aptX HD is not lossless, although it does offer higher bitrate than aptX.
The upcoming aptX Lossless is supposed to be lossless.
https://en.wikipedia.org/wiki/AptX#aptX_HD
-
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S.M.S.L DA-9 vs AO200?
- Thread starter DACslut
- Start date
The upcoming aptX Lossless is supposed to be lossless.
https://en.wikipedia.org/wiki/AptX#aptX_HD
jokan
Addicted to Fun and Learning
I hope you're not replying to me. I have always said that AptX, AptXHD is lossy. Qualcomm announced lossless on 1st, Sept, 2021!
I quoted d'Brit, which means I was replying to him/her.
jokan
Addicted to Fun and Learning
I quoted d'Brit, which means I was replying to him/her.
I get confused a lot. Sorry about that!
Not joking, I really do get confused a lot. I live in Tokyo, It's 05:51AM 9th, September. But most of my closest friends are on in the USA. So I keep the strangest hours. I'm about to take my medication for "nightime" first thing in the morning and the Sun is out. Well it's cloudy but you get what I mean!
- Thread Starter
- #105
NONE of my several other DAC's have the control panel L/R channel sliders reversed, so the problem isn't with Windows but the AO200's hardware, firmware or driver. As I've made clear here and/or elsewhere, I eventually determined the actual stereo playback is correct.
I'm sending back the DA-9 and 2nd AO200 amp. My A20a will soon have an identical companion for a "monoblock" config.
I'm sending back the DA-9 and 2nd AO200 amp. My A20a will soon have an identical companion for a "monoblock" config.
jokan
Addicted to Fun and Learning
I'm sorry for your ongoing problems.
I sent mine back so that it'll they can fix the bluetoot connection!
I figure when it comes to resale, better to have firmware that is not easily dated. Though I bet it'll still say V 1.0.0. lol.
fix the little things. it's not THAT difficult, is it? SMSL/Aoshida!
I plugged in some USB audio devices and tried to see what the balance window would look like.
The AO200 is displayed as L-R, but there are cases where it is displayed as 1 and 2 or the balance window is not displayed.
As you say, only AO200 works in the opposite way to the L-R display.
When a device is connected to USB, Windows 10 will request the connected device to send detailed information.
The USB device side sends necessary information such as device name, device type, supported sample rate, supported bit depth, etc. to Windows 10 according to the request. I think that there is also information on the presence or absence of balance adjustment in that information. Windoes 10 generates various setting items based on the sent information. If there is something about the order of L-R in the exchange of this information, there may be a bug in the data sent by AO200. If you only exchange with or without balance setting, it means that Windows 10 has set the order of L-R, and it is presumed that there is a bug on the Windows 10 side.
We do not know these real things. If you are concerned about this, please contact Aoshida HiFi, the distributor of the product, directly. When I contact SMSL, they don't have the authority, so there is no answer. I don't care about this at all. Also, I don't use the balance setting function.
jokan
Addicted to Fun and Learning
I can only add that in my own case, and with my amplifier which is on it's way back to be replaced for a bluetooth, not bluetoot model did not exhibit such issues.
Win 10, 64-home, Dell Alienware x51 r2. original sound-card. no issues at all with plug and play use.
I'm betting that your amp in particular doesn't like your shoes or something. It's an odd situation and I blame it on your shoes. Sometimes things and people don't like what shoes the other person is wearing.
(trying to add a little humour to an otherwise extremely annoying issue. I hope they sort you out and send you a replacement with no questions asked!)
We know you're just jokan!
i just got my hands on AO200. Fedex arrived to hanoi quickly however i have to paid import taxes (20% value, ouch) .
After 30min usage testing all function, i only encounted a bug windows 10 popping up Volume and Player widget all the time while using USB connection.
After 30min usage testing all function, i only encounted a bug windows 10 popping up Volume and Player widget all the time while using USB connection.
jokan
Addicted to Fun and Learning
Replacement A0200 that reads Bluetooth correctly has arrived.
