Op-Amps, who knew?

[Audiobro]

Let me preface this by stating that I am not an engineer, scientist, or anything of the like. I am just a handy guy with a soldering iron that knows how to read. I, on a whim, replaced the op-amps and a few caps on the input board of my NAD 2600PE and the results are astonishing, well to me at least. I replaced the original JRC 6503's with TI LM4562NA's. At first it didn't seem to make any improvement, in fact, quite the opposite, the bass was diminished and high's & mids sounded much increased. But knowing that the sound has a tendency to change after a bit of running time, I pressed on. After about 15 hrs. of listening, the sound began to change, the bass returned much tightened and the high's & mids had better detail. Also, the stage seems considerably more defined. I have no before and after measurements to prove these improvements. The reason for this post is that I have read a lot of posts concerning recapping (which I done on a number of components with great success), but not much concerning my new little friend, the Op-Amp. I am seeking a further understanding of how these are responsible for sound and their role in audio devices.

 

[Blue Shadow]

They are audio amps in many uses in gear and sound different, new ones can sound so much better. Higher slew rates help. I changed the LPF chip in a couple CDPs with excellent results about 5+ years ago. The one you installed is known to sound pretty good.

 

[Yahgn]

They are audio amps in many uses in gear and sound different, new ones can sound so much better. Higher slew rates help. I changed the LPF chip in a couple CDPs with nest excellent results about 5+ years ago. The one youth rewind there is known to sound pretty good.

+1

 

[Audiobro]

Update! Just finished the Quadrophenia test. Sounds clearer than I have ever heard it before. Keith's drums are much more forward, much tighter, and much more detailed. John's bass is punchy and tight. Horns and piano are very clear, full, and natural sounding. I use this album as my touchstone since it is my favorite album and I have heard it many times more than any other. Also, the banjo in "Had Enough" was more distinct and clear than ever before. Best return on a $13.88 investment yet!

 

[mbz]

I hope you used an opamp socket so you can easily "roll" opamps.
Not familiar with JRC6503, couldn't find datasheets to see if the LM4562 is a good sub.
Need to make sure the power supply voltage/currents are in order otherwise the
opamp may have a short life. Used LM4562 a few times, some suggest OPA2134(?)
is better. Keep in mind, the surrounding circuitry is designed for the original opamp
however the later amps have better S/N, slew,,,

 

[Blue Shadow]

I used an OPA2228 in one unit and like it. Those 4558 and 5532 really are old designs and don't sound as good.

 

[wyn palmer]

I used an OPA2228 in one unit and like it. Those 4558 and 5532 really are old designs and don't sound as good.

Why an OPA2228 rather than a 5532. What was better? From a spec performance the 5532 is same/better in almost everything that matters in audio except, if I remember correctly, input noise.

 

[wyn palmer]

They are audio amps in many uses in gear and sound different, new ones can sound so much better. Higher slew rates help. I changed the LPF chip in a couple CDPs with excellent results about 5+ years ago. The one you installed is known to sound pretty good.

The LM4562 (same die as the LME49720) was designed to produce a low open loop distortion - likely better than a 5532.
The 5532 has a slew rate of 10v/us, or about half that of the 4562- and it's very hard to see why this is important for any audio applications as the full power bandwidth for the 5532 with 15v supplies is about 110kHz, and that's with >9vrms at the output.
The 4562 has about 300kHz under the same circumstances. It seems unlikely that either opamp would enter a slew rate limited situation under normal audio operating conditions. In addition, the gain bandwidth product of the 4562 is 5x that of the 5532, so you would get an extra 14dB or so due to that.
The reality is that the measured results for harmonic distortion plus noise at 20kHz with about 3vrms out and translated to -1 gain are about 0.00007% for the 4562 and 0.0002% for the 5532, so there appears to be a ratio of about 3- or pretty close to what the gain bandwidth product will give you. At lower frequencies than about 20kHz the noise dominates.
The 4562 has somewhat better noise.
So, can you actually hear the difference?
There are many truly poor opamps out there but the 5534 is not one of them, which is why it remains in the catalogue.
I pulled up the NAD2600 service manual and checked out the schematic. The opamps are the NJM2043.
The GBW product is 14MHz, the slew rate is 6v/us and the full power bandwidth is, surprisingly, actually higher than the 5532, so there should not be any issues from that perspective, however there does not seem to be any info. on distortion.

 

[Audiobro]

Here's a pic of the Opamp I replaced. I can definitely hear the difference. I apologize for my inability to define the difference in technical terms, so I will attempt it in layman's. The most noticeable is the reorganization of instruments or something like different EQ settings (If I had an EQ), most notably is drums and bass guitar. I had to turn down my bass control since it had become quite overwhelming. It has also had an effect on how the amp sounds when warming up, it used to have quite muddy bass when cold and sharpen up once it warmed up, now it has a diminished bass output and gets louder once warmed up. Clarity has improved across the board, I compare it to getting a new pair of glasses with the proper prescription. I am completely happy with the improvement and now seek to understand it.

 

[Audiobro]

I hope you used an opamp socket so you can easily "roll" opamps.
Not familiar with JRC6503, couldn't find datasheets to see if the LM4562 is a good sub.
Need to make sure the power supply voltage/currents are in order otherwise the
opamp may have a short life. Used LM4562 a few times, some suggest OPA2134(?)
is better. Keep in mind, the surrounding circuitry is designed for the original opamp
however the later amps have better S/N, slew,,,

I did install a socket. See pic in post #9 for pic of pulled opamp. I also have a couple other opamps to try in the future, AD823ANZ and OPA2604AP. It may be a while before I experiment with these, I am really happy with the way it sounds now.

