Please register or login. There are 0 registered and 1295 anonymous users currently online. Current bandwidth usage: 326.30 kbit/s December 18 - 12:19am EST 
Hardware Analysis
      
Forums Product Prices
  Contents 
 
 

  Latest Topics 
 

More >>
 

    
 
 

  ExtremA, a reference class-A DIY amplifier. 
  Feb 22, 2007, 07:30am EST 
 

Transistors


By: Sander Sassen

The design is largely executed using commonly available parts such as the BC550C and the BC547C/BC557C. The reader might wonder why fancier Japanese transistors like the popular 2SA970/2SC2240 were not used. Basically that is because the areas where these transistors excel at arenít really of concern here. Their strongest points are a combination of low noise, high maximum Vce and constant Hfe, neither of which are critical in this circuit. The design of this amplifier dictates a virtual short input, making the feedback network's Johnson noise the dominant noise source. The output stage is bridged, halving the supply voltage required for rated power. 60V rated transistors are wholly sufficient here. As for the transistors having a constant Hfe, simply matching the Hfe of the input transistors will be all that is required here, in other parts of the design a constant Hfe will not give better mileage, or better performance.

2SC2922/2SA1216 transistors

Fig 1. The 2SC2922/2SA1216 transistors as used with this amplifier.

For driving the output stage we have used common BD139/BD140 transistors that have long since been given this task in numerous other amplifiers for the simple reason that they work very well in this respect. Due to the requirements for dissipation and speed the output transistors however are of a less common variety. Here Sanken 2SC2922/2SA1216 ring-emitter transistors are used, which have found their way in many amplifiers of fame and are known for their excellent performance and reliability. Two pairs of these transistors are used in a bridged configuration with a maximum dissipation of about 60W per transistor, for an output power of 100W/8-ohm. We should mention that only genuine Sanken transistors should be used, equivalents, or counterfeits made by other manufacturers unfortunately will not suffice.



1. Introduction
2. Transistors
3. Concept and design
4. Scalability and construction
5. Measurements
6. Copyrights, Updates etc.

Discuss This Article (13 Comments) - If you have any questions, comments or suggestions about the article and/or its contents please leave your comments here and we'll do our best to address any concerns.


Rate This Product - If you have first hand experience with this product and would like to share your experience with others please leave your comments here.

 

    
 
 

  Related Articles 
 
 

  Newsletter 
 
A weekly newsletter featuring an editorial and a roundup of the latest articles, news and other interesting topics.

Please enter your email address below and click Subscribe.