Maplin MosFET Amplifier GA28F construction thread

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#101
Here's mine. Must have made it getting on for 20 years ago.
 

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#109
jamesfeline said:
Hello Nigel

To be honest not bothered about solder resist or silk screening .. plus I have my own PCB fabricator at min cost
but thanks for the heads up

all the best
Click to expand...

I did an update pcb to the Maplin mosfet amp a couple of years back.
I changed the transistors for easy to get modern types.
The original sometimes had problems with hum so I decoupled the front end.
I added CCS on front end and made current mirror two transistors instead of transistor and diode.
It sounded very good.
An externally hosted image should be here but it was not working when we last tested it.
 
#110
chalky said:
Here's mine. Must have made it getting on for 20 years ago.
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I made my first Maplin mosfet amp in 1981.
It was built for a mobile disco but wasn't loud enough.
So I bought the Maplin disco amplifier which was 225WRMS into 4 ohms.
A couple of years back I spotted a Maplin mosfet kit on ebay which hadn't been built. So I bought it and built it up, worked great. I maybe should have kept it unbuilt for the rarity ?
 
#111
Fired up my amp pictured in post #101 and it still works fine. I think I still have a few unbuilt kits in the depths of my workshop, maybe I'll make them up. It never fails to surprise me that such a simple circuit gives such good performance with pretty low distortion.
 
#112
chalky said:
Fired up my amp pictured in post #101 and it still works fine. I think I still have a few unbuilt kits in the depths of my workshop, maybe I'll make them up. It never fails to surprise me that such a simple circuit gives such good performance with pretty low distortion.
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Hello

Exactly my thoughts ... nice little retro project, easy to make and can bridge if needed, make a couple of monoblocks with big power supply
results nice deep bass easy to repair and mod .. and with decent heatsink / cooling will take loads of abuse.
Also the 1st amplifier that I made in my youth that actually worked - still pleases me today. hence why I made the PCB with supporting gerber files

best regards
 
#113
chalky said:
Fired up my amp pictured in post #101 and it still works fine. I think I still have a few unbuilt kits in the depths of my workshop, maybe I'll make them up. It never fails to surprise me that such a simple circuit gives such good performance with pretty low distortion.
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Hello Chalky .. if you find those unbuilt kits I would pay a good price for them 🙂
 
#114
Hello

Just made the new heat sink bracket .. this is just a trial fitment, better 3mm bolts will be used and the mounting bracket will be polished
Just shows what you can achieve when you put your mind on to it and stay focused
 

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#118
jamesfeline said:
Also do I keep tinned the tracks or keep bare copper .. just wondered forum members thoughts
as bare copper you could use any solder that you are happy with ?
best regards
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Copper shows up fingerprints after a few months, tinned doesn't. Soldermask will also prevent these cosmetic issues and help protect from oxidation over the years. Commercial PCBs are always tinned/wave soldered or gold-plated in my experience, and only the cheapest avoid soldermask.
With very fine tin layer the tracks change from silver coloured to brick-red over the years as the tin atoms diffuse into the copper track. Hot dipped tin (or wave-soldered) will stay silver (well, greyish)
 
#120
Mark Tillotson said:
Copper shows up fingerprints after a few months, tinned doesn't. Soldermask will also prevent these cosmetic issues and help protect from oxidation over the years. Commercial PCBs are always tinned/wave soldered or gold-plated in my experience, and only the cheapest avoid soldermask.
With very fine tin layer the tracks change from silver coloured to brick-red over the years as the tin atoms diffuse into the copper track. Hot dipped tin (or wave-soldered) will stay silver (well, greyish)
Click to expand...

HASL is common now (hot air solder levelling.)
 
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