GA28F Mosfet Amp

hungeryhippie · 15th May 2006, 04:44 PM

Hello All,

I am still new to this forum but am now asking a few questions.
I got given a GA28F 100W mosfet module awhile ago now, i spent some time looking at it and decided it wouldnt be to hard to copy it. So it did! I took a photo of the under side of the PCB, put it into photoshop, worked it out and then etched my own PCB, I have populated it and its tested and working.

I now have two 100W mosfet modules. I am not sure what to do with them!

I have put it all together in a box and tryed it out runing in bridged as a sub amp. However it wasnt that loud!

The power supply I used is a 35 0 35 @ 160VA toroidal. From what i have read this isnt enough to drive two of the modules. I have put together seperate rectifiers and caps for each module but they share the PT.

I do however have an other toroidal not the same make though but is 35 0 35 @120VA. How much would it improve things if i use a seperate PT for each module? Even though they are different VA ratings?

I dont have enough cash to buy a new 500VA PT . But i do have another transformer in a Toa TA-957 (PA) that i could use but i have no info on it.

Any ideas on what to do?

Thank you for reading.

elviramjw · 7th October 2006, 05:59 PM

To bridge 2 GA28F ampls you need to invert the input signal to one of the module, that way when one output is positive the other is negative, this give you twice the voltage swing. You must connect you speakers between the two outputs of the modules and not to ground.

Anyproblems let me know.

bigpanda · 8th October 2006, 04:00 AM

I am greedy for schematics,

Can you post the schematic? Or even tihe pcb?

Tks a lot.

jacco vermeulen · 8th October 2006, 12:18 PM

BP,

Study schematics instead of only collecting,the GA28F is the Maplin Mosfet kit.
(the largest electronics store chain in the UK)
Several variations of the 150W design have been posted on diyA.(including the 1987 original and 1990 update)

Mefiboset · 5th May 2007, 12:43 AM

Hi!
You may be the only preson in this world who can help me, and may be I also can help you wit your amp?
I have a Mosfet amp. 2x100W, but by a mistake I bave distroid three resistors on both chanals. I want to replace these, but the problem is: I am not able to reed the value on them(they are burned). But may be you have a circuit diagram that shows the value of R7, R11 and R15?
Can you help me?

Dag in Norway

jaycee · 5th May 2007, 01:11 AM

If it's the MOSFET amp I'm thinking of (one pair of outputs on an L-bracket), then it's basically just Hitachi's application note for those outputs.

Leolabs · 5th May 2007, 01:58 AM

Schematic pls??

jaycee · 5th May 2007, 03:57 AM

Maplin 150w MOSFET regulation?

Schematic:
http://www.cpemma.co.uk/map_100w.html

15th May 2006, 04:44 PM	#1
hungeryhippie diyAudio Member Join Date: Nov 2005	GA28F Mosfet Amp Hello All, I am still new to this forum but am now asking a few questions. I got given a GA28F 100W mosfet module awhile ago now, i spent some time looking at it and decided it wouldnt be to hard to copy it. So it did! I took a photo of the under side of the PCB, put it into photoshop, worked it out and then etched my own PCB, I have populated it and its tested and working. I now have two 100W mosfet modules. I am not sure what to do with them! I have put it all together in a box and tryed it out runing in bridged as a sub amp. However it wasnt that loud! The power supply I used is a 35 0 35 @ 160VA toroidal. From what i have read this isnt enough to drive two of the modules. I have put together seperate rectifiers and caps for each module but they share the PT. I do however have an other toroidal not the same make though but is 35 0 35 @120VA. How much would it improve things if i use a seperate PT for each module? Even though they are different VA ratings? I dont have enough cash to buy a new 500VA PT . But i do have another transformer in a Toa TA-957 (PA) that i could use but i have no info on it. Any ideas on what to do? Thank you for reading.

7th October 2006, 05:59 PM	#2
elviramjw diyAudio Member Join Date: Oct 2006	Bridging amps To bridge 2 GA28F ampls you need to invert the input signal to one of the module, that way when one output is positive the other is negative, this give you twice the voltage swing. You must connect you speakers between the two outputs of the modules and not to ground. Anyproblems let me know.

8th October 2006, 12:18 PM	#4
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	BP, Study schematics instead of only collecting,the GA28F is the Maplin Mosfet kit. (the largest electronics store chain in the UK) Several variations of the 150W design have been posted on diyA.(including the 1987 original and 1990 update) __________________ Looks like Sponge Bob has killed another thread.

5th May 2007, 12:43 AM	#5
Mefiboset diyAudio Member Join Date: May 2007	GA28F Mosfet Amp Hi! You may be the only preson in this world who can help me, and may be I also can help you wit your amp? I have a Mosfet amp. 2x100W, but by a mistake I bave distroid three resistors on both chanals. I want to replace these, but the problem is: I am not able to reed the value on them(they are burned). But may be you have a circuit diagram that shows the value of R7, R11 and R15? Can you help me? Dag in Norway

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8th October 2006, 04:00 AM	#3
bigpanda diyAudio Member Join Date: Jun 2004 Location: HKSAR	I am greedy for schematics, Can you post the schematic? Or even tihe pcb? Tks a lot.

5th May 2007, 01:11 AM	#6
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	If it's the MOSFET amp I'm thinking of (one pair of outputs on an L-bracket), then it's basically just Hitachi's application note for those outputs.

5th May 2007, 01:58 AM	#7
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Schematic pls??

5th May 2007, 03:57 AM	#8
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Maplin 150w MOSFET regulation? Schematic: http://www.cpemma.co.uk/map_100w.html

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