ZA3 - XLR Op Amp swap

[DanWesson357]

I've pre-ordered two ZA3s to run in mono and will use XLR input. Which opamp should I replace, the XLR opamp or R-OPAMP or both?

 

[D1N0##]

I think the right channel opamp will resort most effect. Maybe @will williams can enlighten us what is the purpose of the op amp behind the xlr input? Why is it even there. Could somenone at Fosi who was involved with the design of the ZA3 answer this?

 

[D1N0##]

I asked bard if it could be used for cancelling out interference. Of course I do not know if it is telling the truth or just making stuff up since it doesn't seem to know the difference.

Here is a simplified example of how an op-amp can be used to cancel out interference when summing the two signals from an XLR cable:

1. The two signals from the XLR cable are fed into the two inputs of a differential amplifier.
2. The op-amp amplifies the difference between the two signals, while rejecting any common-mode signals that are present in both inputs.
3. The output of the op-amp is the summed signal with the interference canceled out.

For verification reasons I asked it:

so because one of the signals is inverted it is seen as different from the other one, so it is amplified. While the random noise in both cables are seen as the same and therefore filtered out?

Answer

Yes, that is correct. The process of inverting one of the signals and adding it to the uninverted signal is called differential amplification. This technique is used in balanced audio systems to reject common-mode interference.

When the inverted signal is added to the uninverted signal, the common-mode interference is effectively canceled out. This is because the common-mode interference is present in both signals, and when the signals are added together, the interference components cancel each other out.

The audio signal, on the other hand, is not affected by this cancellation process, because the audio signal is different in each conductor. This is why the audio signal is amplified, while the common-mode interference is rejected.

The ground conductor in an XLR cable further helps to shield the signal from noise. This is because the ground conductor creates a common reference point for the two signal conductors. This helps to ensure that the common-mode interference is canceled out more effectively.

As a result of these features, XLR cables are very effective at rejecting common-mode interference and providing a cleaner and more accurate audio signal.

 

[Fosi Audio Team]

Normally speaking, we can just replace the R-OPAMPs on two ZA3s.

 

[Kwatch]

Normally speaking, we can just replace the R-OPAMPs on two ZA3s.

So, I don't have to replace the XLR OP AMP even though I will use the XLR input only in mono mode?

 

[Fosi Audio Team]

So, I don't have to replace the XLR OP AMP even though I will use the XLR input only in mono mode?

No, it is not required to do so.

 

[Kwatch]

No, it is not required to do so.

Then why is there an OP amp for the XLR? When is it supposed to be replaced?

 

[D1N0##]

Then why is there an OP amp for the XLR? When is it supposed to be replaced?

It serves as a differential amplifier. The two signal cables of the xlr carry an out of phase signal and random noise from interference.

The opamp substracts the noise from the signal because it is largely the same for each signal cable. The noise in the left cable is in phase with the noise right one because the cause of interference in both cables is the same for both.
The audio signal is out of phase and so it is seen as different by the opamp. The opamp only amplifies the unique parts in the left and right signal cable and discards the parts that are the same (the noise). That is called common mode rejection.
It works differently from the op-amps in the left and right channel which pre-amplify the left and right channel signal. The same type op-amps are used but the pin configuration of the socket determines their function. I guess the left and right channel op-amps have a greater influence on sound quality than the differential op-amp that rejects the common mode signal.

If you want to know more about it and don't hate diagrams and equations: https://www.electronics-tutorials.ws/opamp/opamp_5.html

 

[DanWesson357]

Good information. It would be interesting to find out more about the audible impact of upgrading the differential op-amp.

 

[D1N0##]

Just try it out. I guess. Put it in the xlr in one and in the right channel in the other and listen (not at the same time and both amps in mono).

 

[psylence]

I've tried to change op-amps in the XLR (ss3602), it sounds much better than stock, but when you swap them in the right channel, it sounds the best. Interesting to try to swap op-amps both in the right channel and the XLR. Would there be an additional benefit in sound?

 

[DanWesson357]

I've tried to change op-amps in the XLR (ss3602), it sounds much better than stock, but when you swap them in the right channel, it sounds the best. Interesting to try to swap op-amps both in the right channel and the XLR. Would there be an additional benefit in sound?

I have a pair of ss3602 and a pair of MUSE02. I intend to run two amps mono, with MUSE02 in XLR and SS3602 in right channel. Should be fun to play with. Just waiting on the amps to ship!

