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Old 1st May 2011, 08:33 AM   #1
BrianVG is offline BrianVG  Belgium
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Default Easy and low cost: IRF540/9540 amp

Hi all,

I completed my first amp a few months ago. It was more a test than really something to listen to. It used the 9240/240 Mosfets.
Now I want to make a more serious amp, but still keep the cost low and the circuitry simple. I've found a very easy schematic with not much components. I'm going to make a few of them to sell to my friends.

Click the image to open in full size.

I'm going to add somethings myself; thermal compensation, DC protection, inrush current limiter,..

This is the website where I found it 100 W 8 ohms MOSFET amplifier with IRF9540 - IRF540 | Electronics Circuits Diagrams

I know some of you don't like V-Fets and schematics from that kind of website but what do you think of the circuit? Any major drawbacks?

Thanks
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Old 1st May 2011, 08:52 AM   #2
lineup is offline lineup  Sweden
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!00 Watt with only one pair of IRF540/9540 sounds a bit optimistic.

Thermal compensation, first replace P1 with one IRF510 or IRF610 HEXFET vbe-multiplier.

Otherwise the schematic is good. Can be an amplifier that works well.
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Old 1st May 2011, 09:01 AM   #3
BrianVG is offline BrianVG  Belgium
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I'm not really aiming for 100W, ~30W is more then enough, I'm using +-35V rail voltage.
I'm going to check that vbe multiplier out.
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Old 1st May 2011, 09:25 AM   #4
lineup is offline lineup  Sweden
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Quote:
Originally Posted by BrianVG View Post
I'm not really aiming for 100W, ~30W is more then enough, I'm using +-35V rail voltage.
I'm going to check that vbe multiplier out.
+/-35VDC Was my thoughts, too, when I looked at the schematic.
This will be alright
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Old 1st May 2011, 10:21 AM   #5
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Quote:
Originally Posted by BrianVG View Post
Hi all,

I completed my first amp a few months ago. It was more a test than really something to listen to. It used the 9240/240 Mosfets.
Now I want to make a more serious amp, but still keep the cost low and the circuitry simple. I've found a very easy schematic with not much components. I'm going to make a few of them to sell to my friends.

Click the image to open in full size.

I'm going to add somethings myself; thermal compensation, DC protection, inrush current limiter,..

This is the website where I found it 100 W 8 ohms MOSFET amplifier with IRF9540 - IRF540 | Electronics Circuits Diagrams

I know some of you don't like V-Fets and schematics from that kind of website but what do you think of the circuit? Any major drawbacks?

Thanks
An important disadvantage is the use of apparently but not really "true complementary" output stage and thus too much differences between the pos. and neg. half.
Avoid additional typical quasi complementary designs like that one from post #166 about
Power amp under development
because the clipping behaviour isn't good.

I would prefer this circuit:
http://www.amplimos.it/images/N-CH1.JPG
ask Mr. Antony Holton about
http://www.aussieamplifiers.com/
and check out this thread:
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?

Last edited by tiefbassuebertr; 1st May 2011 at 10:28 AM.
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Old 1st May 2011, 08:54 PM   #6
BrianVG is offline BrianVG  Belgium
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Conclusion; this circuit is not going to explode into my face when I turn it on (unless I did something stupid)

Thanks for the info tiefbassuebertr! But I want to use this design, I've already got a +-35V supply so I'm going to order the IRF540/9540, other components still here from 9240/240 project. Hopefully it works, then I'm going to order a bunch of PCB's and make my friends pockets lighter

Thanks for the info tiefbassuebertr! But I want to use this design.
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Old 2nd May 2011, 12:48 AM   #7
ontoaba is offline ontoaba  Indonesia
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Yes irf540 is the cheapest Rp5000 here (~$0.5), but without classH or tracking rail, it will need big heatsink. Their TO220 case not suitable for dissipating power more.
Btw total cost of my 200W into 4 ohm with irf540/9540 is around $50 (large 5A 32V transformer, 2x10kuF, no case), but I am not to sell it here.
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Old 5th May 2011, 07:53 PM   #8
BrianVG is offline BrianVG  Belgium
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I think I've found a more reliable design

Click the image to open in full size.

I've simulated this and it works fine, 200mV is near clipping.
Only problem that I have (it's a simulation) is that I cant adjust bias current and when I put a dummy load on it it draws 37A. Probably a problem with Multisim because the scope shows a perfect sinewave.

I've also simulated the design in the first post, Multisim shows exploding caps and resistors ^^

source: http://www.redcircuits.com/Page2.htm
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Old 5th May 2011, 08:08 PM   #9
BrianVG is offline BrianVG  Belgium
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Simulation

Click the image to open in full size.

Any ideas what's wrong? Or just a problem with te software?

Input signal is 200mV, 1kHz.
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Old 5th May 2011, 08:34 PM   #10
CBS240 is offline CBS240  United States
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Hi

I suspect a real world version of this circuit would self destruct with a fast signal transient. You need to AC couple the gates of the N-ch and P-ch outputs. Without significant bias, >100mA, crossover distortion products will be high. With adequate bias, these devices need thermal compensation. It is pointless to dredge through simulation problems if you know there will be problems with the 'real' circuit, that is if your intent is to build an actual amp. OTOH, Learning simulation parameters and experience is valuable info.


As for the circuit in question, the input stage Z out may be too high to drive the VAS. Try a VAS buffer. What is the bias of the output devices?
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Last edited by CBS240; 5th May 2011 at 08:37 PM.
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