About amp "immediacy"

[Dave H]

Why doesn't it surprise me that the person who's never met a conspiracy theory he couldn't believe in would also be an audiophool.

[g1]

Edit: Has The Trinity recruited a 4th member?

There was previous mention about a "team member" being held up in the moderation queue, is that what you are referring to? (ie. plant, not recruitment)

[Mike Sulzer]

@Mike Sulzer
Ceteris Paribus and assuming the impedance, phase angle and damping factor issues of the drivers are sorted out, my statement stands. I've read your posts and know you're a smart guy Mike, why align yourself with these dullards on this? Yes, nowadays chips operate in the GHz range which makes the 1,000x number invalid when citing those but common audio amps don't typically use them.

No it does not. A tube amp has an output transformer; it is last, and therefore its frequency response also makes the limitation in slew rate. An SS amp can have many times that slew rate, depending on the design.

[nsubulysses]

Never mind the discourse saboteur

[R.G.]

I admit to being baffled at this thread.

I had no idea that "immediacy" was a thing. But OK, some people conceive of an amp has having more or less immediacy. The OP wants to know how to design/modify amps to have more "immediacy". I can go with that - there is some audible quality with an ill-defined something that the guy wants to design in.

My immediate problem as a techie is that although I think I have a pretty good idea how to get any more-or-less arbitrary frequency response and at least how to crudely hack out various distortion profiles, or at least have some idea of what does what, I have no clue what to do to a circuit to make it more "immediate". That would not be too earth shaking, excepting that I've been a practicing circuits engineer for decades, and have studied widely both the hard-edged tech side and the soft-and-fuzzy side of circuits which make sounds with a start of rutabagas and a finish of oak.

If I could get a definition of "immediacy" in terms of frequency response, time response, phase response, any-dang-thing at all, I could probably come up with some suggestions for the OP. Maybe something like the old description of "presence" as "a mild hump in frequency response in the upper midrange, maybe around 2kHz that's there but not too noticeable all on its own". But I'd need SOMETHING that told me what to design.

Slew rate was brought up and used as both a sword and a cudgel in the thread. That's fine - if "immediacy" is "slew rate is greater than X volts per microsecond", or "slew rate is greater than X% of signal range per nS" or something, I could work with that. Modern devices, tube or solid state, let you design amplifiers with responses from DC to daylight. The issue is largely one of deciding when to quit as a result of diminishing returns. Slew rate might mean something for "immediacy"; it might not. How could we tell?

My conundrum is this: until "immediacy" is reduced to something that can be measured, it can't be designed for in any way other than tossing in parts like throwing darts.

I'm really perplexed here. If I knew what it was, and a way to tell when I was achieving it, I could design for it.

[Dave H]

There was previous mention about a "team member" being held up in the moderation queue, is that what you are referring to? (ie. plant, not recruitment)

"Appen you are right" as we say up here in t' north of the UK. It's a plant, another sycophant saying all praise to the glorious leader.

[yldouright]

A tube amp has an output transformer; it is last, and therefore its frequency response also makes the limitation in slew rate.

Granted but the limitation is introduced earlier in the circuit when the gain device is only capable of 50KHz. Does this matter for group delay and feedback design decisions? I think we can all agree that slew rate only matters for immediacy when there isn't enough of it. None of what you said disproves the potential slew rate of tubes compared to sand.

@Netfences seemed to have understood this even with all the noise and conflations introduced by the usual suspects. The question of how to get it in your amp design requires the 'blameless' approach. It was suggested that clarity=immediate. I don't think it does and the following states that case:

I once used a Pioneer Spec amp with a DSP256XL pre. The sound was very clear and chimey but definitely polite. Fast transitions seemed to lose their edge and the emotion failed to come across. Switch in a MacCormick DNA-2 amp and everything comes to life again. The dynamics that were missing with the Pioneer unit suddenly returned without question. The clarity was the same so what caused this change? Was it just the mac's ability to drive the cabinet better? Was it a difference in the distortion profiles of the two amps, the bandwidth/rolloff or some other characteristic?

This is the problem with limiting the desired outcome to just one, well understood parameter. We know the characteristic we want. We don't want to hear a note while we play the next one. If we're 50' from the speaker stacks, it could just be a matter of raising the treble response but I'm willing to bet there's more to it than that. High 2nd order harmonics are known to emphasize notes in key and make them more quickly recognized. Is this contributing? A more aggressive decay profile will contribute to note definition. Is this part of the answer?

I've thrown out my opinions of likely suspects but I'm sure you guys can come up with your own. I know we're going into touchy feely territory and that drives many hard core engineers to drink but artists may be hearing and feeling things you don't, that's no reason to dismiss their observations. Many prominent artists refuse to play on SS and there are an equal number who have permenantly parted ways with their tube gear. This proves to me that immediacy is attainable with glass or silicon when we know what's doing what.

[Chuck H]

I'd offer a thumbsup for the above post but for principal. DO NOT FEED THE ANIMALS! But I basically agree, with this caveat...

Will people please stop using phrases like "Fast transitions seemed to lose their edge and the emotion failed to come across."

