# Modified 2sk1058 mosfet amplifier

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#### techn0

First i want to say hello to everyone! Im new here.
Im electrical engineering student and i have some interests in amplifiers.
I want to build "ZCA amplifier" it's class A. Problem is, i can't get 2sk1058!
Im beginner in this world, but i learn quick..

Yesterday i pulled of two pairs of irfz44n from old pcb, and i found a lot of irf630 in box from old projects.
I started with basic schematics from.. link^^

I have done some simulations with these and i will post it in atachments.
But i have several questions for this design.
Do i need 24v supply? Can i get just 12v without 40w resistor?
Can i put this two mosfets in parallel to get more performance, curent and beter heat disipation??
Is pc power supply enough to power this amplifier?
I'm planing to build stereo version! I have several transformers laying around, case! Hopefully i will put together some decent amplifier.
Thank you for any kind of resposne!

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#### AndrewT

You have shown a single ended amplifier (SE).
The maximum output is approximately 1/3rd of the supply rail voltage.
i.e. with a 24Vdc supply your maximum output is ~8Vac
When you add on a load the maximum output voltage drops, maybe ~6Vac trying to drive an 8ohms load
The maximum power from 24Vdc will be very approximately 5W (6Vac² / 8ohms)
At anything above half maximum voltage the 2nd harmonic will become gross.
So for clean power expect 2W to 3W as a reasonable maximum.

For a 5W amplifier you don't need dual output devices.

Assuming you have 12.1V across the three drain resistors, you have a bias current of 12.1/{5.6+5.6+5.6} = 0.72A
The total dissipation in the three resistors is 0.72A*12.1V = 8.7W (use 5W or 7W or 10W resistors)
The mosFET dissipation is also 8.7W (use a 2C/W sink per device). That should keep your sink below 55°C during summer (Ta=30°C).
0.72A through an 8ohms load needs 5.76Vpk. That is 2W. The bias of 0.72A cannot drive an 8ohms load. It needs a 16ohms load just for non reactive operation.

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#### techn0

I will be happy if i get 5 wats, it's enough for my personal use.
And i have stocked some ceramic resistors (5w, 7w, 10w, 15w), that part is solved.
Is it beter to use transformer ( 19vDc (2.5amps)) or smps (pc supply), somehow i will crank it's 12v rails..

#### Bangla H

Hallo techno.

Hope this can inspire you a bit in direction you will go.
I catchet that Franse PDF because i am like also the 5-25W power range.
AndrewT could take a little observe view to this, i think L'Audiophile Magazin Amp?https://drive.google.com/file/d/0BwTS40IaQa16eFNSd05OejBXQk0/view?pli=1
Main Page:6.9.7- Les Schemas Single End- scroll near down to: Le SingleMos
2x6,5W- it is with SK1058.
Hope it works.

The ZCA i have build for testing- all done like Marks project and lowered the
1M Resistor to 470k - sounds better. After paralleling the 470k with 220k it is now 150k and comes a bit magic in sound, but not real satisfying- missed a bit in top end highs. Staging is surprisingly good.
Why don't build the very nice ACA?- Boards are here in Store available.
So you have Reference to comparing.

Cheers Bangla.

#### Melosound

Hello, techn0!

What is the result of your experiment? Which max power have you managed to achieve?

Regards,
Andrew.

#### mhouston

You have shown a single ended amplifier (SE).
The maximum output is approximately 1/3rd of the supply rail voltage.
i.e. with a 24Vdc supply your maximum output is ~8Vac
When you add on a load the maximum output voltage drops, maybe ~6Vac trying to drive an 8ohms load
The maximum power from 24Vdc will be very approximately 5W (6Vac² / 8ohms)
At anything above half maximum voltage the 2nd harmonic will become gross.
So for clean power expect 2W to 3W as a reasonable maximum.

For a 5W amplifier you don't need dual output devices.

Assuming you have 12.1V across the three drain resistors, you have a bias current of 12.1/{5.6+5.6+5.6} = 0.72A
The total dissipation in the three resistors is 0.72A*12.1V = 8.7W (use 5W or 7W or 10W resistors)
The mosFET dissipation is also 8.7W (use a 2C/W sink per device). That should keep your sink below 55°C during summer (Ta=30°C).
0.72A through an 8ohms load needs 5.76Vpk. That is 2W. The bias of 0.72A cannot drive an 8ohms load. It needs a 16ohms load just for non reactive operation.

Mate, thanks for the info and calcs . My MCA is a betterr beast and really just as simple.

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