Reminiscing thanks to a Maplin 150W MOSFET Amplifier on my bench. Wyeminster Slave amp repair.
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- เผยแพร่เมื่อ 29 ก.ย. 2024
- I get to reminsce about my youth with the welcome return of the Maplin 75/150W MOSFET amplifier module to my bench.
I built a few of these in the 80's and used them in various projects, including an in-car amplifier!
Getting hold of these is encouraging me to make a video series about improving the performance of these. That could involve studying the circuit and understanding it's operation, working out what is holding it back and seeing how far we can push it. If that sounds interesting then give me a comment below, that will encourage me more :)
Excellent channel, it helps oyu learn a lot watching channels like yours
Thanks, I appreciate it!
Lovely to see those modules again, I built a load of amps for mobile DJs, clubs and bands using those and ILP MOSFET amp 'bricks', I think I've still got an unbuilt PCB for one somewhere.
Does seem a tiny bit unfair to complain about 'construction quality' on an amp that's been 30 or more years out of the builder's hands, *anyone* could have messed about with it (and if my experience with DJs, bands etc. is anything to go by, probably will have)...
You could be right but everything about it looks original. I would guess that all the parts likely came from Maplin since I have some of those heat sinks which I bought for my first amplifier using these modules. I used two per amplifier on the outside of the case though and that was just about enough, I hate to think how hot these ones will get but we’ll find out soon! The transformer also looks the same as one in my original build.
@@Eclectronicschannel pretty sure you're right it's all Maplin, it looks familiar.
An awful lot of them were built with less than ideal heatsinks, it's kind of testament to the design and those MOSFETs how many survived.
Some of the gear where DJs had 'adjusted' or 'modified' it were the stuff of nightmares and occasionally I thought twice about putting my sticker on their stuff in case they decided to 'improve' things and killed someone or burned a place down.
On occasion I've taken one look and told them to go away.
One mobile DJ was using 13 amp mains plugs and sockets for speaker extensions, another was using RG-58 coax to carry mains power inside a lighting effect he'd 'designed and built' for himself...
@@M0UAW_IO83 Our school technician, the guy in the white coat who wheeled in the TV & Betamax for classes, made an extension with a 13 amp plug on both ends for lighting boxes I made as a kid.
@@Eclectronicschannel The case is a Maplins one too. I bought it once - to rackmount two huge 100V line audio transformers in a rack (the 4U version) - but couldn't make full use of the grid of holes as any bolt heads fouled whatever was underneath in the rack - infuriating on site!
I found this video as I am presently rebuilding a mono amp that uses the Maplins module. There was slight mechanical damage to the toroidal (a Maplins ILP one intended for a 2x100 Amp I think), thankfully just scratched-off lacquer. So that is in process, then to test the PS, then I will test the module on the bench, before reassembly.
It uses a larger version of the same heatsinks (also Maplins), but mounted through the back of the case. OK, it's too small for continuous music, but OK for speech PA. It might seem a bit naff doing it that way, but it lets you have a bigger heatsink, and to be honest I've never known it get more than just detectably warm.
This one was used by me as a simple bass amp back in the day, and spent about 10 years loaned out as an induction loop amp in a church, from where I rescued it recently, Obviously you have to watch the DC resistance of the loop, but with a decent sized room, no matching transformer is really necessary (mains flex gives you a three-turn coil and a good compromise resistance - the impedance is fine). I'm sure the posh amps, with equalizers, bandwidth limiting, compressors, etc., work better, but not better enough to justify the considerable cost.
Maplin Electronics eventually sold upgraded Mosfet transistors with a higher voltage rating topping out at 140v to 160v breakdown voltage. Also sold a bridging module with a speaker protection and a claimed 400W output. Projects by them peaked in the late 1980's to early 1990's pre MPS era and the rise of Velleman and Quasar Electronics.
MPS was just an (ultimately doomed) attempt at a trade offering to go up against RS & Farnell. It was the terms of the investment Maplin took in the early 90's that was the beginning of the end. We'd previously had a lot of freedom to manage our own stock levels - but the edict came down that we were no-longer allowed to - that the value of inventory had to be reduced. The stock levels of many items no-longer made sense. We lost regular customers who understandably didn't react well to being told that if they wanted to buy speakers in pairs, or cabinet feet in fours, and so on, they'd have to pre-order them in or get them mail-order.
