John Curl's Blowtorch preamplifier part II - Page 1933 - diyAudio
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Old 16th December 2011, 04:46 AM   #19321
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Quote:
Originally Posted by SY View Post
He's adding a physical resistance rather than creating a "virtual" one in the source impedance of the driving amp. The efficiency argument is, IMO, not totally honest.
Maybe the efficiency argument is not totally honest, but my mean intent was to show how increasing source resistance affects frequency response of the dynamic speaker near its resonance. The result is same in both cases, either I increase voice coil resistance (for simulation purposes) or add resistance to the source (generator, amplifier).
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Old 16th December 2011, 05:12 AM   #19322
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Pavel,

Quote:
Originally Posted by PMA View Post
Maybe the efficiency argument is not totally honest, but my mean intent was to show how increasing source resistance affects frequency response of the dynamic speaker near its resonance. The result is same in both cases, either I increase voice coil resistance (for simulation purposes) or add resistance to the source (generator, amplifier).
Why not show something real instead of building straw-men to scare people with "look how bad current drive is"?

Create the same curve twice.

Once use voltage drive to your model.

Then derive the TS Parameters of the driver, set Qt = Qm and use these numbers to create a linkwitz transform to match the original systems Fs and Qt.

Add this into the signal before the current generator and drive your ersatz lautsprecher with current.

What you will find is that frequency response between both cases is essentially identical. If your model is sufficiently abstract but precise you will find no difference at all. You can also X(f) and others and you will find them identical.

Now for the next step.

Please add the necessary non-linearites for Le(i) to your model (which makes a little closer than before to a real speaker) and run distortion curves for both systems at 100W input to the tenth harmonic.

Then add Le(x) and Re(i) to the model and do the same thing again, including frequency response curves, where the voltage drive system will show interesting effects.

Next we can add BL(x) and Km(x) to your model to get it even a bit closer to reality and we can re-run the curves...

After this we can add all the more minor stuff to your model and eventually we may have something that begins to resemble a real speaker somewhat, instead of being an academic construct that bears scant relation to what it is supposed to model.

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Old 16th December 2011, 12:27 PM   #19323
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I think that the most important thing is that the 'efficiency' of the loudspeaker is NOT necessarily compromised by current driving the speaker. Why you guys want to go at each other is beyond me. I respect you both, and I have told you both this, but I respect Ed Simon and many others here too.

Last edited by john curl; 16th December 2011 at 12:43 PM.
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Old 16th December 2011, 02:05 PM   #19324
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I am doomed!
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Old 16th December 2011, 02:46 PM   #19325
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Cool opamps for phono stage

Quote:
Originally Posted by john curl View Post
Not really, I don't need to take anyone's secret find of the best sounding op amp. After all, many here think that all IC's sound the same anyway. If you have a technical secret, please keep it to yourself, but please don't ask anything extra out of me, either.
Walt Jung had some ideas about using an opamp for a phono stage using the AD745 designed by no less than........... Scott Wurcer.
See page 6.22 in the link.
http://www.analog.com/library/analog...h6_final_I.pdf

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Old 16th December 2011, 02:56 PM   #19326
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Quote:
Originally Posted by QSerraTico_Tico View Post
Walt Jung had some ideas about using an opamp for a phono stage using the AD745 designed by no less than........... Scott Wurcer.
See page 6.22 in the link.
http://www.analog.com/library/analog...h6_final_I.pdf

Probably won't get away with that again . You can use two of them cross-coupled open-loop with the null pin feedback to make a fully differential preamp. At 2nV this is the best you can do with two JFET IC's.
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Last edited by scott wurcer; 16th December 2011 at 03:02 PM.
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Old 16th December 2011, 03:30 PM   #19327
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You can also put the RIAA in the feedback, but Walt thought that was going too far for an ADI app note.

Anyway Ed, Thorsten was talking about two speakers in essentially an acoustic bridge to null the difference. You mentioned using one speaker as a drive and another as a microphone to measure the absolute frequency response without a microphone. I sent that B&K link because it is a no holds barred math and apparatus description of the process. Spare the maths spoil the project.
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Last edited by scott wurcer; 16th December 2011 at 03:41 PM.
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Old 16th December 2011, 03:55 PM   #19328
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Quote:
Originally Posted by john curl View Post
Why you guys want to go at each other is beyond me.
I do not understand it as well, and I do not feel like that.

I only thought it was necessary to explain how current drive affects frequency response of the dynamic speaker (for those who might not be aware of it). It was purely technical explanation, nothing personal.
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Old 16th December 2011, 03:56 PM   #19329
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It is better to put RIAA in opamp feedback that using it passive.
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Old 16th December 2011, 04:05 PM   #19330
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Quote:
Originally Posted by scott wurcer View Post
You can also put the RIAA in the feedback, but Walt thought that was going too far for an ADI app note.

...
It is in the feedback in fig 6.15. Walt also did a passive RIAA in fig 6.17
For a balanced MC stage one can use a SSM2017 (now SSM2019) that will outperform the Mark Levinson JC1-AC.
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