 

[psylence]

I have a pair of ss3602 and a pair of MUSE02. I intend to run two amps mono, with MUSE02 in XLR and SS3602 in right channel. Should be fun to play with. Just waiting on the amps to ship!

I also decided to swap the opamps in the XLR. But I would also like to change the opamp(s) for the Sub Out.
Do you need to change one or both Sub Out opamps in mono mode?

 

[diodiel]

How did you like it after changing both the r channel and xlr op amps?

How did you connect you sub in mono mode?

I'm also interested in knowing what kind of of improvements will changing the 2 sub op amps will do.

Thank you.

 

[psylence]

How did you like it after changing both the r channel and xlr op amps?

How did you connect you sub in mono mode?

I'm also interested in knowing what kind of of improvements will changing the 2 sub op amps will do.

Thank you.

I connected subwoofer to the sub out of one of the amplifiers with RCA. Low frequencies are usually the same on both channels.
That was surprising, but after many years with high level connection, I feel that it just integrates better and sounds better with low level input.
I’ll swap opamps in the XLR tomorrow (same SS3602) and I’ll also swap both subwoofer opamps for OPA2124PA. Then I’ll let them burn in with pink noise for at least 24 hours and after that I’ll try to tell about changes in sound. Discrete opamps need a lot of time to burn in, but the sound signature changes most dramatically in the first 30 hours.

 

[diodiel]

Thanks for the input psylence. Looking forward to your results. So far, I ordered 2 MUSES02 for the two R-OP AMPs. One day I can afford a pair of SS3602 and follow in your footsteps depending on which you noticed the most improvement on. =)

 

[psylence]

Many people prefer MUSES02 for their warm sound, maybe I'll try to play with different op-amps later
I've swapped op-amps in XLR for SS3602 and immediately noticed that a little harshness in the high frequencies went away, but at the same time the highs became much darker. I waited about a week while they warmed up. After a week, the high frequencies returned to normal, the stage has become wider. I felt the sound became softer without loss of detail. Overall, I don't think replacing a second pair of op amps is a good decision, considering their price, but they definitely make some difference.
At the same time I'm very impressed with performance of this two little amps, I have class A Atoll IN100 amplifier, but I don't use it anymore. A pair of Za3's with SS3602 provide higher detail, better soundstage, bass control, instruments separation. They perform much better at low volumes. Atoll is a good amp, but but for the genres of music that I listen to (rock, heavy metal) it's not the best choice.
I didn’t hear any noticeable changes (and didn't expect) changes from replacing the op amps (OPA2124PA) in the sub out.
Setup: Gustard R26, ProAc DB3, Rel Quake.

Update: Today I saw a video on YouTube (channel VirtualHiFi) where the author recommends removing unused opamps, since they are still in the power circuit and will affect the sound. I'll definitely try it in the next few days.

Update 2: Removed all unused opamps and...wow! This immediately made a big difference, much bigger than replacing the second pair of opamps for xlr. The sound became much softer, adding width and openness to the sound stage. And this upgrade was absolutely free

 

[diodiel]

The video was very informative, thank you. The MUSES02 from Fosi came as 2 qty. Now I have 4 which I'll be putting in R and XLR, and remove the opamp on the L channel. Everything is looking perfect now. The last thing is for my 2nd ZA3 to arrive.

 

[TomaszK]

Very informative, thanks! Got two ZA3’s and removed left opamps and did manage to smear a bit off the grease, hope this won’t affect that one unit. Also, can you tell me if I should take out the subwoofer out opamp as I’m not using that connection on the back of the amps. I do however have my passive subwoofer connected via speaker cables to both ZA3’s, and my main speaker cables are connected to and through my subwoofer. Your advice would be appreciated.

 

[psylence]

Very informative, thanks! Got two ZA3’s and removed left opamps and did manage to smear a bit off the grease, hope this won’t affect that one unit. Also, can you tell me if I should take out the subwoofer out opamp as I’m not using that connection on the back of the amps. I do however have my passive subwoofer connected via speaker cables to both ZA3’s, and my main speaker cables are connected to and through my subwoofer. Your advice would be appreciated.

Hello! I recommend erasing the old thermal paste and applying new one (arctic cooling mx-5, for example) so as not to accidentally overheat the amplifier. If you don't use sub out, you can remove these opamps. I pulled them out at the same time as the left channel opamp. In my opinion, the presence of NE5532 in the circuit makes the sound much more closed.