Agreed, if only audio always followed engineering principles it would all be so much easier.
One paradox with opamps I have noticed is that the higher the PSRR (usually caused by higher loop gain) the more the "sound" of the power supply and decoupling is apparent. Indeed this provides a real dilemna with "rolling" opamps.... the PS and decoupling can make more difference to the sound than changing the opamp.
Hmm. Never thought about that. Just always assumed that opamp circuits are as picky with respect to the ps parts as tubes. Top quality caps, chokes, shunt regulators, well chosen diodes can sometimes make them sing. As can batteries. By the time you have done all to please their fussiness you are looking at parts count and expense similar to a well tuned tube circuit.
I tend to go for Naim style decoupling nowadays i.e. each part of the circuit fed from an RC filter. Although is gives a relavitely high impedance supply, it is very beneficial for keeping the ground clean. You still need a good PS upstream of this thuogh.
IME shunt regulators are no better than series regs and you have to be careful with the ground return for all the "wasted" current.
IME shunt regulators are no better than series regs and you have to be careful with the ground return for all the "wasted" current.
I have seen distributed RC decoupling in Broadcast mixing desks....IIRC 10 ohms series and 100uF (10uF ?) shunt at each TL072 opamp supply pin.
Dan.
Dan.
Remember, anything you can hear, we can measure can't we?
The late Richard Heyser would've easily proved you wrong!!!
The late Richard Heyser would've easily proved you wrong!!!
I don't have the answer but I think it depends. How good are your ears? How good is your knowledge in understanding measurement?
You have the right to say so if you have good ears. If you don't, you don't know what you don't know.
What do you think? And what will you measure if you can't hear? Yes, I believe that anything I can hear can be measured. But people don't know what measurement is correlated with what I hear...
Many people make misleading measurements. Many people don't know what to measure. Worse, many people don't know their limitations.
I don't have vast experience of comparisons between series and shunt but one episode of upgrading the supplies to the opamp front-end to my Xindak integrated amp converted me to shunts from LM317/337s.
Engineering-wise, shunts do present lower output impedance across the band than LM317/LM337 when the latter are running at relatively low currents. The output impedance graph of the LM317 in the DS is shown at 500mA (from memory) but this can be expected to rise 20dB per decade as the output current goes down. A TL431 is typically 0.2ohms when shunting @2.5V but higher voltages can be assumed to be higher in proportion. A single transistor 'assist' lowers the output impedance by an order of magnitude or more.
Well, you chose a gross, totally blown out of proportion example to illustrate your theory.
What we are comparing here is subtle differences, not, say, a plugged amp to an unplugged one (that would be the gross difference between solid ice and liquid water).
Suppose you have two glasses of water, one at 24.05 degrees C and another at 24.09 degrees C .
You take a sip out of each ... can you reliably tell which is which? 🙄
Or would you rather have to trust ... ugh !!! 😱 .... a thermometer? 😀
I'll say this, after working with op amps for only about 12 years now. They are wondrous things, and are mathematically marvelous. Honestly, this world is a better place because of them. However, I find that although simple, they're not simple things to use.
I will say there is a massive audible difference between a simple audio op amp circuit and a simple discrete audio circuit. But this speaks to the designer. I have found that op amps are very finicky, and the power supply is difficult to tame if you don't know how. And one mistake leads to incredible amounts of hum and buzz. A discrete circuit is (in my experience) much easier to get quiet and stable. But if both are properly designed, I can't say anyone could hear a difference, let alone measure any real difference.
I have an op amp based guitar preamp and a discrete one. They do essentially the same thing, but the discrete one is much more stable. They sound the same too. I am really no good at designing stable op amp circuits. There's always something wrong - high distortion, instability, noise, buzz, etc.
I will say there is a massive audible difference between a simple audio op amp circuit and a simple discrete audio circuit. But this speaks to the designer. I have found that op amps are very finicky, and the power supply is difficult to tame if you don't know how. And one mistake leads to incredible amounts of hum and buzz. A discrete circuit is (in my experience) much easier to get quiet and stable. But if both are properly designed, I can't say anyone could hear a difference, let alone measure any real difference.
I have an op amp based guitar preamp and a discrete one. They do essentially the same thing, but the discrete one is much more stable. They sound the same too. I am really no good at designing stable op amp circuits. There's always something wrong - high distortion, instability, noise, buzz, etc.
Very few here will express agreement or even sympathy with your predicament 😀
Nothing easier than to get an opamp circuit stable, noise and hum free. Extracting really good sound is another story altogether.
I wouldn't say it's that trivial either, even if the symptoms mentioned pretty much translate to "my layouts suck". There's too many ways things can go wrong - bad supply bypassing plus low-impedance feedback network or load, high-impedance feedback network with no compensation cap, bad routing of inverting input node, capacitive loading, even something as subtle as a ground plane under the inverting input can be enough to trip up some circuits.
