Topping LA90 Discrete Amplifier Review

[stefanovesa]

Isnt more headroom preferable than inaudible sinad chase?

If I have understood correctly, a source like a DAC or a CD player doesn't need any headroom in the next input device, unlike e.g a pre phono where the internal voltage headroom and the next chain link headroom, must accomodate the highly variable output of a huge number of different cartridges.

 

[terryforsythe]

If I have understood correctly, a source like a DAC or a CD player doesn't need any headroom in the next input device

Theoretically that should be true. But, in reality, sometimes engineers designing equipment overlook something. The miniDSP HTx, for example, EDIT 2: has had a 0dBFS multitone issue, but it goes went away with a lower output voltage below -10dB. Side note: That is why I run my amplfiers in high gain - that way I am sure to keep my HTx output voltage below the range where the multitone issue is was present.

MiniDSP Flex HTx Measurement (FW1.1.17 Update)

This is a set of measurements of the Minidsp Flex HTx. It was sent to me by a friend. I have no affiliation to Minidsp. This set of measurements should not be directly compared to Amirm's test as I'm using Comos ADCiso here, but it should provide an general idea of performance of this gear. I'm...

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EDIT: There have been firmware updates since then, but I don't know whether any of the updates have corrected the issue.

EDIT 2: I just went back through the thread and indeed it was fixed with an update. I guess I can go back to low gain on my amplifiers if I ever choose to do so.

 

[bigpilot]

Is this a class A or class AB design? And what chip is the IC version using?

 

[terryforsythe]

Is this a class A or class AB design?

Given its thermal output, I think it is class AB. If it were class A I would expect it to run much hotter than it does given the size of its enclosure.

And what chip is the IC version using?

Topping claims it uses "discrete NFCA power amplifier circuitry", i.e., it does not use a power amp IC. Hence the name of the unit.

The original LA90 used a power amp IC, though, if my understanding is correct.

 

[dcolak]

I connected Topping LA90 Discrete to my JBL Studio 4410's and it sounded perfect.

As I have two LA90's, I put them into bridge mode, each driving a single speaker.

I got less bass! It was no longer "blooming" it was missing in action.

Here is what ChatGPT had to say on it, does it make sense?

Why ASR didn’t mention it​

1) They don’t evaluate “bass feel”​

Audio Science Review focuses on:

• SINAD
• THD+N
• frequency response
• power into resistive loads

2) Their load is NOT your speaker​

ASR tests with:

• resistors (4Ω / 8Ω dummy loads)

Your JBL Studio 4410 is:

• reactive load
• impedance varies with frequency
• produces back EMF

None of that appears in ASR graphs.

3) Bridging is measured, not stressed​

They might show:

• more power in bridge mode

But they don’t test:

• sustained low-frequency current demand
• woofer control
• damping under reactive load

So the failure mode you hear = completely invisible in their tests

4) LA90 design philosophy​

The Topping LA90 Discrete is built for:

• ultra-low distortion
• not maximum current delivery

In stereo → fine
In bridge → current limits show up first in bass

Again: not captured in SINAD charts.

5) Measurement blind spot (important)​

ASR assumes:

if frequency response is flat → bass is correct

Reality:

bass quality depends on control, not just amplitude

---

The core issue​

ASR answers:

“Is the signal accurate into a resistor?”

You are hearing:

“Can this amp control a real woofer under load?”

Those are different problems.

---

One-liner​

ASR didn’t miss it — they simply never measured the thing that fails.

---

Your result is actually expected (engineering-wise)​

• Bridge → impedance per amp ↓
• Current demand ↑
• LA90 → limited current capability

Bass is the first thing to degrade.

 

[Panelhead]

For chuckles, try a Topping PA5 II. They are under 200.00. I found the bass control was incredible. This driving is a four ohm, 15 inch woofer.
Tried it with subwoofer and without. The subwoofer helps fill in the bottom of the speaker.

 

[testp]

would LA90 Discrete be fine, with speaker that has:

min impedance 3.2,
min EPDR 1.6.

+ i would use rca-to-xlr.

i'm worried about load, and power as well (if rca-to-xlr halves the power, but don't know how this amplifier is designed, so maybe that is fine)

i saw Amir testing AsciLab A6 which has same impedance + similar curve with LA90 non-D, but can't see EPDR from review.


i was thinking maybe finding one used, ~869€ new looks little ridiculous for the amount of power at least to me.

