I put more 'lectric in my amp and all I get is smoke & sparks, not more sound. Dag nab it!
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Replace OP amps. Completely pointless, or not?
- Thread starter DanielT
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Barrelhouse Solly
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Hmm... I think we have a a semantic problem. Maybe I should have said chrome valve covers or tuck and roll back seat. How about putting something with mystery in the name in the gas tank. Add a spoiler to a car that's never going to go faster than freeway speeds? My point is that this kind of hobby involves tinkering. I'm not saying that fooling around with different op amps will increase performance necessarily. It's the act of doing something whether it results in a measurable change or not. Op amps aren't the same as putting a cinder block on top of your power amp. At least it involves actual electrical properties. BTW, I know the human ear has well known limits and all amps at or above a certain level of quality can only produce imperceptible improvements in performance.
DonR
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Pinstripes are good for 5hp more. Fact.
Ricardus
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Flames are good for 10.
DonR
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Fact
erintse
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If any interested, I would share the article here~
Further reading: LM4562 vs NE5532: What are Differences and How to Choose
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DSJR
Major Contributor
Do you *really* need bandwidth out to 55MHz? In some circuits, I gather there's a greater risk of oscillation and all manner of related nasties...
Heck, most so called 'audiophiles' can't hear above 15kHz anyway (not unless they wind the gain up higher at these frequencies to claim they can 'hear' higher!).
Heck, most so called 'audiophiles' can't hear above 15kHz anyway (not unless they wind the gain up higher at these frequencies to claim they can 'hear' higher!).
DSJR
Major Contributor
But but but 
.... That's nothing to do with limited bandwidth audio which has nothing we can hear above 20kHz and with often all manner of s**t over 100kHz, either switching supply/amp noise, AM radio and so on and so forth. I remember the Quad 405 current dumping circuit which in that version, had an op-amp on the signal input side (later moved to the feedback path in subsequent amps they make). replacing said original op-amp with a fancy-foo 'audiophool' type could lead to ringing and all sorts happening.
Staying with Quad and showing just how far we've come, the mid 60's 303 power amp has what are now almost unobtainium original output transistors. Simply replacing these with a modern spec version can apparently, introduce some form of instability with some samples in the now ancient design. Properly qualified service techies and engineers can test for this, but domestic based DIY amateurs may not be able to do this and I remember one chap deliberately increasing the bias on the output stage because he wanted the amp to feel comfortably warm to the touch, even if no technical or subjective benefit was possible by increasing this...
.... That's nothing to do with limited bandwidth audio which has nothing we can hear above 20kHz and with often all manner of s**t over 100kHz, either switching supply/amp noise, AM radio and so on and so forth. I remember the Quad 405 current dumping circuit which in that version, had an op-amp on the signal input side (later moved to the feedback path in subsequent amps they make). replacing said original op-amp with a fancy-foo 'audiophool' type could lead to ringing and all sorts happening.Staying with Quad and showing just how far we've come, the mid 60's 303 power amp has what are now almost unobtainium original output transistors. Simply replacing these with a modern spec version can apparently, introduce some form of instability with some samples in the now ancient design. Properly qualified service techies and engineers can test for this, but domestic based DIY amateurs may not be able to do this and I remember one chap deliberately increasing the bias on the output stage because he wanted the amp to feel comfortably warm to the touch, even if no technical or subjective benefit was possible by increasing this...
OP
DanielT
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- #510
Certainly for HiFi no higher frequencies than 20 Khz are needed, because of our how high frequencies we can hear. However, when measuring and/or designing HiFi related products, frequencies above 20 kHz may be good to take into account as it may trickle down in frequency. Take a measurement of a class-D amplifier or switching amplifier. If a sufficiently high bandwidth is not used during the measurement, it may be more difficult to determine distortion levels in the audible range. That because of IM distortion. I have heard that at least 80 kHz for this type of measurement is needed. If such a high bandwidth is needed for this type of amplifier measurement, I do not know. That's for those more knowledgeable about amplifiers and measurements of them to clarify.But but but
Staying with Quad and showing just how far we've come, the mid 60's 303 power amp has what are now almost unobtainium original output transistors. Simply replacing these with a modern spec version can apparently, introduce some form of instability with some samples in the now ancient design. Properly qualified service techies and engineers can test for this, but domestic based DIY amateurs may not be able to do this and I remember one chap deliberately increasing the bias on the output stage because he wanted the amp to feel comfortably warm to the touch, even if no technical or subjective benefit was possible by increasing this...
