PMA, if you have then time and have the feeling for it over the Christmas holiday, it would be very interesting to see two versions... 1) an updated version of the existing follower, and 2) a version capable of about 30W into 8 Ohms.
I will sit quiet and hope!
I will sit quiet and hope!
Gordy, thanks for your ideas. Please take into account that for 30W/8ohm of single-ended class A you would need some 2.8A idle CCS current and about 50V supply voltage (voltage drop on the CCS about 4V). Both follower transistor and CCS transistor would dissipate some 70W at idle. This seems to be unrealistic.
This topology is usable for low power, and its weak points are heat and output current limited by CCS - low impedance load is a big problem, current limitation sounds horrible.
This topology is usable for low power, and its weak points are heat and output current limited by CCS - low impedance load is a big problem, current limitation sounds horrible.
Gordy,
The topology is doable, and amplifier is just as PMA alludes - 2.8A quiescent, 50V supply. However, there are four IRF mosfets sharing the load.
It is reduced power into 4R (16W measured) and 28W into 8R. Extremely inefficient (15%) but wonderful sounding, with tube front end. Distortion from the output stage simulates to around 0.1% at full power, mostly H2/H3/H4. Heatsinking is an issue, but my variant has 50 milliohm Zout and works well with conventional speakers, particularly well with ESLs.
It is a commercial product from years past, unfortunately circuit is proprietary. Point is, it is highly practical and peforms very well.
The topology is doable, and amplifier is just as PMA alludes - 2.8A quiescent, 50V supply. However, there are four IRF mosfets sharing the load.
It is reduced power into 4R (16W measured) and 28W into 8R. Extremely inefficient (15%) but wonderful sounding, with tube front end. Distortion from the output stage simulates to around 0.1% at full power, mostly H2/H3/H4. Heatsinking is an issue, but my variant has 50 milliohm Zout and works well with conventional speakers, particularly well with ESLs.
It is a commercial product from years past, unfortunately circuit is proprietary. Point is, it is highly practical and peforms very well.
lumba, yes...
i posted a graph showing the influence of the hexfet current source
gate stopper resistance....seems that no one see it..here again the graph..
the stopper resistance which influence is shown is the one of the CURRENT SINK....
Hugh, that’s interesting to know. In my ignorance about solid state I did not realise that you can parallel devices in a source follower configuration.
I presume that parallel output devices have to be matched in some parameters?
I understand that you do not want to publish your circuit so I will assume that it included a CCS as a load. From the posts of yourself and PMA I realise that heat-sinking is a major issue with a single ended output of this type.
I think I will build the lower power version, get it working properly, and then experiment.
Gordy,
Yes, you can parallel mosfets like any other, but matching is a good idea. First parameter to match is Vgs, second is transconductance.
Heatsinking is crucial. I use four 300mm x 150mm 30 fin sinks, each dissipated around 75W, and is rated to 0.3C/watt. They run predictably hot, particularly on hot days (35C+) in Oz. No fan cooling, a resolve I made, perhaps I should have tried forced air, more efficient and less bulky.
Email me through my website, happy to talk about it.
Wahab,
I saw it. Nice graph, useful information. Thank you!
Hugh
Yes, you can parallel mosfets like any other, but matching is a good idea. First parameter to match is Vgs, second is transconductance.
Heatsinking is crucial. I use four 300mm x 150mm 30 fin sinks, each dissipated around 75W, and is rated to 0.3C/watt. They run predictably hot, particularly on hot days (35C+) in Oz. No fan cooling, a resolve I made, perhaps I should have tried forced air, more efficient and less bulky.
Email me through my website, happy to talk about it.
Wahab,
I saw it. Nice graph, useful information. Thank you!
Hugh
this one should work....supply is reduced to 30 V, as
even at this level, each hexfet eat 25W at iddle...
output voltage max is 27V PP, wich is quiete enough..
atached are the schematic and two graphs of THD
at 1 and 10 Khz , output level is 10V peak.(20V PP).
even at this level, each hexfet eat 25W at iddle...
output voltage max is 27V PP, wich is quiete enough..
atached are the schematic and two graphs of THD
at 1 and 10 Khz , output level is 10V peak.(20V PP).
wahab,
I see it but it lacks importance in this non-switching circuit. Parasitic capacitances and resistances in the base-emitter and gate-source path do not promote the switching performance anywhere. It is very unwise not to use gate stoppers.
i didn say that gate stopper are unecessary...
i used a 1R gate stopper just to increase the difference thus making
it easily displayed...in the little schematic i published, i took 27R..
the other side is shunted to earth via a caps added to the zener
reference diode...
wahab,
people are occupied with a nonexistent problem here, delivering confused explanations. Forget about it and go on. FETs are superior to BJTs regarding both switching and high frequency performance and have far better properties for a CCS. You should focus on the circuit, what I`ve seen so far is nothing to be proud of.
people are occupied with a nonexistent problem here, delivering confused explanations. Forget about it and go on. FETs are superior to BJTs regarding both switching and high frequency performance and have far better properties for a CCS. You should focus on the circuit, what I`ve seen so far is nothing to be proud of.
lumba, you are right , my friend, what is your(technical) proposition
to definitly make this circuit work da best possible?..
be asured that i m all ears..
Me too.
Lumba has been uninterruptedly quite mysterious in his past posts. This indicates he definitely has a trump card in his hands. So mysterious. I'm so excited. Expecting an explosive "final blow" from him; one that blows all the "non-existent" "not to be proud of" discussions going on here to weeds. Hope he will not disappoint us by any absurd or mean action, I'm sure he won't. So mysterious... really so mysterious.
shaan
the point is there s one dyier that wants to..
your point is to say that these kind of design is pointless..
in a way i agree with you, but i m not here to discuss about
the validity of shaan s tastes...and we are turning
around his schematic since he asked for some help..
myself, i use a fet ouput device amp, but in a
push pull class AB, with a (very) very simple classic schematic..
i ll publish it soon..
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