It was drop-shipped from the factory directly to me. Very fast turn around.
Firmware reads as 1.1, I am not sure of what else they've done, the internals look the same. I have absolutely no issues with the unit.
No popping noises with source selection, no noticeable EMI/RFI noise issues.
I will let it run for a few days before I take any measurements.
And I won't bother with DC-Offset for a few days. It's high when they're brand new so there's no point really.
It was drop-shipped from the factory directly to me. Very fast turn around.
Firmware reads as 1.1, I am not sure of what else they've done, the internals look the same. I have absolutely no issues with the unit.
No popping noises with source selection, no noticeable EMI/RFI noise issues.
I will let it run for a few days before I take any measurements.
And I won't bother with DC-Offset for a few days. It's high when they're brand new so there's no point really.
jokan
Addicted to Fun and Learning
Bluetooth correctly spelled!
Replaced the op-amps from the opa1678's to my current favourite opa1656's, I'm guessing the ST72c's are for the subwoofer outputs. I couldn't be bothered to replace them.
I also fitted heatsinks on the chipsets, just to be extra-extra. No actual need for it. I just thought they look cool. I have to try and take a shot of the OS loading up so I can take a photo of the firmware display. It's definitely different.
Op-amp changes. There are a pair of 1678's and though you could use opa1612's, I prefer the opa1656's for a few reasons.
The gain isn't changed that drastically with the 1656's, but there is more clarity watching Youtube video podcasts. Listening to music, it's much improved as you would expect. If you're confident that you can replace the op-amps and solder well, then it's worth trying. You need to have some sort of "Heat-Clip" or Aluminium construction alligator clips or you'll never get the surface mounted op-amps off without overheating the nearby components. Is the modification worth it? I would say absolutely worth it. Everything about the sound is better presented. I didn't do the best job soldering the last op-amp, mostly it's difficult to get even a thin tipped iron in there and at the same time make sure you mounted the op-amp square. It's soldered, it's connected, there are no pops, or oddities so I'm okay with the angle that it wound up being soldered at. I will eventually go back in and make it square. It's already bothering me.
I'm no expert when it comes to op-amps. I understand valves or tubes more than op-amps. I can't see how a chip works, it's just a black square.
But I've used the 1612 in the past, had the 1678 as standard items, and the 1656's I chose from the specs.
An article on op-amp noise by TI comparing the 1612 and 1656.
I can tell you that with my speakers, and my previous A0200 which I also modded (actually used the same op-amps again as I sent the original A0200 with only bluetoot displayed) and I noticed the same improvement with the 1656's. It might be worthwhile for some of the people who enjoy potentially damaging or destroying an amplifier by over heating discrete surface mount components on the same trace with a different op-amp.
Do any mods at your risk. The tiny pins on these tiny 4.5mm x 5.5mm chips with 8 legs does not leave much room for a bad solder connection which is easy to do and easy to miss. Use a magnifying glass or zoom with your mobile to check your solder joints.
There is a very different sound to the amplifier once you roll out the original 1678's with something better. The measurements from the factory pdf's explain what you need to know at a bare minimum for specifications and comparative data however with different generations it seems that the measurements are not necessarily taken at the same frequency or impedance/capacitive loading so you do need to have some basic knowledge before you go rolling op-amps like crazy. I also wouldn't recommend applying so much heat to the PCB and replacing op-amps so many times. You can always get adaptors that sort of lift up the op-amp and you can use another adaptor to mount the miniature chips. There are sonic benefits that are clear once you do the modification.
Meanwhile, no operational issues have happened, the sound quality coming from the new A0200 is superb and getting better.
