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Op Amp Rolling

EERecordist

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In the review of the Fosi V3 (Fosi Audio V3 Amplifier Review), Amir wrote “There are replaceable op-amps for those of you who have nothing better to do than mess with the design.” For those who want to do just that, it is difficult selecting which op amps to “roll with”.

Both the Fosi V3 and the Aiyima 07Max (and now Fosi ZA3) use NE5532 chips. Perhaps the first move is to drop in a chip from the same series but with a higher specification, and, as suggested in other threads elsewhere, purchased from Mouser or Digi-Key.

Moving on, there are many DIP-8 op amps to choose from, although many from Texas Instruments in this particular packaging are now marked as “End of Life”. As ASR thrives on numbers, what are the most suitable op amps to drop in as replacements for the NE5532, based purely on the specification sheets?

Texas Instruments identifies op amps considered suitable for audio applications: see https://www.ti.com/amplifier-circuit/op-amps/audio/products.html#. This list shows 71 products, with 14 chips in the DIP-8 package. Other forums provide additional suggestions, and the Mouser database provides yet more possibilities.

File 1 (attached) provides a list of possible drop in replacements for the NE5532, where the pin-out and supply voltages are compatible. Measurements such as THD + Noise and CMRR are high on the list and other measurements such as overshoot and settling time may be important for audio applications.

It is also important not to use an op amp that has high gain and/or classified as high speed, as this may lead to ringing and possibly the overall amplifier itself becoming unstable.

File 2 (attached) provides a rough “order of merit” under each of the parameter headings from File 1. The figures suggest the chips to start with would be the LM4562NA/NOPB and LME49720NA/NOPB.

One surprise from this list is the lack of entries for the MUSES01 and MUSES02 chips; MUSES03 is not included as it is a single channel chip and not a drop in replacement for the NE5532.

Finding “the right op amp” is not easy. Any advice on what to look for in the specification sheets will be much appreciated.

I think it is notable the op amp was invented at Bell Labs! I have traveled the op amp journey in my audio career.

Ideally they are a high impedance differential input device with low input current needs, gain, low noise, a high gain-bandwidth product, reasonable voltage supply variation, and current drive.

Early on there was a discussion of slew rate and audio, but likely most audio op amps have adequate slew rate. For small signal, like the Fosi, you can neglect current drive. The amount of negative feedback is specific to the design of the equipment you are rolling the op amps on. That is a source of transient intermodulation distortion. So you probably want greater than or equal open loop gain to whatever Fosi selected.

Audiophiles and designers evaluate the large volume op amps in your list along with boutique op amps like Muse, API, Sparkos, Sonic Imagery, Analog Devices, 990-style, Burr Brown, Burston, and others. Some have been discussed on ASR.

If you have the time find Walter Jung's op amp books. We do have some deep circuit design contributors to ASR. One designs microphone preamps. Their need operating at high system gain is different than a Fosi buffer stage and a microphone preamp or balanced source amplifier may want better CMIR.

Maybe you can find audio people in your city to trade op amps. The other approach is to set up your own measurements with top ADC, DAC, and REW software.
 
Last edited:

dpuopolo

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First thing there is absolutely nothing wrong with the NE5532 opamp. The only place where it's bettered is with regards to common mode rejection, including power supply rejection. This is why Aiyima's recommended upgrade for their amps is the LM4562 because it has 120 FM cmrr (as opposed to the cmrr in the mid 90s that the 5532 has.
In the review of the Fosi V3 (Fosi Audio V3 Amplifier Review), Amir wrote “There are replaceable op-amps for those of you who have nothing better to do than mess with the design.” For those who want to do just that, it is difficult selecting which op amps to “roll with”.

Both the Fosi V3 and the Aiyima 07Max (and now Fosi ZA3) use NE5532 chips. Perhaps the first move is to drop in a chip from the same series but with a higher specification, and, as suggested in other threads elsewhere, purchased from Mouser or Digi-Key.

Moving on, there are many DIP-8 op amps to choose from, although many from Texas Instruments in this particular packaging are now marked as “End of Life”. As ASR thrives on numbers, what are the most suitable op amps to drop in as replacements for the NE5532, based purely on the specification sheets?

Texas Instruments identifies op amps considered suitable for audio applications: see https://www.ti.com/amplifier-circuit/op-amps/audio/products.html#. This list shows 71 products, with 14 chips in the DIP-8 package. Other forums provide additional suggestions, and the Mouser database provides yet more possibilities.

