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Old 16th May 2007, 10:04 AM   #1
tawn10 is offline tawn10  United Kingdom
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Default OP AMP EXPERIENCES and HOW TO

ok so ive read and looked and scuffed and scraped the forums for various information on 'HOW TO' with opamps (for the uneducated!) and ive learned a thing or two, but I know that there are people out there who can shed more light on these little buggers for us so I want to start a thread that people can write some up to date experiences in for descusion,
I am going to start with an experience !! and a question ??

I have implemented the new LM4562 into my ARCAM DV89 which used to have 2x OPA2134, to be honest I think they are far better than any I have heard before, tonally a lot more balanced its like someone has gone accross the sound stage with an iron! I found that the 2134 in this app was fatiguing in the upper mid, sometimes drowned out and sometimes aggressive in a small bandwith. iv'e also used the ad8620 and found that the low end was very fake sounding a bit cloaked like all basslines sounded the same, also I have fiddled with the ne5532's and found them to be very honest indeed but a little lathargic.

and so bringing me to....
what on earth is it that influences the sound and why and how in different curcumstances, ive read that I/V configuration requires a fast opamp, and that the datasheet only reveals data for a specific test case which more often is far from the actual reality and also that what one considers to be necessary for accuracy is only applying a perceived fix when is actually just the brain telling you i like it cos i did it!
I think what we need is like all the information whacked onto a table or something like that containing the underpinning variables like configurations loads capacitance and other variables
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Old 16th May 2007, 10:29 AM   #2
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Quote:
what on earth is it that influences the sound
And what is the meaning of life


Wouldn't we all want to know? But why start with such a complicated device? Why not first ask how capacitors, resistors and wire influence the sound?
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Old 16th May 2007, 11:58 AM   #3
tawn10 is offline tawn10  United Kingdom
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Quote:
Originally posted by analog_sa


And what is the meaning of life

Would'nt you like to know!
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Old 16th May 2007, 12:09 PM   #4
tawn10 is offline tawn10  United Kingdom
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Quote:
Originally posted by analog_sa


But why start with such a complicated device? Why not first ask how capacitors, resistors and wire influence the sound?
exactomondo!
I do beleive that consideration runs both ways so I mean in any 'system' resistors and capacitors and wire affect the functionality of any said connected device and here I wish to discuss the outline, exactly what does and crucially under what circumstances (system) they affect (ie does this affect any system in a positive manner)
its really about gaining prospective.
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Old 16th May 2007, 12:32 PM   #5
tawn10 is offline tawn10  United Kingdom
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Default opamp impedance input output

Quote:
Originally posted by tawn10


exactomondo!
I do beleive that consideration runs both ways so I mean in any 'system' resistors and capacitors and wire affect the functionality of any said connected device and here I wish to discuss the outline, exactly what does and crucially under what circumstances (system) they affect (ie does this affect any system in a positive manner)
its really about gaining prospective.
I quote myself and start with a basic contribution to the thread please if you contribute then place a subject to make searching easier for those that are hunting

now OP AMP out impedance, in general driving a lower impedance affects the linearity of 'a' device a 600ohm load is usually the cutting point for an average opamp, (the standard set by old equipment using very low <by todays standard> impedance transformers) any lower than this and the opamp cant handle the AMPAGE to drive the load. most new kit has input impedance around 1-10k sometimes higher for solid state gear but watch it because the gain needed to drive the higher impedance is graeter, this can also contribute to distortion as some devices don't like driving high gain (like my bicycle wont go on the motorway) and some devices will drive low impedance loads (my bike does however go better than my car down a towpath)

Quote:

most new kit has input impedance around 1-10k
you will see that between stages in an audio out or input are often 2k2 resistors or 1k or something similar
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Old 16th May 2007, 02:00 PM   #6
KP11520 is offline KP11520  United States
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Hey Tawn 10,

I am sure this will start an uproar, but this needs to be addressed.

I feel for ya! I am new here and to electronics DIY. Every time I start a thread, I Post what I am looking to do (end result). Obviously there are many paths sometimes and sometimes just one path. What I get here and there is a "one liner" of about 5% of the information I need. And when I ask for more information and to elaborate..... Nothing. What is the purpose of the post, to make me feel stupid? It certainly didn't accomplish anything else. I don't understand what is really going on. This is supposed to be a DIY site that people help each other. Obviously the more experienced will do more of the helping but that is how it works and some day the beginner will be the teacher. One guy at least tried to nudge me along to the next step in the thought process about what I need to learn and I think that is acceptable if they don't just want to outright give exactly what you need.

I can build an entire house (except the foundation and don't ever want to) and if someone (a beginner) asked How can I put a big picture window in where I have a very small one? I wouldnt flip off, "well determine the R/O needed and get the materials required. Send pictures of the finished window." If someone cuts an area big enough for a huge window on a supporting wall without supporting everyting until the Header can be installed, it can do a lot of structural damage and sometimes bring down the roof and/or floor above. This can get expensive and do irrepairable damage and give someone a bad taste on DIY.

