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Old 24th May 2012, 06:15 AM   #1
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Default N-mos Power Amp , my project need some help , Thanks .

Hello every body
First i'm sorry for my English , i knew little .
_____________

- I'm doing a project Power Amp , using full N-mos , because i have some IRFP450 (and some IRFP460) , so i need some help , i need a good schematic and complete .
- I knew this schematic , "Legend Stage Master MK2" , but it not has overcurrent protection circuit . So i modify it , but I don't know to calculate the resistor values ​​in this circuit , so I ask you to help me calculate the value , i don't know it OK or Bad ?
- Or help me , give me a good schematic , high power , has protection , and using full Nmos Output .

I'm thanks you very much
And again sorry for my English .
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File Type: jpg Legend Stage Master MK 2 Driver.jpg (93.4 KB, 460 views)
File Type: jpg Legend Stage Master MK 2 Output eeerrewrwerwerwrwer.jpg (97.2 KB, 445 views)
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Old 25th May 2012, 08:14 AM   #2
wahab is offline wahab  Algeria
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This amp has some design flaws and wont be reliable.
As an exemple , the MJE340/350 are used at too high current,
moreover variable with temperature since the 10K that feed
the MJE350 base has too high value.
It should be reduced to 1K, while the 22R resistor on its emitter
should be increased to a value between 150 and 220R.

The input transistors will run hot at about 100mW each.

Also , the very high voltage can be lethal , perhaps it would
be better to start with a lower power by using a +-40V supply
that would reduce components thermal dissipation to safer levels.
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Old 25th May 2012, 09:16 AM   #3
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Its not the best of circuit but it worked out for me with quite good sound: http://i.imgur.com/GcRco.png

A video of the test setup: NMOS amp in stereo - YouTube

This is NOT a circuit i would recommend though. Instead i would advice you to look at Quasi's nmos amplifier.
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Old 25th May 2012, 12:49 PM   #4
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Quote:
Originally Posted by wahab View Post
This amp has some design flaws and wont be reliable.
As an exemple , the MJE340/350 are used at too high current,
moreover variable with temperature since the 10K that feed
the MJE350 base has too high value.
It should be reduced to 1K, while the 22R resistor on its emitter
should be increased to a value between 150 and 220R.

The input transistors will run hot at about 100mW each.

Also , the very high voltage can be lethal , perhaps it would
be better to start with a lower power by using a +-40V supply
that would reduce components thermal dissipation to safer levels.
Oh , i thanks you very mcuh because for me know that information .
Maybe i 'll not do follow this schematic diagram .
I need some help , some reliable schematic , and high power , has protection . Maybe i too greedy , but i'm very needed a good schematic , to doing my project .
Thanks you wahab
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Old 25th May 2012, 01:09 PM   #5
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Quote:
Originally Posted by Tekko View Post
Its not the best of circuit but it worked out for me with quite good sound: http://i.imgur.com/GcRco.png

A video of the test setup: NMOS amp in stereo - YouTube

This is NOT a circuit i would recommend though. Instead i would advice you to look at Quasi's nmos amplifier.
hi , thanks you very much .
But i wanna a high power amp , used high voltage power supply for high power at 8 ohm and 4 ohm .
Iknow this schematic , Nmos power amp , but it not has protection , i'm afraid damaged speaker , or speaker wire has been short , so my power amp 'll be damaged .
Can you help me a better schematic , or modify this schematic .
I'm thanks you very much
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File Type: jpg Nnmos350-500schematic.jpg (121.7 KB, 353 views)
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Old 25th May 2012, 02:08 PM   #6
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VI limiters will have no effect on preventing damage to your speakers, only you and the volume control can prevent that.

Also VI limiters will not protect against a short, only slightly reduce the risk of blowing the output devices, allowing the rail fuses to blow first, but a dead shor will blow up the amp no matter what.

Only a circuit like this that this into the dc protect circuit can protect against a dead short: http://i.imgur.com/dkyhe.png

This circuit was replicated from a yamaha brand amplifier.

However not even a short circuit detection circuit can fully prevent the output devices from blowing as there always is some propagation delay from the circuit detecting the short contidion to the relay contacts opening.

However for a quasicomplementary output stage, a short circuit protection circuit cannot be implemented as easily.

Anyways if you worry about shorting the outputs, you either let the speaker wires fray and dont bother fixing it or using low quality terminals that easily allows shorts or just have exposed wires hanging all over.
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Old 25th May 2012, 06:21 PM   #7
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Quote:
Originally Posted by thienchay View Post
Hello every body
First i'm sorry for my English , i knew little .
_____________

- I'm doing a project Power Amp , using full N-mos , because i have some IRFP450 (and some IRFP460) , so i need some help , i need a good schematic and complete .
- I knew this schematic , "Legend Stage Master MK2" , but it not has overcurrent protection circuit . So i modify it , but I don't know to calculate the resistor values ​​in this circuit , so I ask you to help me calculate the value , i don't know it OK or Bad ?
- Or help me , give me a good schematic , high power , has protection , and using full Nmos Output .

I'm thanks you very much
And again sorry for my English .
In the circuit ready have protection for all pair of mosfet .you want more protection --> it is only use when your power wasnot enought with load ? remove it. should think more how to make it hight quality ..
check by occillocope with all freq (20Hz---20KHZ) ...
see more detail some cap of mr Quang hao-Trinh anh tu'Telos amp and you can modify it.
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Old 26th May 2012, 07:15 AM   #8
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Location: Coffs Harbour
Like Tekko suggested - have a look at quasi's design and read the detailed posts. A very long thread but plenty of
additional features are added later - Power amp under development. There is plenty to learn there.
__________________
regards
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Old 26th May 2012, 11:40 AM   #9
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Quote:
Originally Posted by Tekko View Post
VI limiters will have no effect on preventing damage to your speakers, only you and the volume control can prevent that.

Also VI limiters will not protect against a short, only slightly reduce the risk of blowing the output devices, allowing the rail fuses to blow first, but a dead shor will blow up the amp no matter what.

Only a circuit like this that this into the dc protect circuit can protect against a dead short: http://i.imgur.com/dkyhe.png

This circuit was replicated from a yamaha brand amplifier.

However not even a short circuit detection circuit can fully prevent the output devices from blowing as there always is some propagation delay from the circuit detecting the short contidion to the relay contacts opening.

However for a quasicomplementary output stage, a short circuit protection circuit cannot be implemented as easily.

Anyways if you worry about shorting the outputs, you either let the speaker wires fray and dont bother fixing it or using low quality terminals that easily allows shorts or just have exposed wires hanging all over.
Thanks you very much .
but i don't intend to protect the speaker , i'm wanna if my speaker is damage , the amplifier will not be damaged , or speaker wire is short , my amplifier will be protected .
Can you show me the protect circuit in Output Stage amp , thanks a lot
I will be study the Quasi 's design power amp .
But i want a high power , about 400 W to 500W 8 ohm , and 800W to 1000W 4 ohm , maybe i'm too greedy .
Thanks .

thienchay
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Old 26th May 2012, 11:52 AM   #10
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thanks dungdochi1987 and Ian Finch
i'm have a Quasi 's design power amp , about 600W .
Please help me , this circuit is reliable and safe ? , if i used 12 x IRFP450 , and +/- 90VDC , i would have how much Watt Output ?
And help me a protect circuit in output stage , first is protect power amp , and if my amp damaged , protect the speaker .
Thanks so much .

thienchay

____________
regards
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