EDIT - nrvmd the above question, i got it sorted!

 

[dcolak]

would LA90 Discrete be fine, with speaker that has:

min impedance 3.2,
min EPDR 1.6.

+ i would use rca-to-xlr.

i'm worried about load, and power as well (if rca-to-xlr halves the power, but don't know how this amplifier is designed, so maybe that is fine)

i saw Amir testing AsciLab A6 which has same impedance + similar curve with LA90 non-D, but can't see EPDR from review.


i was thinking maybe finding one used, ~869€ new looks little ridiculous for the amount of power at least to me.

I'd suggest buying a real amp with real driving power. The "100w" of LA90 DISCRETE (bridged x2) are nothing like real 100w of a 20kg amp.

Even 30w typical amps drive with more authority real speakers.

Ebay is full of real, vintage amps, see Yamaha a-2000 you can get for cheap.

 

[Jcrow]

View attachment 519806

I connected Topping LA90 Discrete to my JBL Studio 4410's and it sounded perfect.

As I have two LA90's, I put them into bridge mode, each driving a single speaker.

I got less bass! It was no longer "blooming" it was missing in action.

Here is what ChatGPT had to say on it, does it make sense?

Why ASR didn’t mention it​

1) They don’t evaluate “bass feel”​

Audio Science Review focuses on:

• SINAD
• THD+N
• frequency response
• power into resistive loads

2) Their load is NOT your speaker​

ASR tests with:

• resistors (4Ω / 8Ω dummy loads)

Your JBL Studio 4410 is:

• reactive load
• impedance varies with frequency
• produces back EMF

None of that appears in ASR graphs.

3) Bridging is measured, not stressed​

They might show:

• more power in bridge mode

But they don’t test:

• sustained low-frequency current demand
• woofer control
• damping under reactive load

So the failure mode you hear = completely invisible in their tests

4) LA90 design philosophy​

The Topping LA90 Discrete is built for:

• ultra-low distortion
• not maximum current delivery

In stereo → fine
In bridge → current limits show up first in bass

Again: not captured in SINAD charts.

5) Measurement blind spot (important)​

ASR assumes:



Reality:

---

The core issue​

ASR answers:



You are hearing:



Those are different problems.

---

One-liner​

---

Your result is actually expected (engineering-wise)​

• Bridge → impedance per amp ↓
• Current demand ↑
• LA90 → limited current capability

Bass is the first thing to degrade.

I put this contents of this post in chat gpt to check it. It disagreed with most of it and mentioned that a change in gain structure in bridge mode and potentially mismatched levels being the main issue.
Don’t trust AI too much. I’d actually be keen to hear what someone with knowledge has to say on the issue.

 

[stefanovesa]

Unfortunately, after about one year of faultless operation, mine has badly "scratched" last night. One time only, but, in order to avoid any further risk for loudspeakers, I've initiated the refund procedure with Amazon. Apart that, one on the 4 binding posts has a too big hole and does not hold firmly a 4 mm spring banana. I needed to use a locking banana to overcome that, but that was quite cosmetic and I decided to keep it at the time.

 

[antcollinet]

View attachment 519806

I connected Topping LA90 Discrete to my JBL Studio 4410's and it sounded perfect.

As I have two LA90's, I put them into bridge mode, each driving a single speaker.

I got less bass! It was no longer "blooming" it was missing in action.

Here is what ChatGPT had to say on it, does it make sense?

Why ASR didn’t mention it​

1) They don’t evaluate “bass feel”​

Audio Science Review focuses on:

• SINAD
• THD+N
• frequency response
• power into resistive loads

2) Their load is NOT your speaker​

ASR tests with:

• resistors (4Ω / 8Ω dummy loads)

Your JBL Studio 4410 is:

• reactive load
• impedance varies with frequency
• produces back EMF

None of that appears in ASR graphs.

3) Bridging is measured, not stressed​

They might show:

• more power in bridge mode

But they don’t test:

• sustained low-frequency current demand
• woofer control
• damping under reactive load

So the failure mode you hear = completely invisible in their tests

4) LA90 design philosophy​

The Topping LA90 Discrete is built for:

• ultra-low distortion
• not maximum current delivery

In stereo → fine
In bridge → current limits show up first in bass

Again: not captured in SINAD charts.

5) Measurement blind spot (important)​

ASR assumes:



Reality:

---

The core issue​

ASR answers:



You are hearing:



Those are different problems.