The amps been in my hands for about 12 hours now and I've already modded it because it was working as expected. The DC-offset looked well within reason and I know it'll go down over the next week or more. I'm not worried about any issues with the amplifier. There is a small PSU adjustment that you can make, I don't recommend it without electrical knowledge but you can optimise the PSU just a tiny bit. I wouldn't say that you can truly hear any differences that are significant compared to rolling the op-amps.
If you are good at soldering, have the experience to remove these tiny chips then I would recommend the mod. You are as always responsible for any modification and potential failure of your amplifier due to modification.
I'm switching over to another amplifier to let the A0200 shut down for a few hours, and it'll give me time to catch some sleep myself.
Taking the shot of the startup screen after a full reset took several tries. Sorry I couldn't get a clearer picture but you can see the info on the screen.
Replaced the op-amps from the opa1678's to my current favourite opa1656's, I'm guessing the ST72c's are for the subwoofer outputs. I couldn't be bothered to replace them.
I also fitted heatsinks on the chipsets, just to be extra-extra. No actual need for it. I just thought they look cool. I have to try and take a shot of the OS loading up so I can take a photo of the firmware display. It's definitely different.
Op-amp changes. There are a pair of 1678's and though you could use opa1612's, I prefer the opa1656's for a few reasons.
The gain isn't changed that drastically with the 1656's, but there is more clarity watching Youtube video podcasts. Listening to music, it's much improved as you would expect. If you're confident that you can replace the op-amps and solder well, then it's worth trying. You need to have some sort of "Heat-Clip" or Aluminium construction alligator clips or you'll never get the surface mounted op-amps off without overheating the nearby components. Is the modification worth it? I would say absolutely worth it. Everything about the sound is better presented. I didn't do the best job soldering the last op-amp, mostly it's difficult to get even a thin tipped iron in there and at the same time make sure you mounted the op-amp square. It's soldered, it's connected, there are no pops, or oddities so I'm okay with the angle that it wound up being soldered at. I will eventually go back in and make it square. It's already bothering me.
I'm no expert when it comes to op-amps. I understand valves or tubes more than op-amps. I can't see how a chip works, it's just a black square.
But I've used the 1612 in the past, had the 1678 as standard items, and the 1656's I chose from the specs.
An article on op-amp noise by TI comparing the 1612 and 1656.
I can tell you that with my speakers, and my previous A0200 which I also modded (actually used the same op-amps again as I sent the original A0200 with only bluetoot displayed) and I noticed the same improvement with the 1656's. It might be worthwhile for some of the people who enjoy potentially damaging or destroying an amplifier by over heating discrete surface mount components on the same trace with a different op-amp.
Do any mods at your risk. The tiny pins on these tiny 4.5mm x 5.5mm chips with 8 legs does not leave much room for a bad solder connection which is easy to do and easy to miss. Use a magnifying glass or zoom with your mobile to check your solder joints.
There is a very different sound to the amplifier once you roll out the original 1678's with something better. The measurements from the factory pdf's explain what you need to know at a bare minimum for specifications and comparative data however with different generations it seems that the measurements are not necessarily taken at the same frequency or impedance/capacitive loading so you do need to have some basic knowledge before you go rolling op-amps like crazy. I also wouldn't recommend applying so much heat to the PCB and replacing op-amps so many times. You can always get adaptors that sort of lift up the op-amp and you can use another adaptor to mount the miniature chips. There are sonic benefits that are clear once you do the modification.
Meanwhile, no operational issues have happened, the sound quality coming from the new A0200 is superb and getting better.
The amps been in my hands for about 12 hours now and I've already modded it because it was working as expected. The DC-offset looked well within reason and I know it'll go down over the next week or more. I'm not worried about any issues with the amplifier. There is a small PSU adjustment that you can make, I don't recommend it without electrical knowledge but you can optimise the PSU just a tiny bit. I wouldn't say that you can truly hear any differences that are significant compared to rolling the op-amps.
If you are good at soldering, have the experience to remove these tiny chips then I would recommend the mod. You are as always responsible for any modification and potential failure of your amplifier due to modification.
