The Opamp thread

[raoultrifan]

Have not tried nor used the O2 design by this is what the designer said is THE best for voltage Stage is to use the NJM 4556. I love to try this op amp.[...]

Actually, the best Voltage-Amplification Stage is the default NJM2068 or, for a gain higher than 5X, LM4562/LME49720. The NJM/JRC 4556 is a very good output buffer able to drive headphones; it shouldn't be used in VAS, well...at least not inside the O2.

[...] A lot of fake "MUSES" opamps BTW seem to be re-badged 4556 or 4580s.

I always got those MUSES from authorized partners only; they're all listed on their website.

 

[raoultrifan]

True but it’s also true that MUSES are made by the same manufacturer: New Japan Radio.

I’m sure that they share a lot in common. [,...]

Well, yes and no. It's yes because it's indeed the same manufacturer, but it's no because MUSES opamps are manufactured by using a different process (in regard with Q&A, laser trim and time to complete the device) and on a different "bench". Also, legs are made of more copper and they can bend very easy.

 

[HeyManslowdown97]

Actually, the best Voltage-Amplification Stage is the default NJM2068 or, for a gain higher than 5X, LM4562/LME49720. The NJM/JRC 4556 is a very good output buffer able to drive headphones; it shouldn't be used in VAS, well...at least not inside the O2.

Yep that's correct. Thanks for the clarification. The NJM/JRC 4556 is best used as a output buffer able to drive headphones.

I’d be curious to see how it fairs matched up with the TI’s improved BUF634 in testing!

Impressive!

“The NJM4556 is the optimal speed for audio use and no faster. This makes it very stable without any fussy special requirements, output inductors, or series resistance required.”

(Updated: Found this by the O2 maker)

Spoiler: JRC NJM4555 vs BUF634

JRC NJM4556 – JRC is an interesting company with its roots in audio and analog. Unlike the big US companies like National, TI, etc. they tend to either offer lower cost versions of existing designs, or they design application-specific analog parts. I suspect the NJM4556 is one of the latter as it’s unique and almost made to order as a headphone op amp. It’s rated at 70 mA of current specified into 150 ohm loads. It was designed for audio use. In the eBay Cmoy it managed around 100 mA peak and overall rather impressive performance. In the same prototype setup as the OPA551 the NJM4556 performed significantly better in several tests and was much more stable. The NJM4556 is the optimal speed for audio use and no faster. This makes it very stable without any fussy special requirements, output inductors, or series resistance required. That’s worth a lot in this application. The one remaining problem is the output current. The 4556’s 70 – 100 mA obviously falls short of the 166 mA requirement. But, the 4556 is a dual op amp with two well matched amps on a single silicon substrate (die). What will it do with both amps in parallel to double the current capability? The answer is, with appropriate measures, it does good things! It produces over 200 mA which approaches the 250 mA of even the LME49066 and BUF634 above. It turns out using one 4556 with paralleled sections for each channel meets all the requirements. I’ve also tried to blow one up with brief short circuits playing music at clipping and so far so good. And you can buy 7 of them for the price of one OPA551. To my knowledge, this is the first time the 4556 has been paralleled for headphone duty and it’s a big reason the O2 can deliver great performance at such a low price.
2-15 OUTPUT STAGE DESIGN – With the 4556 specified, the rest of the output stage needs to be optimized. First, you usually can’t simply connect two op amp outputs in parallel. They may not share the current equally and any difference in offset voltage will significantly increase the quiescent current. Measurements with the dScope demonstrated just 1 ohm of series resistance works nicely with half a dozen different 4556 samples (some from different production lots). These are effectively in parallel so the output impedance is approximately 0.5 ohms which is well under the 2 ohm goal.”

Interesting tidbit about the lasers trims and copper manufacturing differences. I wonder if the process is improved makes the fundamental improvement to better circuitry in overall performance or it’s just the claims of making up R&D cost. If so it doesn't justify the jacking up the price hikes from .73 cents to 46 dollars! That’s a shrewd business model which is driven by subjective forum-based audiophile self branding marketing of the MUSES line.

The funny thing about the counterfeit markets is that is feeds off this model with the popularity of certain models desired by audiophiles. I for one won’t mind and prefer if the say the Chinese market development their own designs in regards to OP Amp as originals. But then again China isn’t known for their originality and like to copy existing designs or take an existing op amps and repackage them into the more desired op amp sought by audiophiles.

There are some sellers on AliExpress that do sell original op amps and it would be interesting if they were tested with the same vigor as the genuine popular ones found on threads like this. The more the merry (provided they don’t flood the markets with counterfeits that are inferior in quality). Fat chance that will happen!

It just seems that unless it comes from the major Chinese manufacturers like Huawei and Xiaomi (that don’t make op amps) it appears that the Chinese can’t make nor design their original designs[/Spoiler]

 

[Rroff]

Actually, the best Voltage-Amplification Stage is the default NJM2068 or, for a gain higher than 5X, LM4562/LME49720. The NJM/JRC 4556 is a very good output buffer able to drive headphones; it shouldn't be used in VAS, well...at least not inside the O2.

