What is most linear power Mosfet around?

[Charles Hansen]

Uh, well, besides the fact that some people don't like the sound of a CFP, that's not what the poster was asking about.

The original thread (started a year ago) was about linearity. The thread was "resurrected" (some would say hijacked) today by a poster having trouble with oscillations. Since he is from Argentina, I am not going to give him a hard time about starting a new thread, etc.

I don't think that using a CFP will solve his oscillation problems. If anything, they would tend to exacerbate them.

 

[amplifierguru]

"Uh, well, besides the fact that some people don't like the sound of a CFP"

Interesting, CFPs have a sound?

And I thought I had a good ear (only one though).

Greg

 

[luclucmir]

Also, I have put the heatsink to connected chassis with GND.
These oscillations that I have had queerly appeared in a design of amplifier of 2 pair of 1058/162 and alone I have been able to stop them adjusting the Bias. However when it assembles an amplifier of 4 pair of 1058/162 I was able to stop the alone oscillation connecting the heatsink to GND.
Should I use lateral mosfet matched pair or quad perhaps.? Maybe, I have good luck with the choice mosfet for the 4 pair of 1058/162 and have a coincidence with the similar Beta and don't have bigger oscillation.
I am also using a wide band in frequency response very High in the order of 1 MHz and perhaps the oscillations appear there. But, I loved this sound so detailed and I don't want to lose quality audio!
Also, I have noticed improvement in sound quality in low levels in audio when the Bias adjusts to stop the oscillations. But maybe, this is a masquerade, because in high levels the sound isn't the very best (keeping in mind the normal distortion of the used volumes).

You have the kindness to explain me, what denominates a CFP?

Sorry, isn't my intention to deviate the original thread.

I'm very grateful for your kind disposition and I will try to put in he practices your advice. In the next week I will assemble a new amplifier to make the laboratory tests and I will inform them of my results.

Regards Luc Mir

 

[ilimzn]

If you are concerned with linearising your MOSFETs AND allaying some temp/bias vagaries, why not do a CFP ? A quite low power driver like 2n5551/5401 would ensure low Vas loading c.f. HF gate capacitance drive.

Yes, but getting low rail loss is not trivial - the CFP needs to have less than 100% feedback and thus some gain, which may complicate things stability-wise. To be honest, I have not investigated how introducing gain affects the required thermal stabilisation methods...

Another thing to consider is that the gate damper resistor becomes a current limit for the driver transistors should zener Vgs limiting be employed for current limit of the output stage. In the event of clipping due to current limiting, the driver transistors become the output transistors sourcing current through the zener, gate damper and through C-E into the output. For an output short, and typical 6V or so zener and 100 ohm damper, on say 40V rails, this will be some 340mA at full saturation, but if it happens slow enough, a small driver may pass outside it's SOA and die...

 

[Charles Hansen]

Also, I have put the heatsink to connected chassis with GND.

Yes, of course. But you still need to add small bypass caps located as close as physically possible from the drains of the output transistors to the heatsink. (Again assuming that you have a source-follower output stage.)

I am also using a wide band in frequency response very High in the order of 1 MHz and perhaps the oscillations appear there.

Again, you need to use gate "stopper" resistors as close as physically possible to the gate of each output device. These will reduce the bandwidth below 1 MHz, but the amplifier will sound much better when it isn't oscillating...

It would help us tremendously if you posted a schematic of the circuit you are using.

You have the kindness to explain me, what denominates a CFP?

"CFP" stands for "Complementary Feedback Pair". This is when two transistors are connected together with a short feedback loop around them. I'm sure if you search the archives that you will find some postings that include schematics of this circuit.

 

[AndrewT]

Hi,
CFP sounds better than EF, so says Ampslab in comparing their topologies in their amp series.
I have Crimson amps that sound really good and as far as I know they have allways run CFP. There are many other good commercial designs that are CFP some in the High End market.
This may only apply to BJT outputs but some of that characteristic may carry over to FET outputs as well.
Let's hear some other opinions.

 

[Nelson Pass]

CFP sounds better than EF, so says Ampslab in comparing their topologies in their amp series.

I routinely use Common-Source and Common-Drain, and while
they are different in their performance, both have their charms.

 

[lumanauw]

My long time burried question : why Threshold changes to CFP in the later desings?
I have my own answer, but what is the real answer from you, Mr. Pass?

 

[Nelson Pass]

Later Thresholds had a combination of Common-Collector and
Common-Emitter. The Common-Collectors look like drivers for
a CFP stage, but keep in mind that they were big power devices
connected to the output and capable of driving the load by
themselves. In that sense they were capable of bypassing the
Common Emitter devices, which acted in support, handling most
of the output current, but operating in parallel with the hybrid
Common-Collectors.

In any case, Common-Emitter banks were the logical choice for
the job.

 

[amplifierguru]

NP you an insomniac, right? Or is this board so rivetting?

