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Topping LA90 Discrete arriving in 1-2 days. Question vs. LM3886 version

mike7877

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OK, so my LA90 Discrete is arriving soon! Obviously I'm excited...
Strange thing: I didn't get notified that duty was due, so unfortunately, after an order mishap causing an initial 1.5 month delay for my order, I recently had to wait another two weeks with my unit in limbo at customs. Good thing I randomly decided to check the tracking number and paid it!

I have a question before it arrives...
Why are some people here so against the discrete version of the LA90 vs the first one?
I've read through reviews of both, and subjectively, performance is the same!

The small measurable differences there are always (except once) place the LA90 discrete (newer version) ahead of the original.

What's marginally better in the discrete?
Power handling: ~1dB
Power vs distortion 20Hz, 500Hz, 1k, 5k: 5dB
Power vs distortion 10k, 20kHz: 10-15dB

What's marginally better in the LM3886 (that's what they used, right?)
Stereo crosstalk: ~10dB better (discrete is already below -90dB by 5kHz. Like I said "subjectively, performance is the same!"

The discrete version is spec'd to run 4 ohm bridge mode, but it's not much of a feat. Why not?
Because, 4 ohm bridge gives you 180W @ 1% distortion. Non bridged you get 120W x2! Probably better in most situations to bi-amp then, no? 120W to 180W and giving up an entire channel is nothing compared the gains gotten with 8 ohm bridge: 56W x2 into 8 ohms becomes 180W x1! Pretty great!
Literally the power output into 4 ohm in bridge mode is the same as 8 ohm! I've never seen that anywhere lol
* just don't bridge! *

Distortion and power over the audible spectrum (the 20Hz, 500Hz, 1k... 20kHz test), technically the discrete is better, but they're both at -100 for all of it and only usually 5-10dB different, so... no huge deal.


CLEARLY the Topping LA90 Discrete is technically better than the non-discrete version when it comes to measurements.
Why is it, then, that I've seen it written the LA90 is good, whilst the LA90 Discrete (LA90D) is bad?

My LA90D will be here imminently. I'm not expecting a pile of trash on the porch, but I am very curious as to why some are vehemently opposed to the D?


Also: I'll do a mini review of it here after I've had the thing for about two weeks. I need time to see how it sounds and behaves with my different speakers, with different music, at different levels, at different times!
 
Because there are dozens of LA90Ds failed within a month.
 
Because there are dozens of LA90Ds failed within a month.

Do you know how they failed? And is that it?


I got mine a couple days ago, and it is CLEAN.
I have to say: I'm happy with it!


I'll have to see how it does with bass at higher volumes, because, so far, I've only been able to test it at relatively quiet levels (~2W). If bass performance is anything like what I've heard in my sub 2 watt listening, I don't think I'll have anything to complain about. At all!

I see in some LA90 discrete pictures, that four, 35V, high quality Nakamichi bulk capacitors are used for the power amp section. Since the LA90 uses 64V rails, I'm going to assume those two pairs of 35V caps in series, and each series pair is shared between channels.
The caps are 4700uF each, and when you put identical caps in series, capacity is maintained while voltage is doubled.
And... since 70 > 64, the smoke stays in while the music comes out! :D

I've never seen a good and powerful (more than 20W) AB amp that used a regulated power supply before, so I don't know appropriate sizing... But since there's no rectified AC to minimize the ripple of, I'd guess (very conservatively) that size they need to be is at least halved.

Normally, for a 50W, 8 ohm amplifier, I'd say 10,000uF per channel is very good (when all else is as good, lol)

I don't presume the voltage drop on the transistors during transients while driving my 8 ohm nominal (~6 ohm minimum) speakers {they're verrrrrry nice!), to be more than a volt when music is the signal and the output isn't clipped, so I'm not anticipating any bass response issues. But if there are... I have four, massive, 63V 33,000uF cans, with insanely low ESR that I bought for an amplifier that might not actually be able to be fixed anymore...
So, if I find LA90 Discrete's bass to be lacking in any way, I might DO SOMETHING ABOUT IT!!!! lol
 
They failed on their own. Happened two weeks after I got them. Topping got them fixed about a month ago and they've been working fine since then. The aftersales team of Topping told me the the modules were defect.

Hmm. I bought mine (one) on Amazon. I'll have to contact the seller and see what's up. When I made my initial order in late June, it was delayed due to "error". Maybe they were told to stop selling because of the defect and it wasn't available, and the one I have is OK.
I hope it is...

