Maplin 160W (225W) bipolar amplifier design

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Ed Holland

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Joined 2004
For stuff about the MOSFET amps, I found this:

http://www.eastmarinedrive.com/contents/non-static/audiodgoodman-content.htm

EDIT: Sorry, I notice that was posted earlier - should have read more carefully!


As for the 50W kit, it's all come flooding back :D

I seem to remember the 50W circuit has a common emitter o/p configuration, which makes it somewhat unusual (I could be wrong, it's so long since I looked)


By way of some reference, thanks to my mate Google:

http://www.soton.ac.uk/~apm3/diyaudio/Maplin_50W.html

No circuit diagram though

Ed
 
Mooly

Mooly

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Joined 2007
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I think you are right about the output stage.
Funny how you remember things. The heatsink, it was an L shaped bracket wasn't it for bolting to a larger one. The picture in the catalogue I remember, always looked like one of the holes was way off centre.
 
E

Ed Holland

Member
Joined 2004
That's it! Eventually, a kind friend of my Dad's made me an aluminium case, which solved a very difficult (and expensive) problem at the time, and provided the perfect heat sink.

Later I upgraded the power supply with two stonking great Elna Cerafine caps and a beefy rectifier. This configuration never looked back and is still a mainstay in the system, some 20 years later.

Been scouring the 'net but can't find any more info. Maplins have become a toy shop and this fine chapter of DIY hi-fi & electronics is retreating rapidly into history... A Maplin shop employee once told me they were "Turning into Tandy"

Cheers,

Ed
 
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DaveCl

Member
Joined 2008
Maplin 160W (225W) bipolar amp design

Does anyone have any info on this amp. Circuit Dia would be fantastic. I asked Maplin about back issues with no luck.

Please help, i'm desperate to fix it.
 

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Henry8

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Joined 2010
Regarding the 50w, i ran 4 of these in active system. A couple of r's 18/19? were overheating/pcb charred even when the amp was idling, i think the amp was not as stable as others, although i did run them without the o/p ind and probably no zobel.
As for the sound, i thought they were ok at the time, but no reflection other amps ive since used in the same setup proved that these amps lacked clarity.
 
Mooly

Mooly

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It presents a low impedance path to AC (audio). Without it the junction of R13 and R14 would be modulated with the audio, the emitter of TR5 would "see" 133 ohms" rather than 100 ohm at audio frequencies and the base network of D1/R3 would also be modulated by audio.

Its reason for being included is to increase power supply rejection from noise on the negative rail.
 
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