MOSFETS and BJTs are completely different animals. They are not directly interchangeable.
Hi thank you very much for your very valuable advice.
But before anything else I have to apologize to everyone If I had done more adequate research on thermal pads I wouldn't have asked the question
And thank goodness I asked here before acting It seems that when the thermal power to be dissipated is high there are no alternatives to thermal paste and heatsink obviously
The thermal pads don't conduct heat enough
And in fact even for the computer CPUs they use paste and not thermal pads
Issue closed
And the old rule do not touch what works is also very sane
Yes there is space for more uF on the board I only wonder if using caps of different quality and uF could be an issue
I have also bought some new diodes to replace the ones on the board now
these should withstand better some surges at the switch on There is no relais that i can see
and you say that they can sound good without the need of big changes to the circuit ?
Could be useful if i measure the voltages on the output mosfets legs ? would that measurement provide any useful information ?
at least i could see if there is some kind of unbalance between the two channel And maybe check also the offset
I guess that i have to conduct measurements with the inputs shortcircuited and the speakers connected to the amp ?
After all the sound is not offensive It sounds a little too rounded for my taste The best amp i listened to was an old Krell KSA 80 many years ago
For me it was the perfect amp Very clean with a great low end at least when the power needed is not great For most home listening it could be a final amp
That low end ... granitic 😳👍
Mosfets don't "sound" on their own. They are used in a circuit. And that circuit has a sound.
Without knowing too much I would say output devices have rather low influence on sound characteristics.
If I'm not mistaken your amp has well regarded hitachi lateral mosfets, they are perfect - treat them well and they will reward you with perfect reliability.
You should download datasheets of your existing mosfets and eventual replacements from exicon and compare them.
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Thanks again and now i am scared to even add some caps Because for sure i will have to unscrew the mosfets from the bottom plate of the chassis
But the temptation is strong I bought already wonderful diodes
I have some old Nichicon Gold that could be used I would be willing to add some 2x4.7mF caps in the empty holes already drilled
The temptation is very strong
About uF quantity in the power supply there is a canadian audio designer who is selling upgrading caps packs for existing amps
The caps packs are external and connected with an umbilical cord to the amp board
What i do not like very much is when i see a certain distance from the bigger caps and the output devices
My best layout would be something like this in the pic below Just to give an idea
But the temptation is strong I bought already wonderful diodes
I have some old Nichicon Gold that could be used I would be willing to add some 2x4.7mF caps in the empty holes already drilled
The temptation is very strong
About uF quantity in the power supply there is a canadian audio designer who is selling upgrading caps packs for existing amps
The caps packs are external and connected with an umbilical cord to the amp board
What i do not like very much is when i see a certain distance from the bigger caps and the output devices
My best layout would be something like this in the pic below Just to give an idea
This is your chance to give back to the community: trace the PCB and produce a schematic yourself. We've all done it at some point, and yes, it can be difficult and tedious, but other owners will appreciate your effort and that way you will have a real chance to understand it, mod it and troubleshoot it. Just measuring some voltages here and there and blindly swapping components will get you nowhere.
Cheers,
Cabirio
you just brightened my day.
I looked closely at your PCB and I said to myself that it reminded me of something and then when you answered the name and model of your amp, I went to look on the net and I discovered the history of AC Magnum Ltd whose I had heard about it a quarter of a century ago, I found the origin of the schematic which was literally used and abused on most Magnum electronics and immediately, it lit the light in my head.
I have an English integrated amp with J118 and K413 outputs which has been annoying me for years because I can't stabilize it and it burns regularly.
Now I have a working basis to understand the basic diagram which is close to this: Ambit Pa100.
Be grateful.
source : http://www.cma4ch.org/chemo/attivita/MF125magnum.html
History
Here a text on the history of the brand:
Anthony Colin Magnum Ltd was founded by Tony Relph who was also one of the co-founders of Rega. Rega is the abbreviation of the names RElph and Gandy. Tony Relph went on to found A. C. Magnum. Tony Relph has since retired and these amplifiers are no longer manufacturer. Magnum used Colin Wonfor circuit designs and there was definitely some collaboration between Colin Wonfor and Tony Relph at the beginning. Maybe the company name was actually stands for Anthony. Colin. Magnum (just guessing here but it would be plausible?) (from Audiokarma).
