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Old 4th June 2011, 05:59 AM   #1
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Default My new design of differential buffer I/O board for fully balanced design

My new design of differential buffer I/O board for fully balanced design!

Material rough estimation: Dual OPAMP x1, Resistor x 6, Socket x2 pcs

(Reference: http://jensentransformers.com/an/an003.pdf)
Attached Images
File Type: jpg Diiferential buffer design.JPG (79.0 KB, 890 views)
File Type: jpg Differential buffer application.JPG (69.7 KB, 853 views)
File Type: jpg Gain structure.JPG (25.2 KB, 821 views)
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Old 4th June 2011, 11:40 AM   #2
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To have a fully differential interface with ICs, with maximum CMMR, you will need instrument-type arrangement on first chip, with three chips. Or a balanced IC, which does have 3 instrument chips inside. You may also need R and C trimming.
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Old 4th June 2011, 01:25 PM   #3
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Quote:
Originally Posted by carlmart View Post
To have a fully differential interface with ICs, with maximum CMMR, you will need instrument-type arrangement on first chip, with three chips. Or a balanced IC, which does have 3 instrument chips inside. You may also need R and C trimming.
Dear carlmart,

First of all, thank you for your comment. For self-improvement, I always listen to anyone's idea. Accept or not, subject to the ground of statement. For your statment, please show your theory, calculation or something else to support your reason.
My design is based on Jensen's article as reference which was well developed for a long time. If wrong, then Jensen's idea is wrong too. Anyway, thank you for your writing.
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Old 4th June 2011, 02:03 PM   #4
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Quote:
A BALANCED input or output uses two signal conductors
which have equal impedances to ground. Balanced inputs and
outputs are widely used in professional equipment because the input
differential amplifier can, in theory at least, totally null its response
to ground noise which exists equally on both signal lines. Examples
of typical circuits are shown below.
Because of its low cost and small size, this "active balanced"
differential input circuit (or some variation of it) is very widely used.
The pairs of 10 kS resistors are trimmed to match within 0.01% in
order to null response to ground noise. When used in real-world
systems, however, a major drawback of this circuit is its exquisite
sensitivity to unbalances in the output (source) impedances of the
line driver. This seriously compromises ground noise rejection or
CMRR (Common-Mode Rejection Ratio) of the system.
go and read this para again.
Then look at fig2.3

Your interpretation is wrong, not Jensen.
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Old 4th June 2011, 02:36 PM   #5
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Hi AndrewT,

Thank you for your explanation. Long time no talk, my last talk with you back to year 2008 at this thread National LME49810TB/LME49830TB UltraHighFidelity HighPower Amplifier Reference Design with Lineup too. Did you retire or still teaching at school in Scotland?
My buffer I/O design is an effective tool to reduce noise, theorically at zero noise level, but very simple design and extremely low cost. I am just an audio amateur, thus make it “Not-for-profit”.
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Old 4th June 2011, 03:06 PM   #6
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If you really want a fully diff I/O with good CMR (after all, why bother if you get only part of the benefit), look at the OPA1632. There are more like that, which would perfectly fit your need.
Or, look at the 'InGenius' chip from THAT Corp. Designed by Bill Whitlock, who took over Jensen from, ehhh, Jensen, many years ago.

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Old 5th June 2011, 02:59 AM   #7
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Dear Jan Didden,

Appreciate your comment. I believe that the design concept of TI’s OPA1632 and my buffer I/O is similar. But, I do not know for any difference or exactly equivalent unless TI discloses the secret of circuit topology inside chipset. TI is only willing to tell you the application of chipset or I accidentally disclose the secret of TI. TI has just acquired National Semiconductor to be the market leader in this industry. I am a result-oriented person, the best choice is the one best fit to my goal, but not insisting in my design. One advantage of own design is better customization and flexibility. TI OPA1632 or my buffer I/O which one is better is not important, the most important is that both of our approach is correct.
I would like to remark that noise damages the quality of sound in analog signal transmission. But, it does not guarantee a good quality of sound even though you achieve the goal of theoretical zero noise level. The first priority depends on the source of sound that is the one in master recording room and the post processing unit to fit your taste of sound including digital module, multi-stage analog amplification module and the electro-mechanical vibration of speaker which is an integrated system approach in signal modeling.
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Old 5th June 2011, 03:43 AM   #8
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Be careful with phrasing concerning zero noise. In a perfect world a balanced differential scheme can reject low frequency noise pickup, but there is a price to pay. The system will typically have a higher internal (thermal and internally generated) noise level than if it were single ended! It's very appropriate for professional sound systems in contaminated environments, but IMHO doesn't offer any advantages in a home set up.

To work right you need identical impedances on both lines, something the single opamp differential amp doesn't have. As said above, you need to go to either the three opamp instrumentation arrangement, or there's a two opamp cascaded opamp circuit that can probably be used. It's also important to understand the difference between differential signals and balanced differential signals because that will make the impedance issue clear to you.
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Old 5th June 2011, 05:30 AM   #9
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Quote:
Originally Posted by Conrad Hoffman View Post
Be careful with phrasing concerning zero noise. In a perfect world a balanced differential scheme can reject low frequency noise pickup, but there is a price to pay.
Dear Conrad,

1) "a price to pay"? I suppose not to pay to anyone unless patent issue, but people need to pay to me. Just kidding!
2) My buffer I/O is in conceptual design stage, need fine tuning, but not a big change. Your comment is valuable and will be put into consideration.

Nice to speak with you.
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Old 8th June 2011, 01:45 AM   #10
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Here are some examples of audio amplifier using buffer I/O device such as OPAMP or transformer:

Pre-amplifier:
1) MBL6010D Pre-amplifier (Buffer NE5534 + Amp AD797 + Balanced Output NE5534)
2) Jeff Rowland Corus & Criterion Pre-amplifier (TI OPA1632 + Lundahl LL7902 + Lundahl LL1588)

Power Amplifier:
3) Wured4Sound SX-1000 Power Amplifier (Buffer I/O + B&O Icepower 1000ASP)
4) Bel Canto S500 Power Amplifier (Buffer I/O + B&O Icepower 1000ASP)
5) Jeff Rowland Model 201 Power Amplifier (Model 201 Lundahl LL1545A + Icepower 1000ASP or Lundahl LL7902 + Icepower 1000ASP)
Attached Images
File Type: jpg Bel-Canto-S500.jpg (108.6 KB, 656 views)
File Type: jpg Jeff Rowland Criterion.JPG (100.1 KB, 625 views)
File Type: jpg Jeff Rowland M201.JPG (33.8 KB, 239 views)
File Type: jpg MBL6010D.JPG (97.3 KB, 368 views)
File Type: jpg Wyred4sound SX-1000 [2].jpg (102.6 KB, 354 views)
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