About amp "immediacy"

[Dave H]

PRAT - British slang: A stupid or foolish person

[Leo_Gnardo]

Perhaps someone could post an example of a tube circuit, complete with power supply, that exploits their fast rise time potential.?.

I'd look at some oscilloscope input circuits, from the time just before they went solid state.

Another anecdote about ear satisfaction - Back when DAT recorders first hit the market in the USA, I was doing some work for a local college's music department. The head of the dep't bought herself a portable Panasonic DAT but was immensely dissatisfied with recordings she got using built-in mic preamps. A consultation with the manufacturer revealed the mic pre's were designed by one of their metering specialists, and had slew rate out the wazoo. So... supposedly it was state of the art, right? Except it sounded like dreck. Hmmm..... Soon as it was available our music professor bought herself the second generation Panasonic portable DAT and was immediately much more satisfied. This time Panasonic used a mic pre design from their mic pre specialist, and stopped honking about stratospheric slew rate. A win for the ears!

From the late 60's on for a couple three decades there was a movement among studio gear manufacturers to "get the iron out of the signal path." Transformers = poison was the line of thinking. Well they might have been successful in improving their gear so that it could pass clean square waves up to a gazillion hertz, and that's fine for the meter readers. But engineers, producers and musicians kept hauling old fashioned gear into the studios. Transformer coupled, tube populated EQ's, compressors, limiters, preamps etc. Some techs made a fortune ripping apart early transistor Neve consoles - that couldn't pass a square wave to save their life - selling the preamps & eq strips all handily rack mounted - at nosebleed prices. Why? Because they sounded good! Over the last 25-30 years there has been a resurgence of "old school" studio gear being manufactured fresh, copies of classic studio gear, sometimes with extra bells & whistles but often transformer coupled and nobody in the production end of the biz gives a crap about slew or PRAT. Not that any of it guarantees good sounding music on the market... an awful lot is rubbish, but some of it is quite good. It's all how the engineers & producers use the gear, and what the execs at the record companies decide is fit to send out the door as finished product. But that's been the case since the beginning of time.

[Leo_Gnardo]

PRAT - British slang: A stupid or foolish person

I wuz gonna mention... but it really is best to hear it from a native. Now, how about "pillock."

[yldouright]

@Leo_Gnardo aka Conflator #2
No one is suggesting slew rate is the only parameter leading to good sound. The focus here was for one specific attribute and its relation to one specific outcome.

Any difference to be made in the slew rate of a tube circuit to make it faster than a transistor is indeed mitigated by coupling requirements.

No, the VT is already faster than a chip with a ~ 1 nanosecond rise and fall time and when you add the analog profile of this rise and fall and contrast this with the asymptote profile of silicon, most understand you can only reduce the slew of a VT circuit down to silicon performance levels with design intention or stupidity. You're calling me a jackass when you're the only one braying in here.

Further, I don't think I've ever seen a voltage amplifier that instigates significant grid current.?.

What are you trying to conflate here? There are lots of schemes and drivers designed to maintain steady grid current >1mA. At what point will you just wipe the egg from your face and admit your ignorance instead of leaving it there with the hope others won’t notice it?

It is so sweet watching how you smooth over and apologize for each others rubbish after it's exposed. It reminds me of the males in the whale pod who fail to mate the female in the chase. So pathetic and so obstructive to the pursuit of truth.

[pdf64]

I suspect that amp slew rate is a complete red herring, surely most any reasonable guitar amp will be order(s) of magnitude faster than that of the speakers used? eg https://celestion.com/product/18/Classic_Lead/
@Dave H are you able to derive a slew rate from the freq response plot?

My experience is that AB1 amps which have a lot of sag, squish and bias shift may seem to have a softer attack, which may perhaps be described as less 'immediate'.
Hence stiff HT nodes and fixed bias, along with suitable mitigation for bias shift / blocking distortion, may be a good starting point for an 'immediate' tube amp.

[Mike Sulzer]

[/QUOTE=yldouright;509683] Tubes have ~1,000x faster rise times than transistors which gives them greater potential for higher slew rate circuits. [/QUOTE]


Of course that is not true. I do not know what kind of misunderstanding leads to that statement, but until you figure out why that is wrong, there is not much point in criticizing what others say.

[Leo_Gnardo]

I suspect that amp slew rate is a complete red herring, surely most any reasonable guitar amp will be order(s) of magnitude faster than that of the speakers used?.

Excellent point! Same for hi fi and sound reinforcement. Some relief from "slow speakers" may be found with electrostatics, mostly being due to their super light membranes that respond quickly to changes in the nearby electric field. But they tend to be quirky and prone to breakdown due to the super high voltages involved. 'Stats gathered a little bit of the home listening market in the 70's & 80's. The ones I got to hear did sound very clear, but needed a cone woofer to handle 200 Hz on down. Similar membrane-panel speakers, mostly Magnepan, also earned their fans, and needed no high voltage supply, a maintenance advantage. There was a brief experimental period with using electrostatics in PA - I remember reading about a concert using QUAD speakers to broadcast Ravi Shankar's show to the audience. But they had a notoriously low efficiency, and not much in the way of controlling coverage pattern, so that idea was nixed in short order.

One thing that I never ran across was using electrostatics for guitar amps. There were a couple Fender amps that had Yamaha speakers with super light polystyrene plastic cones, driven by the usual magnet/voice coil arrangement. Another idea that came and went fast, can't imagine why...

