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Old 22nd September 2012, 06:19 AM   #1
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Default Need help to simulate my MOSFET Amplifier using TINA

I don't have much experience with Audio amplifier design. I found one 25W MOSFET audio amplifier circuit. 25 Watt MosFet Audio Amplifier - RED - Page2
I like to start this design with simulation. My TINA simulation get clipping at output.
The circuit is proven & working but i don't know what is wrong with the simulation...
Facts and Figures - RED

Regards
Udhay
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File Type: jpg tinadiag.jpg (219.1 KB, 125 views)
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File Type: zip 25W Mosfet.zip (4.1 KB, 13 views)
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Old 22nd September 2012, 06:36 AM   #2
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I don't use TINA but the amp seems to have a voltage gain of around 70 (R7/R6) and runs on 66 volts .

So applying 2 volts peak to peak as an input will clip on those rails. Try reducing the input voltage down to say 200mv peak to peak initially and see what happens.
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Old 22nd September 2012, 07:11 AM   #3
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Mooly,
Thanks for the reply. Yes i got the output for 200mV & 300mV Input. Is it Gain=70 too high? What will be the recommended input voltage or how much gain i can set?

Regards
Udhay
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Old 22nd September 2012, 07:13 AM   #4
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My simulation waveforms....
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File Type: jpg 300mV Input.jpg (179.0 KB, 111 views)
File Type: jpg 500mV Input.jpg (268.4 KB, 104 views)
File Type: png CIRCUIT TINA.png (35.4 KB, 112 views)
File Type: jpg tinadiag.jpg (267.2 KB, 107 views)
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Old 22nd September 2012, 07:16 AM   #5
Mooly is offline Mooly  United Kingdom
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The gain of 70 is fine and the amp and its compensation and so on will have been designed around that figure. Although you could alter the value of R6 (increasing lowers the gain) I wouldn't do so in practice. It just means the amp has a high input sensitivity and as it says, no need for a preamp.
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Old 22nd September 2012, 07:20 AM   #6
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Not to sure about running HEXFET's with a simple resistive bias generator (the preset pot) as it will be very prone to thermal runaway. Normally a transistor vbe multiplier type circuit is used.

If you build the amp for real be very aware of this
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Old 22nd September 2012, 07:25 AM   #7
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Default PCB Placement

Can i use this for 5.1 Surround? Can i connect it into my DVD player or PC sound card? (Sorry i don't know the p-p signal Output voltage) without clip?...
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Old 22nd September 2012, 01:48 PM   #8
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by udhay_cit View Post
Can i use this for 5.1 Surround? Can i connect it into my DVD player or PC sound card? (Sorry i don't know the p-p signal Output voltage) without clip?...
Yes you can. The high sensitivity should work with most source components.

Just remember what I said about the bias stability though
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Old 22nd September 2012, 03:35 PM   #9
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udhay

I dont understand why the output waveforms from post #4 look as they do.

Are you sure the feedback resistor (R6, 33K) is actually connected to the output node?

Thanks
-Antonio
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Old 23rd September 2012, 11:26 AM   #10
Mooly is offline Mooly  United Kingdom
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I threw the circuit into LTspice. This is at the point of clipping into 8 ohms.
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File Type: jpg Simple HEXFET Amp.JPG (128.7 KB, 52 views)
File Type: jpg 10Khz at point of clipping.JPG (132.9 KB, 47 views)
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