op-amps with wide open-loop bandwidth ?

: > : ** The OP is of the view - first brought to international notoriety by : > : Matti Otala in 1980 IIRC - that an audio amplifier needs to have an : > open : > : loop bandwidth that includes the audio band : > : : > : It was bunkum. : > : : > : Many have since proved it was bunkum. : > : : > : Matti was a troll. : > : : : > Awfully presumptuous of you Phil. : : : ** Not a single presumption was involved. : : : > I am of no particular : > view at all other than collecting empirical data on my own and : > drawing my own conclusions. : : : ** Yawn ....... : : " It is a bad scientist who experiments on himself ...." : : : > It has worked well for me over the years to do so. : : : ** Yawn ....... : : Exactly what every fake, kook and charlatan says. : : : > Perhaps this is why I am able to : > design solid-state guitar amps that are indiscernable from : > tube amps. : : : ** Yawn ........ : : Turned any lead into gold lately ?? : : : : : ........ Phil

Cleaned any pots with WD40 lately ?

: : : :

: > Thanks for an answer without a healthy dose : > of pseudo-intellectual one-upmanship thrown : > in for good measure :-) : : : ** The only op-amps that meet your superfluous criterion are intended for : Radio Frequency ( RF) work and are quite ill-suited for general audio : frequency applications. : : However, a guitar amplifier is not a normal piece of audio gear. : : It is a signal modification & " sound " creation device.

Quite true and why some people attempt to understand the science of the "signal modification"

Ok Phil, listen and learn. Before one can genuinely hear the sonic impact that various components such as coupling and carbon comps and what have you..., one must start with a good clean colorization minimimised baseline.

Here's something you can do that might just git yer head outa yer arse for for a brief and sobering moment..

Build yerself a super clean amp with your so-called "ill-suited for audio video op-amps". Direct couple stages wherever possible by balancing input currents or trimming offsets or employing output bypassed DC servo's. Then couple at least one stage with a relatively large oil/paper cap bypassed with a smaller value oil/paper cap. Or if you want silkier highs bypass it with a styrene.

Now, when you're done doing that, yank the video IC's, pop in some 741's and couple all of the stages with mylar caps and proclaim to the world "this is the amp for me"

Oh, and don't ferget ta spray da pot's with WD40

Dave Moore (Eternity's greatest and humblest guitar amp designer)

: : : :

"Dave Moore"

** The "science" involved is however NOT electroncis.

Rather, it IS human psychology.

** Not from the likes of you.

I used to design & build SS & tube guitar amps for a living, back in the '70s.

They hold no magic for me.

But old Fenders DO have a pleasing tone.

...... Phil

: > Well John, that's all fine and well in the world of pseudo-intellectual : > EE-expertism, however in the real world of empirical eveidence, : > it don't pan out. There are op-amps with specs far exceeding your : > limited definition of what's necessary to 'dissappear the source of : > sound coloration' that sound entirely different in the same circuit : > and exhibit very different qualities of dynamics in the feel of a guitar : > when you're playing it. : : Then I suspect that the circuit is not well designed (is making : demands on the opamp that do not allow the assumption of excess gain : to apply). By the way, sorry if I underestimated your experience. : The question just sounded like one from a newbie. I was sincerely : trying to be helpful.

My apologies. I was extremely hurried at the time and probably due to the influence of a flurry of ankle-gnawing by another poster, your post seemed to take on a negative tone. It occured to me later that perhaps you didn't have a specific answer to my trying to find out more about the intended application so that you might be helpful in another way.

: : > I started out designing guitar amps over 20 years ago and quickly : > learned that the op-amps of the era couldn't compare with my discrete : > designs. I only recently started to look at op-amps again as a viable : > possibility due to recent advances in op-amp design. : : Like any component, there is some art in getting the expected : performance form them. No audio circuit, especially one in an : instrument amplifier should ever let the opamp output saturate, even : under severe signal overload conditions. That is when you hear the : opamp, as it struggles to recover closed loop operation and can do all : sorts of strange and prolonged things. The feedback should keep the : loop closed for any signal it can reasonable be expected that someone : will put through the amp.

