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Old 18th February 2007, 10:02 AM   #1
beppe61 is offline beppe61  Italy
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Default Open loop bandwidth in op-amp.

Dear Sirs,

I understand that op-amps are all characterized by a wide closed loop bandwidth.
Speaking instead of open loop bandwidth which are the best op-amps in this regard ?
My "feeling" is that the opinion of Mr John Curl about the importance of keeping a high open loop bandwidth in audio amplification stages makes very much sense.
Is there "a op-amp champ" in this regards ?

Thank you very much indeed.
Kind regards,

beppe
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Old 18th February 2007, 12:33 PM   #2
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Generally, the open loop bandwidth is called the 'gain bandwidth product' (GBW). If the GBW is 10e6, the gain will be 1 at 10 MHZ. Taking this example further, the gain=10 at 1MHz, 100 at 100kHZ, etc. The gain will level off at some low frequency.
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Old 18th February 2007, 12:50 PM   #3
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by sawreyrw
Generally, the open loop bandwidth is called the 'gain bandwidth product' (GBW).
If the GBW is 10e6, the gain will be 1 at 10 MHZ.
Taking this example further, the gain=10 at 1MHz, 100 at 100kHZ, etc.
The gain will level off at some low frequency.
Thank you very much Sir for your very kind and welcome reply.
First of all I would like to explain better.
I believe in John Curl and in what HE says.
He says that the open loop bandwidth must be wide on principle.

If the GBW is 10e6, the gain will be 1 at 10 MHZ
OK. But applying this formula, and if I don't understand wrongly, when the gain is made equal to the open loop gain then the bandwidth could be very small.
Much smaller than the audio bandwidth actually.
Mr Curl mentioned the AD825 as an example of op-amp with a good bandwidth even if operated open loop.
Unfortunetely the AD825 comes only in the smd package.
So it is not convenient for me.
I need a op-amp in mini-dip package.
If I am not wrong I read that also the cheap NE5534 is not bad in this regard.
I know that is used also in high-end equipments.
So very bad it should not be.
So I am trying to select a op-amp with a very wide open loop bandwidth.
I will be using it as a buffer (gain=1).

Thank you very much indeed.
Kind regards,

beppe
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Old 18th February 2007, 12:56 PM   #4
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The NE5532 has a large open loop bandwith of app. 1kHz.
"Champs" like OPA2134 have a small open loop bandwith of 10Hz.
Both have a similar GPW of 10MHz resp. 8MHz.
So the GPW is misleading as it is strongly dependent on dc-gain.
Regards
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Old 18th February 2007, 01:27 PM   #5
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by juergenk

The NE5532 has a large open loop bandwith of app. 1kHz.
"Champs" like OPA2134 have a small open loop bandwith of 10Hz.
Both have a similar GPW of 10MHz resp. 8MHz.
So the GPW is misleading as it is strongly dependent on dc-gain.
Regards
Thank you very much indeed Mr Juergenk.
The NE5532 has a large open loop bandwith of app. 1kHz
So these op-amps would not be John Curl approved

If this principle is valid my question is now: do op-amps exist that have a open loop bandwith wide as the whole audio bandwidth ?
If not I would not feel comfortable about using any op-amp in the signal path.

Thank you very much again.
Kind regards,

beppe

P.S. By the way, what do you use as line preamp in your system ?


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Old 18th February 2007, 01:39 PM   #6
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hi,
Quote:
P.S. By the way, what do you use as line preamp in your system ?
currently I´m using a passive preamp eq. a 10k pot.
Quote:
If this principle is valid my question is now: do op-amps exist that have a open loop bandwith wide as the whole audio bandwidth ?
this is unusual with audio-opamps. The open loop bandwith is always smaller than audio-bandwith.
Maybe video-opamps have wider open loop bandwiths.
I´ve good experiance with OPA2134 and it has a poor open loop bandwith.
So maybe this specific criteria should not be overestimated.
Regards
Jürgen
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Old 18th February 2007, 02:00 PM   #7
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Beppe - I have noticed you have asked some interesting questions in this forum before, and I think you're on the right track for making good audio. In answer to your question about opamps, you might try just looking (Googling I think might be the term here) at data sheets for yourself just to get a scope of the field of interest. There doesn't appear to be that many as opposed to the regular type of small BW units so they might stand out. Elantec and T.I. make some that look wide but I forget which ones right off hand. Models and numbers change pretty fast sometimes so you'd just have to look to see what's current. Video opamps are others of possible interest. Don't be afraid to venture out on your own there, it's what DIY is all about. I've had very good luck with such an approach.
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Old 18th February 2007, 02:20 PM   #8
lineup is offline lineup  Sweden
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Default NE5534 and dual NE5533

Quote:
Originally posted by beppe61


If I am not wrong I read that also the cheap NE5534 is not bad in this regard.
I know that is used also in high-end equipments.
So very bad it should not be.
Quote:
Originally posted by juergenk

The NE5532 has a large open loop bandwith of app. 1kHz.

"Champs" like OPA2134 have a small open loop bandwith of 10Hz.
Both have a similar GPW of 10MHz resp. 8MHz.
So the GPW is misleading as it is strongly dependent on dc-gain.
Regards

As usual
people judge NE5534 by using performance/data of NE5532.

They do not know that NE5534 ... IS NOT a single version of NE5532
They are 2 different op-amps
We who knows this fact, make a difference.
NE5534 is good!

A lot of people judge NE5534 performance
because they have used or tested NE5532 .....
This is unfair!

---------------------------------

OPA2134 is a dual version of OPA134.


But NE5532 is NOT a dual version of NE5534.
The dual version is called NE5533

This is from Philips datasheet:
Quote:
Philips Semiconductors Linear Products Product specification
NE5533/5533A/ ... NE/SA/SE5534/5534A

Dual and single low noise op amp
August 31, 1994 114 853-0222 13721
DESCRIPTION

The 5533/5534 are dual and single high-performance low noise
operational amplifiers.

.

Regards
lineup
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Old 18th February 2007, 02:32 PM   #9
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Quote:
As usual people judge NE5534 by using performance of NE5532
seems to be a misunderstanding
I didn´t mention NE5534 or was referring to it
Quote:
They do not know that NE5534 ... IS NOT a single version of NE5532
I´m aware of the difference. My experiences with NE5534 are bad. I don´t like the sound. Maybe at higher gains they should be considered. But compensated for unity gain, there is nothing special about them.
Regards
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Old 18th February 2007, 02:51 PM   #10
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It might be more beneficial to Beppe to keep this thread concerned with wide open loop BW units as per his request, as I'm sure there are other threads he could reference if needed for other opamps.

Beppe, I also recall seeing something about an opamp that is a "diamond" buffer, or some such name. You might try a search on that.
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