Maplin GA28F mosfet modules
I have just bought a couple of Maplin GA28F mosfet modules second hand, the later version with 2SK135 and 2SJ50 transistors and a a pair of 33-0-33V transformers giving +/- 47V supplies.
I am looking for a copy of the Maplin construction notes/manual. Does anyone have a copy they could send me or post?
I do already have Dave Goodman's original article from the Maplin Magazine (published in the 1980s?) which covers the earlier version (with 2SK133/2SJ48 transistors).
I have just bought a couple of Maplin GA28F mosfet modules second hand, the later version with 2SK135 and 2SJ50 transistors and a a pair of 33-0-33V transformers giving +/- 47V supplies.
I am looking for a copy of the Maplin construction notes/manual. Does anyone have a copy they could send me or post?
I do already have Dave Goodman's original article from the Maplin Magazine (published in the 1980s?) which covers the earlier version (with 2SK133/2SJ48 transistors).
MAPLIN FET
Hi Craig,
If you are using a toroid transformer, just remove some turns, to get the voltage you want. Remember to remove equal number of turns in both secondairies sumultaneously. You can start with removing five turns, measure the resultant DC voltage, to get a feeling about how many turns you have to remove in total.
Roar
Hi Craig,
If you are using a toroid transformer, just remove some turns, to get the voltage you want. Remember to remove equal number of turns in both secondairies sumultaneously. You can start with removing five turns, measure the resultant DC voltage, to get a feeling about how many turns you have to remove in total.
Roar
Re: Maplin GA28F mosfet modules
GA28F was just the PCB; the circuit, inductor construction and set-up details are linked in post#29.
If you need the Maplin parts list let me know; though there's nothing esoteric in it, it was a cheap kit.
Their suggested PSU (for a single module) was a bridge and simple smoothing (10,000uF 63V + 100nF) on each rail with a 4k7 1W bleeder on each, speakers and signals star grounded to the caps. 3.15A AS fuses.
HBrunt said:
GA28F was just the PCB; the circuit, inductor construction and set-up details are linked in post#29.
If you need the Maplin parts list let me know; though there's nothing esoteric in it, it was a cheap kit.
Their suggested PSU (for a single module) was a bridge and simple smoothing (10,000uF 63V + 100nF) on each rail with a 4k7 1W bleeder on each, speakers and signals star grounded to the caps. 3.15A AS fuses.
Just saw this thread pop back up, id forgotten to update the thread a long time ago then forgotten completely i started it. My outcome.. if anyone is interested was a rather rude bang!
I used a different circuit to the maplin one, the quasi complementary circuit from Ampslab in the end. As far as i remember the regulator worked well but under testing the amp i slipped with my DMM leads and blew just about everything of any value.. i was a little p&%£ed of i remember. Mj21194's = not particularly cheap..
Ayway it all looked good and seemed to work with all my measuremnts apart from the fatal one.
So this project literally died a death.
I used a different circuit to the maplin one, the quasi complementary circuit from Ampslab in the end. As far as i remember the regulator worked well but under testing the amp i slipped with my DMM leads and blew just about everything of any value.. i was a little p&%£ed of i remember. Mj21194's = not particularly cheap..
Ayway it all looked good and seemed to work with all my measuremnts apart from the fatal one.
So this project literally died a death.
David
Thanks for the offer of the build manual. That would be useful. I'll see if I can enable my email address.
Incidentally, I discovered today (while browsing for something completely different) an almost identical schematic for a 100W mosfet amp in an old book by RA Penfold published by Babani in 1983 entitled "Audio Amplifier Construction". It includes a brief explanation of the design and how it works and construction and set up details. The title now seems to be out of print.
He also seems to have written another title "High Power Audio Amplifier Construction", published by Bernard Babani in 1991, which might be worth a look.
regards
Harry
Thanks for the offer of the build manual. That would be useful. I'll see if I can enable my email address.
Incidentally, I discovered today (while browsing for something completely different) an almost identical schematic for a 100W mosfet amp in an old book by RA Penfold published by Babani in 1983 entitled "Audio Amplifier Construction". It includes a brief explanation of the design and how it works and construction and set up details. The title now seems to be out of print.
He also seems to have written another title "High Power Audio Amplifier Construction", published by Bernard Babani in 1991, which might be worth a look.
regards
Harry
please remove my email , i recive spam because of it is listed on your public site
dear daatkins,
plz send me the copy of maplin for the 2sk135 and 2sj50.plz also send me the pcb copper side my email is khan.shahid251@gmail.com
thanking you
plz send me the copy of maplin for the 2sk135 and 2sj50.plz also send me the pcb copper side my email is khan.shahid251@gmail.com
thanking you
I have just rediscovered this amp module.