I have no way to measure it but I suspect that a design that is close to instability may also color the sound some even if it is : : > I didn't ask for a lecture on tone. I asked for knowledge of any : > op-amps that have a flat open-loop response beyond 20KHz : > instead of the typical corner of 100Hz to 19Khz. : > The open-loop gain in V/mv I don't give a rats ass about other : > than that it's relatively flat to 20KHz or higher. : : That is becoming clear. : : > I realize that I didn't do a very good job of communicating : > my quest, but cut me some slack here. Ever since hurricane : > Katrina waxed my estate, I've been averaging 5-7 hours sleep : > per night sometimes even skipping sleep altogether in an effort to : > complete a very important project for a rather important person : > on schedule in spite of the hurricane induced setback. : : You have my sympathy. : : > I can't tell you about the circuit it's going to go in because it's : > not for any circuit in particular but rather for sonic evaluation : > for exacly the reason that in the work I do, sonic evaluation is : > the only thing that means diddly-poop. : : I'm interested. What are the test conditions for this test? Will the : opamp output saturate during this test?

I've only recently started thinking about possibly using op-amps and I'll have to confess that most of my observations about that variations in 'op-amp tone' haven't come about in the most scientific manner. Mostly they have come about in the process of repairing or upgrading opamp based guitar amps for some of the musicians that I deal with fom time to time. However, that's exactly why I'm trying to collect op-amps with varied specifications, so that I can make some observations under more controlled and *fair* circumstances.

In the past I've plunked a variety of op-amps into pre-designed circuits and though analysis of those designs didn't reveal anything to me that could account for the obvious difference in tone (other than some near-instability issues), I hope do a better study and compare the op-amps in circuits that are more individually optimized. Perhaps Kevin is right and it's all been done before, but regardless, I like to prove things for myself.

: : > I've heard the theories : > of the "experts" on the subject of tone fall by the wayside over : > the years and watched rather bemusedly as they scramble to : > come up with new theories as to why the old theories didn't : > account for fact that people can hear the difference in circuits : > that so-called experts would logically conclude : > (according to the theory du juor) should be sonically : > indiscernable. : : There are lots of poorly designed audio (especially instrument) : amplifiers out there. The good ones sounds impressively similar.

I'll buy that. Most of the op-amp based amps that I've upgraded did tend to sound like they were headed in a similar direction.

: : > IOW, the reason I want such an op-amp is to collect empircal : > data rather than rely on the opinion of self-proclaimed experts : > such as yourself that don't know near as much as they think : > they do. : : Now, you are the one presuming. If you don't like the advice, you are : guaranteed double the purchase price refunded.

Yes, my humblest apologies.

: > Now, if you want to rail on and hurl insults because I : > misinterpreted your question and gave a seemingly non-sequitur : > answer, do carry on. : : I guessed wrong on your skill level and made what I hoped was a useful : suggestion.

Yeah, I knida figgered out later on that that may have been the case and that my perceptions may have been a bit off on that one. I plead sleep-deprivation. :-)

: People get lots of helpful hand holding on the basics : group. The designers are more critical of each other, here, where : they are more of a club.

Yeah, I already thought of that also. It occurred to me that perhaps since the newsgroup has grown so immensely since 'the old days'. you're just getting a bit annoyed at the changes. I do realize that there's a newsgroup for component type inquiries, but SED seems like the more likely place to get a better result for my trivial request.

: : Get over it, please.

I'm over it, and thanks for the advice and any opinions you may have about how to do a *fair* op-amp evaluation.

: > However, a guitar amplifier is not a normal piece of audio gear. : >

: > It is a signal modification & " sound " creation device. : >

: >

: > Quite true and why some people attempt to understand : > the science of the "signal modification" : : : ** The "science" involved is however NOT electroncis. : : Rather, it IS human psychology.

Yes, I'm fast learning that in your case, it's probably

*all* psychology. Perhaps it's a side effect of WD40 ?

: > Ok Phil, listen and learn....... : : : ** Not from the likes of you. : : I used to design & build SS & tube guitar amps for a living, back in the : '70s. : : They hold no magic for me.

So, in essence you designed crap "SS & tube guitar amps" completely devoid of magic back in the 70's....

Listen and learn again Phil. Everything has magic. Yourself being the one probable exception.

: : But old Fenders DO have a pleasing tone. : : : : : ...... Phil

"Dave Less"

** YOU are fast at learning NOTHING Dave. ** Not from the likes of you.

I used to design & build SS & tube guitar amps for a living, back in the '70s.

