Once again, I have to disagree about recommendations for quasi comp output stages. It is true that one will never get perfect complements between P and N MOSFETs, simply due to the laws of physics concerning carrier mobility differences. That having been said, the fact that two N devices can be very well matched is of no help or relevance in a quasi comp design because the circuit itself is fundamentally asymmetric and unmatched top to bottom. The top guy is in source follower mode while the bottom guy is a CFP.
Use of complementary MOSFETs is the way to go. Nothing is perfect, but this is far less imperfect. BTW, the Toshiba verticals are quite well matched.
They are relatively expensive, around $10, but are a BEST BUY when compared to lateral prices.
Cheers,
Bob
Thanks for the insight Mr. Cordell. Now you made my decision more difficult
Is there a holy grail 200W-300W class AB mosfet amps? Still looking...
It was found that improvements could be made by adding a Baxandall diode to the lower driver. This makes it approximate more an emitter followers characteristics.
Crowbars are excellent for protecting loudspeakers, BUT the amplifier driving them must be fully capable of surviving a dead short at its output.
I use flying catch diodes and a crowbar across the bias spreader to disable the output stage. When there is a fault, you collapse the bias spreader; the triac stays on with the bias current of the VAS. The VAS must be current-limited. The flying catch diodes, connected from either end of the bias spreader to the output node, prevent the MOSFETs from getting adequate forward bias to turn on when the bias spreader is collapsed. However, this approach limits the forward bias on the FETs to no more than about twice the Vgs turn-on voltage in normal operation. This is a big problem for laterals, which have a low Vgs bias voltage and a need for quite high gate forward bias voltages to produce high signal current. It works great with IRF verticals that need about 4V to turn on.
This technique is mainly for short circuit protection of the output stage. Such protection is especially important for vertical MOSFETs because they will gleefully conduct perhaps 30 Amps into a short. Laterals are far less needful of an approach like this because they are not that great about producing high currents and their temperature coefficient of current tends to make them self-limiting as they get hot. Laterals are pretty robust in this respect. They will usually survive long enough for a fuse or relay to intervene.
This technique will also not protect speakers in the event that one of the output transistors shorts, so a relay or output TRIAC crowbar is still needed.
Cheers,
Bob
Look at my thread maybe you get some idea.Thanks for the insight Mr. Cordell. Now you made my decision more difficult
Is there a holy grail 200W-300W class AB mosfet amps? Still looking...
http://www.diyaudio.com/forums/solid-state/162043-mosfet-amplifier-irfp240-irfp9240-20.html
Regards
Thanks for the insight Mr. Cordell. Now you made my decision more difficult
Is there a holy grail 200W-300W class AB mosfet amps? Still looking...
Not sure about Holy grail, but a really good 200W/8-ohm MOSFET amplifier might be made with four pairs of Toshiba 2SK1530/2SJ201, each pair biased at 150 mA. These might be driven by MJE15032/33 drivers biased at 50 mA, with 2SC3503/2SA1381 pre-drivers biased at 10 mA. I would also use the 2SC3503/2SA1381 pair for the VAS and bias it at 10 mA. I would use an N-channel JFET input differential pair, enclose the whole thing with TMC-compensated NFB with a gain crossover frequency of 1 MHz, and use a DC servo for offset.
Cheers,
Bob
Hi Bob,
... in generall or only by certainly topologies? All me known output power stages topologies, where only N-Channel MOSFET's in use, I have listed here:
http://www.diyaudio.com/forums/soli...better-audio-non-complements-audio-power.html
check also my post #43 from this thread.
Regarded the CSPP (circlotron) topology I can not imagine that you really believe this.
Hello Bob Cordell
I confirm....
this is true and theory,...but do you hear it and can hear really a difference in Sound between N-Channel Mosfet Amp compare to complementary MOSFET Amps with the same circuit ?
we dont and have test it carefully, and you can build with N-Channel Mosfets low cost very rugged excellent sounding Mosfet amps
Class D amplifier are all quasicomplementary amplifier and reference in Sound
Important for sound is quality of circuit and not only output stage technology
(in my views...complementary or quasicomplementary this is not important with todays devices) devices cost and stable working is important
In the 80s complementary lateral MOSFETs was the way to go, but against high cost without really big benefit...the Audioindustrie didnt use long time and change to BJTs and now obsolet
With a quasicomplementary Mosfet Amp DIY have excellent sounding amp, with complementary Mosfet Amp too but very much higher component cost without benefit in Sound or stable working
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The world is not enough-----with N-channel never say never again....!!!
I Disagree that having n-channel outputs the upper is follower and lower becomes CFP.
Also what exactly you term as quasi-complementary, by just having N-channel polarity of devices at outputs doesn't means that amp is quasi-complementary.
What will you say if the open loop gain and voltage swing of both half polarities will match under 0.5% for a given pair of device, do it with so called complementary mosfets, you will see the differnce in current waveform
The traditional way of using a pnp transistor as phase splitter/driver for negative rail device as in old bipolar design is not the way of doing N-channel amplifier.