Good catch on that one! yes the 4556's advantage is its ability to deliver current with low distortion when you actually need a decent buffer.

“The NJM4556 is the optimal speed for audio use and no faster. This makes it very stable without any fussy special requirements, output inductors, or series resistance required.”

One of my concerns here - though he is right in what he says - the 4556's slew rate and other relevant specifications are quoted as typical rather than minimum as you see on some other opamps - which potentially means there are situations where they are performing below an adequate level maybe I think he does provide some graphs but how comprehensive over a wider usage scenario range they are valid for I don't have the experience to know - though there is a bit of headroom there isn't a huge amount depending on the actual operating range and what the actual minimums and how critical they are is. While theoretically it shouldn't matter I definitely see (hear) the best results with things like slew rates approaching double figures rather than in the 2-5 range or so - IMO it is one of the reasons the OPA2228 is generally preferred over the OPA2227 despite on paper being very closely related opamps.

 

[HeyManslowdown97]

While theoretically it shouldn't matter I definitely see (hear) the best results with things like slew rates approaching double figures rather than in the 2-5 range or so - IMO it is one of the reasons the OPA2228 is generally preferred over the OPA2227 despite on paper being very closely related opamps.

Honestly it’s not such an issue to select a high performance op amp that’s sound preferences you prefer provided you know to how to monitor its performance and give it what it needs fussy requirements, output inductors, series resistors, etc.

Unless, op amp rolling is a perfect swap. I (personally) don’t have the skill to fine tune a op amp that I like the sound of.

I don’t think it’s matter of saying yourself ‘any’ Dual op amp will do to swap for another dual op (per se) as the only requirement nor if this or that op amp is performs well in a particular stage. I think it’s more than just plug and play.

I have no idea how to Proof if whether an op amp is perform up to task unless they’re are noticeable signs like overheating, noise, volume issues, etc.

I’d love to have the know-how to fine tune an op amp and get to perform like it should and hit all of its benchmarks that are pertinent to audio signals.

As an open question I love if someone could provide the know-how or the procedure of how to give the op amp with the sound you love som’ much needed love to make it perform healthy on a dap.

 

[Rroff]

At a basic level you can feed various test frequencies and patterns through an opamp while monitoring the output with an oscilloscope to check the behaviour is as expected. That very quickly identifies things like clipping and ringing even with test equipment in the $/£/€100 kind of price range.

 

[raoultrifan]

Yep that's correct. Thanks for the clarification. The NJM/JRC 4556 is best used as a output buffer able to drive headphones.
I’d be curious to see how it fairs matched up with the TI’s improved BUF634 in testing![...]

Well, BUF634 and LME49600 are dedicated for use as output buffer, these will strive NJM4556 when using planars or hard to drive cans. It's like comparing gold with silver, so not quite OK to compare an opamp for general use (even paralleled) with another one especially designed to be used as output buffer.

[...] That’s a shrewd business model which is driven by subjective forum-based audiophile self branding marketing of the MUSES line[...]

MUSES01 measures and sounds very well in my PLAYMATE, although not the same happens inside PLAY, nor Essence One, so it's all about the surrounding circuitry, power supply ripple & noise, PCB traces, ground plane and...probably some luck too.

MUSES02 sounds and measures better than LME49860 when used inside HPA-3B, same applies to V5 and V6 opamps from Burson, although same expensive opamps may not measure so well inside PLAY. etc.

 

[HeyManslowdown97]

Well, BUF634 and LME49600 are dedicated for use as output buffer, these will strive NJM4556 when using planars or hard to drive cans. It's like comparing gold with silver, so not quite OK to compare an opamp for general use (even paralleled) with another one especially designed to be used as output buffer.



MUSES01 measures and sounds very well in my PLAYMATE, although not the same happens inside PLAY, nor Essence One, so it's all about the surrounding circuitry, power supply ripple & noise, PCB traces, ground plane and...probably some luck too.

MUSES02 sounds and measures better than LME49860 when used inside HPA-3B, same applies to V5 and V6 opamps from Burson, although same expensive opamps may not measure so well inside PLAY. etc.

Ugh, why must it be so complicated! Is there a way you can help them play nice in a specific dap I.e. resistor series, output inductors, etc!

 

[raoultrifan]

More or less, they'll all sensitive to voltage noise and also external noises too (EMI/RFI), so it's normal to perform differently from one player to another (more or less, most likely inaudible to most of us).

 

[HeyManslowdown97]

Th

More or less, they'll all sensitive to voltage noise and also external noises too (EMI/RFI), so it's normal to perform differently from one player to another (more or less, most likely inaudible to most of us).

The thing I’m confused about is the non inverting vs inverting op amps with the resistor series location and how it operates on the dap.

Does the negative feedback loop operate inside the op amp or does the schematics have to be calculated on the dap itself. It’s stuff like that I don’t know think about.

I’ve had instance where it isn’t a “clean” swap between op amps and It’s always a head scratcher since I KNOW there's a reason and yet I don't what it is.