I'm switching over to another amplifier to let the A0200 shut down for a few hours, and it'll give me time to catch some sleep myself.
Taking the shot of the startup screen after a full reset took several tries. Sorry I couldn't get a clearer picture but you can see the info on the screen.
Attachments
Since they chose to send you a new unit instead of upgrading firmware on the old unit, does this indicate that firmware isn't upgradeable, even at their service center? Or did they just do it because it was faster that way?
jokan
Addicted to Fun and Learning
I can't honestly say. Purchased the amp through Amazon Japan. Through Aoshida Hi-Fi Japan, the seller on Amazon.
They immediately offered to send out via FedEx a new amplifier that is confirmed as working correctly and tested (mine arrived with the amp set on BT at max volume, so I know that it was tested for sure.) I immediately did a hard reset and then saw the firmware version etc.
I was told by the representative for Aoshida Hifi Japan that they know of the problem and will send a new unit to me. It was drop shipped yesterday. 1 week or so turn-around. I am 99% sure that the amplifier cannot be flashed by the user. That the manufacturer has to go in and program the firmware. They could have potentially made the amplifier USB firmware upgradeable but that would probably cost too much. The internal DAC I believe is piggy backed off of the BT module, and also the volume pot has 4 settings, so they used up the digital volume controller and maximised performance.
Also, they did still manage to keep the cost ridiculously low! I don't think that user updateable firmware is ultra expensive, but I think it costs a lot when selling an amplifier at this price point.
Cheers!
jokan
Addicted to Fun and Learning
@altme It's made by a company called NFJ FLAT Japan. They're a company that modifies certain specific models of FX-Audio devices and improves them vastly.
https://store.shopping.yahoo.co.jp/nfj/
They're also on amazon Japan.
https://www.amazon.co.jp/-/en/s?k=N...qid=1631794802&rnid=388332011&ref=sr_nr_p_6_1
Cheers!
https://store.shopping.yahoo.co.jp/nfj/
They're also on amazon Japan.
https://www.amazon.co.jp/-/en/s?k=N...qid=1631794802&rnid=388332011&ref=sr_nr_p_6_1
Cheers!
Antirabbit
Member
- Joined
- Aug 27, 2021
- Messages
- 5
- Likes
- 6
FYI, i just received a "new" SMSL AO200 through Amazon. It has the dreaded Bluethoot display. Its likely going back, but not after I side by side listened to it against my DA-9. It sounds better to my ears on my system (running a desktop system with some NOS Mission 771's in a near field set up. By better I mean, the separation is more distinct, there seems to be more space and generally I like the sound better-the musical imaging is better in my opinion with the AO200 vs. the DA-9. With these speakers, it seems to unlock more of what they are capable of. I ran through a number of Radiohead tracks, my stand by series of highly dynamic recordings of Shostakovich symphonies which really test the system well-the natural details that pop with this is impressive.
Infact, the more I listen to it, I am beginning to not really care that it says Bluethoot...can any one confirm its just a spelling error or is it indicative of other issues as well?
Infact, the more I listen to it, I am beginning to not really care that it says Bluethoot...can any one confirm its just a spelling error or is it indicative of other issues as well?
Last edited:
jokan
Addicted to Fun and Learning
FYI:
Hardware version 1.0 is the same as my new replacement unit.
Firmware is 1.1
The only difference I could hear is nothing!
It's just the Bluetoot display.
It sort of bothered me as time went by. Fortunately the Japanese importer was overly helpful.
If like me, you have your amplifier set to turn the screen off after a delay, you'll never care about the display saying toot or tooth!
It's the same amplifier is the bottom line. I did post that you can improve the overall sound of the amplifier with an op-amp change (2 op-amps). It is a significant change. I linked the PDF files with the manufacturers description including recommended use. TI/Burr-Brown has a line they call "Sound Plus", which is a big leap from the factor opa1648's, which is a huge leap from the older opa1612.
