beppe61 said:
In a data sheet you find two sections:
- a table with numeric data
- a series of graphs
In the table section you can find
- the numeric value of the open loop gain (large signal voltage gain AOL usually expressed in V/V)
- the numeric value of the Gain Bandwidth Product (GBW usually expressed in MHz)
The open loop bandwith is = GWB/AOL (if the AOL is expressed in V/mV you have to divide the result by 1000)
In the graphs section you can find a graph titled Open Loop Frequency Response. The Open loop bandwidth is the frequency where the line of the graph starts to tilt down.
The numbers you find using the two ways I suggest have to be equal (more or less)
Regards
Marco
Dear Marco,
Thank you very much fro your kind and valubale reply.
Am I wrong or the open loop bandwidth for the majority of op-amps is very small ?
What can this imply ?
I am referring to all those discussions about TIM distortion and so on.
I am very intersted in knowing your point of view.
As you can see from my posts here I am looking for simple line preamp schematics.
I posted one.
Do you have any suggestion?
Thank you very much indeed.
Regards,
beppe61
Thank you very much fro your kind and valubale reply.
Am I wrong or the open loop bandwidth for the majority of op-amps is very small ?
What can this imply ?
I am referring to all those discussions about TIM distortion and so on.
I am very intersted in knowing your point of view.
As you can see from my posts here I am looking for simple line preamp schematics.
I posted one.
Do you have any suggestion?
Thank you very much indeed.
Regards,
beppe61
Low open loop bandwidth in reasonable (single pole compensated) op amps implies high gain at low frequencies
What this means for audio is subject to some debate here
Feedback theory and distortion measurement (IMD distortion as well as harmonic) of feedback amplifiers shows that more loop gain lowers distortion
Some people claim that high feedback amplifiers don’t sound as good as similar technology amplifiers with less loop gain, or flat loop gain over the audio frequency range
TIM, PIM distortion mechanisms that Otala discussed in JAES in the ‘70’s are often cited as technical reasons to explain the perceived differences
I don’t find PIM to be a convincing argument for preferring low gain-high bandwidth circuits – the missing link has to be demonstrating that PIM is audibly 100x more objectionable than “AM” IMD products since both are reduced by high negative feedback whereas wide bandwidth-low loop gain designs accept higher AM distortion over the whole audio band to avoid the AM to PM conversion that comes from using a integrating loop gain characteristic over the audio band
What this means for audio is subject to some debate here
Feedback theory and distortion measurement (IMD distortion as well as harmonic) of feedback amplifiers shows that more loop gain lowers distortion
Some people claim that high feedback amplifiers don’t sound as good as similar technology amplifiers with less loop gain, or flat loop gain over the audio frequency range
TIM, PIM distortion mechanisms that Otala discussed in JAES in the ‘70’s are often cited as technical reasons to explain the perceived differences
I don’t find PIM to be a convincing argument for preferring low gain-high bandwidth circuits – the missing link has to be demonstrating that PIM is audibly 100x more objectionable than “AM” IMD products since both are reduced by high negative feedback whereas wide bandwidth-low loop gain designs accept higher AM distortion over the whole audio band to avoid the AM to PM conversion that comes from using a integrating loop gain characteristic over the audio band
Dear Mr. Jcx,
Thank you for your kind and thorough reply.
But I understand that Mr. Otala became famous not on the basis of his theory but in relation with the sonic quality of his well received projetcs, or I am mistaking ?
Someone became audio classics (Harman Kardon Citation XX for instance. A every audio lover dream).
What I wanted to imply is that a low open loop bandwidth is a situation that worries me on principle.
May be I am too banal.
Kind regards,
beppe61
Thank you for your kind and thorough reply.
But I understand that Mr. Otala became famous not on the basis of his theory but in relation with the sonic quality of his well received projetcs, or I am mistaking ?
Someone became audio classics (Harman Kardon Citation XX for instance. A every audio lover dream).
What I wanted to imply is that a low open loop bandwidth is a situation that worries me on principle.
May be I am too banal.
Kind regards,
beppe61
Op amps often have open loop bandwidths near 100 Hz.
They are intended to be used closed loop, which has all
sorts of consequences, including wider bandwidth.
If you desire a "linear" amp, i.e. low distortion, you must
use negative feedback to linearize the horribly non-linear
gain devices. If not "loop" feedback, as in an opamp, it
is "local" feedback. I can't comment on whether anyone
can hear the difference.
Best Regards,
They are intended to be used closed loop, which has all
sorts of consequences, including wider bandwidth.
If you desire a "linear" amp, i.e. low distortion, you must
use negative feedback to linearize the horribly non-linear
gain devices. If not "loop" feedback, as in an opamp, it
is "local" feedback. I can't comment on whether anyone
can hear the difference.
Best Regards,
Dear Mr. Stevebeccue,
Thank you very much for your kind reply.
If understand well (please be sure that I don't want to be ironic at all, I am just trying to understand) you mean that no difference between two preamps with similar measurements?
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.
Thank you very much for your post that I think useful to the discussion.
Kind regards,
beppe61
Thank you very much for your kind reply.
If understand well (please be sure that I don't want to be ironic at all, I am just trying to understand) you mean that no difference between two preamps with similar measurements?
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.
Thank you very much for your post that I think useful to the discussion.
Kind regards,
beppe61
Mr. Otala is the base of Electrocompaniet power amplifier company.
There's one man that can comment about High OL, Low OL, TIM, PIM, AM-PM, etc impact to sound (how audibly they are). He is called John Curl (JC) here.
I'm sure he is able to comment, but wheter he is willing or not is another question, since he is a professional designer, still making commercial amps now. These things are "secrets" for designers like him.
There's one man that can comment about High OL, Low OL, TIM, PIM, AM-PM, etc impact to sound (how audibly they are). He is called John Curl (JC) here.
I'm sure he is able to comment, but wheter he is willing or not is another question, since he is a professional designer, still making commercial amps now. These things are "secrets" for designers like him.
Hi, Janneman,
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.
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.
beppe61 said:
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/showthread.php?s=&postid=489927&highlight=#post489927
beppe61 said:
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,
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.
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.
beppe61 said:
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,
stevebeccue said:
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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