I also find that some op amps in particular package like Vsson??? are use there own pcb to be a plug and play op amp. (The 1622 comes to mind.)

 

[raoultrifan]

All I can tell is that today amplifiers are measuring so well that I don't think you could pick-up the inverting vs. non-inverting amplifier in a properly conducted A/B test.

For me, the most important advantage of an inverting amplifier is its ability to operate with gains lower than 1X, which means lower background noise and less power, so best headamp for very sensitive headphones.

 

[Rroff]

I also find that some op amps in particular package like Vsson??? are use there own pcb to be a plug and play op amp. (The 1622 comes to mind.)

The 1622 is a 10 pin propitiatory IC that isn't drop in pin compatible with the generic 8 pin opamp - I don't really recommend using it on a breakout board as a drop in replacement for an 8 pin opamp as that will degrade its performance and potentially run into some of the same kind of issues like with the virtual ground on a basic CMOY amplifier design while not fully utilising the chip for some of its audio specific features like enable (which can be driven by GPIO, etc.).

The thing I’m confused about is the non inverting vs inverting op amps with the resistor series location and how it operates on the dap.

Does the negative feedback loop operate inside the op amp or does the schematics have to be calculated on the dap itself. It’s stuff like that I don’t know think about.

I think you are over-thinking this aspect - most audio applications use non-inverted with a negative feedback loop and you do have to take into account external components that are part of the feedback loop - whether an opamp is unity gain stable or not and whether internally compensated on opamps optimised for higher gains. I'd recommend spending some time reading up on https://tangentsoft.net/ (such as the opamps in detail section under audiologica) as it gives a good grounding in the basics.

I’ve had instance where it isn’t a “clean” swap between op amps and It’s always a head scratcher since I KNOW there's a reason and yet I don't what it is.

Often it will come down to things like bandwidth limiting capacitors that are part of the feedback loop which might be required to stabilise some opamps but might destabilise others and what kind of circuitry is on the output to deal with things like capacitance which some opamps might be sensitive to - some opamps for instance without a couple of resistors on the output can be upset by trying to drive headphones with long leads like the Sennheiser HD600 while others might be perfectly happy.

 

[HeyManslowdown97]

The 1622 is a 10 pin propitiatory IC that isn't drop in pin compatible with the generic 8 pin opamp - I don't really recommend using it on a breakout board as a drop in replacement for an 8 pin opamp as that will degrade its performance and potentially run into some of the same kind of issues like with the virtual ground on a basic CMOY amplifier design while not fully utilising the chip for some of its audio specific features like enable (which can be driven by GPIO, etc.).

Oh I’m well aware of the op amp 1622 and alerted an “experted” modder about CMOY reference and on Head fi thread and reported me and had me banned from a thread belligerently called me all kinds of labels and hid behind esoteric knowledge with embellished empirical jargon but I KNOW even as a newbie the he was full of crap!

Unfortunately, on the thread he had developed a cult-ish following and sadly they “sided” with him. My intention wasn’t to question his ability nor knowledge to make him look bad but that I was skeptical of what he was saying because it didn’t sound right (based on what I read)!

Funny part was he did say he had virtual ground issues with his mod and wanted to trade with members the said portable dap to conduct “ground experiments” to eradicate the problem. Lol.

 

[Rroff]

Oh I’m well aware of the op amp 1622 and alerted an “experted” modder about CMOY reference and on Head fi thread and reported me and had me banned from a thread belligerently called me all kinds of labels and hid behind esoteric knowledge with embellished empirical jargon but I KNOW even as a newbie the he was full of crap!

Unfortunately, on the thread he had developed a cult-ish following and sadly they “sided” with him. My intention wasn’t to question his ability nor knowledge to make him look bad but that I was skeptical of what he was saying because it didn’t sound right (based on what I read)!

Funny part was he did say he had virtual ground issues with his mod and wanted to trade with members the said portable dap to conduct “ground experiments” to eradicate the problem. Lol.

There is a whole load of information about the IC from johnc124 around the web about it - he actually works for the company that developed and manufactures the chip I assume you aren't getting him mixed up with a modder? there are all kinds of potential problems with DC offset, etc. if you just slap one into a circuit on a breakout board.

 

[HeyManslowdown97]

There is a whole load of information about the IC from johnc124 around the web about it - he actually works for the company that developed and manufactures the chip I assume you aren't getting him mixed up with a modder? there are all kinds of potential problems with DC offset, etc. if you just slap one into a circuit on a breakout board.

Nope, I cited johnc124 as well and am well aware that he’s the lead marketing guy for that particular project at TI who said it wasn’t a diy friendly package. My citation taken from “DIYAUDIO” thread when it was launched was the exact thing I used as to why I thought it wasn’t just matter of slapping on a circuit board and the dude (aka: modder) went ballistic.

My main point was that it wasn’t designed In the way he was using it & he became enrage with every post I posted of potential problems with what he was doing but since he sounded like knew what he was doing provided “changelogs”, pics of his modifications and sounded convincing and influential people just took his word for it.