Chucko said:
I have to disagree. Practically ALL linear amplifier data sheets show a gain/freq response showing the ol bandwidth. Furthermore, most also show curves of OL gain versus temp, OL versus supply voltage etc.
Please note also that manufacturers don't measure every and all specs in each chip. Some specs are measured in each chip at manufacturing, but some specs are guaranteed by design and therefore only spot checked, if at all. Most of the times the data sheet specifies what is individually checked and what is guaranteed by design.
Data sheets hold a wealth of infornmation and also let you get an idea of the tradeoffs in design if you compare data sheets from different devices. Very often, people on this forum ask questions that could easily be found in a data sheet. While a full-length data sheet (and they seem to become longer and longer all the time) can be intimidating, picking just those parts important for your application can be very enlightening.
Jan Didden
janneman has already commented this but the remark is rather interesting. My question is: Chucko, can you point out _any_ chipmaker that supports your theory?Chucko said:
The datasheet for TPA6120 is the only one at the moment (that I know about) which has some important parameters msssing and the is the input bias current which in this case is more important than usual since they are so big (12 uA).
peranders said:
TPA6120 is only a renamed selection (with relaxed requirements
) of an ADSL driver THS6012, and there is a proper datasheet on that chip:http://focus.ti.com/lit/ds/symlink/ths6012.pdf
Cheers
Alex
I know that but it took a while to get that information when I made my TPA6120 amp. It's a mystery why they have omitted some very important data. 
I don't know of a single IC op amp that has a guaranteed specification for open loop bandwidth. Does anyone here know of even one? Many have minimum guarantees for DC open loop gain, gain-bandwidth product, and slew rate. I have even seen a few with noise voltage and current guarantees.
Do not mistake "typical" graphs on a data sheet as evidence of a manufacturer's commitment to a particular performance level. More often than not, these graphs are made during the initial production runs and never updated.
Do not mistake "typical" graphs on a data sheet as evidence of a manufacturer's commitment to a particular performance level. More often than not, these graphs are made during the initial production runs and never updated.
Hi beppe,
But always there is a graph called "open loop frequency response", "open loop gain/phase vs frequency" or something like that.
Have a look at the gain. It is constant from dc to a certain frequency and then falling of with 6dB/octave.
This certain frequency gives you the open loop bandwith.
Because of limited resolution, the exact point, when gain is 3dB below dc-gain, could not always be extracted.
But for comparison purposes the exact value is not important.
Sometimes the graph does not include dc. But maybe dc-gain is specified elsewhere. So its up to you guessing the open loop bandwith.
Regards
Jürgen
as already stated, typically there are no numbers for open loop bandwith in opamp datasheets.beppe61 said:
But always there is a graph called "open loop frequency response", "open loop gain/phase vs frequency" or something like that.
Have a look at the gain. It is constant from dc to a certain frequency and then falling of with 6dB/octave.
This certain frequency gives you the open loop bandwith.
Because of limited resolution, the exact point, when gain is 3dB below dc-gain, could not always be extracted.
But for comparison purposes the exact value is not important.
Sometimes the graph does not include dc. But maybe dc-gain is specified elsewhere. So its up to you guessing the open loop bandwith.
Regards
Jürgen
juergenk said:
Thank you very much again Mr Jurgen !
By the way searching for info about good sounding op-amps I found some info about a "unfortunately" obsolete par, the BB OPA603.
In the first page of the data sheet there is the schematic of the op-amp.
Transistors count stops at 8
This is very uncommon, as figures of even 40 are not unusual.
My trivial reasoning is: less gain stages > less open loop gain > more open loop bandwidth.
On this basis I think it is a pity that this part is now obsolete also because I read positive comments on its sound.
I really do not know that there is a new op-amp from TI that has the same simple and elegant schematic.
I would be extremely interested to know this if anyone has information.
Thank you very much again.
Kind regards,
beppe
pinkmouse said:
Beppe, the example chip schematics shown in datasheets are very much simplified.
Thank you very much indeed Sir,
Actually it seemed extremely strange to me.
I think I will end with a diamond buffer.
For my needs ( a line stage to drive a tough 5K load with the signal sourced by a cd player) it seems indeed the simplest and most promising solution.
Thanks again and kind regards,
beppe
beppe61 said:
beppe61,
this is a good choice!
Here at Lineup Audio Lab we use nothing but discretes = transistors.
And very often Diamond Buffer will give the perfect sound.
I attach one of our models, for Pre-Amplifier Diamonds
The Secrete trick here (please do not tell anybody!!! ) in this circuit .. and what is my Own Unique idea
are those 2 capacitors ... something like 1.0 - 4.7 Film Cap is enough!
