Audio (Lateral) MOSFET's for Class AB - Overview, P-Spice URL's - Page 2 - diyAudio
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Old 11th May 2011, 08:48 PM   #11
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Quote:
Originally Posted by tiefbassuebertr View Post
Not listed here are the IRF/IRFP/IRL and IRF related types, because this types actually appropriate only for class-D and pure class-A, but not for class AB push pull with 100-200 mA idle current.
?
I find the IRFP240/9240 work well with low bias currents as low as 7mA.
Despite the irfp's being switching transistors they all sound very good in class AB amps.
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Old 11th May 2011, 09:07 PM   #12
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Originally Posted by nigelwright7557 View Post
I find the IRFP240/9240 work well with low bias currents as low as 7mA.
Despite the irfp's being switching transistors they all sound very good in class AB amps.
What? 7 mA idle current by this MOSFET's?
Interesting to know, how looks the input signal gate current of the IRFP240/9240 just below the clipping aera by complex usual load at the output (min. 2 ohms).
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Old 11th May 2011, 09:12 PM   #13
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Quote:
Originally Posted by tiefbassuebertr View Post
What? 7 mA idle current by this MOSFET's?
Interesting to know, how looks the input signal gate current of the IRFP240/9240 just below the clipping aera by complex usual load at the output (min. 2 ohms).
The input signal isnt important, its what is at the speaker and that looks great, no distortion into 4 ohms.

Peavey also have a low bias current approach and it works well for them too.
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Old 12th May 2011, 12:26 AM   #14
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Quote:
Originally Posted by tiefbassuebertr View Post
Audio (Lateral) MOSFET's for Class AB - Overview concerning Types and some URL's (also for various P-Spice Parameter)

Not listed here are the IRF/IRFP/IRL and IRF related types, because this types actually appropriate only for class-D and pure class-A, but not for class AB push pull with 100-200 mA idle current.

Who knows more currently produced lateral MOSFET's for replace vintage types?
Hi tiefbassuebertr,

Thanks for posting all of this very useful information about MOSFETs.

However, you are unfortunately repeating a common misconception that IRFP vertical MOSFETs are not suitable for class AB amplifiers. This is completely untrue and many people have built the amplifiers to prove it. They work perfectly well with 150mA bias per pair. There are pros and cons when comparing vertical to lateral MOSFETs, but in many ways the verticals are even better. This is all explained in Chapter 11 of my book, "Designing Audio Power Amplifiers".

I prefer vertical MOSFETs over laterals and among verticals I prefer the Toshiba parts, but they have been discontinued.

The MOSFET power amplifier with error correction that I published in 1983 used IRF HEXFETs and produced lass than 0.001% THD at full power at 20 kHz. Moreover, it had substantially better thermal stability than BJT amplifiers.

Although you may be misled by thinking that they were designed for switching applications, when properly applied they are every bit as linear as laterals (and far faster and capable of much higher current).

Cheers,
Bob
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Old 12th May 2011, 09:26 AM   #15
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Originally Posted by Bob Cordell View Post
Hi tiefbassuebertr,
Thanks for posting all of this very useful information about MOSFETs.
However, you are unfortunately repeating a common misconception that IRFP vertical MOSFETs are not suitable for class AB amplifiers. This is completely untrue and many people have built the amplifiers to prove it. They work perfectly well with 150mA bias per pair. There are pros and cons when comparing vertical to lateral MOSFETs, but in many ways the verticals are even better. This is all explained in Chapter 11 of my book, "Designing Audio Power Amplifiers".
I prefer vertical MOSFETs over laterals and among verticals I prefer the Toshiba parts, but they have been discontinued.
The MOSFET power amplifier with error correction that I published in 1983 used IRF HEXFETs and produced lass than 0.001% THD at full power at 20 kHz.
http://www.cordellaudio.com/papers/MOSFET_Power_Amp.pdf
Moreover, it had substantially better thermal stability than BJT amplifiers.
Although you may be misled by thinking that they were designed for switching applications, when properly applied they are every bit as linear as laterals (and far faster and capable of much higher current).
Cheers,
Bob
I have heard and perform repair services of variuos of such amps, e. g. from the french brand "Cairn EZO". From the view of THD values you are right. Even by the use of only 5-10 mA the measuring results not really bad. But from the view of listening tests the difference between 100-150mA idle current to 500 mA idle current (like pure class A by medium levels) is much more larger than one might suspect the differences in the THD measurement, especially in the upper midrange/high frequency aera (voices e. g.).
And additional also larger than by the use of audio MOSFETs like Hitachi/Semelab and BjTs by compare of similar values for idle current.
From my audible experience IRFs in PP power follower output stages need at least 300-350mA idle current, if the amp was provided for full range applications (and not only for the lower frequency aera in bi-/multiamping systems).