How do we get this back to what it is supposed to be? I am sure the Pros and true EE types get bored with us new guys but something has to give. It's like politics, Feed the rich at the expense of everyone else and bring down the middle class to low class. Now there only two classes and revolution is soon to follow. Hopefully there won't be just two types here, the knowledgeable/experienced and the beginners (me) and rarely will we be at the same party.

I hope everyone can understand this point of view. I am just explaining what is like down here at the bottom and I am sure I am not alone! It's just so dark I can't see anyone else! LOL

Regards//Keith
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Old 16th May 2007, 02:00 PM   #7
johnrtd is offline johnrtd  Belgium
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Default op amp audio quality

We should diversify between the advances of new circuitry inside op amps and the interaction with the outside world.
The 4562 indeed is a very nice one. The reason WHY is not to be found in the spec file, but you may find a kind of answer when looking at the article published in the EDN magazine:
http://www.hawkaudio.nl/news.htm. Just download the article (and my comments) there. It's remarkable that major manufacturers now are actually "listening"!
The matter of in- and output impedances is an entirely different thing. The output impedance is quite low because of the feed back. Without that feed back it would be quite high. Looking at the "open loop response" you'll see the amplification dropping down with some 6 dB/oct starting at a very low frequency. The newest op amp types now start falling down from around 1 kHz and that's a real improvement.
Now if you load an op amp with 600 Ohm the feedback factor will go down with frequency. This means that distortion goes up! And the output impedance goes up as well.
Considering the small transistor dies in the totem pole at the output of the op amp it cannot dissipate very much power, happily there's a current protection in it.
So whenever using an op amp consider to use a circuit thereafter with a relatively high input impedance, in that way avoiding the distortion going up.
This phenomen is one of the reasons tube preamps, when connected to a common CD-player or tuner, sound better then SS ones. The input impedance is high!
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Old 16th May 2007, 04:01 PM   #8
tawn10 is offline tawn10  United Kingdom
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Default Re: op amp audio quality

Quote:
Originally posted by johnrtd
We should diversify between the advances of new circuitry inside op amps and the interaction with the outside world.
The 4562 indeed is a very nice one. The reason WHY is not to be found in the spec file, but you may find a kind of answer when looking at the article published in the EDN magazine:
http://www.hawkaudio.nl/news.htm. Just download the article (and my comments) there. It's remarkable that major manufacturers now are actually "listening"!
The matter of in- and output impedances is an entirely different thing. The output impedance is quite low because of the feed back. Without that feed back it would be quite high. Looking at the "open loop response" you'll see the amplification dropping down with some 6 dB/oct starting at a very low frequency. The newest op amp types now start falling down from around 1 kHz and that's a real improvement.
Now if you load an op amp with 600 Ohm the feedback factor will go down with frequency. This means that distortion goes up! And the output impedance goes up as well.
Considering the small transistor dies in the totem pole at the output of the op amp it cannot dissipate very much power, happily there's a current protection in it.
So whenever using an op amp consider to use a circuit thereafter with a relatively high input impedance, in that way avoiding the distortion going up.
This phenomen is one of the reasons tube preamps, when connected to a common CD-player or tuner, sound better then SS ones. The input impedance is high!
so is it that as the feedback factor lowers (as with open loop) the circuit (source) impedance is seen by the load? and the reason that the feedback factor lowers is that the gain required to drive the 600ohm load is less?
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Old 16th May 2007, 04:36 PM   #9
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Default Re: Re: op amp audio quality

Quote:
Originally posted by tawn10


so is it that as the feedback factor lowers (as with open loop) the circuit (source) impedance is seen by the load? and the reason that the feedback factor lowers is that the gain required to drive the 600ohm load is less?
The output impedance of the opamp is always 'seen' by the load. The feedback factor lowers the open loop output impedance with the same factor as it reduces the ol gain to the closed loop gain.
The feedback factor is the difference between ol gain and cl gain. As ol gain fall with frequency, the feedback factor falls with frequency, so the positive effects of feedback, like lowering the output impedance and distortion, also fall with gain.

The reason these opamps are designed with the particular fall of of ol gain with frequency is the phaseshift by internal caps. If the phase shift reaches 180 degrees, then the negative feedback turns into positive feedback and the opamp will oscillate. So, they roll of the gain such that before the 180 phaseshift frequency, the gain is reduced below 1. An opamp with gain below one will not oscillate at that frequency.

Jan Didden
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Old 16th May 2007, 05:52 PM   #10
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Default Re: OP AMP EXPERIENCES and HOW TO

Quote:
Originally posted by tawn10
what on earth is it that influences the sound and why and how in different curcumstances

I think what we need is like all the information whacked onto a table or something like that containing the underpinning variables like configurations loads capacitance and other variables
There are so many possible combinations of contributing factors that interact with the specific application (I/V converter, noninverting line stage, multiple-feedback active filter) that a comprehensive list correlating contributing factors with end results is not really available.

The two weak points in op amps that I believe can cause major interaction with an application are the thermal coupling of input and output stages and the imperfect electrical isolation of the input stage transistor pair from the chip substrate, these are well-known issues that Walt Jung has written about and proposed solutions for, but these solutions require additional components.
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