Hey guys, I hope this topic has not yet been discussed in that way.
I am interested in how to choose the right Op-Amp for specific circuits, like:
I wonder in which circuits it is beneficial to use a Bipolar, JFET or CMOS input Op-Amp
As I understand some things are just down to personal preference, but I would like to understand the technical background behind the decision.
So which specifications are taken into account?
The goal for me is minimal distortion and noise.
Happy to hear about your decision process 🙂
I am interested in how to choose the right Op-Amp for specific circuits, like:
- Unity gain buffer (non-inverting)
- Summing amplifier (inverting)
- Filters (i.e. Linkwitz-Riley, Butterworth etc.)
- Phono preamps
- Headphone amps
I wonder in which circuits it is beneficial to use a Bipolar, JFET or CMOS input Op-Amp
As I understand some things are just down to personal preference, but I would like to understand the technical background behind the decision.
So which specifications are taken into account?
- Gain bandwidth product
- Slew rate
- Input noise
- Offset voltage
- Input bias current
- Common-mode rejection ratio
- Input impedance
- Open loop gain
- Output current
- Capacitive load drive
The goal for me is minimal distortion and noise.
Happy to hear about your decision process 🙂
For noise, it depends a lot on the source impedance. For example, noise-wise, the op-amps that are most suitable for moving-coil phono preamplifiers (very low source impedance) are the worst for moving magnet (much higher source impedance).
Phono preamps: MM need low current noise, so JFET or NE5534A typically, for MC low voltage noise is paramount, so AD797 is a strong contender, as are hybrid designs with low voltage noise transistors like the ZTX951.
buffers/summing amp/filters - all the same requirements really, but if there's a pot a JFET opamp doesn't require caps in the wiper path to prevent scratchiness. Headphone amps require more current drive than many opamps.
buffers/summing amp/filters - all the same requirements really, but if there's a pot a JFET opamp doesn't require caps in the wiper path to prevent scratchiness. Headphone amps require more current drive than many opamps.
Op-amps are designed for a variety of applications and so being good at some parameters is not essential for audio. For example, input bias and offset voltage are important for measurement.
Op-amps have extremely high open-loop gain to minimize error in the feedback loop. However, the gain starts falling at a low frequency (10-100Hz). Make sure that enough open-loop gain remains at 20KHz.
Ed
Op-amps have extremely high open-loop gain to minimize error in the feedback loop. However, the gain starts falling at a low frequency (10-100Hz). Make sure that enough open-loop gain remains at 20KHz.
Ed
Messing around with various opamps lately I’ve had very good luck with the old warhorses of audio - 5532, 2068, 4580, 833, etc… as all of these were designed when audio was a market leader and the big engineering fabs would put top people and top money into development. Are there better ones today? Probably, but as analog audio has not appreciably changed in 40-50yr, so the engineering that was cutting edge then is still doing an admirable job today.
If the circuit doesn’t work well and sound great with a 5532, there’s something wrong with it.
If the circuit doesn’t work well and sound great with a 5532, there’s something wrong with it.
OPA1642/1652/1656/1612 spring to mind, LM4562 as well
Some circuits need the low low bias currents of a JFET opamp such as the OPA1656. JFET inputs mean you can lose large electrolytics from the wipers of potentiometers too, and are usually less sensitive to EMI (more of an issue these days).
Golden rule though is ensure decoupling is adequate and stability isn't borderline.. Either can lead to degraded performance.
Some circuits need the low low bias currents of a JFET opamp such as the OPA1656. JFET inputs mean you can lose large electrolytics from the wipers of potentiometers too, and are usually less sensitive to EMI (more of an issue these days).
Golden rule though is ensure decoupling is adequate and stability isn't borderline.. Either can lead to degraded performance.
The OPA1656 is a MOSFET op-amp, rather than JFET. Not that that makes much of a difference; the corner frequency of the 1/f noise is somewhat higher.
Thank you for all the replies so far.