Some months after there is a reply from Colin Wonfor the owner and designer of Magnum:
Sorry No, this is wrong, Magnum was formed from my company MIH, which became Pro-Ac Magnum, then Tony Relph joined me as a business guru, then after 3 yrs managed after locking me out after a holiday stole the company and I was force to take legal action for use of some patents and stealing my company. Meanwhile I started Inca Tech producing no electronics until the legal action was resolved but the world first Gold Plated Power Connectors for the audio world, now be warned never share a company 50/50 if you have started it you partner may not be so trustworthy as you. And for folk out there here is a rough list of other things I have designed. In order: Pushpull 1 Germanium Amp at 1971 , V1 Tube amp at 1972 , 12W Single Ended A Class at 1974 , MIH 100W at 1975 , MIH 400W, ProAc stereo 100w at 1980 , ProAc 3 Channel 100W , Magnum A100, 400W at 1982 , Magnum A200 , Magnum Pre-amps , Inca Tech Sabre Iss 1 at 1983 , Inca Tech Prelude , Inca Tech Claymore 1 at 1983 , Inca Tech Claymore Gold , Inca Tech Claymore S , Inca Tech Claymore 2 , Inca Tech FMT Tuner , Inca Tech IT50,IT100,IT200 , Inca Tech IT1P preamp , Inca Tech Sabre Iss 2 , Inca Tech Dirk , Inca Design ID25,ID50,ID75 , Inca Tech MSB (a monster) , Inca Design Oberon Classic , Inca Design Oberon (standard) , Lescon , Oxford Acoustic's "Mystic" , TOCA SECA 20W,50W,100W,200W,300W single ended class A,s at 1995 , TOCA I75 , TOCA Pre A , TOCA 75W , Tellurium Q Cables at 2009 , Tellurium Q, A Class 20W, 100W at 2011 , Tellurium Q Headphone/Phono Amp , Tellurium Q Pre-Amp , Products worked on Naim Nait 5i , other bits also for Naim and Cambridge Audio at 2008- 2010, Colin Wonfor, Jul 14, 2012. (more from Audiokarma)
History
Here a text on the history of the brand:
Anthony Colin Magnum Ltd was founded by Tony Relph who was also one of the co-founders of Rega. Rega is the abbreviation of the names RElph and Gandy. Tony Relph went on to found A. C. Magnum. Tony Relph has since retired and these amplifiers are no longer manufacturer. Magnum used Colin Wonfor circuit designs and there was definitely some collaboration between Colin Wonfor and Tony Relph at the beginning. Maybe the company name was actually stands for Anthony. Colin. Magnum (just guessing here but it would be plausible?) (from Audiokarma).
Some months after there is a reply from Colin Wonfor the owner and designer of Magnum:
Sorry No, this is wrong, Magnum was formed from my company MIH, which became Pro-Ac Magnum, then Tony Relph joined me as a business guru, then after 3 yrs managed after locking me out after a holiday stole the company and I was force to take legal action for use of some patents and stealing my company. Meanwhile I started Inca Tech producing no electronics until the legal action was resolved but the world first Gold Plated Power Connectors for the audio world, now be warned never share a company 50/50 if you have started it you partner may not be so trustworthy as you. And for folk out there here is a rough list of other things I have designed. In order: Pushpull 1 Germanium Amp at 1971 , V1 Tube amp at 1972 , 12W Single Ended A Class at 1974 , MIH 100W at 1975 , MIH 400W, ProAc stereo 100w at 1980 , ProAc 3 Channel 100W , Magnum A100, 400W at 1982 , Magnum A200 , Magnum Pre-amps , Inca Tech Sabre Iss 1 at 1983 , Inca Tech Prelude , Inca Tech Claymore 1 at 1983 , Inca Tech Claymore Gold , Inca Tech Claymore S , Inca Tech Claymore 2 , Inca Tech FMT Tuner , Inca Tech IT50,IT100,IT200 , Inca Tech IT1P preamp , Inca Tech Sabre Iss 2 , Inca Tech Dirk , Inca Design ID25,ID50,ID75 , Inca Tech MSB (a monster) , Inca Design Oberon Classic , Inca Design Oberon (standard) , Lescon , Oxford Acoustic's "Mystic" , TOCA SECA 20W,50W,100W,200W,300W single ended class A,s at 1995 , TOCA I75 , TOCA Pre A , TOCA 75W , Tellurium Q Cables at 2009 , Tellurium Q, A Class 20W, 100W at 2011 , Tellurium Q Headphone/Phono Amp , Tellurium Q Pre-Amp , Products worked on Naim Nait 5i , other bits also for Naim and Cambridge Audio at 2008- 2010, Colin Wonfor, Jul 14, 2012. (more from Audiokarma)
From a thermal performance and thermal stability it is the best way you can use.
