Maplin 160W (225W) bipolar amplifier design

[Ed Holland]

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 😀

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]

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.

 

[Ouroboros]

Yes, it was a common-emitter output stage using two-transistor compound-feedback-pairs.
When I get home tonight I'll see if I have the schematic. If I have I could scan it and post it here.

 

[Ed Holland]

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

 

[jaycee]

Yep turning into Tandy for sure. The guys who run the parts counter at my local one aren't even familiar with the parts and what theyre used for!

Well... they will soon go the same way Tandy went!

 

[DaveCl]

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.

 

[Ouroboros]

I looked for it last weekend, but couldn't find it. I need to clear out some stuff over Christmas so I may well find the Maplin data. If I do I'll scan the schematic and post it here.

 

[Ouroboros]

Whoops! Just realised that you want the high power schematic. The one I have is the 50W design. Sorry!

 

[balaboo]

Ouroborous;

I for one, would be interested in the 50W design !

 

[DaveCl]

i'm still on the hunt for any info on the amp. Maplin 160W (225W) bipolar amp design
A Circuit Diagram and parts list would be fantastic. can anyone help.

 

[stainless]

Here's one from November 1996
based on older design
but pcb is diffrent.
might help.

 

[stainless]

here's the pic.

 

[madog]

Maybe a bit late for this but here is a scan of the circuit diagram and parts list. I may even have the other 225w one will have to dig out the old Maplin mags.

 

[freblogs]

I have a copy (scanned) of the page from a 1992 catalogue, it includes the circuit diagram, parts list and set up details. Happy to send you a copy.

hi would it be ok if you could send me a copy too many thanks richard

 

[masood]

Hi, I would like to have a copy of that too.

Thanks and regards,
Vivek.

 

[masood]

maplin ampli.

dear sir,
do you have construction manual plz. send me.at khan.shahid251@gmail.com
thanking you

 

[Henry8]

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.

 

[masood]

can any body send me this two items:-
1-THE PCB PHOTO GRAPH OF 1500W AMPLI.USING 10 PIECE TR.MJ 15024& MJ15025 AT OUT PUT TRANSISTOR
2-stachino circuit pcb. AT- khan.shahid251@gmail.com
yours ,masood

 

[GEirin]

Post 32

Hi all.
Someone could explain the function of C9. Improves sound?
Thanks

 

[Mooly]

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.