Topping LA90 Review (Integrated Amplifier)

[KSTR]

This means the amp is either bridged on the output or there is split power supply in there.

The obligatory connecting of - outputs to enable bridged operation suggests the amp is already bridged inside.

No active split. The split appears to be done with the 2 e-caps, providing a AC "gnd" that is probably within the feedback loop. They also double up as supply buffers. The "gnd" node is the feedback reference. For bridged mode they must be connected together.
Years ago I did a similar concept for an ICEpower compatible tweeter amp that only had single supply. By chance, that also was a LM3886-based composite (LM4780 duals, actually).

 

[nagster]

A little addition.
Resistance value. (Power is on!)

 

[daniboun]

You would think so with the three pins, but Amir checked it and it is +64V, with the other pin no connection.

You're right, the picture clearly shows that it is a 64 +- Pin.

 

[antcollinet]

Pictures below show this as well 64V only.
This means the amp is either bridged on the output or there is split power supply in there.

The obligatory connecting of - outputs to enable bridged operation suggests the amp is already bridged inside.

Maybe the LM317/337 have something to do with this but these are current limited below the output current capability of the amp.
2 of these in parallel would limit the LF output current to 3A, for higher frequencies the power supply caps could provide extra current.

Too bad the one that took it apart and found out about the LM317/337 did not show the power amp part number(s).

Would be fun if @JohnYang1997 would give some hints about the internal structure.

No active split. The split appears to be done with the 2 e-caps, providing a AC "gnd" that is probably within the feedback loop. They also double up as supply buffers. The "gnd" node is the feedback reference. For bridged mode they must be connected together.
Years ago I did a similar concept for an ICEpower compatible tweeter amp that only had single supply. By chance, that also was a LM3886-based composite (LM4780 duals, actually).

I think the regulators must be splitting the rails. Firstly I can't imagine what 4 regulators per channel would be doing if not providing the amp power.

Second although the devices are rated 1.5A min they are 2.2A typical (at least the on-semi ones I looked at). Topping may well be taking the view that two in paralell will (on average) be closer to typical then just 1 would be. It is also likely to be a thermal limit - so short duration peaks above that probably wouldn't be an issue. Topping may also be relying on the fact that real music can't normally drive continuous full power out of an amp.

Further, the amp clips at 56W into 4 ohms. This is less than double the 8ohm clipping point which suggests that it is current limited rather than voltage limited. That may well also explain Toppings caution in specifying minimum speaker impdeances of 4ohm/8ohm bridged.

56W requires 3.75A at 4ohm. which is a little below the 4.4A "typical" rating for two devices in parallel.

 

[Selkirks]

I wonder if using Martin Logan Montis with the LA90 had something to do with the failure.

 

[antcollinet]

I wonder if using Martin Logan Montis with the LA90 had something to do with the failure.

What failure? And why?

 

[daniboun]

After a few hours of listening, here's what I can say about the LA90. First I admit that my choice was conditioned by the fact that it is a class AB amp. The ASR measurements don't lie, I had no doubts about its performance but rather about its listening level.

Frankly I'm not disappointed) It is more than enough for a room of 30M2 at an honorable listening level.

For those in doubt :

VS my Purifi (Kayamb OPA2210 buffers) VS my PA5: I wanted to know how well an AB amp mounted in the rules of the art could sound compared to a Class D amp mounted in the same rules of the art.
In all honesty I find the same "grain" that I had on my MOS-120 (MOSFET IRFP240 / IRFP9240) but with the surgery and righteousness of PA5 and Purifi.

What I noticed, I nitpick but I share it all the same: when I put my ears on my Seas Beryllium tweeter, the PA5 and the LA90 are absolutely silent, so that we have the impression that the amps are totally off. With my two Purifis, there is a very slight hiss, almost inaudible, but with your ears glued together you can hear it.

Now on the overall listening, the LA90 provides a lot of pleasure, I find it generally softer but that does not surprise me. Like I said, that's the feeling I've always had with Class AB amps.
It drives my speakers very elegantly, everything is clear across the all spectrum, it has excellent holography and the good quality recordings are simply amazing! I will continue my listening and see how it behaves over time

I had a doubt about its power, but in volume bypass mode and high gain, my DAC set to the same volume as my PA5, it's quite comparable. The Purifi on the other hand is more powerful, no doubt )

My first listens let me say that this is an excellent amp, admittedly a bit expensive but what does it sound good!