I summarize:
MM Phono Preamp (High Source Impedance):
- low current noise
MC Phono Preamp (Low Source Impedance):
- low voltage noise
Suboptimal Decoupling/Stability
- low slew rate
DC-coupling Potentiometers
- low input bias current
Headphone Amp
- high current drive
In another thread some popular op-amps were simulated in both inverting and non-inverting amplifier topology and the results showed, that all the op-amps showed less distortion in the inverting topology. the best op-amps in the test for the non-inverting amplifier were LM4562 and OPA1612. I wonder which feature of these op-amps made them give the lowest THD in the non-inverting mode?
So still unclear to me:
Non-inverting Buffer:
?
Summing Amplifier:
? (same as inverting amplifier?)
Active Filters:
? (high load drive capabilty?)
I summarize:
MM Phono Preamp (High Source Impedance):
- low current noise
MC Phono Preamp (Low Source Impedance):
- low voltage noise
Suboptimal Decoupling/Stability
- low slew rate
DC-coupling Potentiometers
- low input bias current
Headphone Amp
- high current drive
In another thread some popular op-amps were simulated in both inverting and non-inverting amplifier topology and the results showed, that all the op-amps showed less distortion in the inverting topology. the best op-amps in the test for the non-inverting amplifier were LM4562 and OPA1612. I wonder which feature of these op-amps made them give the lowest THD in the non-inverting mode?
So still unclear to me:
Non-inverting Buffer:
?
Summing Amplifier:
? (same as inverting amplifier?)
Active Filters:
? (high load drive capabilty?)
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Erm, the OPA189 cannot drive low impedances well, its distortion rockets as the load impedance falls from 10k, being pretty shoddy by 600 ohms. The distortion also rises rapidly with frequency, so the 1kHz distortion figure is misleading. It's a chopper opamp designed for low frequency DC precision applications. The low 1/f noise is attractive, but it looks like care is needed to get the best from it - its full power bandwidth is less than 20kHz for instance, ruling it out for some applications with high (intermediate) signal levels. 5Vrms is about the limit at 20kHz.
So limit it to 10k loads, low signal levels, and don't expect particularly low 10k distortion figures - and its going to fare well.
So limit it to 10k loads, low signal levels, and don't expect particularly low 10k distortion figures - and its going to fare well.
The LM4562 is providing a very natural, neutral, and clear sound that is well-suited for high-fidelity audio applications like phono preamps. The "bipolar" design of the op-amp contributes to its excellent timbral accuracy and ability to faithfully reproduce the nuanced tonality of analog vinyl playback.
The "natural" and "neutral" qualities doesn't overly color or alter the inherent character of the audio signal. This allows the true timbres and textures of the original vinyl recording to come through without unwanted coloration.
And the "clear" sound quality speaks to the op-amp's low distortion and noise levels, which are crucial for preserving the delicate inner details and dynamics of vinyl playback.Overall, the LM4562's strengths in timbral accuracy and transparency make it an excellent choice for the critical task of phono preamp amplification. The nuanced reproduction of the analog source material must be very engaging to listen to.
The "natural" and "neutral" qualities doesn't overly color or alter the inherent character of the audio signal. This allows the true timbres and textures of the original vinyl recording to come through without unwanted coloration.
And the "clear" sound quality speaks to the op-amp's low distortion and noise levels, which are crucial for preserving the delicate inner details and dynamics of vinyl playback.Overall, the LM4562's strengths in timbral accuracy and transparency make it an excellent choice for the critical task of phono preamp amplification. The nuanced reproduction of the analog source material must be very engaging to listen to.
I just look at the specifications, that's where reality lies. LM4562 is not very low current noise and this rules it out for top-flight MM preamps - NE5534A is still probably the best bipolar for that purpose, beats the LM4562 by a full 12dB (and of course JFET opamps have insignificant current noise and are a good choice too).
MC preamps need ultra low voltage noise, and current noise is not an issue due to the low impedances, so AD797 is a choice that makes sense there, although often a hybrid approach using low noise transistor(s) and an opamp is probably the best approach for top performance.
MC preamps need ultra low voltage noise, and current noise is not an issue due to the low impedances, so AD797 is a choice that makes sense there, although often a hybrid approach using low noise transistor(s) and an opamp is probably the best approach for top performance.