Your amplifier will sound better over about 3-7 days depending on usage. Though the first time you used it and UNPLUGGED the unit for over an hour will make the biggest change. You should be able to hear the improvement immediately, but you do need to unplug the amplifier not just switch it off at the back plug or by remote. Wait an hour before plugging the amplifier back in. You should notice a change! If you don't that's ok too and normal. It depends on your equipment, how good or bad your hearing loss is compared to others. It's important to do these comparisons with the amplifier at the same volume, same music source so that your references are clear.
Glad to hear that you're not sending your back. I was only concerned about resale in case something significantly better comes along. And I need the amplifier to be the same size as the A0200, give or take 1/4 inch in depth, and width, but no taller or higher. So I'm limited in choice. Only Mytek fits the bill but they're having issues with QC at the moment as they reengineered the current brooklyn amp+ and moved factories.
Cheers!
jokan
Addicted to Fun and Learning
FYI for all those who have read and are contemplating swapping the two opa1678's for something different:
Make sure you unplug the amplifier and preferably let it sit for a while, maybe 30 minutes to deplete the capacitors of any stored electricity as a precaution.
Make sure you are very comfortable with a soldering iron. It's better to have temp control. You need to wick the solder across the pins and do it gently so you do one leg at a time. You need a "Heat-Clip", do a row of 4 legs 1 leg at a time, only let your soldering iron have contact for 3-5 seconds at a time. You run the risk of overheating the trace itself that has what I assume is a Discrete Surface Mount (DSM) capacitor on two sides of the op-amp. So do one leg at a time of the eight legs, one row at a time, all the while lightly tugging on the heat clip. Once you get a row of 4 done, do the other side, the other side of 4 legs will be much easier and do the same, one leg at a time. use good soldering wick. I use Hako wick with wax, the thinnest one and then the next step thicker ones for this sized op-amp. Once you have the first row of 4 legs unsoldered, you can apply just a tiny bit more upward force, it's ok to bend the legs a little since you can easily bend them back into place. All the while make sure you don't stay in one spot for more than those 3-5 seconds. It's tedious work. Once you get probably 6 of the legs unsoldered, you can use your wick and soldering iron and go across the legs and it should just lift straight off with next to zero effort. The trick is to get the wick to do the work for you. Don't try and unsolder the op-amp with a vacuum pump style de-soldering tool, it'll take too much space, and it'll obscure your view.
When soldering on your new op-amps do the reverse, but make sure you remove all the flux from the board and excess solder from the circuit board using the wick. I just use my soldering iron at a slightly higher temp when soaking up excess solder. Then use flux remover, or Isopropyl alcohol with a q-tip to clean off the resin and flux. Readjust the temperature on your soldering iron that you just had raised a short while ago, lower the temp to the appropriate melting temp of your solder of choice. Apply a tiny dab of new solder on each of the 8 spots on the PCB where the op-amps will be placed. This is done so that when you locate and centre the new op-amp all you have to do is heat up a leg at a time. All this time you should have the new op-amp held with a pair of "Heat-Clips" for maneuvering and locating the chip. You can press down hard with the op-amp and heat clip when soldering the eight legs, do one at a time. And remember that 3-5 second rule still applies. Use your mobile and zoom in to make sure you're centred and have indeed applied solder completely on each leg, without having solder touch the next pin over! It'll just set the op-amp into protection if you do, and it won't blow up your amp, but it will make noise if you mess up with soldering. A tiny amount of excessive solder can easily cause a short. Once you get both chips done, it's finished.
Make sure that you are clearly identify that you are only attending to the two opa1678's! The reason why (part of the reason why DC offset is different on the two channels is the obvious length of the circuit board.