They hold no magic for me.

** I got news for you - Dave Less.

There is no Santa Claus.

There is no Tooth Fairy.

There is no Magic.

And, as a sobering thought, we are all there is in the universe.

How disappointing.

........ Phil

Dave Moore wrote: (snip)

You are missing my point.

I'll start over.

Tube amplifiers tend to be made with as few tubes as possible, for obvious reasons of cost, size and complexity. This usually means that each stage up to the final output is a single tube, with minimal feedback around it. When such stages are over driven, as the output voltage approaches the highest and lowest possible values, the stage gain drops off smoothly and cleanly and the output slides in to a nearly steady value, and waits for the signal to reverse directions. And then the gain rises smoothly and the voltage takes off cleanly in the other direction. Saturation of the output is a graceful and simple process, as is recovery from saturation.

Opamps are completely different. They are complicated systems of up to dozens of devices that all work together as long as inputs stay inside the input common mode range, and the output is not saturated fully positive or negative, or asked to change voltage faster than it is able (exceed the slew rate limit). Under these conditions, an opamp is a programmable device, It performs an almost unlimited number of functions that are very strictly controlled by the input and feedback networks connected around them.

However, if the input common mode specs are violated, or the output is allowed to saturate (because the input and feedback networks in conjunction with the input signal asked it to), or to a lesser extent, if the output is asked to change voltage faster than it is able, the internal circuits go to hell. And when the input signal and external network, once again, puts the inputs back inside the common mode range, or asks the output to come out of saturation, or slows the request for output voltage change to within the slew rate limit, There is a period of time (sometimes surprisingly long) that the opamp struggles to regain normal operation, and can do all kinds of unpleasantly sounding things.

So, while it is perfectly good to have single active device stages be slapped with overdrive, and use them to obtain a pleasing sound coloration, this is not the way to do such coloration with opamps. All the "effects" have to be built into the input and feedback networks, so that the opamp is externally programmed to produce the colored overdrive sound without it actually ever being over driven, itself. If this is done correctly, there is a range of effects limited only by your imagination and time to experiment, that, if the opamp stays in its normal operating conditions every microsecond, it will have almost nothing to do with the sound quality. It will just be following its program. If you change opamps, the limits that it can tolerate, and still be an opamp every microsecond, change, and allow you different freedom as far as the program (external network) goes but it still won't produce ant "sound" that is separate from the program.

So I don't approach a sound effect task by surveying opamps for their sound, I design the input and feedback networks that produce the programming I want to hear, and then figure out what opamp specs are needed to be able to execute that program. Or I build the networks and check with test equipment that the opamp is able to keep up with it.

This is how engineers "see" opamps in a circuit, and why you are receiving so much static from them, here, when you say you want to listen to some opamps to hear what they sound like. An opamp you can hear is an opamp that is not being an opamp all the time. Some of the time, it is a failure.

Now, if you have a particular programming network in mind and a signal you want to pass through it, that you want to listen to, we can help you figure out what opamp specs are required to carry out that program.

...

An excellent exposition that should be carved in letters 6 feet high on a cliffside, to be shown to audiophools when they need enlightenment.

But you missed out a list of opamps with deoxygenated copper leads.

Paul Burke

Ideally, yes, However, the only place I've ever seen an ideal opamp is in some of my CAD programs.

: If you change opamps, the limits that it : can tolerate, and still be an opamp every microsecond, change, and : allow you different freedom as far as the program (external network) : goes but it still won't produce ant "sound" that is separate from the : program.

: : So I don't approach a sound effect task by surveying opamps for their : sound, I design the input and feedback networks that produce the : programming I want to hear, and then figure out what opamp specs are : needed to be able to execute that program. Or I build the networks : and check with test equipment that the opamp is able to keep up with it. : : This is how engineers "see" opamps in a circuit, and why you are : receiving so much static from them, here, when you say you want to : listen to some opamps to hear what they sound like. An opamp you can : hear is an opamp that is not being an opamp all the time. Some of the : time, it is a failure.

