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jamesfeline 22nd June 2012 03:41 PM

Maplin 1kw mosfet amp build thread
Hi Every one

I have started a new thread to show you the construction stages of the Maplin 1KW mosfet amp that I am making, with hopefully all the feedback that I have learnt from my other builds on this site.

I have all eight mosfets mounted on the hetsink and the PSU PCB's have just come in fresh from the PCB makers, I will load up some pics tonight.

Just some specs for now:

RMS power 775 Watts RMS (4 ohm load)
Peak power 1.3Kw
Average power 650 Watts

Full power bandwidth - 10Hz - 50kHz
Slewing rate = 24v/us
damping factor = 110 (4 ohm load)
Distortion = 0.2% at 1Khz (90% full power)
input sen = 775 mv (0db) into 30k for rated output

The details can be found in the Maplin electronic magazine March to May 1988

design is full mono block (1000va mains transformer)



AndrewT 22nd June 2012 07:32 PM

Is this for PA duty?

homemodder 23rd June 2012 10:45 AM

:eek: Slewrate only 24v/us for 775 Watss.

I would rather build something else.

KatieandDad 23rd June 2012 10:49 AM

If my memory serves me correctly these amps were not very reliable and easilly destroyed.

homemodder 23rd June 2012 10:55 AM

Topology ??

Tekko 23rd June 2012 11:19 AM

Its the usual "Too few output devices at too high rail voltages" topology.

wahab 23rd June 2012 11:22 AM


Originally Posted by homemodder (
:eek: Slewrate only 24v/us for 775 Watss.

I would rather build something else.

Actually this is enough since this is on a 4R load ,

10V/us should be the maximum slew of a 20Khz sine
at such a power output.

jamesfeline 23rd June 2012 02:48 PM


Please find some pictures of the heat sink assembly for one channel, as I said before I have built these before, and have been 100% reliable and sound just as good as any Marantz gear I used to own.

Sometimes when people build these amplifiers they do not pay enough attention to the detail or just don't know what they are doing and their construction skills are not mature enough.

Also people on this site just spend to much time theorising, or just be armchair critics but never make anything. Sometimes its better just to make the thing and trust you ears etc ... this was how JLH used to work.
Anyway enough ramblings from me, have a look at the heat sink assembly, this was the one I made years ago. This will be stripped down and rebuilt all the mosfets are 2SK176 AND 2SJ56 etc.



Bonsai 23rd June 2012 03:51 PM

Now, I like that!!! Decent size and plenty of dissipation capability. You can probably bias up to 5-10w class A. That usually sweetens things up quite a bit!

Good luck with your project.

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