John Curl's Blowtorch preamplifier part II

[scott wurcer]

Originally Posted by simon7000

If the issue of TIM is well understood, then one could calculate for any given design, how much would be present and use that in design trade-offs. ES

Yes but it is just a subset of general large signal limitations of amplifiers which is/was understood. You know slew as in slewing a coastal gun in WW2. An unnecessary extra acronym made up by the audio community.

[simon7000]

Originally Posted by scott wurcer

Yes but it is just a subset of general large signal limitations of amplifiers which is/was understood. You know slew as in slewing a coastal gun in WW2. An unnecessary extra acronym made up by the audio community.

The information added when the phrase TIM got invented was the issue not just of slew rate but gain (or transconductance) also counted.

When doing the classic control loop for gun control undershoot and overshoot were big issues. Nyquist gets the credit for that bit of math and increased understanding. Those are stability issues.

What in my OPINION was new was that with identical gain bandwidth products, amplifiers could produce internal distortion if the gain was too high and the bandwidth (or slew rate) too low. (Implying that increasing the gain of a circuit without increasing the bandwidth might not result in decreased distortion... under some transient conditions.)

This added to the knowledge of the large signal/small signal bandwidth (Slew rate) which came from the problems with higher speeds and larger swings on triangle waves.

It is a fine point of distinction.

[jan.didden]

Bandwidth is (unless noted otherwise) a small-signal spec, slew rate is a large signal spec.
If you make sure your amp can handle the max signal amplitude and rise time it will enconter in normal use, there's no TIM or slew rate limitations. Straightforward engineering.

I cut my teeth, slew-rate wise, on Bofors 40L70 air defense guns.
We build an interface to connect these guns to a digital air defense processor. We learned very quickly that lower slew rate without overshoot was faster than high slewrate with a lot of overshoot, especially if it is you against a heavily armed jet fighter...
Absolutely the same as in electronics, replacing mechanical properties with capacitance, power and acceleration.

Many people here know quite well how to explain it, and many did.
But then some time later somebody comes along who should know better but spreads the same old disinformation again. Makes one tired.

jan

[gpapag]

Originally Posted by jan.didden

I cut my teeth, slew-rate wise, on Bofors 40L70 air defense guns.
jan

These guns ruined my ears

George

[Kindhornman]

You can't be that old George! You would have to be in your 90's at least I would think.

[bcarso]

Originally Posted by scott wurcer

Yes but it is just a subset of general large signal limitations of amplifiers which is/was understood. You know slew as in slewing a coastal gun in WW2. An unnecessary extra acronym made up by the audio community.

I think my first encounter with slew as a verb and adjective was when I joined the Astronomy Dept., where it applied to the rapid motion and associated motors of a telescope. On the control paddle, there was a big toggle switch you had to throw in order to enable it, as of course inadvertent actuation would cause you to "lose everything" if in the middle of a specific observation.

I once arrived at the site of the Dept.'s Ojai Field Station telescope, perhaps for some equipment changeout or responding to another problem. I was unexpectedly met by the late George O. Abell and a cute co-ed, respectively academic director and participant in that year's version of the long-running Summer Science Program at the Thacher School, in which I'd been a student in 1965. Chitchat ensued, and I asked George if the rules for appearance at dinner had changed after so many years, i.e. did one still have to dress for dinner. No, he said, the rules haven't changed, and gesturing toward her, for dinner she'd have to take all of that off.

But George went on to say how timely my visit was, as he had just been demonstrating telescope slewing and the protective limit switches in right ascension and declination. He learned that his recollection of limit switches in declination was faulty as he had slewed the tube into a grinding halt against the fork, thoroughly jammed.

[simon7000]

Jan,

We are talking, but I don't think we are communicating.

If I have an amplifier with a gain of 100 at 1,000 hz. and another with a gain of 1000 at 100 hz. They both can be rated as having the same gain bandwidth. If they both have a thd of 1% at 500 hz, must they have the same TIM?

ES

[scott wurcer]

Originally Posted by simon7000

Jan,

We are talking, but I don't think we are communicating.

If I have an amplifier with a gain of 100 at 1,000 hz. and another with a gain of 1000 at 100 hz. They both can be rated as having the same gain bandwidth. If they both have a thd of 1% at 500 hz, must they have the same TIM?

ES

The use of transient in that term is inaccurate, the input transfer function is there for contiuous time signals. The tanh shape for an undegenerated bipolar is directly related to the total current i.e. when at max there is the onset of hard slew. R.D. Thornton and J.K. Roberge at M.I.T were teaching it this way in 1969, Barrie Gilbert was already preaching from this pulpit in 1968 and before.

[bcarso]

Originally Posted by scott wurcer

The use of transient in that term is inaccurate, the input transfer function is there for contiuous time signals. The tanh shape for an undegenerated bipolar is directly related to the total current i.e. when at max there is the onset of hard slew. R.D. Thornton and J.K. Roberge at M.I.T were teaching it this way in 1969, Barrie Gilbert was already preaching from this pulpit in 1968 and before.

And Tek and others were figuring out some ingenious ways around the limitations of tanh, as it were, mostly applied to global-feedback-free 'scope amps.

[Esperado]

Originally Posted by simon7000

If I have an amplifier with a gain of 100 at 1,000 hz. and another with a gain of 1000 at 100 hz. They both can be rated as having the same gain bandwidth. If they both have a thd of 1% at 500 hz, must they have the same TIM?

As you don't provide the transition frequency of each amp (or open-loop gain), this question cannot be answered.