First off, you haven't told me a thing yet that I don't already know. Secondly, I never intentionally program opamps to fail at being an opamp for the sake of any sound coloration or effects simply because to do so IMO would be a problem if you ever wanted to go commercial with a design and that particular opamp were discontinued. So, in essence what I want from an opamp is as little coloration as possible and leave the coloration to components that will be available for future support. : : Now, if you have a particular programming network in mind and a signal : you want to pass through it, that you want to listen to, we can help : you figure out what opamp specs are required to carry out that program.

I can pretty much do that myself. I've got opamp application notes and network theory articles up the whazoo. Up until now, all I've done is take note of the networks and which opamps sound different in them. Soon I plan to sit down and pour over the specs of the opamps and determine if there are some specs that are being violated. However, there doesn't seem to be anything that really stands out about some of these networks that could intuitively account for an opamps inability to track well. Some are very basic networks and the signals are small. However, perhaps after I review the specs, something may stand out.like a sore thumb. And also, as I mentioned before, perhaps a comparison of reasonably spec'd opamps in within networks designed to complement them will reveal absolutely no difference in sound or tone, dunno. I do know however that the ear is remarkably sensitive to various distortions that are virtually undetectable with a scope. I do hope to eventually acquire some more sophisticated means of measuring distortion

However, the main limitation I encounter in guitar amp design is in the coupling caps. I always seem to get better sound out of high speed opamps operated at lower impedances, but this tends to dictate larger coupling cap values. Since I've never gotten any results with coupling caps that I like asd much as the results I get with oil/paper caps, generally I'm forced to operate at high enough impedance values to keep the oil/paper caps down to reasonable values and physical sizes. I've had good results coupling through large value electrolytics or other large value "crap-acitors" such as mylars and using some negative feedback to linearize them. Also had good results coupling through what I call a "crap-acitor parasitic nulling divider" which entails sending the signal through a resistor on top of a cap on top of a cap on top of another resistor to ground with the resistors being equal in value as well as the "crap_acitirs" You of course take the signal out at the center of this nulling divider which is the node where the two caps connect. Abd of course you also have to suffer some signal loss. I have even combined the two aforementioned methods. These methods do indeed reduce the coloration of the coupling caps. However, oil/paper caps seem to impart a very special coloration that most ( actually all so far) of the guitarists I deal with like very much.

I'm aware of opamp theory and I understand why some engineers think there's no reason to "sonically evaluate" opamps. However, I have my reasons for doing so and if anyone thinks me a fool for doing so, so be it. They ain't got'ta be so arrogant and snobbish about it however.

Dave Moore ( Just a fool that gets results)

"Phil Allison" wrote

: And, as a sobering thought, we are all there is in the universe. : : How disappointing. : : : : : ........ Phil : :

Yes, in your case, truer words were never spoken and most certainly spoken words were never truer:

"John Popelish" wrote

: This is how engineers "see" opamps in a circuit, and why you are : receiving so much static from them, here, when you say you want to : listen to some opamps to hear what they sound like. An opamp you can : hear is an opamp that is not being an opamp all the time. Some of the : time, it is a failure.

Let me set the record straight. I never said that I wanted to hear the sound of opamps. I said that I wanted to understand why some opamps sound different when placed in the same network. Design constraints sometimes force me to use opamps in less than optimal conditions. So my "sonic evaluation" has to do with understanding which specs translate into the differences I hear under these circumstances.

So, perhaps therein lies the controversy.

Now, if you'll excuse me, I'm off to look for some NOS vintage opamps :-)

"Dave Moore"

( snip idiotic abuse )

** Mr Moore,

You are merely another self obsessed, know nothing, pig arrogant pile of autistic shit wasting their own time and other folks' hard earned money while messing about with bits and pieces of audio you have no inkling of.

I sincerely hope they gang up and electrocute you.

...... Phil

Not a fool, just a bit naive. You are giving little credit to other qualified people who have actually looked at these issues in depth. You are making the assumption that *they* are the fools. For example, some actually have extensive professional experience in analogue design and pro audio, from both a technical point of view and as a musician. Some of these, after such extensive study, indeed conclude that it there is no reason to listen to an amplifier in order to design a straight piece of wire with gain. Its purely a technical issue based on gains, distortion, bandwidth, noise etc. Sure to design a tube distortion circuit does require listening to it, but thats irrelevant to the design of the actual amplifier circuits.

