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Old 3rd February 2006, 11:57 AM   #1
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Question Has anyone built AN-211 current feedback amp ?

Has anyone built AN-211 current feedback amp by graham Alaxander ?

How relevant is it to build these days? What about the availability of opamp SSM-2131. Can we use any substitutes for SSM-2131 & IGBTs GT20D101/201 ?


Why DIY community is scared of current feedback.
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Old 3rd February 2006, 12:54 PM   #2
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It was Mark Alexander.

I have used CFB amplifiers in RF applications -- from Intersil and Texas Instruments. Ron Mancini has a good note in the current edition of EDN --> www.ednmag.com -- you have to be quite careful of layout with CFB opamps due to the very high slew rate.

The SSM2131 is no longer in production, shouldn't stop you, however.

The IGBT's of this approximate description are readily available from a number of sources, but some of the other values may have to change.

No, I haven't built this particular amplifier, but had the application note in my files.
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Old 3rd February 2006, 12:57 PM   #3
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Quite a few people have built this amp, but using conventional power MOSFETs as the output devices. There's a website giving lots of information and photos of the amp that one guy built. I'm sure a Google for 'Alexander current feedback power amplifier' would find it.
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Old 3rd February 2006, 09:01 PM   #4
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I have help a friend long time ago with a power amp but I don't remember which opamp we used. The output stage was mosfets.

I have designed a headphone amp based on the idea.

http://home.swipnet.se/~w-50719/hifi/qrv03
For those who wonders, yes, I have a written permission from Analog Devices to use their patented design.

Ampslab has also an Alexander amp
http://ampslab.com/bi300_schematics.htm

The danish magazine High-Fidelity had an article series together with pcb's. Could it have been 1995? Some dane maybe can enlighten me.

If you want a better quality of the app note than from Analog Devices, it can be found here.
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Old 3rd February 2006, 09:07 PM   #5
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Default Re: Has anyone built AN-211 current feedback amp ?

Quote:
Originally posted by Prasanna
Can we use any substitutes for SSM-2131 & IGBTs GT20D101/201 ?
The design is not dependent of any special kind of part. The opamp should have certain properties like rather low power consumption and high output current. Any output stage can be used.

Quote:
Originally posted by Prasanna
Why DIY community is scared of current feedback.
They don't know what it is... I think. Fear for the unknown but I don't fear current feedback if you check what I have done so far.

SonnyA doesn't fear current feedback either.
http://mirand.dk
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Old 4th February 2006, 08:08 AM   #6
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Default The design is not dependent of any special kind of part. The opamp should have certai

Great pleasure to see design based on same principle. This has boosted my moral :


If I design my own amp using same CF principle then will it be violation of patenet of anaolog Devices. P-A please clear

Can anybody discuss the Do's & Don'ts in building current feedback Amps.
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Old 4th February 2006, 11:24 AM   #7
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Shubham Prasanna,

Nice to see you,

If you design your current feedback amp with Discrete Frontend instead of using opamps, then its very easy to stabalize and give you better understanding, besides its very easy....I have also build it using N-channel Mosfets at the output......

Shubhkamnayein,
K a n w a r
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Old 4th February 2006, 11:40 AM   #8
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Default Re: The design is not dependent of any special kind of part. The opamp should have certai

Quote:
Originally posted by Prasanna
If I design my own amp using same CF principle then will it be violation of patenet of anaolog Devices. P-A please clear
First it's a US patent.

Second, if you don't plan to make fully working commercial products, then you can relax.
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Old 4th February 2006, 11:47 AM   #9
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Default Re: The design is not dependent of any special kind of part. The opamp should have certai

Quote:
Originally posted by Prasanna
Can anybody discuss the Do's & Don'ts in building current feedback Amps.
There is much inforamtion out there about the subject. Walt Jung and others have written good stuff.

Suggestion: Search here and use "current feedback". Lot's of threads will appear.

Since you ask, there are a couple real important "don't's" and this is concerning the feedback.

Here are two reference sources:

http://www-s.ti.com/sc/psheets/slod006b/slod006b.pdf
http://www.analog.com/library/analog..._handbook.html

Check also my designs, QRV-03, QRV-07, QRV-08, all current feedback with excellent performance. The QRV-08 design is measured to 0.00046% distortion.
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Old 4th February 2006, 12:11 PM   #10
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Quote:
Originally posted by peranders

The danish magazine High-Fidelity had an article series together with pcb's. Could it have been 1995? Some dane maybe can enlighten me.
The article ran over a few issues of High Fidelity in 1994 and 1995. IIRC the design was pretty much straight out of the app. note. with the author's own PCB-layout.


/U.

EDIT: The author received permission from AN to manufacture and sell 75 sets of PCBs to the magazine's readers, but I believe the PCB artwork was published in the article.
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