Do you know if the problem typically (or possibly) results in the board outputting DC at rail voltage upon failure?
Or is it something benign? I've seen an LA90 Discrete "crackling" complaint which sounds like cold solder joint or bad connection of some kind, not faulty to the point of destroying any speakers connected to it. I'd really hate that... I'm so happy with my speakers that I don't plan to replace them until I have to (I also plan to keep them in working condition as long as possible by never abusing them and always considering their surroundings down to low humidity (40%) and temperature (no higher than 26)
 
Hmm. I bought mine (one) on Amazon. I'll have to contact the seller and see what's up. When I made my initial order in late June, it was delayed due to "error". Maybe they were told to stop selling because of the defect and it wasn't available, and the one I have is OK.
I hope it is...

Do you know if the problem typically (or possibly) results in the board outputting DC at rail voltage upon failure?
Or is it something benign? I've seen an LA90 Discrete "crackling" complaint which sounds like cold solder joint or bad connection of some kind, not faulty to the point of destroying any speakers connected to it. I'd really hate that... I'm so happy with my speakers that I don't plan to replace them until I have to (I also plan to keep them in working condition as long as possible by never abusing them and always considering their surroundings down to low humidity (40%) and temperature (no higher than 26)
I only know very few people from the first 2 or 3 batches of LA90D who hasn't had their LA90D repaired. They all failed because of the modules. I do not think any of them are due to cold solder joint or bad connection. I also don't think any of the failed LA90D had destroyed any speaker. But most people should have stopped using their amp after noticing popping noise, so I wouldn't try to drive speakers with broken amp for a long period.
 
I only know very few people from the first 2 or 3 batches of LA90D who hasn't had their LA90D repaired. They all failed because of the modules. I do not think any of them are due to cold solder joint or bad connection. I also don't think any of the failed LA90D had destroyed any speaker. But most people should have stopped using their amp after noticing popping noise, so I wouldn't try to drive speakers with broken amp for a long period.

OK.
I'll reach out to the seller, and in the mean time continue to use my LA90D. If I hear popping, I'll turn it off.
 
Updates! GREAT NEWS!!!

The seller contacted the manufacturer with my serial number, and my unit is not affected by any manufacturing defect.

*** There was never an "all units before July 15" (or any date) problem. ***

I won't say there wasn't a problem with a few units with the same cause which caused popping after a few weeks use - clearly something like that happened here. Could've been a cold solder joint (on a larger connection for example), faulty transistors, incorrect transistors, fraudulent transistors, used transistors, (hey, it's China... they could be communist transistors!) - popping on some units requiring a common board replacement: TOTALLY possible.

What definitely wasn't, was a systemic issue with ALL LA90 Discrete amps manufcatured before a date. The cause was NOT from an unspecified systemic issue with all LA90 Discrete amps, making all those units a horrible day waiting to happen.

Which makes me happyyyyy
Hopefully it lasts longer than me (and I last a long time...)
 
I won’t speculate too much here, but my info came directly from JohnYoung himself. Before I sent Topping those two failed LA90Ds, he explicitly pointed out that LA90Ds failed so far were due to modules. “Sealing them in plastic chambers created lots of troubles” he said. And I asked whether this will happen after replacing modules and he said they made refined modules. He then said that he will talk to after sales and informed me that modules made after July 15th will be good to go later in that conversation.
 
I won’t speculate too much here, but my info came directly from JohnYoung himself. Before I sent Topping those two failed LA90Ds, he explicitly pointed out that LA90Ds failed so far were due to modules. “Sealing them in plastic chambers created lots of troubles” he said. And I asked whether this will happen after replacing modules and he said they made refined modules. He then said that he will talk to after sales and informed me that modules made after July 15th will be good to go later in that conversation.
So they replaced the modules with refined modules?
Let's see the new beta test.
 
So they replaced the modules with refined modules?
Let's see the new beta test.
Mine were replaced in late July. They worked fine for 2 months now. I did know someone got their LA90D fixed for three times. I also knew people who never had a problem even with the original module. My point here is that there are so many Topping fanboys around that in some sense covers the underlying QC problem. And arguably I used to be one of them. Obviously it’s nice to see cheap gears that measure well. But hay, face the problem. It’s better to speak out it loud so that manufactures realize that they need to be fixed.
 
