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Old 22nd September 2002, 12:27 PM   #1
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Question 200 Watt Lateral Mosfet Amplifier

I just like to ask if someone have built this amplifier?

I think there's a couple mistakes in the circuit diagram...
R3 and R8 should be 75ohm (not 470) if u don't use IRF610.
Is that correct?
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Old 22nd September 2002, 02:48 PM   #2
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I can't see where the resistors are but if they are gate resistors, the value is OK.

Groundrule is as low as possible to avoid (MOSFET-) oscillations but not too large because the output stage will get slow.

The value is easy to check if you have an oscilloscope. Usually it the N-channel which oscillates, also when the current is over a certain value. This type of oscillation can be real nasty and you can also hear them. It's important to get rid of these oscillations.
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Old 22nd September 2002, 07:27 PM   #3
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I think that I had same problems that macgyver have.

If you build that amplifier, it doesnt work if there is MJE340 (Q3) as voltage gain stage and resistors R3 and R8 are 470ohm. Voltage gets too high at base of the MJE340 and output is driven to - supply rail. I put 75ohm resistors to R3 and R8 and amplifier worked fine.

R3 and R8 are at emitters of current mirror.

I think that R3 and R8 should be 470ohm when you use IRF610 as voltage gain stage (Q3).

It would be nice if someone could confirm my conclusions.
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Old 17th October 2002, 12:17 AM   #4
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Anthony could answer this!
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Old 17th October 2002, 01:14 AM   #5
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and you know what i can answer it too.. my n-channel amps run just fine just the way they are no problems and makin them distort is hard and ect ect the amps runs verry strong i love it im glad that i bought and built one..


Jason
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Old 17th October 2002, 10:12 AM   #6
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I just want to unsterstand it better, as I'm only a newbie, I thoght Anthony could give better explanatios, it's his project!
And I want to understand how it works, every resistor, the ones in this topic for example, I don't understand well.
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Old 17th October 2002, 10:42 AM   #7
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I have checked the schematics (my first answer wasn't exactly) and I suspect something is wrong in the interfacing between the first and the second stage. At DC Q3 must have the same current as the Q10 which is 10 mA. R3, R8 and R16 don't match.

Anthony Holton, have you any explaination of this?

Whitout any further investigation I suggest R3, R8 to be 100 ohm.
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Old 17th October 2002, 12:50 PM   #8
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But to use Q3 as IRF610 are these values correct?
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Old 17th October 2002, 04:26 PM   #9
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When I looked at this blurry schematic: http://www.aussieamplifiers.com/images/chpsch.jpg I noticed that R3 and R8 have 2 digit value, so I guessed that they are 75ohm.

In construction manual Anthony writes about another schematic, but that little blurry schematic was only I found.

I am currently building another channel and I am going to try that IRF610 and 470ohm resistors.
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Old 17th October 2002, 07:34 PM   #10
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Quote:
Originally posted by amalin
When I looked at this blurry schematic....
You can download the pdf file of this project, much clearer...
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