I prefer Texas Instruments Burr-Brown op-amps and have done for years, something about their tone has always seemed a little bit wetter and a bit more authoritative while maintaining crystal clear highs. The newer the op-amp the better in general. Look at slew rates, compare the data sheet that I posted with PDF files included earlier in the thread. You want to look at the date of publication to confirm how new or old the op-amp is. Just because an op-amp is old doesn't mean it's bad btw. Some are excellent performers on paper and also have the sound to back it up. With TI/Burr Brown, they have a line called "Sound-Plus" that is designed for higher fidelity use. Some have higher temperature ratings as well.
I do have some LME49680's, also a TI part that is excellent sounding.
https://www.ti.com/lit/ds/symlink/l...https%3A%2F%2Fwww.ti.com%2Fproduct%2FLME49860
A completely different character to the sound. I tried them both on the A0200. Sure one is much older in design, but that definitely doesn't make it a poor performer. However the op-amp is more designed for headphone amps as they are totally capable of driving a 600ohm load with no difficulty.
I'm still trying to figure out where the ST72C op-amps go to. I'm assuming still that it's for sub-out, though it could just as easily be used for RCA/Single ended input though I doubt it highly. Actually, I can test it very easily with a continuity test but I don't want to tear the amplifier back down again!
Please understand that when you are modifying anything that you are doing so of your own free will. I am not responsible for any equipment failures or damage or burns caused by your modification.
You WILL hear a significant difference with different op-amps. I had mentioned in other posts that op-amp rolling is almost useless, but that is completely dependent on how it is implemented. The circuit is far more important than the actual op-amp itself to be able to hear significant improvements. The implementation of the op-amp into a circuit is critical to the performance benefits or lack thereof. The A0200 definitely will benefit from a better op-amp. Just be careful of how much additional gain you might put through the amplifier. But then there's always the soft-clipping feature. You will not always hear clipping, if you hear clipping, usually some damage is done to a speaker or other components within an amplifier as you've sent a DC signal through an analogue portion of the amplifier. They're not supposed to see any form of DC voltage or squared off sinewaves.
I have not managed to drive the A0200 with the OPA1656's op-amps with my RME ADI DAC-2 fs into clipping. In fact the amplifier and speaker combination in my room is excessively loud if I try and get close to clipping levels of Decibels. I have to leave the room! And zero evidence of clipping.
It is in my personal opinion a modification that is well worth the effort. Even the several generations older OPA1612 which is a solid performer on which the 1656 is based is still a solid performer though the bass is less forceful.
With the new op-amps, I can say that the bass has much more force than with the standard op-amps. The rest of the sound is just on a different level. It's a huge improvement. Now I can truly say that the A0200 is as close to my tiny tube amplifier and probably beats it. Not hands down, but I would be comfortable in saying that it definitely can play music extremely well. It will not only shock you at how much better it sounds, but will outshine so many amplifiers in the sub $1500 price point that is a power amplifier that has XLR inputs and single ended inputs.
You do need to know which op-amps work in what type of circuit, but the information is floating out there and so is actual TI customer support.
Newer op-amps seem to have the edge over the older generation in very broad terms. The MUSES01 is extremely expensive, that is all. It's about 10 years old. And back then it was indeed a revelation, today most op-amps comprehensively outperform them at a mere fraction of a fraction of the price. In Japan, the MUSES01 is about $35 each even today. You can buy op-amps that out class, out perform it for $3 each! Every measurement, every sound test and graph will show you that the 01 op-amp is living on legacy rather than performance. Also, maybe there's a little bit of a status symbol type of reverence given to it due to the price?
Happy listening, and if you do decide to mod your amp and it's your first time doing so, find something else that is basically scrap so you can practice removing parts. And also have the necessary heat-clips. Glorified crocadilly alligator clips made of aluminium. They have both straight and angled types. I prefer the angled type so as to give me a clearer view of the op-amp. But you can certainly use either. Have your supplied on hand and ready. Practice with something that you don't care about before embarking on the modification if you're not sure about your skill/comfort level. I've made a tutorial of sorts to help with those with less experience with removing the original op-amps. You should certainly save the originals. You can re-use them and would want to re-fit them in the event you need to send your amp in for repair/service. The cleaner your soldering job, the less likely you are to be flagged for modification resulting in failure.