My Setup :

Gustard AK4499 DAC set @ -2DB
Orbit MK2 speakers Cables
LA90 set @ volume Bypass / high gain
Playlist : Audiophile Master 2019 (HD audio)
Floor Speakers : XTZ 100% Seas woofers + Seas Beryllium Tweeters (88DB)
3th order XTZ special CrossOver.

 

[solderdude]

Congratulations to all of topping. Keep going further.

===
board, power consumption, temperature.

So Topping covered the poweramp IC with a PCB to clamp it on the heatsink...

Looks like a rail splitter.

Firstly I can't imagine what 4 regulators per channel would be doing if not providing the amp power

I suspect at least 2 of the LM317/377 are there to provide +/- 15V or something like that for the used opamps.

The other 2 could be part of a rail splitter or pre-regulation or 2 different +/- voltages ?

56W requires 3.75A at 4ohm. which is a little below the 4.4A "typical" rating for two devices in parallel.

I think the current limiter may either be in the output IC or the power supply. Would need to redo the 4 ohm (bridged) test feeding just 1 channel.
That could give some clues.
Current limiter clips hard at 190W (28Vrms/4ohm (bridged) = 7.1Arms (peaks required = 9.9A) but this does not have to pass through a virtual ground.

Also what would be weird is that L and R channel would have their own rail splitter but expect the ground reference to be the same on both amps.
It would be silly to not use the same reference.

At 2 ohm (stereo) the current limits hard at 50W = 10Vrms (2 ohm) = 5Arms (peaks required = 7.1A) per channel.
Those currents would thus have to come through the rail splitter (also one channel used) or come from the reservoir caps.

Hoping @JohnYang1997 chimes in one day...

 

[KSTR]

I think the regulators must be splitting the rails. Firstly I can't imagine what 4 regulators per channel would be doing if not providing the amp power.

Second although the devices are rated 1.5A min they are 2.2A typical (at least the on-semi ones I looked at). Topping may well be taking the view that two in paralell will (on average) be closer to typical then just 1 would be. It is also likely to be a thermal limit - so short duration peaks above that probably wouldn't be an issue. Topping may also be relying on the fact that real music can't normally drive continuous full power out of an amp.

Further, the amp clips at 56W into 4 ohms. This is less than double the 8ohm clipping point which suggests that it is current limited rather than voltage limited. That may well also explain Toppings caution in specifying minimum speaker impdeances of 4ohm/8ohm bridged.

56W requires 3.75A at 4ohm. which is a little below the 4.4A "typical" rating for two devices in parallel.

You sure have some good points here.
Then again, the potted modules and the other opamps need a supply (+-15V supposedly), too. Paralleling the 317s/337s would require load sharing resistors which I have not spotted. And when the splitter (zero follower) has some DC standing current (class A/B operation) this would require "degeneration" resistors as well given the tremendous gain of the 3x7s, so that would be 4pcs rather large SMD low valued resistors.

Only closer examination could tell what's going on here.
@JohnYang1997 obviously cannot leak specific details unless he's looking for a new job ;-)

 

[BoredErica]

What I noticed, I nitpick but I share it all the same: when I put my ears on my Seas Beryllium tweeter, the PA5 and the LA90 are absolutely silent, so that we have the impression that the amps are totally off. With my two Purifis, there is a very slight hiss, almost inaudible, but with your ears glued together you can hear it.

What is sensitivity of the tweeter? If sinad of purifi is not high enough that concerns me.

 

[daniboun]

What is sensitivity of the tweeter? If sinad of purifi is not high enough that concerns me.

Checkout

Paire de tweeters à dôme SEAS T29B001, 6 ohm, bobine 29 mm

www.toutlehautparleur.com

 

[pma]

What is sensitivity of the tweeter? If sinad of purifi is not high enough that concerns me.

It is rather power amp gain x noise of the preceding DAC. Do not get trapped by a single component SINAD, it does not tell the story.

 

[jjmanda]

After a few hours of listening, here's what I can say about the LA90. First I admit that my choice was conditioned by the fact that it is a class AB amp. The ASR measurements don't lie, I had no doubts about its performance but rather about its listening level.