(Depending on load and output level)
They will lower distortion as much as 10-20 dB at higher current outputs!
I am sure you can figure out suitable resistor valuesthat will fit your needs and your power supply voltages.
Regards
lineup
Attachments
Chucko said:
Yes, this is a good old dual bootstrapping.
AKSA and also some other good designers
like amplifierguru Greg SKA Killer Ball
.. I can not recall Nelson Pass does this, but I am sure he does!
and of course Lineup Audio Lab
uses this great technique.
It keep amplifier simple and easy, while improving performance considerably.
you only have to do a Simulation run, to verify this.
The diodes are the usual 1N4148 diodes
which will give like 0.40-0.50V across output Transistor Emitter resistors.
Those resistors are selected to a value
to get your desired Idle current in the Push-Pull stage.
beppe61 said:
We are moving to a new and better website.
I have only just begin to set up pages at new Lineup Audio site.
I don't think I can explain my attached pre-diamond circuit any more.
Is there anything special you wonder, beppe?
Regards
lineup
if you want to know the open loop bandwidth of an op amp, look for a graph that looks like the one below. the olb is usually not expressed numerically in many data sheets, but in the form of a similar graph, expressing gain and sometimes phase as a function of frequency. btw, you want to pay attention and make sure the phase never gets to 180 degrees before the amp gets to unity gain, unless there's a way to compensate the amp.
in the graph below, the olb is about 30hz, and the gbw is 3Mhz.
in the graph below, the olb is about 30hz, and the gbw is 3Mhz.
Attachments
unclejed613 said:
Thanks a lot !
Clearly op-amps' open loop bandwidth is not considered an important figure for design with op-amps.
As it seems to be open loop gain.
By the way I have not seen figures under 60 dB for the OLG, with a more common value of 100 dB.
Thanks again and kind regards,
beppe
I would like to make a few points to clarify my position:
Otala did not originate the 20KHz open loop bandwidth criterion.
Actually it was in a graduate thesis by Daughority(sp) and Greiner(his thesis advisor), published in partial form in the 'IEEE Transactions in Audio ... ' in 1966. Dr. Greiner had already published a textbook at this time. 'Semiconductor Devices and Applications' McGraw Hill, Electrical and Electronic Engineering Series, 1961 and was a professor at the time.
I point out, that he was not a crazy amateur, but a full professor, yet he published the 20KHz criteria, based on the mathematics, rather than some sort of guess.
In the late '60's, Otala, independently found by LISTENING that a 20KHz open loop bandwidth was better, and he footnoted Greiner's paper in his first offering in the IEEE in 1970. I read both of these papers in real time, not 20 years later, and I was at first confused and facinated.
Before IC op amps were made practical, we did not use op amps for audio. We made AC coupled stages of gain, that automatically had fairly high open loop bandwidth. Only analog computers and DC servos used op amp technology which was next to impossible with tubes and barely possible with solid state at the time. It was expensive too.
Linear IC's changed all that, but that does NOT mean that they were designed for audio applications. NO! Just military-industrial servo and op amp applications.
In fact, in 1974, I asked Bob Widlar, the designer of the ua702, 709, LM301 (741 is derived from the 301) etc, etc, and the greatest designer of the IC op amp of all time. He said that IC's up to that time were really not made or optimized for audio, so we should build our own circuits.
At this time, 1/3 of a century ago, both Walt Jung and I were looking at what Otala had stated in his paper and were attempting to come to terms with it. We KNEW that the standard IC's would measure well, but sound disappointing, so what were we missing?
Well, in 1973, I designed line stage of the JC-2 preamp, to test Otala's theory. IT WORKED! For some reason, a 20KHz open loop bandwidth DID sound better, all else being equal, which meant more linear circuitry, open loop, since I didn't have much feedback to reduce (hide) the distortion.
Independently, Walt Jung found that he could change the open loop bandwidth of many op amps by using the offset pins to change the circuit, and he heard significant improvements also.
TIM or SID, which are the same thing, are not directly related to open loop bandwidth in most designs, and that is all that we could measure that was different than our already precision IM or THD measurements. However, Otala persisted in recommending 20KHz open loop bandwidth, but realized that his original hypothesis regarding TIM being the only factor was incomplete, and other distortions must be present that are audible to the trained ear. We still think this today, but we don't have a standardized test to measure PIM or any other distortion that might be important.
In any case, the 5534 was introduced in 1976, and we all tried it. It was the first real op amp that was designed specifically for audio. It works pretty well, but you will find that we can find better sounding op amps, but they may be more expensive to buy. We have also found, that all else be equal, that the higher open loop bandwidth op amps tend to sound better, so video op amps are sometimes found to be a better choice.
