[ppl]

I am not a big MOSFET fan (Metal Oxide Field effect Transistor) Wow how did I remember that after just putting an LED in Backwards on something was just working on>

However not only does Amplifiers designed with this device that was By the way, originally implemented in Audio amplifiers as a cost saving measure still
Endure it is plliferent in
http://www.perreaux.com/history.php
“With the release of the "SA80B" and "PMF2000", Perreaux won the distinction of being the first Western world company to commercially utilize power MOSFETs in an audio application. The reaction in the marketplace was very favorable. “
(Quoted from above link)
In addition new designs keep appearing with them and a substantial amount of professional amplifiers use MOSFETS outputs because of there Claimed ruggedness over equivalent Rated BJT Devices. The Primary disadvantages are the BJT will suffer thermal Runaway and enter into secondary breakdown at lower output power. Ok so MOSFET’s are almost Bullet Proof but reliability can be obtained in a BJT design by using high voltage devices to raise the level of secondary breakdown.

The Real reason IMHO that MOSFETS survived and also are so proliferate today is the Actual lower cost of the complete amplifier by exploiting some of the attributes of the MOSFET. The driver circuitry power requirements could be greatly relaxed so a lower current driver stage would drive the theoretically infinite input impedance of the MOSFET and the typical output protection eliminated resulting in a substantial cost savings as a complete system. And this brings me to the point of this thread.

Depicted in this link is a 6-transistor Mosfet amplifier that is an excellent guide to the actual design considerations for any audio amplifier and in particular Mosfet output stages. Another interesting aspect of this circuit is its Topology is dated this style was quite the norm for Early Hi-Fidelity solid state Power amplifiers including an output coupling capacitor in addition to a single ended power supply and non differential input stage. However despite the fact that other than the Amplifiers output stage the preceding circuitry and power supply are again IMHO less that Audiophile grade and quite dated nonetheless do not on one way distract from the design rules required and the author gives some interesting reasoning behind his designs http://www.angelfire.com/ab3/mjramp/simple1.html


Moving on to state of the art in MOSFET Amplifiers is described in a project launched I believe by Toshiba in order to promote there New MOSFET complementary pair optimized for Audio output stages in High-Fidelity Audio Power amplifiers http://translate.google.com/translat...lr%3D%26sa%3DG

This is translated from Japanese to English and the original website is http://www.ne.jp/asahi/evo/amp/J200K1529/report.htm

Again just great info on the design process and using what I consider and again is mearly MHO a state of the art topology taking you from a two stage design all the way up to the definitive edje of mosfet technology and utilizing some absolutely fantastic mosfet Devices the 2SJ200 and 2SK1529
http://www.alldatasheet.co.kr/datash...BA/2SJ200.html

http://www.alldatasheet.co.kr/datash...A/2SK1529.html

These are also great equivalents or shall we say the previous reference MOSFET standard as considered the case by many die hard Mosfet users
http://www.alldatasheet.co.kr/datash...HI/2SJ162.html

http://www.alldatasheet.co.kr/datash...I/2SK1056.html


So ok homework assignment Go Forth yee prospective audio designers and bring back fruit of original Creations and or extensions of these works as you can never learn more than by actually doing it and with such wonderful guides for the novice available,

surly only inspiration or lack of time is the only thing holding you back.

 

[andante]

I won't pretend that I understand much of this, but I am wondering, isn't M3 amp just an example of this design approach, using MOSFETs for output stage?

Cheers.

 

[amb]

Quote:

Originally Posted by andante I won't pretend that I understand much of this, but I am wondering, isn't M3 amp just an example of this design approach, using MOSFETs for output stage?

Yes indeed. The MOSFET vs. BJT debate has gone on for a couple of decades now. There are technical advantages and drawbacks to each. Whether one favors one over another often boils down to "religion". Obviously, you could guess where I stand on this

.

 

[jasonhanjk]

BJT are better in THD but Mosfet have other advantages. Like soft clipping and lower break down.

 

[ppl]

Oh no please do not turn this into a MOSFET vs BJT debate because that was not the intention of this thred. The intent was to allow one to explore the technicial decesions in Audio power amplifire design with emphisis upon compont part selection and sutch in otherwords an Educational thred

 

[rickcr42]

For voltage amplification stages the jfet is for me the ideal device and all I use in every line level low current voltage follower or gain stage.No transisitors or opamps here but only jfets all the time,period.

In the current amplification stages the bjt is the way to go because it is ideally suited for current delivery but I still have only used mosfets here for years and those at full Class-A where they be most linear thus avoiding the signature sound of the mosfet which is a soft upper register.

These devices,the mosfets,are far from perfect or easy to implement and a plug and play device it is not,the gate capactiance being a very real problem requiring attention to overcome or you WILL get high frequency rolloff (consider like miller cpacitance at the input to a triode stage).

Correctly done and the mosfet is my personal favorite in solid state audio but use sloppy techniques and you are toast and will end up with a very bland and soft sound.Even too high an input impedance from a potentiometer will muck up the sound so anything seen by the gate should be suspect when designing with the mosfet

Treat that puppy like a Triode and you will have an easier time getting a handle on the design work but treat it like a transistor and you open up a real can of worms.

Just my experience folks

 

[rickcr42]

Quote:

With the release of the "SA80B" and "PMF2000", Perreaux won the distinction of being the first Western world company to commercially utilize power MOSFETs in an audio application. The reaction in the marketplace was very favorable. “

BTW-My memory says it was the Hafler DH-200 that first used the mosfet successfully in a commercial design.i don't remember Perraeux even being on the scene until the DH-200 was well entrenched as an entry point into high end audio.
Next was NOT Perreaux either but XXX (company name eludes right now me dammit,they made ES speakers and a speciallized amp to drive them which was later purchased by Hafler and is now used as their high end pro power amp topology).