---

One-liner​

---

Your result is actually expected (engineering-wise)​

• Bridge → impedance per amp ↓
• Current demand ↑
• LA90 → limited current capability

Bass is the first thing to degrade.

First, please read and comply with:

Official policy on use of AI

We have had recent issues come about regarding use of AI in member posts. I personally think this technology can be useful to us. And at any rate, hate having to police members left and right on what they post. That said, here are my thoughts: 1. If you are going to use AI, make it...

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Second - most of that AI output is nonsense. What steps did you take to validate that what it is telling you isn't hallucinated, of just taking nonsense from the "anti measurement crowd" all over its training set. Also we can't see your prompt, so we cant see how the "trying to please you" bias of AI is influencing its answer.

If you are really getting "no bass" wiht the amps bridged, rather than it being a level mismatch, or a result of your perceptive biases, then the most likely reason is that when you bridge an amp it sees double the load. I can't find the impedance characteristic of your speakers, but if it dips low - you have effectively halved that dip (say 3 ohms down to 1.5 ohms) and it is possible the amp simply runs out of current.

 

[Le_Passager]

Sorry I am not familiar with entire topic. Are any significant flaws on long term usage of this amplifier? Any potential dangers/ safety concerns? Are there revisions of this amplifier or it is only 1 the same batch/ version? Thank You All in advance

Well, I would like to add a few words based on my experience using two LA90 Discrete units over the past year. Overall, it has been a positive experience. I used them in a stack with a Topping D90 III Discrete and A90 Discrete. My speakers are Davis Acoustics Balthus 90, and my listening room is 20 m².These amplifiers had more than enough power for my speakers.

As I continued to improve my system, I made my listening room progressively quieter. I replaced the fans and the power supply in my source PC, and moved all hard drives to a separate home server. It was after achieving this level of silence that I started having issues with the Topping devices.

The problem is that the external switching power supplies (SMPS) of these amplifiers emit a noticeable noise that can be heard from anywhere in the room. Late at night, in complete silence while sitting at my desk, this sound resembles a high-pitched coil whine or a "beehive" buzz. Since then, I find it hard to talk about true audiophilia and sound quality when a device of this tier simply makes mechanical noise in a quiet room. This is not my only complaint about Topping. The DAC is also very noisy in standby mode — it is simply impossible to use while sitting nearby. I previously described in another thread that I had significant issues with it because of this: https://www.audiosciencereview.com/...discrete-d90-iii-sabre-yet.57466/post-2627533

Returning to LA90 Discrete, at first, I assumed that my power supply bricks were simply defective. I reached out to the manufacturer and ordered brand-new replacements. However, the new units buzzed exactly the same way, and one of them turned out to be even louder than the original. Well, I don't have specialized measuring equipment. Unfortunately, the phone's microphone sensitivity threshold is too high (over 20 dB, apparently). So I can't capture the problem on video. I decided not to bother with the manufacturer. Apparently, this experience has ended my story with Topping.

Someone wrote that the quality of the power supply in our city and throughout the country is to blame. But, to show that this is an objective issue with Topping rather than a subjective bias, I have recently switched to a DAC and a power amplifier from another manufacturer. They feature linear power supplies (LPS), and everything works quiet and as intended.

 

[mike7877]

Well, I would like to add a few words based on my experience using two LA90 Discrete units over the past year. Overall, it has been a positive experience. I used them in a stack with a Topping D90 III Discrete and A90 Discrete. My speakers are Davis Acoustics Balthus 90, and my listening room is 20 m².These amplifiers had more than enough power for my speakers.

As I continued to improve my system, I made my listening room progressively quieter. I replaced the fans and the power supply in my source PC, and moved all hard drives to a separate home server. It was after achieving this level of silence that I started having issues with the Topping devices.

The problem is that the external switching power supplies (SMPS) of these amplifiers emit a noticeable noise that can be heard from anywhere in the room. Late at night, in complete silence while sitting at my desk, this sound resembles a high-pitched coil whine or a "beehive" buzz. Since then, I find it hard to talk about true audiophilia and sound quality when a device of this tier simply makes mechanical noise in a quiet room. This is not my only complaint about Topping. The DAC is also very noisy in standby mode — it is simply impossible to use while sitting nearby. I previously described in another thread that I had significant issues with it because of this: https://www.audiosciencereview.com/...discrete-d90-iii-sabre-yet.57466/post-2627533

Returning to LA90 Discrete, at first, I assumed that my power supply bricks were simply defective. I reached out to the manufacturer and ordered brand-new replacements. However, the new units buzzed exactly the same way, and one of them turned out to be even louder than the original. Well, I don't have specialized measuring equipment. Unfortunately, the phone's microphone sensitivity threshold is too high (over 20 dB, apparently). So I can't capture the problem on video. I decided not to bother with the manufacturer. Apparently, this experience has ended my story with Topping.