This, above 20 kHz, was important in the development of the CD format:
Nyquist frequency
In signal processing, the Nyquist frequency (or folding frequency), named after Harry Nyquist, is a characteristic of a sampler, which converts a continuous function or signal into a discrete sequence. For a given sampling rate (samples per second), the Nyquist frequency (cycles per second) is the frequency whose cycle-length (or period) is twice the interval between samples, thus 0.5 cycle/sample. For example, audio CDs have a sampling rate of 44100 samples/second. At 0.5 cycle/sample, the corresponding Nyquist frequency is 22050 cycles/second (Hz). Conversely, the Nyquist rate for sampling a 22050 Hz signal is 44100 samples/second.[1][2][A]
Typical example of Nyquist frequency and rate. To avoid aliasing, the sampling rate must be no less than the Nyquist rate of the signal; that is, the Nyquist rate of the signal must be under double the Nyquist frequency of the sampling.
When the highest frequency (bandwidth) of a signal is less than the Nyquist frequency of the sampler, the resulting discrete-time sequence is said to be free of the distortion known as aliasing, and the corresponding sample rate is said to be above the Nyquist rate for that particular signal.[3][4]
Nyquist frequency - Wikipedia
But okay those were examples of frequencies in the kHz range and not MHz, but still.
solderdude
Grand Contributor
The issue in DACs (with the IMD hump) seems BW related. There is not only audio going in there but also glitches (very fast narrow pulses)
When these saturate the differential input then you can expect errors. In such cases the BW can make a difference.
This is something different than just an analog unity gain, or inverting buffer and also differs from usage in high gain amplifier stages (phono, mic etc) where a high BW product and gain are needed to ensure an audio bandwidth.
In most cases the opamp just is unity gain or max. 5x or so (headphone amp) and in this case the noise number is more important.
For precision measurements DC offset or THD might be a deciding factor.
When these saturate the differential input then you can expect errors. In such cases the BW can make a difference.
This is something different than just an analog unity gain, or inverting buffer and also differs from usage in high gain amplifier stages (phono, mic etc) where a high BW product and gain are needed to ensure an audio bandwidth.
In most cases the opamp just is unity gain or max. 5x or so (headphone amp) and in this case the noise number is more important.
For precision measurements DC offset or THD might be a deciding factor.
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DSJR
Major Contributor
Daniel, I'm not in the slightest arguing with you there, but it has been commented on in older measurement reviews that it's perhaps a bit silly to have amps with wide open responses much over 100kHz (hopefully an engineer can chip in and comment please), but with so much ultrasonic 'stuff' around in some digital sources (my Philips based CD player has 'stuff' at around the 70kHz region), any filtering has to be done very carefully, as Naim found in the mid 80's when their better preamp design had better filters put in during a model/upgrade change to replace the simpler ones they used before 'digital' sources began taking over. Ideally, a CD source should have nothing over half the sampling frequency, but I'm sure I've seen noise and 'stuff' over say, 40kHz from dacs and so on (I need clarification here though). SA-CD players had plenty of noise going on over 20kHz I remember. Couple this with metal or worse, 'diamond style' tweeters which take off at 25 - 40kHz (one seems to be +30dB at 40k compared to the mid 5 - 7kHz as we hear it level unless I'm mistaken...Certainly for HiFi no higher frequencies than 20 Khz are needed, because of our how high frequencies we can hear. However, when measuring and/or designing HiFi related products, frequencies above 20 kHz may be good to take into account as it may trickle down in frequency. Take a measurement of a class-D amplifier or switching amplifier. If a sufficiently high bandwidth is not used during the measurement, it may be more difficult to determine distortion levels in the audible range. That because of IM distortion. I have heard that at least 80 kHz for this type of measurement is needed. If such a high bandwidth is needed for this type of amplifier measurement, I do not know. That's for those more knowledgeable about amplifiers and measurements of them to clarify.
This, above 20 kHz, was important in the development of the CD format:
Nyquist frequency
In signal processing, the Nyquist frequency (or folding frequency), named after Harry Nyquist, is a characteristic of a sampler, which converts a continuous function or signal into a discrete sequence. For a given sampling rate (samples per second), the Nyquist frequency (cycles per second) is the frequency whose cycle-length (or period) is twice the interval between samples, thus 0.5 cycle/sample. For example, audio CDs have a sampling rate of 44100 samples/second. At 0.5 cycle/sample, the corresponding Nyquist frequency is 22050 cycles/second (Hz). Conversely, the Nyquist rate for sampling a 22050 Hz signal is 44100 samples/second.[1][2][A]
Typical example of Nyquist frequency and rate. To avoid aliasing, the sampling rate must be no less than the Nyquist rate of the signal; that is, the Nyquist rate of the signal must be under double the Nyquist frequency of the sampling.
When the highest frequency (bandwidth) of a signal is less than the Nyquist frequency of the sampler, the resulting discrete-time sequence is said to be free of the distortion known as aliasing, and the corresponding sample rate is said to be above the Nyquist rate for that particular signal.[3][4]
Nyquist frequency - Wikipedia
en.wikipedia.org
But okay those were examples of frequencies in the kHz range and not MHz, but still.
OP
DanielT
Major Contributor
- Thread Starter
- #513
DSJR, I agree with you in what you say.