Discrete designs can be even better than any know IC design, but even more expensive.
What concerns me on this thread is the amount of 'guessing' that many people do about why circuits are designed the way they are.
Otala did not originate the 20KHz open loop bandwidth criterion.
Actually it was in a graduate thesis by Daughority(sp) and Greiner(his thesis advisor), published in partial form in the 'IEEE Transactions in Audio ... ' in 1966. Dr. Greiner had already published a textbook at this time. 'Semiconductor Devices and Applications' McGraw Hill, Electrical and Electronic Engineering Series, 1961 and was a professor at the time.
I point out, that he was not a crazy amateur, but a full professor, yet he published the 20KHz criteria, based on the mathematics, rather than some sort of guess.
In the late '60's, Otala, independently found by LISTENING that a 20KHz open loop bandwidth was better, and he footnoted Greiner's paper in his first offering in the IEEE in 1970. I read both of these papers in real time, not 20 years later, and I was at first confused and facinated.
Before IC op amps were made practical, we did not use op amps for audio. We made AC coupled stages of gain, that automatically had fairly high open loop bandwidth. Only analog computers and DC servos used op amp technology which was next to impossible with tubes and barely possible with solid state at the time. It was expensive too.
Linear IC's changed all that, but that does NOT mean that they were designed for audio applications. NO! Just military-industrial servo and op amp applications.
In fact, in 1974, I asked Bob Widlar, the designer of the ua702, 709, LM301 (741 is derived from the 301) etc, etc, and the greatest designer of the IC op amp of all time. He said that IC's up to that time were really not made or optimized for audio, so we should build our own circuits.
At this time, 1/3 of a century ago, both Walt Jung and I were looking at what Otala had stated in his paper and were attempting to come to terms with it. We KNEW that the standard IC's would measure well, but sound disappointing, so what were we missing?
Well, in 1973, I designed line stage of the JC-2 preamp, to test Otala's theory. IT WORKED! For some reason, a 20KHz open loop bandwidth DID sound better, all else being equal, which meant more linear circuitry, open loop, since I didn't have much feedback to reduce (hide) the distortion.
Independently, Walt Jung found that he could change the open loop bandwidth of many op amps by using the offset pins to change the circuit, and he heard significant improvements also.
TIM or SID, which are the same thing, are not directly related to open loop bandwidth in most designs, and that is all that we could measure that was different than our already precision IM or THD measurements. However, Otala persisted in recommending 20KHz open loop bandwidth, but realized that his original hypothesis regarding TIM being the only factor was incomplete, and other distortions must be present that are audible to the trained ear. We still think this today, but we don't have a standardized test to measure PIM or any other distortion that might be important.
In any case, the 5534 was introduced in 1976, and we all tried it. It was the first real op amp that was designed specifically for audio. It works pretty well, but you will find that we can find better sounding op amps, but they may be more expensive to buy. We have also found, that all else be equal, that the higher open loop bandwidth op amps tend to sound better, so video op amps are sometimes found to be a better choice.
Discrete designs can be even better than any know IC design, but even more expensive.
What concerns me on this thread is the amount of 'guessing' that many people do about why circuits are designed the way they are.
Thanks John!
A most good comment and valuable post.
As often by you.
Regards
from
lineup - had first discussions with John Curl at audioasylum, in 2001 I think it was
I still remember Mr Curl once reply to me in a topic:
'Current is Good'
Meaning that have a bit higher current in input transistors can be a benefit.
Today, a bit 'audio wiser' I know how true his statement is.
... current is good ... a 3 word line that will live in my memory .. for ever
***************************************
I found it!
Was in March 2002:
posted by john curl on March 15, 2002 at 12:09:21:
Most of my discrete designs to replace op amps usually between 50-100ma. More current is good!
***************************************
So the correct quote is a 4 words line:
'More current is good!'
Remember this people
... there is a reason for Class A is good .. and difference is C-U-R-R-E-N-T
A most good comment and valuable post.
As often by you.
Regards
from
lineup - had first discussions with John Curl at audioasylum, in 2001 I think it was
I still remember Mr Curl once reply to me in a topic:
'Current is Good'
Meaning that have a bit higher current in input transistors can be a benefit.
Today, a bit 'audio wiser' I know how true his statement is.
... current is good ... a 3 word line that will live in my memory .. for ever
***************************************
I found it!
Was in March 2002:
posted by john curl on March 15, 2002 at 12:09:21:
Most of my discrete designs to replace op amps usually between 50-100ma. More current is good!
***************************************
So the correct quote is a 4 words line:
'More current is good!'
Remember this people
... there is a reason for Class A is good .. and difference is C-U-R-R-E-N-T
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