My first Maplin catalogue was one with Concorde on the front, late '70s I think, and then all subsequent ones. I built loads of their kits but only got to the dizzy heights of the 30W MOSFET matched pair stereo amp which never worked. Like a schoolboy dream I ended up installing an IT system for them at their new Wombwell site in Yorkshire in 1993. I chatted to a few guys there and mentioned some kits that I had built and one old boy said "That was one of my designs". Their over expansion and move into a disco supply/toy business killed them I think and I mourn their demise.
It was a real shame they changed their market but I guess they had little choice. I have very fond memories of the catalogues back then and remember my first order consisting of some LEDs in various shapes and sizes and maybe some other bits I don’t recall. It was always exciting when a new catalogue was due out, it was like getting a new book, browsing it cover to cover. Fun times.
I still have one working [stereo unit similar to this], that I built in the same casing, but mounted the two modules at the back - with larger heatsinks being able to dissipate heat externally....
I went the extra-mile and supplied each amp with its own separate supply - two mono blocks, in effect. This increases the bass response and punch, and to be honest puts to shame some of today's amplifiers that claim to be '500 Watts' or more 😀
In the 80s I probably built about 20 of those Maplin kits. I never has a single issue with any of them. They all worked on switch on. I made a 5 channel one for a small cinema 100 seats feeding Wharfedale E90 loudspeakers. Very good sound. On my channel I am re looking at some modern FET amplifiers from LJM, they do seam very similar to the original Hitachi design from all those years ago.
I realise this is 3 years old, but did you ever do the follow-up video?
I remember the name Maplin from the early 90's when I was looking at their tube kits. A nice blast from the past. Good video and neat channel name.
I made a fm receiver when I was 14 and never could get it to work, the idea of getting back to those projects feels good now that we have a lot more knowledge. I have recently dug into amplifier design and now I am looking at videos like yours so I can adjust a Quad 303 amp that I have had for 20 years.
You could add a 1 ohm 5 Watt resistor from your transformer center tap to your ground ,it will limit the inrush current when the power supply capacitor are charging on turn-on.It will not affect power output and protect the bridge rectifier forever.
Bye.
Lucien.
I have a pair of these, I'm using on in a guitar amp project. They are great little amps, the MOSFETS are becoming very expensive now if you can even find them.
Have you ever attempted to bridge them? Might be an interesting experiment.
I have a mcgreggor amp that uses 3pairs but 140v 2sk134 and 2sj49. Its rated at 300into 4ohm and 200into 8ohm. What would tha max rail voltage would you reccomend? It sags to 53.4v at full load 4ohms from the unloaded 65v
Hi.I have questions about this amp position R9 if should is 12k or 15 kohm ? Thanks
When I built my second set of these amps I used a signal generator, scope and dummy load and wound it up till the 2A fuses glowed, so around 150W. Pleased with that and took them on the road. 4 x 200W speakers and 4 amplifiers. Never had any complaints about the sound, especially when I used a CD player in 1984. I'm just doing some audio work for a customer, and about to drag them back in from the garage where they have been lurking for nearly 30 years - probably more like 35!
Hmm don’t like the arrogance towards the manufacturer if this device … makes me a bit ashamed to be associated with the electronics trade myself … but each to their own
I see only 4 power MOSFETs. Where is the voltage regulator? Without the regulator and no ics to fix 50Hz, the hoooom will be very noticeable.
I built a stereo amplifier using the Maplin modules back in the early 1990's. I used a 625VA toroidal mains transformer feeding two bridge rectifiers, one for each module with a pair of 10,000uF smoothing capacitors per channel. The transformer was 40-0-40 volt which gave 57-0-57 volt dc split rails. Measured output power into an eight ohm load was 120W per channel. In order to vastly improve sound quality and bass extension I replaced C3 with 220uF and shorted out C1. I then added DC offset loudspeaker protection. The amplifier is still working fine all these years later.
I own a Denon AVR 1910,my problem is after switching on the receiver works for 15 minutes to 30 minutes after that receiver not outputting any sound but display shows sound dtshd or truehd or source sound. can you tell me what is the problem? same happens when receiver in tuner mode also( but when I change to "direct" sound is restored but when I change sound mode to stereo or Dolby music or another mode ,sound output stops again- in tune mode only).kindly give me solution for the problem.
Hard to speculate with that one sorry!