A simple discrete Class A circuit can also be very good and is likely to be less critical about bypassing and such - but it'll probably use a fair bit more power.
A simple discrete Class A circuit can also be very good and is likely to be less critical about bypassing and such - but it'll probably use a fair bit more power.
An opamp has a lot more gain before applying feedback, and sometimes afterward, too. It also depends on the opamp. A 741 is relatively easy to use without it going into oscillation and such, though I do recall having a problem when I directly connected its output to a few feet of shielded audio cable (this wasn't when the 741 was brand new, but it was a long while back). Even a 741 has a lot more gain than a few discrete transistors do, and without knowing some "basic" practical stuff (as already mentioned: what's a good layout, where the bypass caps should go - physically as well as on the schematic) you can get into trouble. The greater the gain or bandwidth, the easier it is to get into trouble. It's like driving a fast car where police are waiting on drivers like you.
Well, the discrete solutions work 100% for me, so I don't spend much time sorting out op amp circuits. This is my preference. My op amp amplifier works 100% with absolutely no issues... Until I use a Fender instrument cable, which trips it up. And discrete preamps can be built safely on strip board, which suits me well. 🙂
Honestly, I would hate to make a guitar amp for someone which doesn't work because they used a cable which caused the amp to oscillate. I am much more certain that my discrete design will be stable all the time.
But still, absolutely nothing wrong with op amps! When they don't work well, it's more than likely the designer...
There a very inexpensive component that will stop that from happening, if you know where to put it.
With great gain comes great responsibility, or something like that.
😀
I agree completely.
The only thing is that PCB prototyping is expensive, so adding one little tiny capacitor changes the layout, and then you need a new batch of prototypes.
I agree completely.
The only thing is that PCB prototyping is expensive, so adding one little tiny capacitor changes the layout, and then you need a new batch of prototypes.
Of course you should trust all your senses to be 100% accurate, and better than any test equipment.
In fact, here is some proof of how perfectly accurate your sense of vision is: Here's why you can't see all twelve black dots in this optical illusion | The Verge
Here is some more proof of your perfectly accurate and always trustworthy vision: 20 Optical Illusions That Might Break Your Mind
Your hearing, of course, is also 100% perfect and 100% trustworthy, just like your vision: https://www.newscientist.com/article/dn13355-music-special-five-great-auditory-illusions/
😀
-Gnobuddy
Spend 8 or 12 years training your ears in a musical program. Protect them from noise sources like motors, weapons, fireworks, excessive electronic "music".
Then listen to a hard to reproduce sound source like bells, cymbals, piano, pipe organ.
does the electronic system sound like the real thing? usually not. I heard one accurate system in a theatre in 1967, a voice of the theater/altec setup, recommended by our band director. I've heard another in my home. Never anywhere else.
All your pop instruments, human voice, who knows what they were supposed to sound like in the first place? All he tricks producers use on the voice these days: Alison Krause from 3' away did not sound like her own records.
A Steinway piano is a Steinway piano, go listen to one to calibrate your ears.
Then blow off the **** instruments. The 10 khz + 15 khz IM distortion test is not even usually run, the results are usually so bad. If your top octave Steinway passage has vibrato, the electronic reproduction system just failed that test, with only a wood/steel calibrator involved (a Steinway piano).
to the base topic, my best sounding but unreliable amp, a roadkill CS800s Peavey, has op amps in the input. My best sounding preamp is a vacuum tube PAS2, but the RA88a with op amps comes a close second. The second was highly modified by me to achieve this level or performance, the base circuit with 4558's was hissy and hummy.
Then listen to a hard to reproduce sound source like bells, cymbals, piano, pipe organ.
does the electronic system sound like the real thing? usually not. I heard one accurate system in a theatre in 1967, a voice of the theater/altec setup, recommended by our band director. I've heard another in my home. Never anywhere else.
All your pop instruments, human voice, who knows what they were supposed to sound like in the first place? All he tricks producers use on the voice these days: Alison Krause from 3' away did not sound like her own records.
A Steinway piano is a Steinway piano, go listen to one to calibrate your ears.
Then blow off the **** instruments. The 10 khz + 15 khz IM distortion test is not even usually run, the results are usually so bad. If your top octave Steinway passage has vibrato, the electronic reproduction system just failed that test, with only a wood/steel calibrator involved (a Steinway piano).
to the base topic, my best sounding but unreliable amp, a roadkill CS800s Peavey, has op amps in the input. My best sounding preamp is a vacuum tube PAS2, but the RA88a with op amps comes a close second. The second was highly modified by me to achieve this level or performance, the base circuit with 4558's was hissy and hummy.
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