My first assumption, the problem could be the absence of an additional driver stage for driving of the internal MOSFET gate caps has not been confirmed - unfortunately.
Perhaps the error correction by fig. 12 about
http://www.cordellaudio.com/papers/MOSFET_Power_Amp.pdf
could help to remove the observed audible effects, this I haven't check out until now.
Attached Files
File Type: pdf C_...A-CAIRN Studio 1.ckt.pdf (13.5 KB, 387 views)

Last edited by tiefbassuebertr; 12th May 2011 at 09:49 AM.
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Old 12th May 2011, 10:00 AM   #16
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Originally Posted by nigelwright7557 View Post
Peavey also have a low bias current approach and it works well for them too.
Which models you mean?
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Old 12th May 2011, 10:51 AM   #17
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Quote:
Originally Posted by tiefbassuebertr View Post
I have heard and perform repair services of variuos of such amps, e. g. from the french brand "Cairn EZO". From the view of THD values you are right. Even by the use of only 5-10 mA the measuring results not really bad. But from the view of listening tests the difference between 100-150mA idle current to 500 mA idle current (like pure class A by medium levels) is much more larger than one might suspect the differences in the THD measurement, especially in the upper midrange/high frequency aera (voices e. g.).
And additional also larger than by the use of audio MOSFETs like Hitachi/Semelab and BjTs by compare of similar values for idle current.
From my audible experience IRFs in PP power follower output stages need at least 300-350mA idle current, if the amp was provided for full range applications (and not only for the lower frequency aera in bi-/multiamping systems).

My first assumption, the problem could be the absence of an additional driver stage for driving of the internal MOSFET gate caps has not been confirmed - unfortunately.
Perhaps the error correction by fig. 12 about
http://www.cordellaudio.com/papers/MOSFET_Power_Amp.pdf
could help to remove the observed audible effects, this I haven't check out until now.
In every type of amplifier, be it vertical MOSFET, lateral MOSFET or BJT, one will always have bad examples of performance and sound that may tempt one to make generalizations about that technology, and this we have to be careful of. The amplifier for which you provided a circuit is a poor example of a MOSFET amplifier, and your speculation about the problem being a lack of a driver is probably right.

It is also true that MOSFETs like higher quiescent current, and this goes for both vertical and lateral MOSFETs, and is a result of transconductance droop.

With a single pair of IRFP240/9240 biased at 150mA without any special measures like EC, I regularly achieve less than 0.03% THD at 20 kHz at any power level and they sound marvelous.

Cheers,
Bob
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Old 20th July 2011, 09:51 PM   #18
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Thanks for the great list of lateral Mosfets and links!

I was wondering has anybody experimented with higher voltage Mosfets that can handle 180V drain source voltage, such as, 2SK2221/2SJ352, ALF08N20V/ALF08P20V, the double die versions ALF16N20V/ALF16P20V, or BUZ series?

How do they compare in terms of parasitic oscillations, cross-over distortion and matching between the N and P pairs?

The 2SK2221/2SJ352 have internal protection zener diodes, which is a bonus.

Thank you,
Alexandru
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Old 26th December 2011, 05:03 PM   #19
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Originally Posted by nigelwright7557 View Post
The input signal isnt important, its what is at the speaker and that looks great, no distortion into 4 ohms.

Peavey also have a low bias current approach and it works well for them too.
I am still looking to Peavey's approach "low bias currents"
I have found this patent:
Smart voltage rail reduction audio amplifier - Patent # 6975172 - PatentGenius
http://www.pat2pdf.org/patents/pat6975172.pdf
but Peavey has earned more than 180 patents.
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Old 27th December 2011, 01:15 PM   #20
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Quote:
Originally Posted by tiefbassuebertr View Post
I am still looking to Peavey's approach "low bias currents"
I have found this patent:
Smart voltage rail reduction audio amplifier - Patent # 6975172 - PatentGenius
http://www.pat2pdf.org/patents/pat6975172.pdf
but Peavey has earned more than 180 patents.
The patent mentioned looks somewhat like a class H or class G design. I did not see any reference to "low bias currents". It is always interesting to see approaches to achieving low distortion with low quiescent bias currents in class AB designs, if that is what you are referring to. Particularly with MOSFETs, transconductance droop at lower bias currents can be a source of distortion. That was the main reason that I introduced Error Correction to vertical MOSFET power amplifiers.

Cheers,
Bob
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