJL4281A (NPN) and MJL4302A (PNP), and feature high bandwidth, excellent SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices arerated at 350V, with the power transistors having a 230W dissipation and the drivers are 50W.
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The basis for this amplifier was originally published as Project 03, and although the base design is almost 30 years old, as an amplifier it remains "state of the art" - this is an extremely good amplifier. It is simple to build, uses commonly available parts and is stable and reliable. The designfeatured is a full update on the original project, and although it has many similarities, is really a new design.
This new amp (like the original) is based on an amp I originally designed many years ago, of which hundreds were built. Most were operated as small PA or instrument amps, but many also found their way into home hi-fi systems. The amp is perfectly capable of driving 4 Ohms, provided thesupply voltage is maintained at no more than ±35V.
This amplifier, although very simple, is capable of superb performance. This is not an amp to be under estimated, as the sonics are very good indeed, and this is due (in part, at least) to the inherent simplicity of the design. The amp is exceptionally quiet, and is reasonably tolerant of difficult loads. It is an ideal amplifier for biampedsystems, and may be operated in bridge mode (BTL) if you use the recommended output transistors (which have the necessary power ratings).

The design has had the benefit of many, many years of consistent use, and this version is the best of all - the refinements ensure minimum "switch on" or "switch off" noise, and the availability of really good output devices has improved on a known and very stabledesign.

I have heard nothing but praise from those who have built this amplifier - all feedback I have received has been very positive indeed. The sound quality is up there with the very best. Highly recommended !
A reader has constructed a site based on the assembly of the P3A amp, and he has some useful information that will be helpful for anyone else looking for equivalent transistors,design guides, etc. Although considerable effort went into the site, it is unfortunately no longer on-line.
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Description
Note that like the original, there is (still) no output short circuit protection, so if speaker leads are shorted while the amp is working with a signal, there is a very real risk of the transistors being destroyed. I suggest and recommend the use of Speakon connectors...
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