File 1 (attached) provides a list of possible drop in replacements for the NE5532, where the pin-out and supply voltages are compatible. Measurements such as THD + Noise and CMRR are high on the list and other measurements such as overshoot and settling time may be important for audio applications.

It is also important not to use an op amp that has high gain and/or classified as high speed, as this may lead to ringing and possibly the overall amplifier itself becoming unstable.

File 2 (attached) provides a rough “order of merit” under each of the parameter headings from File 1. The figures suggest the chips to start with would be the LM4562NA/NOPB and LME49720NA/NOPB.

One surprise from this list is the lack of entries for the MUSES01 and MUSES02 chips; MUSES03 is not included as it is a single channel chip and not a drop in replacement for the NE5532.

Finding “the right op amp” is not easy. Any advice on what to look for in the specification sheets will be much appreciated.
F
 

Doodski

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I used a list of recommended op-amps to try written by the designer of the amp.

(And I heard differences.)
So stuff is in lists like <.txt> or <.doc> etc and can be organized? What would it take to run all these OP amps? How many would be tested?
 

LTig

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I used a list of recommended op-amps to try written by the designer of the amp.

(And I heard differences.)
I've read the article of the designer about Opamps. As an EE I see too much disinformation. Instead of studying the datasheets of the opamps to find the proper one he tests them (which may lead to failure when using other exemplars), and he does not care about thermal overload (use an opamp to drive 0.5V at 33 Ohm!!!. Does he really think the tiny housing is able to dissipate the internal power dissipation of 2 amps safely and without cooling?

Lookin at the schematic there is no design other than what any book about basic opamp circuits (non inverting amplifier) teaches the novice. No compensation caps for some opamp types, no power rail decoupling cap close to the opamp depending on its type, and so on. I advice anybody playing with this circuit to read the datasheet of the opamp and add all components the maker of the opamp recommends for this application.
 

SIY

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More laid back and open, a little dry.
Well, when they're wet, they tend to short out. And rather than laid back, they get positively hinky, really difficult to control, and quite closed up (you have to dissolve the cases in nitric acid to get them open, not recommended for amateurs)..
 

JSmith

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Maybe you are just deaf?
Just stop the trolling.

@Fosi Audio, see what confusion you are causing with recommending people open up and modify a brand new product? Do you realise all this does is create uncertainty about the op-amps used in your products?


JSmith
 

Brian Hall

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The Fosi V3 and ZA3 sound great as they come. Messing around with other op-amps is a waste of time. As useless as "tube rolling". Anything with tubes will add distortion. If you don't like tube distortion, why bother trying for "better" distortion?
 

Mnyb

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The Fosi V3 and ZA3 sound great as they come. Messing around with other op-amps is a waste of time. As useless as "tube rolling". Anything with tubes will add distortion. If you don't like tube distortion, why bother trying for "better" distortion?

better distortion tube trolling with audio note , maybe i should get a plaid jacket...
 

Blumlein 88

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Plaid or tartan? maybe something like this.
1714976859002.png
 

solderdude

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There are quite a few differences when using opamps in Chu Moy amps.
The reason being most opamps are not designed to drive anything lower than 2000ohm.
In general the 'sound' they have is determined by the current limiter behavior which could be an issue for headphones with a low impedance.

Consider that just being a buffer in these power amps ensures none of the opamps will ever be loaded heavily (input R of the poweramp) so none will ever reach their current limits and as they are unity gain or just 2 or 3x max the frequency response, phase response will never be an issue with any of the opamps in this circuit.

The major contributor to the sound is the class-D amp after that opamp.

These days, especially the low voltage ones, can drive 32ohm or lower and are fine for C'Moy type amps but are mainly SMD so need adapters.

It basically is a standard design found in application manuals but made widely known in the DIY crowd by Chu Moy.
That is as long as the max. power supply voltage is not exceeded.
I'm sure people will also find obvious (but not measurable) 'sound signatures' in these opamps too which is not obvious in any tests (until they reach clipping points)
 
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antcollinet

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The reason being most opamps are not designed to drive anything lower than 2000ohm.
Right - so we are not hearing the effects of op-amps primarily. We are primarily hearing the effects of an inadequate (broken) design.

The only way the op amps audibly differ is the way they respond to being operated out of specification.

Just as if (for a really stupid analogy) people jump out of a second story window, some might get away with it with just bruises, some might break their ankles, some their legs and some might die. None of these is a desirable outcome.
 

Sokel

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Serious companies warns about changing any component (specially op-amps) and it usually voids warranty (as it should),I wrote about it before in another thread.
The only thing needed is a big sticker on the device that makes it immediately visible,not only written in the fine print of the manuals.
 
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