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Op Amp Replaced: Fosi V3 Monoblocks LM4562NA/NOPB $8x3

J

jmdesignz2

Senior Member
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Aug 19, 2025
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Well it certainly doesn’t sound worse

I purchased 4 mono blocks from Fosi directly

Two arrived in what I’m calling V3.5 with 19/25db gain RCA switch

Two had 31/26db

One immediately developed a bad RCA connection and that pair are in process of being replaced by Fosi who has been very responsive

I carefully replaced all six op amps in my pair of Fosi V3.5 Monoblocks with the much higher spec

(Also added more Arctic R6 under the amp ic area but this definitely doesn’t have any sound impact lol) taking care to avoid any stray bits

LM4562NA/NOPB​

Link to spec sheet

Took pictures before and after. Also noting there’s room to replace the main 2200mF Nichicon 105 deg capacitors with much fatter higher capacity ones if one is not risk averse lol

Of course my observations are subjective but I am a careful analyst of my music and have listened to these tracks numerous times

Most obviously there’s more tonal textures for certain things such as fingertips on strings, instrument surfaces. Example is hearing a truer representation of a slightly moist finger sticking to a wood surface. Palm vs finger strikes, drum skin textures

Either way these are AFAIK highest bang for buck, lowest risk modification with real spec sheets.

There’s around 20db better PSRR for one

I’m enjoying them even more now and that’s worth it for $8 per op-amp (total $8x6 op amps) and a few minutes

System details:

Philharmonic BMR towers with outriggers, WBC 7AWG ofc 6’ cables, Fosi v3.5 mono blocks 48v/10A on each, XLR WBC ultimate star quad Amphenol 6’, Topping DX5 II fw1.66, Optical from WiiM Ultra.
 
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jmdesignz2 said:
There’s around 20db better PSRR for one
Click to expand...
No there isn't, it will still be 65dB (TPA3255 is the bottleneck) and the op-amps are NOT directly fed from the 48V supply so 'improving' the 48V will not result in improved anything.


jmdesignz2 said:
Of course my observations are subjective but I am a careful analyst of my music and have listened to these tracks numerous times
Click to expand...
You could also do it objectively, level matched and statistically valid knowing you have more than 1 amp ... but that will take away the fun and the ability of telling op-amps apart.

Please don't post misinformation. There is already enough misinformation to be found everywhere.

It is fine to post subjective impressions especially when you mention it is subjective but do not believe that because you find yourself to be a 'careful analyst of my music and have listened to these tracks numerous times' will change anything when it comes to reliability of the observations.
 
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solderdude said:
No there isn't, it will still be 65dB (TPA3255 is the bottleneck) and the op-amps are NOT directly fed from the 48V supply so 'improving' the 48V will not result in improved anything.


You could also do it objectively, level matched and statistically valid knowing you have more than 1 amp ... but that will take away the fun and the ability of telling op-amps apart.
Click to expand...
aren’t the op amps in the signal chain before the TPA amp? Why won’t a cleaner signal be beneficial?
 
@jmdesignz2 Here's a couple of threads to keep you amused.

amirm

'Does Op-amp Rolling Work?'

When I post my last video on review of Douk A5 amplifier, I mentioned that rolling (changing) op-amp ICs in there is fruitless. I got have a dozen comments under that video in youtube asking why so I thought I experiment again with the A5. Note that I have done the same testing with both DACs and Power Amplifiers and found the change to not make a difference. But let's see if the results are different this time.

Op-amp rolling amplifier 994Enh-Ticha Sonic Imagery Labs NE5532P TI Testing Douk A5 Stereo Aud...jpg

The Douk A5 makes this job both easy and hard. It is easy because you can just lift the plexiglass and replace the op-amps. The difficulty was...
  • Like

amirm

'Op-amp Rolling Using Sparkos on Fosi V3 Mono'

This is a study of measured differences if one swaps up the TI NE5532p dual IC op-amp in a Fosi V3 Mono amplifier with a "discrete" opamp from Sparkos. It is a test requested in the youtube comments of my video test of the same using Douk A5 and Sonic Imagery op-amp. The Sparkos SS3602 retails for US $79.80 but I found a discount coupon that brought the cost down to $74.33 with shipping included.
Fosi V3 Mono amplifier SS3602 Sparkos op amp rolling swap Testing Review.jpg


