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Author Topic: Who has Layout for Mosfet P. Amp?  (Read 537 times)

kikback007

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Who has Layout for Mosfet P. Amp?
« on: May 20, 2020, 10:49:56 PM »
Anyone? Im trying to build an amp in new approach. This time by using transistors. Maybe just 50w output is enough.

Loudthud

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Re: Who has Layout for Mosfet P. Amp?
« Reply #1 on: May 22, 2020, 01:37:18 PM »
This is an old design that was in an IR data book in the 80's. It doesn't have short circuit protection, but that can be added. You also need gate protection zeners for the output MOSFETs. I built one and it sounded good. You can get to 50W at 4 Ohms with +/- 25V rails.

Link: http://www.cieri.net/Documenti/Altri%20marchi/International%20Rectifier%20-%20Linear%20Power%20Amplifier%20Using%20Complementary%20HEXFETs%20(AN948).pdf

Edit: Attached below is the PCB layout from the Ap note article edited to show the components X-ray style over the etch.
« Last Edit: May 30, 2020, 10:45:29 PM by Loudthud »

Loudthud

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Re: Who has Layout for Mosfet P. Amp?
« Reply #2 on: May 29, 2020, 02:04:18 AM »
OK, I looked at the Ap Note and it's hard to follow. On the layout they provided there is no Q1 and two Q3's. The board side view doesn't line up with the component side view. There are also places where you need to add jumper wires that are not shown. So I built a new version and I'll show my layout sketch and the mods I did to the schematic. One additional mod I did was to add a capacitor to the input.

Most things I build are on a proto board with holes on 0.1 inch centers and copper pads on one side. To this I add eyelets from Keystone in three sizes. In some places you need to remove the copper pads because the pads cause shorts between eyelets. There are multiple ground wires that come off the power amp board to a star on the power supply board that I haven't built yet. I built the power amp board and got it running on my lab power supplies. Still might make some changes there. Another mod I allowed for is mixed mode feedback. There is an eyelet on the power amp board labeled IFB. That hooks to a low value resistor that goes between the low side of the speaker and ground. If you just want Voltage feedback, ground the IFB pin.

The attached schematic shows the short circuit protection and zener diodes on the MOSFETs.
« Last Edit: May 29, 2020, 02:09:51 AM by Loudthud »

kikback007

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Re: Who has Layout for Mosfet P. Amp?
« Reply #3 on: June 06, 2020, 09:23:55 AM »
Thank you. Ill keep these schematics for later builds

Loudthud

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Re: Who has Layout for Mosfet P. Amp?
« Reply #4 on: June 06, 2020, 07:15:36 PM »
This circuit has a temperature compensation problem, as it warms up, the bias current goes lower and lower. I started a discussion of it here: https://www.diyaudio.com/forums/solid-state/355583-class-ab-hexfet-amp-temperature-compensation.html ... but so far no one has responded.