Cheers guys and gals!
Make sure you unplug the amplifier and preferably let it sit for a while, maybe 30 minutes to deplete the capacitors of any stored electricity as a precaution.
Make sure you are very comfortable with a soldering iron. It's better to have temp control. You need to wick the solder across the pins and do it gently so you do one leg at a time. You need a "Heat-Clip", do a row of 4 legs 1 leg at a time, only let your soldering iron have contact for 3-5 seconds at a time. You run the risk of overheating the trace itself that has what I assume is a Discrete Surface Mount (DSM) capacitor on two sides of the op-amp. So do one leg at a time of the eight legs, one row at a time, all the while lightly tugging on the heat clip. Once you get a row of 4 done, do the other side, the other side of 4 legs will be much easier and do the same, one leg at a time. use good soldering wick. I use Hako wick with wax, the thinnest one and then the next step thicker ones for this sized op-amp. Once you have the first row of 4 legs unsoldered, you can apply just a tiny bit more upward force, it's ok to bend the legs a little since you can easily bend them back into place. All the while make sure you don't stay in one spot for more than those 3-5 seconds. It's tedious work. Once you get probably 6 of the legs unsoldered, you can use your wick and soldering iron and go across the legs and it should just lift straight off with next to zero effort. The trick is to get the wick to do the work for you. Don't try and unsolder the op-amp with a vacuum pump style de-soldering tool, it'll take too much space, and it'll obscure your view.
When soldering on your new op-amps do the reverse, but make sure you remove all the flux from the board and excess solder from the circuit board using the wick. I just use my soldering iron at a slightly higher temp when soaking up excess solder. Then use flux remover, or Isopropyl alcohol with a q-tip to clean off the resin and flux. Readjust the temperature on your soldering iron that you just had raised a short while ago, lower the temp to the appropriate melting temp of your solder of choice. Apply a tiny dab of new solder on each of the 8 spots on the PCB where the op-amps will be placed. This is done so that when you locate and centre the new op-amp all you have to do is heat up a leg at a time. All this time you should have the new op-amp held with a pair of "Heat-Clips" for maneuvering and locating the chip. You can press down hard with the op-amp and heat clip when soldering the eight legs, do one at a time. And remember that 3-5 second rule still applies. Use your mobile and zoom in to make sure you're centred and have indeed applied solder completely on each leg, without having solder touch the next pin over! It'll just set the op-amp into protection if you do, and it won't blow up your amp, but it will make noise if you mess up with soldering. A tiny amount of excessive solder can easily cause a short. Once you get both chips done, it's finished.
Make sure that you are clearly identify that you are only attending to the two opa1678's! The reason why (part of the reason why DC offset is different on the two channels is the obvious length of the circuit board.
I prefer Texas Instruments Burr-Brown op-amps and have done for years, something about their tone has always seemed a little bit wetter and a bit more authoritative while maintaining crystal clear highs. The newer the op-amp the better in general. Look at slew rates, compare the data sheet that I posted with PDF files included earlier in the thread. You want to look at the date of publication to confirm how new or old the op-amp is. Just because an op-amp is old doesn't mean it's bad btw. Some are excellent performers on paper and also have the sound to back it up. With TI/Burr Brown, they have a line called "Sound-Plus" that is designed for higher fidelity use. Some have higher temperature ratings as well.
I do have some LME49680's, also a TI part that is excellent sounding.
https://www.ti.com/lit/ds/symlink/l...https%3A%2F%2Fwww.ti.com%2Fproduct%2FLME49860
A completely different character to the sound. I tried them both on the A0200. Sure one is much older in design, but that definitely doesn't make it a poor performer. However the op-amp is more designed for headphone amps as they are totally capable of driving a 600ohm load with no difficulty.
