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Old 9th April 2005, 07:38 PM   #1
pk386 is offline pk386  United States
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Default Calculating resistor values

Hey ALL,
I'm currently working on my Senior porject for my Electronics Engineering technology degree. I'm building a simple 80W stereo amp.
I'm baiscly useing Randy Slone's book as my refrence.

I understand the basic topologies and how all 3 stages work; The input stage, Voltage amplifier (VA) stage, and the output stage.

I know that the input stage and VA stage have to be built together to funciton properly.

I'm trying to use current sources (3-10mA) on the input and VA Stages. I'm not using a Current mirror iin the input stage yet. (I would like to incoperate one.) and I'm not using a mirror topology.

Here is my problem.... (and I know this mighty be difficult with out seeing a schematic) But I'm confused on how to Calculate the resistor values for the input stage and the VA stage, (IE, The Collector and emitter resistors for the input stage, and the Emitter resistor for the VA stage.) I think I'm missing one little thing to understanding setting up these stages.

Thanks in advance for your input
Please ask if I need to explian any thing in more detail
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Old 9th April 2005, 07:54 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
use resistor loads for the LTP (sounds better and is easier to stabilise). You could design the PCB to add in a mirror later.
The currents are usually driven by a Vbe voltage, about 650mV for a BJT or 1.6v to 2v for an LED.
Look up Leach's site for a good design with lots of theory or Self's site which is based on slightly simpler topology. Both will compliment Sloan.
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Old 9th April 2005, 08:40 PM   #3
Marc Vi is offline Marc Vi  Netherlands
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Hi,

See my website www.suplifier.nl, where you find many examples of configurations.

See also the book of D. Self. Although I don't agree with everything he wrote, his book gives much insight information.

One thing you must decide for your own is the amount of global feedback. If you use no or medium global feedback - which I should do -, use resistors as load of the input LTP. The value of these resistors and of the emittor resistors of the LTP depends highly on this decision.

One configuration of the input stage and the VAS together I will advise you, is the Borbely configuration which I use in my Ultimate Suplifier.

Marc
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Old 10th April 2005, 09:34 AM   #4
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I found the error. Clicking the link puts a trailing comma in the URL.
That's why it doesn't work. here it is again, fixed...

Quote:
See my website www.suplifier.nl
Are you sure? That URL is bad from my end (domain name not found).
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Old 10th April 2005, 02:57 PM   #5
Marc Vi is offline Marc Vi  Netherlands
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Thank you, without the comma in the URL the link will work.

Or click on "www" on the bottom of this post.

Marc.
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