What I said in #508 was just a supplement, beyond the HiFi world. Op-amps have many uses where some with high bandwidth can be good in certain, non-HiFi contexts, while the difference in bandwidth eg NE5532 vs LM4562 for audio does not matter.Regarding sufficient bandwidth in measurements of class D amplifiers, observe measurements of, is nothing strange. You need that if you are to be able to interpret the results. If I understand that correctly that is.
Too low measurement bandwidth can result in a different result vs high measurement bandwidth as far down as 6 kHz. I think Amir uses 45 kHz when measuring class D amps.
The Nyquist frequency, if I understand it correctly, because the CD format would have a straight FR to 20 kHz, a cut off filter was needed higher up in frequency. Nyquist's theoretical ideas were then applied, which became part of the solution for the CD format, the CD technology.Which became the standard solution that all manufacturers used.
Don't ask me to elaborate. I'm out on thin ice now with a lack of my technical knowledge on this subject. Might be worth a new thread to sort it out.
(if there aren't already such threads)
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popej
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It is not "Bandwidth" but "Gain Bandwidth Product". In case of LM4562 we have gain 140dB which gives bandwidth 5.5Hz.
For comparison, NE5532 has gain 100dB and bandwidth 100Hz.
True! You need to re-cam your DAC to take full advantage
That is not needed. If IM Distortion components appear in the audible frequency range, they will be there whether or not we measure higher (ultrasonic) frequencies.
To clarify, the high frequencies that inter-modulate and create audible band component are there in the signal whether we measure them or not. Those components will be visible in a measurement limited to 20kHz.
But only if the opamp is operated open loop. When feedback is applied to limit the gain, we take the actual circuit gain. Otherwise they would be useless for audio applications which need at least 20kHz.
So if we take (for example) a phono pre-amp with 40dB (x100) of gain (most line level opamps won't be used with more than a few dB of gain - mostly less than 10), then the circuit will have a bandwidth of about 550kHz if not limited by other components (normally capacitance in the feedback for stability)
OP
DanielT
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- Thread Starter
- #518
Maybe it could be as you say but this is what an EE who manufactures amplifiers said about the measurement Stereophile performed on the NAD C 298 amp , so I don't know what to believe:
Morello:
Note that the measurements on this class-D device are carried out with the low-pass filter (f=25 kHz) Audio Precision AUX-0025 connected between the output of the power amp and the input of the analyzer, which is why all THD measurements are irrelevant above about 6 kHz. I'm surprised Atkinson doesn't limit the graphs to just this.
....
The reason for the measurement procedure is that the analyzer from Audio Precision that Atkinson uses does not handle copious amounts of high-frequency garbage typical class-D spews out. What I object to is that THD data is still reported up to 20 kHz, even though the data is not relevant above 6-7 kHz. It is also clear that many readers of testers do not reflect on this, which is, of course, completely understandable.(because they don't understand how this thing with measurements should be done, if I interpret what he says)
.....
THD is a measure of the step nonlinearities - quadratic, cubic and higher order terms in the transfer characteristic. The same terms entail intermodulation distortion. If you want a correct picture of the amp's distortion, the bandwidth when measuring THD up to 20 kHz must be at least 80 kHz, which means that harmonics up to and including order four are included.
The Nad C298 shows high THD at treble frequencies above 10 kHz, despite the fact that the numbers are heavily embellished due to the low-pass filter used in the THD measurement.
(with reservation for inaccuracies via google translate)
Note I'm just the messenger so don't shoot me down.
Edit:
I'll translate, or let google do it, a little more from that thread what Morello says:
...measuring THD up to 20 kHz with 25 kHz bandwidth is nothing to have opinions about - if you understand the implications, namely that the harmonics in the top octave are not included, it is easily realized that it is de facto an inappropriate procedure as the result is nonsense. ..
..I don't think you understood what I wrote. If an amplifier exhibits THD of 1% at 20 kHz with a dominant third tone, it means that the third tone has a frequency of 60 kHz. If you measure with 25 kHz bandwidth, the third tone will be attenuated by, for example, 40 dB (depending on the filter's flank attenuation) and the measurement will show a THD of 0.01%. The measurement thus gives a false result. ..
I-or in that thread:
What Morello has tried to convey above (and in many older threads) is that the nonlinearities that give rise to inaudible spectral components above 20kHz when measuring THD also give rise to audible intermodulation distortion (in the audible range). If you measure the IMD instead, this will be clear.
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popej
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Sure. That's why wide GBW product is usable for audio, while wide bandwidth looks excessive.
Yep. Loop gain increases by 20 dB per decade below the GBW so you have about 12 dB more loop gain with the LM4562 than with the 5532. This means that distortions are reduced by 12 dB through negative feed back within the complete audible range. This has nothing to do with being able to hear above 20 kHz. You just have to make sure that the amplifier is stable, which is not too difficult if the gain is high, like in a phono preamp.
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