I'm still trying to figure out where the ST72C op-amps go to. I'm assuming still that it's for sub-out, though it could just as easily be used for RCA/Single ended input though I doubt it highly. Actually, I can test it very easily with a continuity test but I don't want to tear the amplifier back down again!
Please understand that when you are modifying anything that you are doing so of your own free will. I am not responsible for any equipment failures or damage or burns caused by your modification.
You WILL hear a significant difference with different op-amps. I had mentioned in other posts that op-amp rolling is almost useless, but that is completely dependent on how it is implemented. The circuit is far more important than the actual op-amp itself to be able to hear significant improvements. The implementation of the op-amp into a circuit is critical to the performance benefits or lack thereof. The A0200 definitely will benefit from a better op-amp. Just be careful of how much additional gain you might put through the amplifier. But then there's always the soft-clipping feature. You will not always hear clipping, if you hear clipping, usually some damage is done to a speaker or other components within an amplifier as you've sent a DC signal through an analogue portion of the amplifier. They're not supposed to see any form of DC voltage or squared off sinewaves.
I have not managed to drive the A0200 with the OPA1656's op-amps with my RME ADI DAC-2 fs into clipping. In fact the amplifier and speaker combination in my room is excessively loud if I try and get close to clipping levels of Decibels. I have to leave the room! And zero evidence of clipping.
It is in my personal opinion a modification that is well worth the effort. Even the several generations older OPA1612 which is a solid performer on which the 1656 is based is still a solid performer though the bass is less forceful.
With the new op-amps, I can say that the bass has much more force than with the standard op-amps. The rest of the sound is just on a different level. It's a huge improvement. Now I can truly say that the A0200 is as close to my tiny tube amplifier and probably beats it. Not hands down, but I would be comfortable in saying that it definitely can play music extremely well. It will not only shock you at how much better it sounds, but will outshine so many amplifiers in the sub $1500 price point that is a power amplifier that has XLR inputs and single ended inputs.
You do need to know which op-amps work in what type of circuit, but the information is floating out there and so is actual TI customer support.
Newer op-amps seem to have the edge over the older generation in very broad terms. The MUSES01 is extremely expensive, that is all. It's about 10 years old. And back then it was indeed a revelation, today most op-amps comprehensively outperform them at a mere fraction of a fraction of the price. In Japan, the MUSES01 is about $35 each even today. You can buy op-amps that out class, out perform it for $3 each! Every measurement, every sound test and graph will show you that the 01 op-amp is living on legacy rather than performance. Also, maybe there's a little bit of a status symbol type of reverence given to it due to the price?
Happy listening, and if you do decide to mod your amp and it's your first time doing so, find something else that is basically scrap so you can practice removing parts. And also have the necessary heat-clips. Glorified crocadilly alligator clips made of aluminium. They have both straight and angled types. I prefer the angled type so as to give me a clearer view of the op-amp. But you can certainly use either. Have your supplied on hand and ready. Practice with something that you don't care about before embarking on the modification if you're not sure about your skill/comfort level. I've made a tutorial of sorts to help with those with less experience with removing the original op-amps. You should certainly save the originals. You can re-use them and would want to re-fit them in the event you need to send your amp in for repair/service. The cleaner your soldering job, the less likely you are to be flagged for modification resulting in failure.
Cheers guys and gals!
The only way you would know if there is a difference is to do a blind level matched AB test. Yes, look at slew rates for sure. Do a calculation regarding req'd slew rate vs the bandwidth req'd and compare that to the available slew rate of the OP amp and realize that most any OP amp can handle audio bandwidth without issue. OP amps are so fast and have such good slew rate and bandwidth that audio applications are easy peasy stuFF.
There is not a significant difference unless the op amps have different gain and are not implemented properly in the circuit.
You've been at the hooka pipe too much lately?
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