Re: op-amps with wide open-loop bandwidth ?


"John Popelish" <jpopelish@xxxxxxxx> wrote in message news:e_KdnRveTOekOorZnZ2dnUVZ_sadnZ2d@xxxxxxxxxxxxxxx
: Dave Moore wrote:
:
: > : And since, it is fairly obvious that you are not yet a circuit
: > : designer, you would probably get a more helpful response if you start
: > : over in sci.electronics.basics
: > :
: > : Good luck.
: >
: > 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.


.

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