What would be the noise current requirements and the bandwidth of such an op amp?
Cell phone guys are really good at packaging. I think these guys were amateurs (in a bad way).
The obvious trade-offs are there the goal is stabilizing the amplitude of the main laser to some absurd level.
or is it a CFA with a buffered -input masquerading as VFA?
Have you used the LMH5401 in an audio circuits?
-RNM
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I've enjoyed following this thread, and haven't really chimed-in until now because I wanted to soak-in the pure feedback from the market here.
At RMAF last year I had an interesting interaction with an engineer at a booth for a high end audio company. I asked if he might be be interested to see our (TI's) new parts for audio. He was literally appalled that I would even suggest that they use something as disgraceful as an op amp in one of their products. It really hit me how bad of a marketing problem op amps have.
Imagine for a moment seeing an ad in a hi-fi magazine for an amplifier with almost perfectly matched input devices (with fantastic specs), advanced techniques for linearizing the internal circuitry, and a class-A push-pull output stage. The manufacturer brags about how they re-simulated the circuit countless times, considering all the parasitics introduced during the layout process, matching the input capacitance down to the femtofarad, balancing the resistance of metal traces and vias, even considering the effects of thermal gradients on proper operation! They go on to brag about how every unit is meticulously tested to ensure that a large number of the specifications are within extremely well defined limits. In fact, they'll even provide you a LEGALLY BINDING document that spells out the parameter limits that every amplifier they ship will meet. Wow! This product has to cost a fortune!
...or it's basic op amp with a rail-to-rail output...
Maybe we don't brag enough? 😉
P.S. If slew rate is the only parameter that matters I'm going to start making some SERIOUSLY slew-boosted op amps. Get ready for OPAs with 1mA of supply current and 10,000,000 V/us slew rates! Like a Ferrari with 2 throttle positions: idle and floor! Just don't measure the power supply consumption when we're slewing...And if there's time we may even take at look at how the op amp behaves when it's operating linearly.
At RMAF last year I had an interesting interaction with an engineer at a booth for a high end audio company. I asked if he might be be interested to see our (TI's) new parts for audio. He was literally appalled that I would even suggest that they use something as disgraceful as an op amp in one of their products. It really hit me how bad of a marketing problem op amps have.
Imagine for a moment seeing an ad in a hi-fi magazine for an amplifier with almost perfectly matched input devices (with fantastic specs), advanced techniques for linearizing the internal circuitry, and a class-A push-pull output stage. The manufacturer brags about how they re-simulated the circuit countless times, considering all the parasitics introduced during the layout process, matching the input capacitance down to the femtofarad, balancing the resistance of metal traces and vias, even considering the effects of thermal gradients on proper operation! They go on to brag about how every unit is meticulously tested to ensure that a large number of the specifications are within extremely well defined limits. In fact, they'll even provide you a LEGALLY BINDING document that spells out the parameter limits that every amplifier they ship will meet. Wow! This product has to cost a fortune!
...or it's basic op amp with a rail-to-rail output...
Maybe we don't brag enough? 😉
P.S. If slew rate is the only parameter that matters I'm going to start making some SERIOUSLY slew-boosted op amps. Get ready for OPAs with 1mA of supply current and 10,000,000 V/us slew rates! Like a Ferrari with 2 throttle positions: idle and floor! Just don't measure the power supply consumption when we're slewing...And if there's time we may even take at look at how the op amp behaves when it's operating linearly.
Some people seem to forget that for audio you need low noise (voltage and current) and the 1/f noise needs to be under 100 Hz ideally.
They also seem not to be able to ascertain the difference between RF applications and LF ones like audio.
The points you raise are spot on. I think the audio companies that are shifting volume (by audio industry standards) are using them. That's really a consumer electronics business where cool heads and a focus on the bottom line prevail. The high end stuff IMV is not - it's a fashion business that is for the most part shaped by the opinions of a small group of individuals. It's business I am afraid and those folk make a living out of it despite the fact that on technical grounds the stories do not stand up to scrutiny.
🙂
I'm all ears!
It had to happen. Finally - sth. faster than my 50 GHz sampling plug-ins!
cheers, Gerhard
I may include some other inputs from the hi-fi market such as:
1. Feedback sounds bad!
2. All caps inside an op amp are non-linear!
3. THD doesn't matter!
This new extremely fast slewing op amp won't use feedback, or have any internal capacitors, and we won't even show THD in the datasheet!
Unfortunately, upon doing some research, this product already exists 🙁 It's called a "comparator". I'll set up some listening tests today to try them out, they must sound incredible!
Because many "audiophile" looking for unique sound character (effect box), not an "accurate" sound reproduction.
After I modified Apex's FX8 amplifier for lower THD and higher slew rate, I modified it again to increase THD (higher H2 distortion) with adding a resistor at VAS transistors. Some of friends, tested it and they like the last modification 🙂
Many a "designer" has tried to fake comparators from op amps!
And without great success.
> 1. Feedback sounds bad!
That is only because it is usually negative feedback. Positive feedback OTOH
produces well defined levels, essential for a good sound stage.
\ Gerhard
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Bimo,
You just need to add a single vacuum tube like a 12ax7 for the input to give it that tube sound and they would love it! 😀😉 They get old and new and have that SE amplifier 2nd harmonic sound. I'm kind of joking but the reality is it would give the consumer something to talk about even if it is bs and not the best way today to make a great amplifier. Just give it a glowing tube and it is like moths to a flame! 😎
You just need to add a single vacuum tube like a 12ax7 for the input to give it that tube sound and they would love it! 😀😉 They get old and new and have that SE amplifier 2nd harmonic sound. I'm kind of joking but the reality is it would give the consumer something to talk about even if it is bs and not the best way today to make a great amplifier. Just give it a glowing tube and it is like moths to a flame! 😎
It's going to have ridiculously high short circuit output current too. Because if slew rate is a reasonable metric of input stage linearity, then short circuit current is a great way to measure output stage linearity!
Reading you loud and clear, on a 40'' p/c plasma screen with stereo diy ambilight.
(6Н2П doesn't entirely count as a 12ax7, but too tempting a triode dually valve at a buck a pop. Does 20W class A in 4 ohm with a shiner. Beat that, Mr K.lang with your cheapo BC550/BC560 input stage !)
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Not likely in any case bipolar's fail at extremely low T.
Extreme-Temperature Electronics (Tutorial - Part 3)
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