It's almost criminal that all of these bode plots are missing their phase diagrams.
Phase diagrams + OpAmp phase shift specs / phase margin are what you need to predict instability.
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EDIT: IMO it's also a lot easier to explain in the frequency domain. At 180-degree phase shift, all your negative feedback turns into positive feedback, causing instability. You need your amplifier to stay as far away from 180-degree phase shift as possible.
I get that what the author was trying to get to with the 'Tape Delay OpAmp' example. But it should be double downed upon and the starting point of the discussion rather than something brought up later IMO.
Phase Margin (How far away you are from 180 Phase Shift) is a critical parameter used whenever designing any kind of feedback loop and testing for stability.
This is very to measure at the 0dB gain he pointed out, but lacked the phase diagram to show this shift.
This is tangential, but I took an EE class at community college and the very first thing they did was start teaching op-amps. I don't remember ever getting any insight from working with them, only that we had to follow instructions and build one in the lab.
When I see people asking questions about op-amps and doing "deep dives" into op-amps, I'm left wondering what's so deep about these things we do in week 2 of EE 101.
I've forgotten almost everything from that class though, so maybe it was just a bad class? I switched majors and never took another EE class.
If your only interaction was "follow instructions and build one in the lab", doesn't that tell you exactly there is something deep you didn't understand at all?
Sure, the Wien bridge oscillator. But then, oddly enough, even sustained oscillations need to be controlled in their amplitude, and the Wien Bridge has a secondary feedback loop for that purpose -- the temperature dependent resistance of a light bulb.
Those op amp characteristics aren't really coming into play for that delay sound, it's just vanilla digital delay. Most of the "vibe" of the DD-3 is coming from the companding and filtering scheme it uses to work around the limitations of the digital pieces.
You will hear the effects of this in many hard clipping distortion circuits, though, where the amplifier gain factor will far exceed the voltage rails and be pushed into undefined clipping territory. Behaviors in this range can be an important part of the sound, e.g. the Proco Rat and the infamous LM308 op amp with its slow slew rate. Some like the TL072 exhibit a really nasty phase inversion that results in a pretty horrific (usually undesired) distortion.
It's a balancing act, though; search "op amp motorboating" in any DIY stompbox forum and you'll find thread after thread of people trying to keep op amp gain stages from oscillating. I know more than a few noisier artists who enjoy when designs can be tortured into doing that, though :)
To the degree that society is a complex system with feedback.
But notice that the Gartner hype cycle is full of unjustifiable hidden assumptions (like the fact that the thing being hyped is useful at all) so it has no predictive power. It only happens that some times people act like that.
Also, there's no guarantee that the society's response to a change will be stable.
The tape delay methaphor confused me. Tape recorders do not record DC or other frequencies much lower than, say, 20 Hz. So that circuit would run into one of the rails just as quickly as the previous cirquit without DC feedback.
It must be an FM encoded tape, which can record DC. There were upgraded versions of both VHS and Betamax with FM audio support (although I expect in practice the inputs were AC coupled).
It's almost criminal that all of these bode plots are missing their phase diagrams.
Phase diagrams + OpAmp phase shift specs / phase margin are what you need to predict instability.
-------
EDIT: IMO it's also a lot easier to explain in the frequency domain. At 180-degree phase shift, all your negative feedback turns into positive feedback, causing instability. You need your amplifier to stay as far away from 180-degree phase shift as possible.
I get that what the author was trying to get to with the 'Tape Delay OpAmp' example. But it should be double downed upon and the starting point of the discussion rather than something brought up later IMO.
I agree.
Phase Margin (How far away you are from 180 Phase Shift) is a critical parameter used whenever designing any kind of feedback loop and testing for stability.
This is very to measure at the 0dB gain he pointed out, but lacked the phase diagram to show this shift.
This is only true for LTI (linear time-invariant systems).
Nonlinear systems responses to a sine signal are in general not just a change in phase and amplitude.
It works if the perturbation stays small and within a linearised version of the dynamics.
This is tangential, but I took an EE class at community college and the very first thing they did was start teaching op-amps. I don't remember ever getting any insight from working with them, only that we had to follow instructions and build one in the lab.
When I see people asking questions about op-amps and doing "deep dives" into op-amps, I'm left wondering what's so deep about these things we do in week 2 of EE 101.
I've forgotten almost everything from that class though, so maybe it was just a bad class? I switched majors and never took another EE class.
If your only interaction was "follow instructions and build one in the lab", doesn't that tell you exactly there is something deep you didn't understand at all?
These are pesky little things
But the ringing, sustained oscillations, and excessive gain are sometimes desired characteristics of a particular op-amp implementation.
https://youtu.be/SrS9EtfcANg?si=MwbtbuPWu85Tbjzq
Sure, the Wien bridge oscillator. But then, oddly enough, even sustained oscillations need to be controlled in their amplitude, and the Wien Bridge has a secondary feedback loop for that purpose -- the temperature dependent resistance of a light bulb.
Those op amp characteristics aren't really coming into play for that delay sound, it's just vanilla digital delay. Most of the "vibe" of the DD-3 is coming from the companding and filtering scheme it uses to work around the limitations of the digital pieces.
You will hear the effects of this in many hard clipping distortion circuits, though, where the amplifier gain factor will far exceed the voltage rails and be pushed into undefined clipping territory. Behaviors in this range can be an important part of the sound, e.g. the Proco Rat and the infamous LM308 op amp with its slow slew rate. Some like the TL072 exhibit a really nasty phase inversion that results in a pretty horrific (usually undesired) distortion.
It's a balancing act, though; search "op amp motorboating" in any DIY stompbox forum and you'll find thread after thread of people trying to keep op amp gain stages from oscillating. I know more than a few noisier artists who enjoy when designs can be tortured into doing that, though :)
to what degree does the Gartner hype cycle resemble the Gibbs phenomenon?
To the degree that society is a complex system with feedback.
But notice that the Gartner hype cycle is full of unjustifiable hidden assumptions (like the fact that the thing being hyped is useful at all) so it has no predictive power. It only happens that some times people act like that.
Also, there's no guarantee that the society's response to a change will be stable.
The tape delay methaphor confused me. Tape recorders do not record DC or other frequencies much lower than, say, 20 Hz. So that circuit would run into one of the rails just as quickly as the previous cirquit without DC feedback.
It must be an FM encoded tape, which can record DC. There were upgraded versions of both VHS and Betamax with FM audio support (although I expect in practice the inputs were AC coupled).