I used a CFP to drive the multiple MJ15003/4 EF output stage on the Magnet 300F which, rebadged, won TAS golden ear.

As usual someone else got credit.

 

[kASD]

In case of Vertical mosfets their true complementary never exists .... P-channel vertical type has very drawbacks and less efficiency...only the super combination for sheer high power with low distortion could be achieved with N-channel devices at output only when power rails of magnitude greater than +-100VDC are implemented..... and what you get is something to believe....


Kanwar

 

[tlf9999]

In case of Vertical mosfets their true complementary never exists

Have true complementary pairs ever existed for any substrates: bipolar, cmos, jfet, mosfet, sige, gaas, etc.?

The answer probably depends on how you define "true complementary".

 

[lineup]

Re: Re: What is most linear power Mosfet around?

I have a DIY amp based on 2sk1058 and 2sk162 Hitachi power mosfets.
In term of linearity how would it compare with other type of audio power mosfets?
Are there better mosfets around?
.

That would be a Vertical Mosfet.
The other kind is a Lateral,
which has lower transconductance,
but also lower Capacitance Gate-Drain.

There are proponents of both types.
Charles Hanson argues for Laterals,
I tend to use Verticals (HEXFET)
.

I don't know how you would define "better mosfets". There is good news and bad news about these devices, as with most electronic components, and you must make your best judgement call in your design.

These are called "lateral" power MOSFETs, and have much lower transconductance and higher on resistance than typical "vertical" power MOSFETs (that's the bad news). The good news is they can be easily paralleled for higher output, and they need simpler biasing (minimal temperature compensation needed). Unfortunately, they are not well suited for the vast majority of other MOSFET applications, so they have become low volume, high-priced components, compared to vertical MOSFETs.

The advantages of vertical MOSFETs have led them to dominate the market. In fact, there are literally thousands of vertical MOSFETs made, and only a handful of lateral parts available today. The laterals are primarily aimed at the high end audio amplifier market for new design. and replacement market for existing products.

With care in design, the disadvantages of vertical MOSFETs can be largely nullified. Biasing must be temperature compensated. If used in parallel, they must be carefully matched for Vgs(on) and transconductance, and used with large matched source resistors; they should be derated because the sharing will never be perfect.


In your particular design,
there are only two other lateral MOSFET device pairs that might be "better":
the 2SJ352/2SK2221 pair and
the 2SJ201/2SK1530 pair.
.

====================================

The query was 2SK1058 / 2SJ162:

1. In term of linearity how would it compare with other type of audio power mosfets?

2. Are there better mosfets around?

====================================


Me, lineup, is putting my answer the other way.

I think using 2SK1058 to replace IRFP240 would be a considerable improvement.
In such application where 2SK1058 can take the heat and power in question.

IRFP240 Ciss, input capacitance = typ 1300 pF
Hitachi 2SK1058, input capacitance = typ 500-600 pF
Big difference!
Means this hex has 2.1-2.6 higher Ciss, compared to 2SK1058



There is another company that has taken over rights to Hitachi Lateral MOSFET.
---------------------------------------------------------------
Renesas provides lateral construction MOS FET optimum for high fidelity amplifier.
Power MOSFETs for General Amplifier:

Renesas .com - LATERAL MOSFET PRODUCT LIST

They have made new clean and good DATASHEET for each Device!


------------------------
*lineup note and comment:

Lateral MOSFET were specially made for use in Audio Amplfiers.
This is why they have lower Volt-Gate-Source, among other qualities.

IRF HEXFET are primary intended for Switching Heavy Loads very fast.
And NOT for linear and low distortion Audio HiFi amplifiers.

Nevertheless, with smart circuits that take care of HEXFET reuquirements in best way,
you still can use hexfet, vertical mos, for HiFi Audio. Proven many times.

Personally, I am in love with LATERAL MOSFET!
I would never consider using any hexfet
if there in an application was possible
to use a good lateral audio mosfet instead
.... and what really is an issue many times ....
if I could find a dealer in my country with Lateral MOS supply.


lineup
November 2006

 

[lineup]

symmetrical amplifier - what ????

Have true complementary pairs ever existed for any substrates: bipolar, cmos, jfet, mosfet, sige, gaas, etc.?

The answer probably depends on how you define "true complementary".

good question, tlf9999


when someone advocates so called symmetrical amplifiers
I often point out, that they are really not more symmetrical in operation
than so called non-symmetrical or single ended amplifiers


when a so called symmetrical input with 4 transistors
using so called complementary small signal transistors
( even sometimes npn + pnp JFETs !!!! )
is controlling the input and feedback of a such an amplifier

... I would even many times consider an amplifier
with only one As Good as possible MATCHED LTP pair NPN (or PNP)
as being more symmetrical in terms of audio waves output

and this is what counts

Maybe in future we get more 'complementary' devices, of some sort.
But if they haven't solved this yet,
I think it leaves us Not With Much Hope.


lineup
Lineup Audio Amplifiers
http://lineup.awardspace.com/