LM4562 is said to be sensible to EMI/EMC too...
I always found the 4580DD to be a good subjective one in many devices I heard. Not as sota as the nowadays tech opa though.
Ad8597 can be a cheaper alternative to AD797 according what you are looking for. OPA 1641/42 while not very high curent output (but most have >= 47k Z pre or amp) can makes nice buffers if one want it jfet input and has realistic price not as a AD797 for illustration.
OP828 has very low current input noise and below 2k hz one of the quietest at output and is jfet input.
I always found the 4580DD to be a good subjective one in many devices I heard. Not as sota as the nowadays tech opa though.
Ad8597 can be a cheaper alternative to AD797 according what you are looking for. OPA 1641/42 while not very high curent output (but most have >= 47k Z pre or amp) can makes nice buffers if one want it jfet input and has realistic price not as a AD797 for illustration.
OP828 has very low current input noise and below 2k hz one of the quietest at output and is jfet input.
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I'm a huge fan of the OPA1656 due to it's 100ma R-R output current and the over-all performance. I've rebuild a preamp using this op-amp and am very happy with it's performance. The 2156 is the same amp with a full range (R-R) input section which is sometime needed (as in followers or replacing TLO72 in applications with signals near the positive rail).
I have also used the 4562, but it takes more supply current, and delivers less output current. It is quiet and low distortion in low Z circuits, but I find the 1656 is more versatile.
I have also used the 4562, but it takes more supply current, and delivers less output current. It is quiet and low distortion in low Z circuits, but I find the 1656 is more versatile.
Comparing the LM4562, NJM2068, NE5532, and NJM4580, this is my ranking based on my subjective listening impressions:
The LM4562 is the first. It has a brighter and clearer sound among the four other op-amps.
The second is the NJM2068.
The third is the NE5532, which is the most balanced and neutral.
The fourth is the NJM4580, which has a slight sibilance on the high frequencies when tested in my phono preamp.
If I want to listen to classical music, then I would choose the LM4562 and NJM2068 op-amps. For rock music, I would choose the NE5532.
The NJM2068 is the second best. It also has a distinct sound closest to the LM4562.
These are all bipolar op-amps, and I am comparing their sound in the DIY phono preamp I built, based on projects from the DIYaudio projects website.
Switching op-amps and observing the sound of the preamp is important. The surrounding circuit of the op-amp must be properly matched for the sound quality it produces. The passive and active components, especially the resistors and capacitors in the RIAA equalization network, need to be well-designed for proper matching.
The LM4562 is the first. It has a brighter and clearer sound among the four other op-amps.
The second is the NJM2068.
The third is the NE5532, which is the most balanced and neutral.
The fourth is the NJM4580, which has a slight sibilance on the high frequencies when tested in my phono preamp.
If I want to listen to classical music, then I would choose the LM4562 and NJM2068 op-amps. For rock music, I would choose the NE5532.
The NJM2068 is the second best. It also has a distinct sound closest to the LM4562.
These are all bipolar op-amps, and I am comparing their sound in the DIY phono preamp I built, based on projects from the DIYaudio projects website.
Switching op-amps and observing the sound of the preamp is important. The surrounding circuit of the op-amp must be properly matched for the sound quality it produces. The passive and active components, especially the resistors and capacitors in the RIAA equalization network, need to be well-designed for proper matching.
Get a couple of books for your bookshelf to have some references in house:
Walter G. Jung: "Audio IC opamp applications"
Douglas Self "Self on Audio" (more general) and "Small signal audio design"
Should get you started and answer the most questions. They may not cover the latest parts but the general principles are what you need to understand first.
Walter G. Jung: "Audio IC opamp applications"
Douglas Self "Self on Audio" (more general) and "Small signal audio design"
Should get you started and answer the most questions. They may not cover the latest parts but the general principles are what you need to understand first.
Hey, it would be a whole book to answer your questions.
Much practical approach is to have a particular circuit in mind and then finding the op amps that would fit best.