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Old 13th February 2005, 11:40 AM   #11
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Hi, Janneman,

Quote:
He has commented on that in many posts here. If you read them, read the whole thread. There are many knowledgeable people here who don't agree whith with many of his opinions, and back that up with facts. Very educational discussions.
Yes, he involved in almost all discussions about these IM family. But as far as I remember, he hardly gives a clue how they sounds in real world. I'm sure he knows how they sounds in real amp
Many times, other member here argues with him. But I'm sure he's full with real life amplifier audible effect with these IM family, since he already learning about them from the time these IM family is given name.
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Old 13th February 2005, 06:16 PM   #12
jcx is offline jcx  United States
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Quote:
Originally posted by beppe61

What I wanted to imply is that a low open loop bandwidth is a situation that worries me on principle.

beppe61

on 1st sight the phrase "low open loop bandwidth" seems to imply a defect but the proper comparison is between designs with the same GBW - gain*bandwidth at some point on the (unadvoidable) low pass falling slope of the gain curve - where for a 1st order roll off the GBW is nearly constant

when comparing amplifiers with the same GBW product a "high bandwidth" design actualy has lower gain at DC and low frequencies up to the intercept with the constant GBW roll off region, the "low open loop bandwidth" amplifier with the same GBW product has the same gain as the high bandwidth amplifier beyond the "high" 1st low pass corner frequency and lots more gain at frequencies below the "high bandwidth" amplifier's corner frequency

my reasoning:

http://www.diyaudio.com/forums/showt...ht=#post489927
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Old 14th February 2005, 08:00 PM   #13
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Quote:
Originally posted by beppe61

I read the opinions of lots of people that much prefer, sonically speaking, a preamp without feedback (i.e Nelson Pass Aleph P) to an op-amp based line preamp (i.e. Morrison Elad) even if the latter has much better measurements.
I am posting here to try to understand if this is a myth or a reality.

Kind regards,

beppe61 [/B]


Beppe61,
I did not mean to reply that there is no audible difference, just
that I (me myself) can't hear a difference. Many people think they can (but I'm not sure they do double-blind tests....). It is easy to
build both and check for yourself!!!! I've witnessed many listening tests; easily measured distortion CAN be heard.

I also meant to be clear that the Aleph P, and many other amplifiers DO EMPLOY NEGATIVE FEEDBACK. It is local feedback, with little or no global (or loop) feedback. It has all the same (mostly good) characteristics of negative feedback. I just wished to point out that there still is negative feedback, so the real differences are topological only. I also suspect most strongly, that if you can truly hear a difference, you can measure a difference.

I hope this is of some help.....

Best Regards,
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Old 15th February 2005, 08:17 AM   #14
beppe61 is offline beppe61  Italy
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[QUOTE]Originally posted by stevebeccue
[B]

Beppe61,
...
I also meant to be clear that the Aleph P, and many other amplifiers DO EMPLOY NEGATIVE FEEDBACK. It is local feedback, with little or no global (or loop) feedback. It has all the same (mostly good) characteristics of negative feedback.

Dear Steve,

I was referring to the Pass Aleph P line preamp not the power amp.
I believe it does not use negative feedback, neither loop or local.
I am most interested in preamp because if you distort the signal at the beginning of the audio chain then you can only amplify that distortion.

Kind regards,

beppe61
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Old 15th February 2005, 03:55 PM   #15
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[QUOTE]Originally posted by beppe61
[B]
Quote:
Originally posted by stevebeccue


Beppe61,
...
Dear Steve,

I was referring to the Pass Aleph P line preamp not the power amp.

Kind regards,

beppe61

If I am looking at the correct thing.... R25 and R28-R31 are
the negative feedback, and Dr. Pass himself discusses the
lower distortion (higher linearity) that results. Of course, I could be looking at the wrong circuit, in which case, I appologize.

There is, nonetheless, a small amount of negative feedback here. I wonder what is the distortion like? If I have a chance today, I'll simulate and see what THD looks like. JFETs normally have a quadratic transfer function, and one suspects 2cd harmonic distortion would result. (It is precisely this type of distortion, along with TIM distortion, that I think one can hear.)
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Old 15th February 2005, 05:20 PM   #16
beppe61 is offline beppe61  Italy
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[QUOTE]Originally posted by stevebeccue
[B]


If I am looking at the correct thing.... R25 and R28-R31 are
the negative feedback, and Dr. Pass himself discusses the
lower distortion (higher linearity) that results. Of course, I could be looking at the wrong circuit, in which case, I appologize.

Dear Steve,

I am attaching the complete article with the schematics of the Nelson Pass Bride of Zen line preamp.
As you can see is a single mosfet class A single ended no feedback line preamp.
There are no distortion spectrum figures in the article.
My be some of the good reviews are due to some 2nd harmonic distortion of such simple topology. Don't know.
But I understand this is the basic topology that Mr. Pass used in his well regarded old line preamp, the Aleph L and P.
I built one and it sounded nice.
I would like to try a better regulated power supply one day.
The quality of sound depends greatly on the quality of the power supply.

I am looking forward to hearing your opinion.

Kind regards,

beppe

P.S. File too big.
I'll post the URL.
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Old 15th February 2005, 05:25 PM   #17
beppe61 is offline beppe61  Italy
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Dear Steve,

This is the link to the article:

http://www.passdiy.com/pdf/brideofzen.pdf

Kind regards,

beppe

P.S. File too big to be attached.
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Old 15th February 2005, 07:12 PM   #18
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Quote:
Originally posted by beppe61
Dear Steve,

This is the link to the article:

http://www.passdiy.com/pdf/brideofzen.pdf

Kind regards,

beppe

P.S. File too big to be attached.

Thank you Beppe. I was indeed looking at the wrong circuit. Here, R108 is the negative feedback. Notice it is 10 times the
1/gm of the MOSFET. Still, a light feedback. If I get a chance, I'll simulate it....

I looked at www.passdiy.com/projects/pearlono3.html. I did
a quick sim of the output stage of this preamp. With 40mVpp input, and 1Vpp output, this stage had 0.62% THD, predominantly 2cd harmonic.

Of course, if people like what the hear, nothing else matters.

Best Regards,
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Old 18th February 2005, 02:30 PM   #19
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by stevebeccue



Thank you Beppe. I was indeed looking at the wrong circuit. Here, R108 is the negative feedback. Notice it is 10 times the
1/gm of the MOSFET. Still, a light feedback. If I get a chance, I'll simulate it....

I looked at www.passdiy.com/projects/pearlono3.html. I did
a quick sim of the output stage of this preamp. With 40mVpp input, and 1Vpp output, this stage had 0.62% THD, predominantly 2cd harmonic.

Of course, if people like what the hear, nothing else matters.

Best Regards,
Dear Steve,

Are you meaning the people like a certain amount of nice distortion?
This is a very interesting topic.
I could be that some 2nd HD acts as a harmonic enhancer especially with digital sounds sometime poor on harmonic content.
I remember that X10 from Musical Fidelity.

I would be very interested in knowing your opinion.

Kind regards,

beppe61
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