Interested to see how you progress with these modules. The amp I built in the 80's is still going strong, but I probably should change the caps, at least, by now.
If you're using 63 volt caps, they ought to be okay.
Over a year later and no follow up??
Does anyone remember Sage-Audio Supermos modules? and their claimed %0.00018THD and immeasurable IMD? and "no capacitor sound"? "Class-A" (Yes I was scammed).
The name kind of rings a bell. Early/mid 90's? That is quite an impressive number ;) Sorry to hear you got stung on that.
It does ring a bell though I have never come across one. I’ll keep an eye out for one :)
@@Eclectronicschannel Sage-Audio had adverts in Eelektor and radio electronics in the mid 80's, I still have an original brochure tucked away somewhere.. class-A...then "dynamic class-A" whatever that meant, with better than laboratory distortion specs "to die for" figures, The company turned out to be a one person op. putting these things together and molding everything sealed in an epoxy brick & Heat sink, it was my first amp. (with such amazing specs, class-A etc I thought it would be my last). it had awful very audible crossover notch distortion, I didn't realize that at the time, I guess that Is why I always cranked it up loud, else it sounded bit fuzzy, one fine day, an output device shorted to heat sink and DC'ed away my loudspeaker, which could have ended up with a fire, (his manual said no fuse necessary on speaker wire cause fuses ruin the sound and the module is DC protected under normal use ...), that "episode" trained my ears to recognize what crossover notch distortion sounds like in an under biased class-B amp, after that experience I went all tube, as tubes amps cannot go DC blowing things up, and P-P is still so deep into class-A, even with one tube missing out of a p-p pair, still sounds smooth at low levels, now the best of class-D (purifi Hypex ICEpower) have come of age, these new Class-D modules better in almost every way and about the same price as modules from the mid 80's counting inflation, OK enough reminiscing from me for one day...
Is this amp design based off the old Hitachi L MOSFET design? I found schematics of the Hitachi design. I've contemplated building that amp since I have the l mosfets.
Caption plaese
I liked your video and will be subscribing! I hope to see your follow up. You 100ma per module, so 50ma per device?
I must have 8 of those modules. I was collecting to make some bridged amps using the double-die mosfets....
i have also build that circuit in the past it was a very good circuit
Hello. I was Just wonder if you've done a video on upgrading these amp models as mentioned in this video?
I built some Maplin but they were stolen from me, would like to build them again .
estupendo amplificador
I have a pair of these maplin modules and I turned it on a few months ago and it worked for about a couple of seconds then the speaker fuses blew. Now I am trying to build a mono guitar slave amp and I saw your video so though I would investigate further. Trouble is, unlike you, I do have a short between the heat sink and the transistor cases. Looking underneath I see the pcb is brown (worse on one module than the other) and the solder seems to have melted at some point. Although no where near as expert as yourself, I reckon the solder has melted and caused a short. Please can you give me some advice: I reckon if I can remove the solder and remove the transistors then I can clean it all up. Many thanks.
Hi, If there is a short from the body of the MOSFET to the heat sink bracket then it suggests the insulation pad that sits between the two has been punctured or has failed. You would need to desolder the two legs, remove the two screws and take off the MOSFET. Try not to touch the two legs when it’s removed as one of them is very sensitive to damage from any static electricity in your body. Clean off any heat sink grease with isopropyl alcohol and put a new TO-3 thermal pad or mica insulator on with fresh thermal paste. Replace the bolts and check for shorts before soldering the pins so that you can easily remove again if the problem is still there. Once happy re-solder the pins and all should be well.
If you can see any shorts between the MOSFET case and the two terminals then the MOSFET is dead and needs replacing.
Good luck!
@@Eclectronicschannel Many thanks. I shall give it ago. Will follow antistatic procedures too! BTW I have the same heat sinks as the one in your video and IIRC they were the recommended ones in the maplin catalogue. If this works can you recommend a new heat sink? Many thanks M
@@Eclectronicschannel . Sorted. Took the modules out and no shorts so not sure what was wrong. Put one module back, tested as much as I could, and works fine. Didn't run for more than a couple of mins because lack of proper heatsink. I would like to see a video of the performance mods including increasing the gain. I believe the gain is 33 and it can be increased by changing R6 and C3 but not confident enough to so this now I have one module working!
I can tell you're no bench tech.....
Who the hell told you misfits are rugged?
They're wrong!