Someone wrote that the quality of the power supply in our city and throughout the country is to blame. But, to show that this is an objective issue with Topping rather than a subjective bias, I have recently switched to a DAC and a power amplifier from another manufacturer. They feature linear power supplies (LPS), and everything works quiet and as intended.

It really sounds like you're lying and just trying to discredit Topping for something "objective".
The way you're pushing toward an entire different type of product is also suspicious, because a large transformer in a vented chassis is a lot more likely to make an audible buzzing noise. Maybe you're a manufacturer? Or representing one?
Why didn't you contact Topping and get replacement SMPS units?

In the case that they're all bad and you're just so sensitive to the noise, why wouldn't you just put them in a box with sound absorbing material lining it? The LA90Ds each idle at like 10 watts, and don't take much more when listening at normal levels, and the SMPS is extremely efficient, so unless you're blasting music, those supplies could stay in that box all day without getting hot.
Also if you wanted to listen really loud music? Just open the box an inch or two to let the heat out - you're not going to hear anything, the music will be loud and the HF will be attenuated 90+%.

Your whole reasoning is strange... So many things have SMPS in them now and none of them make noise. Even devices that have a big transformer, a lot of them have switching regulators and buck converters for digital parts... To avoid Topping's flagships because they're somehow uniquely physically buzzy? Weird.

 

[Le_Passager]

It really sounds like you're lying and just trying to discredit Topping for something "objective".
The way you're pushing toward an entire different type of product is also suspicious, because a large transformer in a vented chassis is a lot more likely to make an audible buzzing noise. Maybe you're a manufacturer? Or representing one?
Why didn't you contact Topping and get replacement SMPS units?

In the case that they're all bad and you're just so sensitive to the noise, why wouldn't you just put them in a box with sound absorbing material lining it? The LA90Ds each idle at like 10 watts, and don't take much more when listening at normal levels, and the SMPS is extremely efficient, so unless you're blasting music, those supplies could stay in that box all day without getting hot.
Also if you wanted to listen really loud music? Just open the box an inch or two to let the heat out - you're not going to hear anything, the music will be loud and the HF will be attenuated 90+%.

Your whole reasoning is strange... So many things have SMPS in them now and none of them make noise. Even devices that have a big transformer, a lot of them have switching regulators and buck converters for digital parts... To avoid Topping's flagships because they're somehow uniquely physically buzzy? Weird.

I knew my message might provoke this kind of reaction, but my intention was never to discredit Topping. I am simply sharing my personal experience. Let me reiterate: I was completely satisfied with the LA90 Discrete until my room became truly quiet. I actually did contact the manufacturer, described the situation, and purchased a couple of new power supplies - which, as I mentioned above, turned out to be just as noisy. I didn't want to bother with a return because I don't own specialized measuring equipment to officially prove the noise level to the seller. If you can tell me how to do that easily at home, no problem. But honestly, I am just tired of this whole situation.

Also (even though this is slightly off-topic), since the beginning of this summer, I have encountered serious hardware failures with two consecutive D90 III Discrete DACs. A local authorized service center officially concluded that the entire early batch suffered from a manufacturing defect. I will definitely share the details about this in the appropriate thread later.

What I really meant to say is that I find it unacceptable for flagship (as you say) devices to emit such kind of mechanical noise and "beehive" effect. Please don't take this as disrespect, but your logic seemed to me even stranger - suggesting that users should build sound-absorbing boxes for their power supplies is highly amusing. I wonder if Topping is aware of this workaround? Perhaps they should start offering such boxes as an optional extra, instead of making their flagship silent out of the box.

I will repeat that I am just a regular user sharing my personal experience with other regular users. I am not promoting any other brands; I am simply stating that my issues ended after I replaced my DAC and amplifier with devices from another manufacturer. If more professional users with scientific knowledge on the matter want to correct me, I would be happy to hear from them.