Kevin kevin snipped-for-privacy@anasoft.co.uk snipped-for-privacy@blueyonder.co.uk

Yet Another Blondie Tribute "There are none more ignorant and useless,than they that seek answers on their knees, with their eyes closed"

Yes, this is true.

One big problem is that when you're trying to discern differences on the threshold of perception then it's almost impossible not to be influenced by expectation. The only sure way to avoid this is to get somebody to help you to do blind testing. If you know which audio component is being tested, then your perception is biased.

Sorry about that, but we've seen too many people whose "knowledge" of high quality audio consists of pseudoscience, mystique and psychobabble rather than good science, engineering and psychology. The requirement for op-amps with flat open-loop gain is based firmly on pseudoscience so that's why you've not been received well here.

--
Dave Farrance

Dave Moore wrote: (snip)

Great. That puts you ahead of a great many audio "designers". So you check (either with test equipment or with analysis) the three critical aspects of opamp operation for each of your designs to make sure the opamp is keeping up with the program, before evaluating how each circuit sounds.

Good for you.

When the sound you are listening to is mostly distortion (I've listened to your MP3s) you are fooling yourself if you think you can hear a coupling cap. A coupling cap has essentially no AC voltage across it, so it cannot make a signal from nothing, regardless of its characteristics. A capacitor doing audio filtering (changing the frequency response) is another matter, entirely. If you hear a coupling cap, it isn't large enough.

On Usenet, they are what they are. Whining about them changes nothing, just as discussing design issues with you probably does nothing. You seem too proud of yourself to discuss possibilities without getting defensive. I am mostly self taught in this area, so I know the feeling.

I wish you good luck in your quest.

I just ran through all the posts that seemed be on topic and there seems to be tqo issues that were missed.

When OP-AMP makers specify the slew rate of an op-amp they are only giving you the extreme case. As you get near the slew rate limit, many op-amps start to become seriously non-linear.

The gain of the early stages in the op-amp decreases as you get near the slew rate limit. This pushes up the low order harmonics.

The other issue has to do with the common mode input voltage. Many op-amps (perhaps all) have an extra non-linearity when the input section has a common mode swing on it. IME, op-amps are better than their specifications would imply when used in inverting mode. It is likely that this varies enough from op-amp to op-amp that you could notice the difference if the op-amp's specs aren't quite good enough for the suggested circuit.

--
--
kensmith@rahul.net   forging knowledge

I have recently been working with the Burr-Brown (now Texas Instruments) OPA656 and OPA657 and both have flat open loop frequency response to beyond

100 kHz. Have fun testing them by ear.

Bret Cannon

: > Dave Moore : > ( Just a fool that gets results) : : Not a fool, just a bit naive. : You are giving little credit to other : qualified people who have actually looked at these issues in depth. You are making the assumption that *they* are the fools.

You're still absolutely clueless. Let me clue you in. I ask for some information, instead I get a bunch of mistaken presumptions about why I want the information and a slew insults to go along with the mistaken presumptions.

And no, I am not making any assumptions about whether all engineers are the *real* audiophools. I'm quite open minded. And I ususally believe that people have valid reasons based on their experiences for believing the things that they do. One scientist looking at one set of data will draw one conclusion whereas another studying the same phenomena with a different but contradictory dataset may draw a completely different conclusion. In the end perhaps a new conclusion is reached due to the controversy and everyone is happy as they were all proved to be right.

For example, some : actually have extensive professional experience in analogue design and : pro audio, from both a technical point of view and as a musician. Some : of these, after such extensive study, indeed conclude that it there is : no reason to listen to an amplifier in order to design a straight piece : of wire with gain. Its purely a technical issue based on gains, : distortion, bandwidth, noise etc.

The fact that I'd rather prove this to myself doesn't mean that I don't respect the opinions of others. However there's a bit more to this story that might be of significance if anyone cared to find out first before popping off a few rounds and asking questions later. I'm working on more than one front at once. Besides design, I also do repair and upgrades for a select handful of musicians. In some cases an upgrade might entail something as simple as swapping out the opamps in a unit. Under these circumstances there is indeed a quite noticeable difference in the sound from one opamp to another. Also, in the years that I have been doing this I have noticed (as well as the musicians themselves) very definite characteristics that always follow one particular opamp around regardless of which piece of gear it is plunked into. Ok, so I suppose someone is going to say at this point, well of course, because the opamps are being plunked into networks designed for other opamps. Let me address this. Firstly, sometimes it's not possible to get a schematic on a particular piece of gear. Also, often there is a diminishing point of returns to attempt to trace and draw out the schematic or reverse engineer the circuits from the PCB's themselves. So, the 'plunk in' option proves to be the viable alternative

