Very interesting...
I was/am curious if anyone ever built a Mosfet amp with these devices in... Or, such an amp like that...
I've been lately very interested in a DIY Mosfet amplifier - Class AB!
- and saw some interesting projects from folks here.Been a bit fed up with commercial amps.
Probably some folks here don't even buy these anymore...For a first DIY project I'd be more-than-happy with a ≤ 100W project. Even a kit since it is well tried and tested. Separate channels, two toroids, etc. Something between 50W to 100W (into 8 ohms) - a stable amp! - would be great.
I've heard of vertical and lateral ones and these seem to have wide consensus?
These must be very new. Couldn't find info on them...
..
Hi Karl,
Have a look at the following schematic:
http://www.diyresearch.net/data/mp150/MP150_SCH.pdf
I have designed and build following amp:see post 123 for final schematic!
My remaks on Bob Cordell his proposal:
1: 150ma is indeed a good sounding bias current fir these devices, 200ma sounds already totaly different = less good
2: I've tried a few bjt drivers and fet drivers, the 2sk216/2sj79 gave me the best sound! Totally none listening fatique.
http://www.diyaudio.com/forums/solid-state/198209-amp-design-subwoofer-wideband-duty-13.html
Have a look at the following schematic:
http://www.diyresearch.net/data/mp150/MP150_SCH.pdf
I have designed and build following amp:see post 123 for final schematic!
My remaks on Bob Cordell his proposal:
1: 150ma is indeed a good sounding bias current fir these devices, 200ma sounds already totaly different = less good
2: I've tried a few bjt drivers and fet drivers, the 2sk216/2sj79 gave me the best sound! Totally none listening fatique.
http://www.diyaudio.com/forums/solid-state/198209-amp-design-subwoofer-wideband-duty-13.html
Hello, Bensen!
Do you have a sqr wave scope shot of the leading and the trailing edge on the cross over region?
I'm not 100% sure what you mean. Have a look at post119 for sqr wave response.
http://www.diyaudio.com/forums/solid-state/198209-amp-design-subwoofer-wideband-duty-12.html
http://www.diyaudio.com/forums/solid-state/198209-amp-design-subwoofer-wideband-duty-12.html
Ah, OK...
However, I do not see your scope settings, and iIm (sorry) too lazy to read the whole thread... What did you use as the dummy load during testing? You probably have it mentioned somewhere in the description, but (im stupid and lazy)...
Anyways... You could put your scope to 1us/div or even 100ns/div, trigger on the leading, and on the trailing edge of your signal to get the crossover visible on the screen.
What I am after is how your amplifier (this output stage) performs with those gate resistors.
I have not managed to confirm myself that I could use same value Rg on both Nch and Pch with those toshibas (yet), you see...
However, I do not see your scope settings, and iIm (sorry) too lazy to read the whole thread... What did you use as the dummy load during testing? You probably have it mentioned somewhere in the description, but (im stupid and lazy)...
Anyways... You could put your scope to 1us/div or even 100ns/div, trigger on the leading, and on the trailing edge of your signal to get the crossover visible on the screen.
What I am after is how your amplifier (this output stage) performs with those gate resistors.
I have not managed to confirm myself that I could use same value Rg on both Nch and Pch with those toshibas (yet), you see...
Just forget it, it is not audio mosfet, but I just think to try it in audio sometime. I spot them while developing class S-E amplifier.
Ciss only around 350pf for 1000W PD with 225celcius Tj, and less than 100pf for <300W PD. 1-3 nanosecond typical response (on/off delay, and rise/fall). Gold metallization, in high quality ceramic package.
For a first DIY project I'd be more-than-happy with a ≤ 100W project. Even a kit since it is well tried and tested. Separate channels, two toroids, etc. Something between 50W to 100W (into 8 ohms) - a stable amp! - would be great.
You could use F5 with those toshiba mosfets replacing the hexfets and start tweaking in bias current.
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Thank you! I'll have o look at that project as well.
Many, MANY good MOSFET projects I've seen so far here in diyAudio! Pretty HARD to catch only one!
P.S.: Also spending hours readind the threads. Wondering how much better they sound comparing with most commercial amps...
..
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Hi guys,
some time before I found a rule of thumb to calculate the maximum rail voltage in regards of the maximum power dissaption of the used MOSFETs. But I cannot find it anymore So I would kindly ask you to please write it down here again. The rule was something like this: Add up the power dissaption of all MOSFETs used in the final stage, divide by 4 and you got the maximum power your amplifier can handle. But is this meant for 4 ohms or for 8 ohms?
Thank you very much!
some time before I found a rule of thumb to calculate the maximum rail voltage in regards of the maximum power dissaption of the used MOSFETs. But I cannot find it anymore
So I would kindly ask you to please write it down here again. The rule was something like this: Add up the power dissaption of all MOSFETs used in the final stage, divide by 4 and you got the maximum power your amplifier can handle. But is this meant for 4 ohms or for 8 ohms?Thank you very much!
Ah, thank you I found it!
Originally Posted by AndrewT
use one of the SOAR spreadsheet calculators to model the output stage.
Bensen did one for Mosfets, Jan Didden has one.
I modified Bensen's for both FETs and BJTs.
Or use the simple formula
Maximum output power equals the total output device dissipation capability divided by Factor.
For FETs the Factor ~4
For BJTs the Factor is ~5 to ~6
2 125W devices = 250W of device dissipation.
Maximum output power ~ 250/5 to 250/6 = ~50W to 40W
2Pr gets to 100W to 80W
3pr gets to 150W to 120W. This last requires too high a supply voltage for 8ohms, so only possible into 4ohms speaker.
I have read your book and I agree with most of the concepts you propose as a power amplifier design.
I have also designed many power amplifiers most using lateral mosfet. Models of 100 and 200w at 8 ohms, with two pairs of 125W and two pairs of 250w respectively.
Personally I like the lateral mosfet very much, although they are always more expensive, for me have some great advantages, such as thermal stability without the need for temperature compensation, a form of soft "clip" at maximum level and much more robust and durable than bjt or vertical mosfet. I also like their sound more because it seems a bit like the valvular sound.
My question for you is this, I always use the power mosfet directly after the VAS without a pre-driver. The VAS bias I use always 12-15mA and sometimes use cascode, if a mosfet works only by voltage in the gate, why is it necessary one more step of pre-driver? What improvement does it represent?
With 15mA of bias in the VAS is more than enough to directly "attack" the power mosfet, right?
Thanks !!!
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Rest in peace
He contributed many things to the forum. Great person known here!
I always use a driver between the VAS and the MOSFET output transistor gates. Input capacitances of the MOSFETs mean they require current. Those capacitances are nonlinear. I believe in not making the VAS work any harder than it needs to. This is true even if the 15 mA is enough to sufficiently charge the MOSFET input capacitances at maximum voltage slew rate and current slew rate.
Cheers,
Bob
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