The costly Toshibas 2SJ201/2SK1530[esoteric novelty of just 200V rating] and IRF old horses 240/9240[punny current rating of p-channel forces you to uses much more devices] you are talking about is used by everyone who want to claim that they have made a Mosfet amplifier.
One single pair of IRF260 N-channel amp will kick a 3 pair complementary amp made from 240/9240 out of the job.
I Disagree that having n-channel outputs the upper is follower and lower becomes CFP.
Also what exactly you term as quasi-complementary, by just having N-channel polarity of devices at outputs doesn't means that amp is quasi-complementary.
What will you say if the open loop gain and voltage swing of both half polarities will match under 0.5% for a given pair of device, do it with so called complementary mosfets, you will see the differnce in current waveform
The traditional way of using a pnp transistor as phase splitter/driver for negative rail device as in old bipolar design is not the way of doing N-channel amplifier.
The costly Toshibas 2SJ201/2SK1530[esoteric novelty of just 200V rating] and IRF old horses 240/9240[punny current rating of p-channel forces you to uses much more devices] you are talking about is used by everyone who want to claim that they have made a Mosfet amplifier.
One single pair of IRF260 N-channel amp will kick a 3 pair complementary amp made from 240/9240 out of the job.
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The traditional way of using a pnp transistor as phase splitter/driver for negative rail device as in old bipolar design is not the way of doing N-channel amplifier.
One single pair of IRF260 N-channel amp will kick a 3 pair complementary amp made from 240/9240 out of the job.
Which way are you doing if you dont use pnp transistor as phase splitter/driver for negative rail device
can you offer sample schematic ?
I agree One single pair of IRF260 N-channel amp kick a 3 pair 240/9240 out of the job .....
Im using IRFP460 because lower devices cost here in Market by local supplier about 0,56 $ pcs.
N-Channel Amp kick out of the job my previous complementary BJT and Class D amps in house for finest sound,
and we have test Class D from different manufacturer...
Class D dont have finest clear and open natural Sound in MID and High, like N-Channel Mosfet AMP
Complementary BJT Class AB and H amps from different manufacturer are harsh and metallic in MID and High Frequency (its normal for BJT) but sounding often better than class D
last time we did listening different Mp3 with different Class D amps but it did sounding so poor in mid and High.... cant describe it... with BJT and N-Channel Mosfet amp we dont had this effect
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Try to think out of the box, don't get swayed by traditional flawed design approaches used for bjts to serve for n-channels also, search the forum, there are plenty of designs which dont use the UGLY PNP PHASE SPLITTER APPROACH
for a simple rookie example have a look at this
http://www.diyaudio.com/forums/attachments/solid-state/65532d1150022131-nvmos-amplifier-ampdiy.jpg
MP3 files are known to sound metallic when encoded with certain codecs and/or settings.
If you are not able to develop your own class D/H you can always find a good excuse for not feeling inferior, being "class D/H sounds bad" the most usual (and boring).
Bad news is that you must do your own class D or at least class H to become competitive in the professional audio amplifier market, class AB has turned into a dead end.
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I agree. But with quasicomplementary topology (i. e. source follower in the pos. half and CFP structure in the neg. half) there is a agressive clipping behaviour to observe - both by the p-spice sim. and in real life. The reason therefore I don't understand exactly (see attachements). Thus I also don't more about the according topology to avoid this (perhaps anti saturation diodes and additional voltage supply necessary?).
By the so called "true complementary" topology such clipping behaviour isn't prsesent - and this could be the reason, why Bob don't like quasicomplementary topologies.
But by the other "Only N-Channel" topologies, mainly to find about
http://www.diyaudio.com/forums/soli...better-audio-non-complements-audio-power.html
such clipping behaviour like quasi complementary also isn't prsesent (e. g. CSPP, Circlomos, Hiraga and so on).
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Don't dismiss EEEngine. they are simple and really work. based on class AB supplied with simple unstable (self oscillating) power regulator. Class-D even class-H may have death too.
http://www.yamahaproaudio.com/downloads/documents/data/white_papers/yamahapoweramp_whitepaper_en.pdf
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by chance I have found this very easy quasi complementary 22000 watts amplifier circuit in bridge mode:
http://www.diyaudio.com/forums/pass-labs/165431-looking-pcb-22kw-amp.html
http://www.diyaudio.com/forums/pass-labs/165431-looking-pcb-22kw-amp.html
This circuit is a pure fiction..
22KW is impossible with such a circuit..
Most probably , an eventual builder will blow
almost all the components..
Thanks for the insight Mr. Cordell. Now you made my decision more difficult
Is there a holy grail 200W-300W class AB mosfet amps? Still looking...
Not the holy grail perhaps, but will probably be quite good once built and de-bugged. It simulates beautifully at least. The use of Bobs error correction is the key feature, and I recently added extra VAS transistors to make it more linear:
http://www.diyaudio.com/forums/solid-state/127886-designing-amp-2sj201-2sk1530-21.html
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