Let me give you a very recent example (like last night) of how this might go. I have one professional musician friend who is patiently waiting to pick up a completely SS circuit I designed that makes his opamp-plunked and capacitor-upgraded Pearce G1 SS amp sound like a tube amp. Also in his rig is a TC electronics DSP unit that sounds rather dull. I told him that I probably can do a few things to improve the TC. Well he needs the rig for a gig monday and told me to go ahead and do whatever I can before then. About the only thing I'm willing to do whithin those time constraints and no schematic towork from is an opamp-plunking. So how'd the plunking go? First off, I took my best guess at which opamps that I currently have on hand would best complement the unit. This entailed yanking the the NE5532 on the front end and replacing it with a THS2052 and yanking the NE5532 on the tail end and replacing it with an AD828. The result, (in guitar terms) much more detail & clarity on the high notes and much improved tightness and bounce on the low notes. OK, so now the A/B test. Put the NE5532's back in. Sure 'nuff. The sound is muddy again and it's difficult to pull out the low notes whilst finger picking.

So, next up, trying the unit with a number of different opamps with 'better spec's' than the NE5532's Result, all combinations produced better sound than the original 5532's as well as imparting quite predictably whatever flavor or characteristics I have observed to follow each particular opamp as they have been plunked into various units over the years. In the end I settled for the two opamps that I predicted would probably best complement the unit being that of the opamps I currently have on hand, they did just that, they best complemenbted the unit. So riddle me this. Hoiw did I know in advance that those two opamps were probably going to win the contest.

I've also sat down with various musicians and let them decide which opamps they best like when plunked into their gear.

9 times out of ten they choose the same ones that would have chosen. And this is without any pre-suggestion on my part.

So, as you can see, under these circumstances I have very legitimate reasons for wanting as large of a pool of spec-varied opamps that I can get my hands on and taking notes on just what sonic characteristics tend to follow them as they're plunked into one pice of gear after another.

: Sure to design a tube distortion : circuit does require listening to it, but thats irrelevant to the design : of the actual amplifier circuits.

I agree. When I design, I start with as clean of an amp as I can and dirty it up from there. And when it come to designing a "clean amp" I truly do respect the skills of the more advanced engineers. But even here, since there is in reality no such thing as an ideal opamp, the issue becomes just how far which spec's need to go to dissappear coloration. And this opens up another debate about how sensitive the ear is to coloration. My conclusion is that the coloration threshold is probably different for different people. Most of the more accomplished and talented musicians that I've worked with seem to have an extraordinary ability to hear subtle nuances. Quite possibly this ability may be one of the reasons that they chose to become musicians. Or perhaps some of it is a developed skill. Just as an EE becomes intuitively adept at analyzing a network from doing so repeatedly, I suppose a musicians hearing ability would improve with practice also. Regardless, I've found that most musicians notice exactly the same differences that I do. So in answer to Phil Assholesons question about whether I analyze sound for myself or for the masses, the answer would be for myself as I don't have time or the means to set up double-blind studies with mass participants and 9 times out of ten, my perceptions seem to be inline with those of the people I deal with.

So, in short, respect is a two way street. I'll respect anyone that shows me some.by getting the full story before hurling stones.

Dave Moore (disrespectful bastard)

: : Kevin : kevin snipped-for-privacy@anasoft.co.uk : snipped-for-privacy@blueyonder.co.uk :

: Yet Another Blondie Tribute : "There are none more ignorant and useless,than they that seek answers : on their knees, with their eyes closed" : :

Yes I realize this, but though I'm not usually in the habit of broadcasting anything about any of the projects that I'm working on, I suppose it wouldn't be too terribly revealing to say that I do have one design project where that particular spec may well indeeed be of significance. And in short, I have been cloaking my quest somewhat under the pretense of sonic analysis, which is not entirely a pretense as I do have some legitimite reasons for sonically evaluating opamps ( god forbid) as explained in my post to Kevin Aylward

--DM--

: : -- : Dave Farrance