The longer story is that I have just rearranged the equipment on my desk because I wanted to mix the output of a Logitech Squeezebox which I use for listening to music with the sound card output of my work PC which I use for VOIP calls. Previously I had these two (and my home PC) connected to the inputs of a NAD C320 which in turn was connected to two bookshelf speakers - Eltax Monitor IIIs. The NAD has developed a "slow start" problem whereby the speaker protection relay can take anything from a few minutes to half an hour to connect the outputs seemingly dependant on ambient temperature so, for the time being at least, as well as introducing a small mixer, an Alto ZMX52, I have raided the attic and found a power amp made from two of these Maplin 150W MOSFET amp modules and connected this to the output of the mixer and to the Monitor IIIs. Looking in the case the amp is effectively two mono amplifiers each with a toroidal transformer, rectifier, smoothing capacitors and amp module.
My initial impression is that this amp sounds pretty good. It definitely sounds different from the NAD with perhaps the most obvious difference being a fuller bass. This also matches my first impression of one of these amps when I first built one back in the mid 1980s. The extra bass does not seem to be at the expense of other parts of the spectrum, though, with plenty of brightness where it is present on the original recording. On the other hand there have been moments when listening where I wonder if I am hearing a little distortion. Obviously this is not blatant or I would be more sure of it. This seems most noticeable on the louder passages of a piece of music but does not seem to increase with an increase in listening volume. I can think of two possible things going on but I wonder if there are others:
1. Crossover distortion. Is there a point just as the amp is getting out of class A, i.e. where one of the output devices is starting to turn fully off, where crossover distortion is at a maximum? I wonder if, listening at comparatively low volume, the louder bits are in this region.
2. Modern mastering. I have just been listening to a Deutsche Grammophon recording I bought back in the 80s of the Berliner Philharmoniker playing Beethoven's 5th symphony and this recording sounded very full and clear and I could not hear anything that sounded like distortion. I wonder if, in the "loudness war", the mastering engineers are allowing some kind of "soft clipping" on modern recordings and the new amp is just a little bit more revealing.
BTW, although the squeezebox is a digital music player I do not think I am hearing compression artefacts because the files are encoded in FLAC, a lossless format.
I am also wondering what, if anything, I might be able to measure. I don't have a large array of equipment but I will have another look in the attic to see if I have a CRO there and I could also record the output with an RME Multiface and analyse it in software. I think I noticed elsewhere someone measuring harmonic distortion and it looked to me as if the amp was being sent a single frequency (sine wave) and a spectrum analyser was used to find and measure other frequencies that were in the output (and by definition not in the original signal).
The longer story is that I have just rearranged the equipment on my desk because I wanted to mix the output of a Logitech Squeezebox which I use for listening to music with the sound card output of my work PC which I use for VOIP calls. Previously I had these two (and my home PC) connected to the inputs of a NAD C320 which in turn was connected to two bookshelf speakers - Eltax Monitor IIIs. The NAD has developed a "slow start" problem whereby the speaker protection relay can take anything from a few minutes to half an hour to connect the outputs seemingly dependant on ambient temperature so, for the time being at least, as well as introducing a small mixer, an Alto ZMX52, I have raided the attic and found a power amp made from two of these Maplin 150W MOSFET amp modules and connected this to the output of the mixer and to the Monitor IIIs. Looking in the case the amp is effectively two mono amplifiers each with a toroidal transformer, rectifier, smoothing capacitors and amp module.
My initial impression is that this amp sounds pretty good. It definitely sounds different from the NAD with perhaps the most obvious difference being a fuller bass. This also matches my first impression of one of these amps when I first built one back in the mid 1980s. The extra bass does not seem to be at the expense of other parts of the spectrum, though, with plenty of brightness where it is present on the original recording. On the other hand there have been moments when listening where I wonder if I am hearing a little distortion. Obviously this is not blatant or I would be more sure of it. This seems most noticeable on the louder passages of a piece of music but does not seem to increase with an increase in listening volume. I can think of two possible things going on but I wonder if there are others:
1. Crossover distortion. Is there a point just as the amp is getting out of class A, i.e. where one of the output devices is starting to turn fully off, where crossover distortion is at a maximum? I wonder if, listening at comparatively low volume, the louder bits are in this region.
2. Modern mastering. I have just been listening to a Deutsche Grammophon recording I bought back in the 80s of the Berliner Philharmoniker playing Beethoven's 5th symphony and this recording sounded very full and clear and I could not hear anything that sounded like distortion. I wonder if, in the "loudness war", the mastering engineers are allowing some kind of "soft clipping" on modern recordings and the new amp is just a little bit more revealing.
BTW, although the squeezebox is a digital music player I do not think I am hearing compression artefacts because the files are encoded in FLAC, a lossless format.
I am also wondering what, if anything, I might be able to measure. I don't have a large array of equipment but I will have another look in the attic to see if I have a CRO there and I could also record the output with an RME Multiface and analyse it in software. I think I noticed elsewhere someone measuring harmonic distortion and it looked to me as if the amp was being sent a single frequency (sine wave) and a spectrum analyser was used to find and measure other frequencies that were in the output (and by definition not in the original signal).
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