 

[wyn palmer]

I did install a socket. See pic in post #9 for pic of pulled opamp. I also have a couple other opamps to try in the future, AD823ANZ and OPA2604AP. It may be a while before I experiment with these, I am really happy with the way it sounds now.

It's an njm2043. See my earlier post.

 

[wyn palmer]

I'd go for an OPA1612 as an upgrade in virtually every circumstance. At >$6 each it's not cheap, but it's a lot cheaper than the "discrete" opamps out there and at least it has specs, measurements, no obvious failings etc.

 

[Audiobro]

I'd go for an OPA1612 as an upgrade in virtually every circumstance. At >$6 each it's not cheap, but it's a lot cheaper than the "discrete" opamps out there and at least it has specs, measurements, no obvious failings etc.

$6 is a small price to pay for the enjoyment I receive from my system. I had considered a "discrete" opamp, but I do not have the room, there is maybe 1/2 inch of clearance between the top of the board and the rear chassis.

 

[pwauk12]

having done this to a number of NAD 2200/2600/2700- there is a noticeable and measurable improvement in the performance, the distortion and noise is lower and better signal to noise- which sonically to me, sounds like more detail, better transparency and better dynamics.

That said, I also replace all the electrolytics and some of the ceramic caps as well.

as to op amp choice- as the original op amps (2043DD) are BJT, I replace them with other BJT opamps- 4562 in this case.

 

[Karl vd Berg]

Other than surrounding circuitry, it's always good to look at supply voltages, input current, if it is "Unity Gain Stable", etc.

"Absolute Maximum Ratings" and "Recommended Operating Conditions" tables show different numbers.

 

[dlucy]

You all may want to know there are a few companies (or individuals) who create opamp adapters. These are often DIP14 devices (or similar), which are like a vintage opamp (some at least), wired to be pin-compatible with the original vintage opamp, and designed to be fitted with newer or even modern SMD opamps.

This is what is used in the famous BillD mods of the Carver C-1 preamp. The result is not just a better-sounding opamp, but sometimes the ability to roll several new-technology SMD devices.

https://www.cimarrontechnology.com/ BrownDog adapters (and pre-installed SMD devices if your fingers and eyes, like mine, aren't up to the installation task).

Revox-online ebay seller from Germany https://www.ebay.com/usr/revox-online​

 

[wyn palmer]

Here's a pic of the Opamp I replaced. I can definitely hear the difference. I apologize for my inability to define the difference in technical terms, so I will attempt it in layman's. The most noticeable is the reorganization of instruments or something like different EQ settings (If I had an EQ), most notably is drums and bass guitar. I had to turn down my bass control since it had become quite overwhelming. It has also had an effect on how the amp sounds when warming up, it used to have quite muddy bass when cold and sharpen up once it warmed up, now it has a diminished bass output and gets louder once warmed up. Clarity has improved across the board, I compare it to getting a new pair of glasses with the proper prescription. I am completely happy with the improvement and now seek to understand it.

In reality the "warm up time" for opamps is extremely short- they have a very small thermal mass and they achieve near steady state operating conditions very quickly. Also, low frequency response is absolutely the easiest thing for opamps to get right- the gain is extremely high, the open loop distortion is intrinsically lower than at HF also and the frequency response is extremely predictable. It's hard to see why any opamp in and of itself would have an appreciable effect in this domain. Trying to determine what it is that you actually hear and whether or not the opamps are a causative agent is a difficult, time consuming task. There may be other issues that are fundamentally at fault here and what you hear is the opamp reaction, if you will- for example, dynamic range issues induced by supply variations and opamp offset/offset drift, instability induced by inadequate layout/decoupling etc. etc. If I feel so inclined I'll look at the NAD2600 input layout/schematic to see if there's anything obvious that comes to mind. It sometimes does happen that there's a problem. The head preamp of the Studer A810 tape deck is a good example. Earlier designs had an issue that was pretty obvious in simulation and with the application of an experienced eye, and that was fixed later in production, but was not that obvious at the time due to a lack of modern methodologies for design assessment.

 

[wyn palmer]

having done this to a number of NAD 2200/2600/2700- there is a noticeable and measurable improvement in the performance, the distortion and noise is lower and better signal to noise- which sonically to me, sounds like more detail, better transparency and better dynamics.

That said, I also replace all the electrolytics and some of the ceramic caps as well.

as to op amp choice- as the original op amps (2043DD) are BJT, I replace them with other BJT opamps- 4562 in this case.

BJT relative to what? Are you saying a bipolar process rather than CMOS or are you saying a BJT input stage rather than a JFET input stage? There are often specification differences due to pros and cons of a particular technology or design, but are you saying something different from that? Are you saying that you believe there is a subjective difference associated with this choice?
Note that the 4562/49720 has a compensated input stage that cancels much of the input bias current that the outside world sees whereas the NJM2043 does not.

 

[pwauk12]

yes input stage of the IC- I have tried OPA2134 (FET input stage) compared with 4562 (BJT input stage)- and for the me the 4562 performs better- could I tell the difference in a double blind test- I highly doubt it.

 

[wyn palmer]

yes input stage of the IC- I have tried OPA2134 (FET input stage) compared with 4562 (BJT input stage)- and for the me the 4562 performs better- could I tell the difference in a double blind test- I highly doubt it.

There may be technical reasons for that- the OPA2134, if I remember correctly, has higher noise, lower DC gain, lower gain bandwidth product, less tolerance for low loads, higher distortion at higher audio frequencies at all gains but especially at higher gains, inferior PSRR, and perhaps more.
It's, in my opinion, measurably inferior in an audio sense. Now, whether those "deficiencies" mean anything- I cannot say- but they do exist.