[yldouright]

@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.

[Chuck H]

Hey guys. Did I say jackass earlier? Sorry. I meant jackoff.

Do we usually discuss grid current as constant with respect to it's roll in amplification? I guess I was confused.

And indeed, why do the VAST MAJORITY of tube amps employ such ignorant design that ignores the 1000x greater slew rate potential that tubes offer? I'm afraid my ignorance prevents being able to understand.

Potential is an oft misused concept. It should mean "What is achievable". Unfortunately it's commonly employed to exploit a single attribute that can never be idealized. You could fly a passenger plane with a rubber band were it not for pesky things like air resistance and gravity. So using a jackoff's definition for potential a rubber band can power a plane. Why those lazy, uneducated engineers still have us using jet and internal combustion engines must be a conspiracy propagated by big oil... Or aliens.

[pdf64]

Yes, it may be possible that a tube's output electrode can exhibit a fast slew rate under certain conditions (dunno ), but for a tube audio power amp to actually drive a real world speaker load anywhere near 1kV/us seems fanciful.
Please help us out here, are there any commercially available examples of such an amp?

[netfences]

Yes, it may be possible that a tube's output electrode can exhibit a fast slew rate under certain conditions (dunno ), but for a tube audio power amp to actually drive a real world speaker load anywhere near 1kV/us seems fanciful.

I don't think anyone's amp design goal is to achieve 1kV/uS slew when we've already exposed 10V/uS is enough for most applications. I seem to have stumbled upon a prior conflict between members here. Hoping I'm not drawn into this mess, I don't see anything wrong or misunderstood in any of yldouright's posts here. If Mike Sulzer can elaborate on those defects I would appreciate it.

[Dave H]

@Dave H are you able to derive a slew rate from the freq response plot?

Hmm...I'll have to think about that.

I think you'd need more than the small signal frequency response. If I knew the full power bandwidth, output power and load resistance I could derive the the maximum rate of change in Volts per uSec required to follow a full power sinewave at the upper -3dB point. Would that be close to the slew rate? I just don't know.

Edit: Has The Trinity recruited a 4th member?

[Malcolm Irving]

Please be more specific. I'm assuming you aren't challenging the theoretical concepts of circuit time delays and as of yet unmeasurable signal wave smearing. Do you want scientificly quantified corroboration of PRaT or proof of its audible repeatability?

We have to be careful to understand the difference between time-delay and phase-lag. Apart from reverb or other effects, the time-delays in an amp are extremely small and have no significance for audio signals. Phase-lag is completely different and is very significant.

If signal-smearing is unmeasurable how do we know anything about it? Perhaps we just listen to the sound and say ‘it sounds like the signal is being smeared’.

I do not doubt that amps and speakers sound different and some of the differences are quite subtle and difficult to measure. So we resort to terms such as ‘immediate’, ‘smeared’ etc. to try to capture the subjective differences. I am genuinely interested in any scientific work on such things.

[yldouright]

If signal-smearing is unmeasurable how do we know anything about it? Perhaps we just listen to the sound and say ‘it sounds like the signal is being smeared’.

The smearing aspect of sound is easier to detect in well recorded stereo sound. It is typically identified by lack of imaging aka soundstage.

So we resort to terms such as ‘immediate’, ‘smeared’ etc. to try to capture the subjective differences.

Yes, as imperfect as these subjective descriptions are, using them is better than denying their existence when so many people who are qualified to identify them, hear them. This is why I bristled when certain members here tried to suggest their insignificance or worse. They insult music professionals everywhere who have experienced these unmeasurable differences. I've experienced the arrogance of some of these members on other topics too. Go to my profile and look through my past posts to see what I mean.

[Leo_Gnardo]

In this thread, I only wanted to learn about amp immediacy and how to achieve it. As was correctly pointed out, my goal is to build an amp that is pedal friendly, uber clean and fast/present. The players in here seem to know what I mean if others don't.

OK, let's get back to that. One of my observations is that simplicity yields clarity. Perhaps what I call "clarity" is what you call "immediacy." Worth a try anyway. If you're going to build from scratch, leave out anything you don't need, like effects loop, vibrato, master volume, reverb. And pick a "fast" speaker. Of course it's best to audition whatever you can get your hands on, hear if it's right for your ears & guitar. A light cone/voice coil combination will move quickly - the Bulldog is a prime example. Depending on what kind of power your amp turns out, plus how loud you need to be, add extra speaker(s) if necessary.

Another quick observation from years of tweaking & listening, a pair of output tubes will give you better clarity than a quad - or more. Of course design with whichever output tubes are suited to the power level you're seeking, from 6AQ5's for 5W or so, up to KT88 for 60W.

Finally, power supply levels, and another subjective observation. Higher operating voltages tend to yield a brighter, snappier, more forward sound both in preamp and power amp. So keep those preamp plates around 200V, should be fine. Of course there will be naysayers, we have to expect that. But you can experiment with your amp and find out if it isn't so.

Take a look at that Traynor YGM-3 schematic, see how it compares to a Fender Deluxe Reverb. I'm sure you can adapt those circuits to your needs.

Good luck, & don't worry about slew rate or PRAT. Keep it simple, and I'll bet you will be well satisfied.