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Old 11th June 2003, 01:49 AM   #1
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Default MOSFETs or Bipolar Transistors?

Right, well I guess the title says it all here, I will soon be starting on a design for a new high power amp, and I was wondering wether I should go for a design using MOSFETs, or bipolar transistors. Idealy, the amp will be configred into two sections for each channel, so it can be either run in a bridged or parallel configuration depending on the load. The maximum ratings I should be using for each section will be arround +/- 60V and up to 20A of output current.

Now, I relise that the bipolar output devices will increas the complexity of the output stage design (I have been inspired to try something allong the lines of the Bryston output stage), and that they will require thermal runnawy protection, but I have in the past allways assumed that they sound better than MOSFETs. But, if anyone would like to share their experience of how either devices sound, then I would be interested to hear, as I have only really herd two decent amps up till now, one useing bipolars, and one with MOSFETs (the one witht he mosfet output devices sounds better, but it did cost about 50% more than the other amp).

If you aren't familiar with the Bryston output that I was planning on using, have a look here to see what I mean.

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Old 11th June 2003, 03:07 AM   #2
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Will the design use global feedback?

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Old 11th June 2003, 10:31 AM   #3
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Hi, yes the amp will have some global feedback, as well as using local feedback in places to stailise the output section, as I believe that with the output configuration I was planning on, if I go with th bipolars, requires a fairly complex biasing setup, and would benifit from a little more liniarity accross any possible loads.
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Old 11th June 2003, 10:41 AM   #4
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how highly do you plan to bias the amp?
- Dan
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Old 11th June 2003, 12:37 PM   #5
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dependig on how it effects the sound of the amp, I was aiming for arround 2 amps of current flow without any load, so that I get the first 20 - 30W in class A. But this depends on how the bias effects the sound of the amp, and how big the heatsinks I eventulay get are, as I will happily only run a few hundred milliamps if it souds better that way (and saves me another small room heater).
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