I don't have an "emotion" selection on any of my scopes or meters. When terms like immediacy, sound stage, airy, "space between the notes", etc. are given too much credence and power I think it's detrimental to actual, technical definitions of these admittedly real phenomenon. Certainly SOMETHING makes one amp sound more immediate than another. But when a bunch of laymen start using the same term the definition of this quality is reduced to the term itself with no further attempt to define it. Then a bunch of audiophiles who have managed to learn all the acceptable terminology start spouting off like experts regardless of a lack of definitives for a damn thing they say. Sometimes they profess to being experts, or at least accept such treatment from others. What we end up with is a genre where people line up to buy gold plated AC wall plugs and stick small strips of audio enhancing rainbow tape on their speakers. The reason is that if you build a technology without definitions then you allow the most unscrupulous but charming power seekers to step in and take advantage of a very high degree of naivety. They do this because there's no need to actually learn anything but nomenclature and practice their usual con man charm to gain recognition, money, influence, whatever.

This is why the design of common, but loosely or predominantly undefined terms is a detriment to any communal effort. It can utterly remove science from the equation. In this light I think it's completely reasonable to question such terms. Of course it should be done respectfully. But when it's met with some puffed up pontification of unquestionable relevance the problem is distinctly NOT with those questioning the terminology. Even if it's hard for the more uninitiated to even tell the difference between the good guys and the bad guys.

[Mike Sulzer]

Granted but the limitation is introduced earlier in the circuit when the gain device is only capable of 50KHz.

Not necessarily. For example, an op amp might have a gain stage with a corner frequency of 10 Hz, but that alone does not determine slew rate of the amplifier. The product of gain and bandwidth matters as well as how much current drive you can provide to that stage.

[loudthud]

One thing that I have observed is that the more you overdrive an amp, the steeper the edges become. This can be in a preamp stage or a power amp.

One thing that has not been mentioned is a phenomenon that is sometimes called Transient Intermodulation Distortion (TIM for short). It occurs mostly in SS power amps where a steep transition on the input causes a stage inside the feedback loop to clip. Many SS power amps have a single pole RC filter on the input to slow down any fast transitions and thus eliminate the TIM. Trouble is the filter doesn't work if you are overdriving the input to the power amp.

[Enzo]

But...but.. the midrange. It's still so grainy...

[uneumann]

Granted but the limitation is introduced earlier in the circuit when the gain device is only capable of 50KHz. Does this matter for group delay and feedback design decisions? I think we can all agree that slew rate only matters for immediacy when there isn't enough of it. None of what you said disproves the potential slew rate of tubes compared to sand.

@Netfences seemed to have understood this even with all the noise and conflations introduced by the usual suspects. The question of how to get it in your amp design requires the 'blameless' approach. It was suggested that clarity=immediate. I don't think it does and the following states that case:

I once used a Pioneer Spec amp with a DSP256XL pre. The sound was very clear and chimey but definitely polite. Fast transitions seemed to lose their edge and the emotion failed to come across. Switch in a MacCormick DNA-2 amp and everything comes to life again. The dynamics that were missing with the Pioneer unit suddenly returned without question. The clarity was the same so what caused this change? Was it just the mac's ability to drive the cabinet better? Was it a difference in the distortion profiles of the two amps, the bandwidth/rolloff or some other characteristic?

This is the problem with limiting the desired outcome to just one, well understood parameter. We know the characteristic we want. We don't want to hear a note while we play the next one. If we're 50' from the speaker stacks, it could just be a matter of raising the treble response but I'm willing to bet there's more to it than that. High 2nd order harmonics are known to emphasize notes in key and make them more quickly recognized. Is this contributing? A more aggressive decay profile will contribute to note definition. Is this part of the answer?

I've thrown out my opinions of likely suspects but I'm sure you guys can come up with your own. I know we're going into touchy feely territory and that drives many hard core engineers to drink but artists may be hearing and feeling things you don't, that's no reason to dismiss their observations. Many prominent artists refuse to play on SS and there are an equal number who have permenantly parted ways with their tube gear. This proves to me that immediacy is attainable with glass or silicon when we know what's doing what.

Finally - you actually contributed something. Thank you. I was wondering how long it was going to take.
Maybe next time you should just say your piece and skip the bashing of everyone who basically said theirs before you.

[pdf64]

...we've already exposed 10V/uS is enough for most applications...

Sorry, I missed that discussion, and where that number came from? I've got no idea what the slew rate of a regular tube guitar amp may be, or how it's usually measured, but 10V/us seems higher than I would expect, as such amps have significant output impedance and are used to drive complex, mainly inductive, loads, ie speakers.

[Malcolm Irving]

… I know we're going into touchy feely territory and that drives many hard core engineers to drink but artists may be hearing and feeling things you don't, that's no reason to dismiss their observations. ...

It is possible for a person to be both a 'hard-core' technician/engineer and an artist (at least at some level) at the same time. I think quite a few of the regular contributors in this forum do fall into that category.

[Mike Sulzer]

One thing that I have observed is that the more you overdrive an amp, the steeper the edges become. This can be in a preamp stage or a power amp.

One thing that has not been mentioned is a phenomenon that is sometimes called Transient Intermodulation Distortion (TIM for short). It occurs mostly in SS power amps where a steep transition on the input causes a stage inside the feedback loop to clip. Many SS power amps have a single pole RC filter on the input to slow down any fast transitions and thus eliminate the TIM. Trouble is the filter doesn't work if you are overdriving the input to the power amp.

If the edges get steeper as you drive the stage harder, it has not reached slew rate limiting yet. TIM has the same causes as slew rate limiting. If you drive an amp into slew rate limiting with a large steep edge, the other smaller signals are lost.