What is this "module" you're all speaking about?
Isn't the whole thing on one or two boards...

edit: to add... if something is sealed in an aluminum enclosure, and the parts inside get warm, the outside of the case gets warm as well. For example, my G5 is basically a sealed aluminum block - when its internals warm up a bit, so does the outside of the case. I doubt the air internally gets more than 5-8 deg C higher than the case... All metal laptops are another great example. Metal is not a good insulator - try making your front door out of 3mm aluminum and see for yourself lol. I'm not saying a vented design wouldn't have been better, but clearly the internals don't get too hot inside. Besides, other than the transistors, there's almost nothing in there to make heat. The power supply is outboard, so I doubt even the bulk caps contribute much. Everything inside should be perfectly fine to run up to 60C on a regular basis and last at least 5 years, even capacitors that aren't 105C 9000 hour rated. 85C 4000 hour (a low rating) would do 60C for 20K hours, and at that point they're not broken, just not quite in spec anymore. And since regulated power comes in at the rear... At 20k hours on at 4 hours per day that's still 14 years.
Unless these people were playing 50 watt sine waves, I can't see how their amps could break, especially from poor ventilation in the span of a month or two
 
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Yeah that brought up nothing

edit for clarity: nothing relevant
in case you're too lazy to check that there's nothing relevan (I mean, you could explain what a module is - clearly you know, but you passive aggressively sent a search result instead, which leads to these few posts here in this thread, and the rest to threads of other device)
 
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I did know someone got their LA90D fixed for three times.

Module faulty -> new module: module faulty -> new module: module faulty -> new module?

And when they knew they were replacing a faulty module?

The odds of that happening are extremely low. I'd bet misuse or abuse, or poor awareness of the characteristics of their speakers. That's one in four working...

Now obviously I'm not saying everyone who's had this issue is intentionally misusing their amp, or that their amp is even being run out of spec. Just that particular example, is very suspicious
 
Yeah that brought up nothing
then do your own research. I have made myself clear enough. And BTW the enclosure seals the module is plastic as I mentioned previously so the very initial assumption you are trying to use to justify your theory of heat conduction doesn’t hold.
 
Module faulty -> new module: module faulty -> new module: module faulty -> new module?

And when they knew they were replacing a faulty module?

The odds of that happening are extremely low. I'd bet misuse or abuse, or poor awareness of the characteristics of their speakers. That's one in four working...

Now obviously I'm not saying everyone who's had this issue is intentionally misusing their amp, or that their amp is even being run out of spec. Just that particular example, is very suspicious
There are at least ten people in Topping’s group chat had their LA90D failed within 1 month. The odds for all them abusing the amp is very low. And as I mentioned before, JohnYoung clarified to me that mine were also due to faulty modules, before I sent the amps back, obviously before he had any chance even taking a look at them. I know, still not persuasive enough.
But afterall, I provided my data points and all the evidence on the table. I have my own theory explaining these cases, may not be the true model. You can take it or leave it.
 
then do your own research. I have made myself clear enough. And BTW the enclosure seals the module is plastic as I mentioned previously so the very initial assumption you are trying to use to justify your theory of heat conduction doesn’t hold.

Thanks for as much help as I knew you'd give, sarieri
 
There are at least ten people in Topping’s group chat had their LA90D failed within 1 month. The odds for all them abusing the amp is very low. And as I mentioned before, JohnYoung clarified to me that mine were also due to faulty modules, before I sent the amps back, obviously before he had any chance even taking a look at them. I know, still not persuasive enough.
But afterall, I provided my data points and all the evidence on the table. I have my own theory explaining these cases, may not be the true model. You can take it or leave it.

There is no difference between amps made pre July 15 and post July 15 - Topping.

Sure 10 people in a group chat had broken amps.
How many of those amps has Topping sold?
What is the usual failure rate of manufactured electronics like amplifiers?

Your figure is useless

This is the situation: A known issue that can arise is popping which can be fixed by a module replacement.

Some guy got three (3) REPLACEMENTS before he didn't need another...
Since Topping knows what the issue is, and they fixed his amp, shouldn't it be impossible to need three?
 
There is no difference between amps made pre July 15 and post July 15 - Topping.

Sure 10 people in a group chat had broken amps.
How many of those amps has Topping sold?
What is the usual failure rate of manufactured electronics like amplifiers?

Your figure is useless

This is the situation: A known issue that can arise is popping which can be fixed by a module replacement.

Some guy got three (3) REPLACEMENTS before he didn't need another...
Since Topping knows what the issue is, and they fixed his amp, shouldn't it be impossible to need three?
Ask Topping, but I don’t think you will have a reply
 
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