 

[capslock]

Well, you could always try a linear power supply on the LA90D. Or if you still don't like it and are in EU, sell it cheaply to me

I have several PA-5 and a pair of B200 and have not noticed noise from their power supply bricks, and I am usally very picky about such things. In my experience, good old linear power supplies are more likely to emit a hum.

 

[Down South]

It really sounds like you're lying and just trying to discredit Topping for something "objective".
The way you're pushing toward an entire different type of product is also suspicious, because a large transformer in a vented chassis is a lot more likely to make an audible buzzing noise. Maybe you're a manufacturer? Or representing one?
Why didn't you contact Topping and get replacement SMPS units?

In the case that they're all bad and you're just so sensitive to the noise, why wouldn't you just put them in a box with sound absorbing material lining it? The LA90Ds each idle at like 10 watts, and don't take much more when listening at normal levels, and the SMPS is extremely efficient, so unless you're blasting music, those supplies could stay in that box all day without getting hot.
Also if you wanted to listen really loud music? Just open the box an inch or two to let the heat out - you're not going to hear anything, the music will be loud and the HF will be attenuated 90+%.

Your whole reasoning is strange... So many things have SMPS in them now and none of them make noise. Even devices that have a big transformer, a lot of them have switching regulators and buck converters for digital parts... To avoid Topping's flagships because they're somehow uniquely physically buzzy? Weird.

bs - A good transformer doesn't buzz and it certainly isn't because of being in a vented chassis. Actually any chassis which has components that create heat should always be in a vented chassis. Is the transformer mounted on sound insulating material. If it isn't then that is cost cutting and or bad design by the manufacturer. Your maounting a personal attack which should be picked up a moderator.

 

[tmtomh]

I knew my message might provoke this kind of reaction, but my intention was never to discredit Topping. I am simply sharing my personal experience. Let me reiterate: I was completely satisfied with the LA90 Discrete until my room became truly quiet. I actually did contact the manufacturer, described the situation, and purchased a couple of new power supplies - which, as I mentioned above, turned out to be just as noisy. I didn't want to bother with a return because I don't own specialized measuring equipment to officially prove the noise level to the seller. If you can tell me how to do that easily at home, no problem. But honestly, I am just tired of this whole situation.

Also (even though this is slightly off-topic), since the beginning of this summer, I have encountered serious hardware failures with two consecutive D90 III Discrete DACs. A local authorized service center officially concluded that the entire early batch suffered from a manufacturing defect. I will definitely share the details about this in the appropriate thread later.

What I really meant to say is that I find it unacceptable for flagship (as you say) devices to emit such kind of mechanical noise and "beehive" effect. Please don't take this as disrespect, but your logic seemed to me even stranger - suggesting that users should build sound-absorbing boxes for their power supplies is highly amusing. I wonder if Topping is aware of this workaround? Perhaps they should start offering such boxes as an optional extra, instead of making their flagship silent out of the box.

I will repeat that I am just a regular user sharing my personal experience with other regular users. I am not promoting any other brands; I am simply stating that my issues ended after I replaced my DAC and amplifier with devices from another manufacturer. If more professional users with scientific knowledge on the matter want to correct me, I would be happy to hear from them.

In my experience, switch-mode power supplies don’t suffer from transformer hum.

However, what I’ve found them to sometimes suffer from is coil whine - and your description of a “beehive” type sound is consistent with that.

Coil whine can be very annoying. I had a MiniDSP SHD unit that had it. When it was turned on it was silent, and when it was turned off using the rear power switch it was silent (of course!). But when it went to sleep or was turned off using the front switch or the remote - in other words it was in standby rather than fully off - it produced a somewhat high pitched noise that I could hear from all the way across the room, especially in line of sight (at that frequency the sound was more directional than a 60Hz hum would be).

Earlier SHDs had been notorious for this but my unit was a later one that supposedly had a revised PSU design, and MiniDSP support said the units were tested for this at the factory. Nevertheless, they sent me a replacement PSU, which turned out to have some different components and a different layout. It reduced the standby coil whine by about 80%, which I considered acceptable.

The lesson I took away is that a PSU can exhibit coil whine and still be deemed in-spec - but you should never accept that as the end of the matter.

 

[Down South]

In my experience, switch-mide power supplies don’t suffer from transformer hum.

However, what I’ve found them to sometimes suffer from is coil whine - and your description of a “beehive” type sound is consistent with that.