Per Fosi documentation, there are three op-amps. The one at the bottom is only for unbalanced/balanced conversion. That leaves two op-amps to swap. Company says if you...
  • Like

amirm

'Sparkos SS3602 Opamp Rolling In Fosi P4'

This is a detailed measurements of effect of swapping the stock NE5532P op-amp in Fosi P4 preamplifier with Sparkos SS3602 "discrete" opamp. The SS3602 costs US $79.80 and the NE5532P, US $0.47.
Fosi P4 Sparkos SS3602 Opamp discreet rolling swapping 5532 review.jpg

Swapping opamps in P4 is more challenging due to back connectors/switches that need to be disconnected. I am not sure how successful I will be putting it back together as some of the tiny screws are almost stripped now. I looked and there was no obvious mention of swapping opamps in P4 from Fosi so I suggest not trying it regardless of what you are about to see.

So far, we have...
  • Like

Have a read of these threads, and let us know what your thoughts are.
 
audio_tony said:
@jmdesignz2 Here's a couple of threads to keep you amused.

amirm

'Does Op-amp Rolling Work?'

When I post my last video on review of Douk A5 amplifier, I mentioned that rolling (changing) op-amp ICs in there is fruitless. I got have a dozen comments under that video in youtube asking why so I thought I experiment again with the A5. Note that I have done the same testing with both DACs and Power Amplifiers and found the change to not make a difference. But let's see if the results are different this time.

Op-amp rolling amplifier 994Enh-Ticha Sonic Imagery Labs NE5532P TI Testing Douk A5 Stereo Aud...jpg

The Douk A5 makes this job both easy and hard. It is easy because you can just lift the plexiglass and replace the op-amps. The difficulty was...
  • Like

amirm

'Op-amp Rolling Using Sparkos on Fosi V3 Mono'

This is a study of measured differences if one swaps up the TI NE5532p dual IC op-amp in a Fosi V3 Mono amplifier with a "discrete" opamp from Sparkos. It is a test requested in the youtube comments of my video test of the same using Douk A5 and Sonic Imagery op-amp. The Sparkos SS3602 retails for US $79.80 but I found a discount coupon that brought the cost down to $74.33 with shipping included.
Fosi V3 Mono amplifier SS3602 Sparkos op amp rolling swap Testing Review.jpg


Per Fosi documentation, there are three op-amps. The one at the bottom is only for unbalanced/balanced conversion. That leaves two op-amps to swap. Company says if you...
  • Like

amirm

'Sparkos SS3602 Opamp Rolling In Fosi P4'

This is a detailed measurements of effect of swapping the stock NE5532P op-amp in Fosi P4 preamplifier with Sparkos SS3602 "discrete" opamp. The SS3602 costs US $79.80 and the NE5532P, US $0.47.
Fosi P4 Sparkos SS3602 Opamp discreet rolling swapping 5532 review.jpg

Swapping opamps in P4 is more challenging due to back connectors/switches that need to be disconnected. I am not sure how successful I will be putting it back together as some of the tiny screws are almost stripped now. I looked and there was no obvious mention of swapping opamps in P4 from Fosi so I suggest not trying it regardless of what you are about to see.

So far, we have...
  • Like

Have a read of these threads, and let us know what your thoughts are.
Click to expand...
Yes I read those threads using the sparkos which does not have full certified spec sheets afaik?

The v3 mono block also only replaced one out of three or did I misread that?
 
I’m extremely familiar with the tracks having listened to some for more than 10 plus years I’m using to subjectively evaluate them and I’m hearing some obvious differences especially in the higher frequency instruments sounding more true, texture and nuance
 
jmdesignz2 said:
aren’t the op amps in the signal chain before the TPA amp? Why won’t a cleaner signal be beneficial?
Click to expand...

Because the signal is worsened many many times after the op-amp.

Add to that the load impedance dependent frequency response from the V3 output stage (TPA3255) which will not change.

Besides... that is the problem with bottlenecks. It does not matter if the bottleneck is first, last or somewhere else in the chain, the worst one will always determine the end result.

One can use a (theoretical) op-amp that has perfect specs.
0.00000000000001% distortion, 100kV/us, DC-100GHz bandwidth, -350dB (some will see what I did here) SN, -300dB PSSR etc. and feed that into a circuit with -65dB PSSR, 50kHz bandwidth (-3dB), 7V/us slew-rate and you will still have -65dB PSSR, 50kHz bandwidth (-3dB), 7V/us slew-rate as the final result.
 