This is from memory and going back to the '70s but I do not remember Perreaux as being a player in pushing mosfet amps and in fact it was the B&K ST-140 that first cracked into what was considered "true" high end sound and the Perreaux followed even that

 

[trbl]

Quote:

Originally Posted by rickcr42 BTW-My memory says it was the Hafler DH-200 that first used the mosfet successfully in a commercial design.

Whether it was successful or not, the first MOSFET power amp that I recall was a SONY unit that predated designs using Hitachi and IRC power FETs by a fair amount of time. I forget the model number, but I recall a writeup in Audio magazine at the time. What was really interesting is the SONY complementary power FETs had triode-like characteristics (low amplification factor and "plate resistance") unlike the power FETs that followed from other manufacturers. The amplifier was quite complex with lots of power supplies and not very efficient (again due in part to the triode-like characteristics so the output could not be driven to near rail-to-rail voltages).

I think it's too bad the SONY power FETs never caught on.

 

[rickcr42]

Quote:

Whether it was successful or not, the first MOSFET power amp that I recall was a SONY unit that predated designs using Hitachi and IRC power FETs by a fair amount of time.

again from memory this was not a mosfet but a sony device related to the mosfet and found only in sony products.I still think the first "successful" U.S. hifi amp to use the mosfet was the DH-200 and the first to have both reliability AND class B sound was the B&K which was a copy of the AVA circuit.Less "ad copy" so sold less and more unknown but the same essential design

 

[rickcr42]

Oh yeah,the Topology "purchased" by Hafler and still used is the "Transnova" topology formerly used by the Acoustat amps (i knew it would come to me

).

These amps were considered to have great sound and could drive any load,including the capacitive load produced by the electrostatic panels Acoustat themselves made.

I can faintly remember the schematic of the transnova topolgy and it was all about the feedback groups and feedback impedance networks that was the engine for the design topology.Capacitive loads had/have a way of driving feedback nuts and making amps either unstable or unlistenable

the original design schematic was published in Audio Magazine in either the late seventies or early eighties but i DO remeber it well (now !

)

 

[rickcr42]

And "oh yeah" also,i think the Sony devices were "Vertical FETs" and more not true hexfets though i don't remeber the distinction between the two and could even be different names for the same thing though my memory says they were not.

 

[trbl]

Quote:

Originally Posted by rickcr42 And "oh yeah" also,i think the Sony devices were "Vertical FETs" and more not true hexfets though i don't remeber the distinction between the two and could even be different names for the same thing though my memory says they were not.

Yeah, this was all 30 years ago.

I just looked and yes, the SONY devices were called VFETs for Vertical FET as you say. There wasn't much information on the actual fabrication of the devices, but it's likely they were more of an unusual design JFET than a MOSFET as I mis-remembered. HexFET was a trade name used by Hitachi I think (or maybe another manufacturer). Confusing the issue where the power MOSFETs with a V-shaped geometry that were also called V-FETs.

I owned a DH-200 when they first came out. It was a decent amp. I later designed some commercial hybrid power amps that used the IRC devices. the circuit was originally designed for the Hitachi devices, but the manufacturer couldn't get enough free samples from Hitachi to fully develop and test the design so the switch to IRC was made because they were very generous with sample parts.

 

[drewd]

Quote:

Originally Posted by rickcr42 Next was NOT Perreaux either but XXX (company name eludes right now me dammit,they made ES speakers and a speciallized amp to drive them which was later purchased by Hafler and is now used as their high end pro power amp topology).

It was Acoustat - they called their implentation the Trans Nova amplifier.

-Drew

 

[rickcr42]

Quote:

Yeah, this was all 30 years ago.

heh,between age and time passing kinda hard to keep this stuff straight.

especially the way each manufacturer feels a need to come up with a fancy label for their preferred topology or the active devices used that in the end only mucks up the water.

and the secrecy to protect their designs and the detective work becomes one of checking the claims against the known circuit functions then by extropolating this to the knowledge library where surprise surprise,everything is just a solid state implementation of earlier tube designs,mostly worked out in the twenties

I guess that is why I do mosfet design work mostly by using tube data sheets and designs then converting the operating points of the mosfet.
Even the "gate resistor" can be called the "grid stopper" if it were tubes being talked about and just like with SE class-A triode being the preferred method if high power is not the goal then there is absolutely no reason to even consider Class A/B in low-watt mosfet design work.
The current and heat dissapation is way manageable in wats in the 0.5-5 watt range and really the only way to go.

A dual JFET front end with CCS (similiar to the borbely headphone amp) driving a SEPP output stage done right can make a very competitiive headphone amp.
However I don't care for active loading on the output Stage OR paralelled devices if it can be helped.
Looks good on paper,seems like a good idea in theory butsounds less "musical" in reality.

At least to me.

 

[art633]

Quote:

Originally Posted by ppl So ok homework assignment Go Forth yee prospective audio designers and bring back fruit of original Creations and or extensions of these works as you can never learn more than by actually doing it and with such wonderful guides for the novice available, surly only inspiration or lack of time is the only thing holding you back.

Perhaps the key word should be IMAGINATION.

Quote:

Originally Posted by rickcr42 Correctly done and the mosfet is my personal favorite in solid state audio but use sloppy techniques and you are toast and will end up with a very bland and soft sound.Even too high an input impedance from a potentiometer will muck up the sound so anything seen by the gate should be suspect when designing with the mosfet Treat that puppy like a Triode and you will have an easier time getting a handle on the design work but treat it like a transistor and you open up a real can of worms.

To right - but to take it even further that is why I prefer the hybrid. Triodes up front with FETs out back. OpAmps ! What are they

M