Coil whine can be very annoying. I had a MiniDSP SHD unit that had it. When it was turned on it was silent, and when it was turned off using the rear power switch it was silent (of course!). But when it went to sleep or was turned off using the front switch or the remote - in other words it was in standby rather than fully off - it produced a somewhat high pitched noise that I could hear from all the way across the room, especially in line of sight (at that frequency the sound was more directional than a 60Hz hum would be).

Earlier SHDs had been notorious for this but my unit was a later one that supposedly had a revised PSU design, and MiniDSP support said the units were tested for this at the factory. Nevertheless, they sent me a replacement PSU, which turned out to have some different components and a different layout. It reduced the standby coil whine by about 80%, which I considered acceptable.

The lesson I took away is that a PSU can exhibit coil whine and still be deemed in-spec - but you should never accept that as the end of the matter.

Coil winding has to be absolutely tight otherwise noise will occur.

 

[Le_Passager]

bs - A good transformer doesn't buzz and it certainly isn't because of being in a vented chassis. Actually any chassis which has components that create heat should always be in a vented chassis. Is the transformer mounted on sound insulating material. If it isn't then that is cost cutting and or bad design by the manufacturer. Your maounting a personal attack which should be picked up a moderator.

I apologize if my previous observation triggered any unpleasant discussion. I will do my best to avoid getting personal and maintain a constructive tone.

I have several PA-5 and a pair of B200 and have not noticed noise from their power supply bricks, and I am usally very picky about such things.

Thank you, that's an important observation. I appreciate knowing that principled and picky people are paying attention to this, and that not everyone has noise issues with the LA90 Discrete.

Well, you could always try a linear power supply on the LA90D.

I actually considered replacing the stock power supply. The only viable options available to me were industrial-grade switching power supplies from Mean Well, which are known to be physically quiet. However, by default, they aren’t designed out-of-the-box for the exact power parameters required by the LA90 Discrete. While it might be possible to tweak and adjust them to achieve the required 64V / 3.75A, I didn't want to risk it. I couldn't find any ready-made linear power supplies (LPS) with these specifications either. Even a local manufacturer of power conditioners refused to build a custom linear power supply to these specs.
Ultimately, I decided to skip the DIY experiments and simply try a different class of device that ensures silent operation out of the box without any modifications. And so far, I have succeeded.

Or if you still don't like it and are in EU, sell it cheaply to me

That is an interesting offer, but I live in Russia, so I doubt I will be able to sell you anything easily. Though, if I had the opportunity, I would be happy to. Overall, I still think the Topping devices I reviewed are excellent for a desktop setup - compact and powerful. Since these noise issues seem to only affect a few users (like me), most people should be fine. I don't want to question the greatness of this flagship; unfortunately, I just didn't have much luck with it.

 

[Le_Passager]

In my experience, switch-mide power supplies don’t suffer from transformer hum.

However, what I’ve found them to sometimes suffer from is coil whine - and your description of a “beehive” type sound is consistent with that.

Coil whine can be very annoying. I had a MiniDSP SHD unit that had it. When it was turned on it was silent, and when it was turned off using the rear power switch it was silent (of course!). But when it went to sleep or was turned off using the front switch or the remote - in other words it was in standby rather than fully off - it produced a somewhat high pitched noise that I could hear from all the way across the room, especially in line of sight (at that frequency the sound was more directional than a 60Hz hum would be).

Earlier SHDs had been notorious for this but my unit was a later one that supposedly had a revised PSU design, and MiniDSP support said the units were tested for this at the factory. Nevertheless, they sent me a replacement PSU, which turned out to have some different components and a different layout. It reduced the standby coil whine by about 80%, which I considered acceptable.

The lesson I took away is that a PSU can exhibit coil whine and still be deemed in-spec - but you should never accept that as the end of the matter.

Thanks for the reply! Your experience is remarkably similar to what I observed. In my case, the D90 III Discrete DAC produced that annoying coil whine specifically in standby mode, whereas the LA90 Discrete power supply units emitted that 'beehive' buzz while in full operating mode—which, in my opinion, is even worse than standby noise.
I've read quite a bit about this phenomenon, and it's a shame there is no unified industry standard regarding audible coil whine. It seems to heavily depend on specific power supply parameters, component tolerances, and perhaps even the electrical grid conditions at a given location. It manifests differently from one setup to another. I must admit, I've been tempted to buy an oscilloscope many times just to measure and see what is actually going on under the hood, but I haven't taken that step yet.