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jmdesignz2 said:
I’m extremely familiar with the tracks having listened to some for more than 10 plus years I’m using to subjectively evaluate them and I’m hearing some obvious differences especially in the higher frequency instruments sounding more true, texture and nuance
Click to expand...

Please record the output of the amp (with speakers connected) in 24/192 (or at least 24/96) format of the part in the music where you clearly hear differences.
No microphones nor speakers ... simply record the output directly and post those files.
IF there are obvious differences the output will HAVE to be different and that can be shown to exist.

It does not matter what experience one has (I have over 30 years of experience) and still fall into the same trap until I decide to do a proper comparison.
The fact that you hear differences (even when there are none !) means you are human. Congrats with that.
 
Once I get my Buckeye mono blocks I’ll be glad to ship these to Amir and pay for return shipping too.
 
FYI.

Buckeye mono blocks are objectively better performing amps and (depending on the load impedance) could even sound different in a well performed blind AB-test but might not be (as said depends on the load impedance).
There are also TPA3255 amps that can sound different from the V3 amps (again load impedance dependent) when that other amp uses PFFB configuration.

Note: this has nothing to do with the input buffer/gain op-amp used.
 
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solderdude said:
Please record the output of the amp (with speakers connected) in 24/192 (or at least 24/96) format of the part in the music where you clearly hear differences.
No microphones nor speakers ... simply record the output directly and post those files.
IF there are obvious differences the output will HAVE to be different and that can be shown to exist.

It does not matter what experience one has (I have over 30 years of experience) and still fall into the same trap until I decide to do a proper comparison.
The fact that you hear differences (even when there are none !) means you are human. Congrats with that.
Click to expand...
Be glad to if I had the equipment lol
 
I’m extremely familiar with the tracks having listened to some for more than 10 plus years
Click to expand...
Excellent! That can help a lot.

I’m using to subjectively evaluate them and I’m hearing some obvious differences especially in the higher frequency instruments sounding more true, texture and nuance
Click to expand...

OK... Now it's time for a Controlled Audio Blind Listening Test. An ABX Test can help to confirm if you are statistically-reliably hearing ANY difference without regard to preference or what the difference is. This kind of testing is time consuming and you'd need someone to help you. But sighted, uncontrolled tests are simply unreliable so there's not much point of making such claims on this scientific (and skeptical) forum.

If you say something defined and clear like "more highs" or "boosted highs", that's more believable (and easily measurable) but unlikely in an amplifier without tone controls or EQ. Or if you say something like, "There's a buzz in the left channel", I wouldn't question that. :)

When Amir reviews a product he doesn't bother with controlled listening tests but he backs-up what he hears with measurements and although he's a trained listener he does NOT claim to be immune to being fooled with uncontrolled listening. Plus he is only one pair of ears... It's OK to do controlled listening tests for yourself, but if someone is writing reviews and publishing the results it's a lot more helpful to have listening panel. Controlled listening tests are more common in research than in product reviews.

and I’m hearing some obvious differences especially in the higher frequency instruments sounding more true, texture and nuance
Click to expand...
Audiophoolery describes the REAL characteristics of sound quality. For electronics, that's noise, distortion, and frequency response. That MIGHT help to describe what you're hearing, although accurately describing what you're hearing isn't "required" if you can hear a difference in a proper level-matched ABX or other controlled listening test.
 
DVDdoug said:
Excellent! That can help a lot.



OK... Now it's time for a Controlled Audio Blind Listening Test. An ABX Test can help to confirm if you are statistically-reliably hearing ANY difference without regard to preference or what the difference is. This kind of testing is time consuming and you'd need someone to help you. But sighted, uncontrolled tests are simply unreliable so there's not much point of making such claims on this scientific (and skeptical) forum.

If you say something defined and clear like "more highs" or "boosted highs", that's more believable (and easily measurable) but unlikely in an amplifier without tone controls or EQ. Or if you say something like, "There's a buzz in the left channel", I wouldn't question that. :)

When Amir reviews a product he doesn't bother with controlled listening tests but he backs-up what he hears with measurements and although he's a trained listener he does NOT claim to be immune to being fooled with uncontrolled listening. Plus he is only one pair of ears... It's OK to do controlled listening tests for yourself, but if someone is writing reviews and publishing the results it's a lot more helpful to have listening panel. Controlled listening tests are more common in research than in product reviews.