Frankly I'm not disappointed) It is more than enough for a room of 30M2 at an honorable listening level.

For those in doubt :

VS my Purifi (Kayamb OPA2210 buffers) VS my PA5: I wanted to know how well an AB amp mounted in the rules of the art could sound compared to a Class D amp mounted in the same rules of the art.
In all honesty I find the same "grain" that I had on my MOS-120 (MOSFET IRFP240 / IRFP9240) but with the surgery and righteousness of PA5 and Purifi.

What I noticed, I nitpick but I share it all the same: when I put my ears on my Seas Beryllium tweeter, the PA5 and the LA90 are absolutely silent, so that we have the impression that the amps are totally off. With my two Purifis, there is a very slight hiss, almost inaudible, but with your ears glued together you can hear it.

Now on the overall listening, the LA90 provides a lot of pleasure, I find it generally softer but that does not surprise me. Like I said, that's the feeling I've always had with Class AB amps.
It drives my speakers very elegantly, everything is clear across the all spectrum, it has excellent holography and the good quality recordings are simply amazing! I will continue my listening and see how it behaves over time

I had a doubt about its power, but in volume bypass mode and high gain, my DAC set to the same volume as my PA5, it's quite comparable. The Purifi on the other hand is more powerful, no doubt )

My first listens let me say that this is an excellent amp, admittedly a bit expensive but what does it sound good!

My Setup :

Gustard AK4499 DAC set @ -2DB
Orbit MK2 speakers Cables
LA90 set @ volume Bypass / high gain
Playlist : Audiophile Master 2019 (HD audio)
Floor Speakers : XTZ 100% Seas woofers + Seas Beryllium Tweeters (88DB)
3th order XTZ special CrossOver.

I pretty much agree with your comments.

I also have a PA5 and a pair of vintage, but upgraded, set of NAD amps I used in a L/R mono setup.

Questions and opinions on reliability, build quality and costs are one thing that is being debated.
But I find the amp a pleasure to listen to.

 

[BoredErica]

It is rather power amp gain x noise of the preceding DAC. Do not get trapped by a single component SINAD, it does not tell the story.

True, forgot about that. Could just be listening to dac noise. That's what I get when posting at 3am lol.

 

[IPunchCholla]

It is rather power amp gain x noise of the preceding DAC. Do not get trapped by a single component SINAD, it does not tell the story.

Isn’t the noise of the DAC encapsulated in its SINAD? I agree SINAD isn’t everything,

 

[antcollinet]

You sure have some good points here.
Then again, the potted modules and the other opamps need a supply (+-15V supposedly), too. Paralleling the 317s/337s would require load sharing resistors which I have not spotted. And when the splitter (zero follower) has some DC standing current (class A/B operation) this would require "degeneration" resistors as well given the tremendous gain of the 3x7s, so that would be 4pcs rather large SMD low valued resistors.

Only closer examination could tell what's going on here.
@JohnYang1997 obviously cannot leak specific details unless he's looking for a new job ;-)

I guess we'll find out one way or the other, in time.

 

[mdsimon2]

Isn’t the noise of the DAC encapsulated in its SINAD? I agree SINAD isn’t everything,

System SINAD matters, individual DAC / amp doesn't mean that much. In this case DAC was the same but the amplifier with higher gain resulted in more noise which is not surprising. If a lower noise but lower output level DAC was used with the Purifi there would be less noise. The PA5 / LA90 need a higher output DAC as they have low gain. It's all about proper gain staging of components.

Michael

 

[tomchris]

Finally, we get to see the insides of Topping L90

Although, I was hoping for a more traditional and modular design that uses symmetric design, large power supplies, large cap resevoir and separate output stage boards attached to each heatsink, for instance:

 

[solderdude]

Well its got a separate DC power supply so no need for a many hundred Watt transformer and large reservoir caps.

 

[IPunchCholla]

System SINAD matters, individual DAC / amp doesn't mean that much. In this case DAC was the same but the amplifier with higher gain resulted in more noise which is not surprising. If a lower noise but lower output level DAC was used with the Purifi there would be less noise. The PA5 / LA90 need a higher output DAC as they have low gain. It's all about proper gain staging of components.

Michael

Yes. I was just reading the thread on how noise propagates through the stack. Interesting how dependent it is on the exact nature of each component.