But if you are only interested in esthetics there are many other ways of course.
Jan
If you want to change the rectifier diodes in the power supply for something better, I would go with soft recovery ultra fast ones like the UF 5402 or similar. It will get rid of the nasty spikes on your DC supply.
Hitachi also manufactured vertical type mosfets known as their "D" Series, the 2SJ118 / 2SK143 used in the MF160 amplifier were "D" Series, Hitachi Lateral Mosfets were known as "S" Series. There are some differences in their characteristics between the two types*.
Be aware that the profusion lateral mosfets have different pinouts to the 2SJ118 / 2SK143 mosfets.
*Source - 1985 Hitachi Power MOSFET Data Book.
Be aware that the profusion lateral mosfets have different pinouts to the 2SJ118 / 2SK143 mosfets.
*Source - 1985 Hitachi Power MOSFET Data Book.
Hi yes i agree But now i am scared to ruin the obsolete parts I understand that replacing them is not just a drop in of new parts
The circuit does not look impossible I cannot read values That is another big problem
Hi thank you very much for your very kind and valuable advice Mine has one transistor more in the VAS and driver stage (i.e. excluding the output pair)you just brightened my day.
I looked closely at your PCB and I said to myself that it reminded me of something and then when you answered the name and model of your amp, I went to look on the net and I discovered the history of AC Magnum Ltd whose I had heard about it a quarter of a century ago, I found the origin of the schematic which was literally used and abused on most Magnum electronics and immediately, it lit the light in my head.
I have an English integrated amp with J118 and K413 outputs which has been annoying me for years because I can't stabilize it and it burns regularly.
Now I have a working basis to understand the basic diagram which is close to this: Ambit Pa100.
Be grateful.
there are 6 transistors per channel + one output pair
I like your amp a lot I like simple schematics I guess that it can sound pretty good as well
Given that they are Hitachi mosfets i wonder if they can be found in some vintage Hitachi amp Maybe they are worth to be haunted in the used market ?
Sometimes people do not realize how good some products can be I am a perfect example
I did not like mosfets because have read that they are good only when used in class A designs
I like bjts more I had some hopes about darlingtons but now no more I would prefer bjts anytime They seem less picky to me
i like this design a lot indeed It looks quite minimalistic to me And you say that is unstable ? maybe some more small value bypassing caps here an there could solve the issue ? Very very nice schematic
Yes it was essentially an estetic issue
However I was very wrong about thermal silicon pads vs mica pads The mica ones have much better heath conducibility
So they are better Good to know I will try to clean and put new ones in place of the old ones using maybe the paste they use for cpus
I have already use that
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Very very interesting piece of audio history Thank you very much indeed A long list of great designs
I remember a review in a mag of the Inca Tech Claymore integrated praised as one of the few sounding splendid also on the very revealing Yamaha ns 1000
While tube amps had no problems many solid state amps provided a very unpleasant sound Not so the Claymore
Thanks a lot Considering a possible uF upgrade i looked for diodes with higher current than the original model P600D
i ended up buying these ones rated 20A/700V I understand they are used in photovoltaic panels ?
they should be of the Schottky type and should withstand peak current demand from the upgraded power supply
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