Audiophoolery describes the REAL characteristics of sound quality. For electronics, that's noise, distortion, and frequency response. That MIGHT help to describe what you're hearing, although accurately describing what you're hearing isn't "required" if you can hear a difference in a proper level-matched ABX or other controlled listening test.
Click to expand...
Good points but I’m not doing that because it’s still subjective. I am certainly discerning differences that are positive and enjoyable for my experience

I have extensive experience with live orchestra and other real performances as a reference point of what sounds more “correct” with respect to how real instruments sound and feel

If anyone wants to use objective analysis on these I’m ready and willing to ship them after I get my Buckeye mono blocks.
I’d also provide the second pair of stock V3.5 monoblocks and 48v/10A smps

IMG_7330.jpeg
 
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jmdesignz2 said:
If anyone wants to use objective analysis on these I’m ready and willing to ship them after I get my Buckeye mono blocks.
I’d also provide the second pair of stock V3.5 monoblocks and 48v/10A smps
Click to expand...
Has already been done by Amir using TOTL test equipment (analyzer and load).
amirm

'Op-amp Rolling Using Sparkos on Fosi V3 Mono'

This is a study of measured differences if one swaps up the TI NE5532p dual IC op-amp in a Fosi V3 Mono amplifier with a "discrete" opamp from Sparkos. It is a test requested in the youtube comments of my video test of the same using Douk A5 and Sonic Imagery op-amp. The Sparkos SS3602 retails for US $79.80 but I found a discount coupon that brought the cost down to $74.33 with shipping included.
Fosi V3 Mono amplifier SS3602 Sparkos op amp rolling swap Testing Review.jpg


Per Fosi documentation, there are three op-amps. The one at the bottom is only for unbalanced/balanced conversion. That leaves two op-amps to swap. Company says if you...
  • Like

No difference.

Also realize that all people in that picture may well be very experienced in playing instruments but all are likely to have a very limited frequency response in their hearing because of A: age and B: having been exposed to high SPL being so close to instruments.

Fortunately this degradation is very gradual and the brain 'compensates' for the loss so it isn't really obvious. Add to that frequencies above 10kHz are not important when playing or 'evaluating' the sound of instruments.

Any subjective 'opinions', regardless of experience, is pretty worthless in 'court' and not admissible as evidence.
You can use ears for objective evaluations but requires rigorous and statistical valid testing methods. Subjective findings simply aren't that.

jmdesignz2 said:
I am certainly discerning differences that are positive and enjoyable for my experience
Click to expand...

Best to enjoy music. That's what it is there for. If swapping anything does 'help' you that's fine. It just isn't evidence of anything other than being human.
 
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Also have a look at:

pma

'Big test of DIP dual op-amps for audio: LM4562, NE5532, OPA2134, TL072 and LM1458'

There are questions if it matters which type of op-amp is used in the audio amplifier and my answer is that it depends on circuit schematics and op-amp parameters. Some of those parameters are obvious from datasheets, but others may be quite hidden and not clear from the first view. For the test I have chosen well known dual op-amps LM4562, NE5532, LM1458 (bipolar input) and OPA2134, TL 072 (JFET input).
LM1458 is one of the first op-amps usable for audio and it is dated at sixties of the previous century. NE5532 was then a big big improvement in audio op-amps, introduced by Signetics...
  • Like
 
jmdesignz2 said:
Good points but I’m not doing that because it’s still subjective. I am certainly discerning differences that are positive and enjoyable for my experience

I have extensive experience with live orchestra and other real performances as a reference point of what sounds more “correct” with respect to how real instruments sound and feel

If anyone wants to use objective analysis on these I’m ready and willing to ship them after I get my Buckeye mono blocks.
I’d also provide the second pair of stock V3.5 monoblocks and 48v/10A smps
Click to expand...
You should understand that experience doesn't change the fact that hearing is one of our least reliable senses. Your experience is as irrelevant as mine when it comes to sighted testing of audio equipment.

Things to keep in mind:
1) Echoic memory is only a couple of seconds long. You can't make reliable comparisons of details in sound/music without instantaneous switching.
2) Bias is real. Doesn't matter if you are aware of it or not: Bias affects all humans, always. This makes (double)blind testing a necessity.
3) Our hearing is easily tricked. As mentioned, hearing isn't a reliable sense. You're not hearing "sound", you're hearing an interpretation of sound, processed by your ears and brain.
 
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