SMSL’s TPA3255 All-in-One DAC/Amplifier - AL400

[Bleib]

Frequency response is quite impressive :O

 

[Ongaku]

SMSL Just replied to me via FB and told me there's no PFFB in this amp...

 

[Bleib]

SMSL Just replied to me via FB and told me there's no PFFB in this amp...

So how is the response so flat?

Edit: Is that the "Not currently available." reply?
In that case it could also mean that the information is not yet available

 

[Bleib]

This is how SMSL describes the difference between the two models

"AS400 and AL400 share a similar all-in-one concept, but they are positioned differently:
• AS400 uses Infineon’s MA5332MS amp chip (smooth, efficient sound), while AL400 uses TI’s TPA3255 (higher power and stronger dynamics).
• AS400 includes only an MM phono stage, while AL400 supports both MM & MC cartridges.
• AL400 has more advanced EQ functions (3-band EQ with adjustable frequency, gain, and Q).
• Both models use CS43131 DAC and XU-316 USB, but AL400 adds subwoofer management options.
In short:
AS400 focuses on simplicity and an elegant “plug-and-play” sound.
AL400 offers higher power, more flexibility, and more tuning control."

 

[Ongaku]

So how is the response so flat?

Edit: Is that the "Not currently available." reply?
In that case it could also mean that the information is not yet available

You are right! I asked for a clarification...

 

[EJ3]

Great price but LPF should say HPF, no? Every powered sub on earth has LPF built in.

There are many that don't use commercial (ACTIVE [perhaps what you meant to say?]) subs:
Our subs ARE powered (well they are powered: by stand alone amps) subs.
Mine pair have a FR of less than 20 Hz-80 Hz (the raw speaker).
Currently in ported cabs tuned to be flat down to 29 Hz.
Bigger cabs tuned lower are in their next years future.
And the Amp to each (bridged mono) one can put out 2700 watts RMS into 4 ohms.

 

[Guddu]

Hi,
Here are a few clarifications:

1. The PFFB implementation details are not publicly disclosed.
2. The updated frequency response chart is now available.
   You can view the full measurements here:
   https://www.smsl-audio.com/portal/product/detail/id/935.html
3. The damping factor of the AL400 is 74.

Thank you @Kitty (S.M.S.L Marketing).

Published THD+N 0.003% should come around -90dB SINAD which is really good. PFFB or not, there is surely some kind of optimization that has worked nicely here.
Freq. response looks perfect, I am guessing the orange line is for 4ohm.

 

[Roland68]

Thank you @Kitty (S.M.S.L Marketing).

Published THD+N 0.003% should come around -90dB SINAD which is really good. PFFB or not, there is surely some kind of optimization that has worked nicely here.
Freq. response looks perfect, I am guessing the orange line is for 4ohm.
View attachment 496526

Compared to Topping, 3E audio, and other good TPA3255 implementations, the Sinad score is 12 points lower. It's not a bad score, but amplifiers over 30 years ago were already achieving scores of 88-89.

Furthermore, the frequency response curve looks a bit too good in the load-dependent region. Experience with current GaN amplifiers has shown in tests that these specifications were rather misleading. This looks too good even for a very good TPA3255 implementation with PFFB.
I'm curious to see what independent measurements will show.

 

[Guddu]

Compared to Topping, 3E audio, and other good TPA3255 implementations, the Sinad score is 12 points lower. It's not a bad score, but amplifiers over 30 years ago were already achieving scores of 88-89.

Furthermore, the frequency response curve looks a bit too good in the load-dependent region. Experience with current GaN amplifiers has shown in tests that these specifications were rather misleading. This looks too good even for a very good TPA3255 implementation with PFFB.
I'm curious to see what independent measurements will show.

I can definitely understand what you are saying, but they normally I find a few manufacturers more accurate than others, I keep SMSL on the positive side.
I, myself, find this pretty decent but you are correct that other products do have better noise/distortion measurements.

 

[Bleib]

Compared to Topping, 3E audio, and other good TPA3255 implementations, the Sinad score is 12 points lower. It's not a bad score, but amplifiers over 30 years ago were already achieving scores of 88-89.

Furthermore, the frequency response curve looks a bit too good in the load-dependent region. Experience with current GaN amplifiers has shown in tests that these specifications were rather misleading. This looks too good even for a very good TPA3255 implementation with PFFB.
I'm curious to see what independent measurements will show.

Here's hoping SMSL sends Amir an unit to measure (or to Erin's audio corner). The SINAD is high enough for it to be transparent, and if it manages to have that straight of a frequency response then it's should be a pretty sweet amp with quite many functions

 

[Kitty (S.M.S.L Marketing)]

Thanks Kitty. Any chance you could also clarify the unit's bass management capabilities (low and high pass filters)?

Please click the link for details.

 

[EJ3]

Compared to Topping, 3E audio, and other good TPA3255 implementations, the Sinad score is 12 points lower. It's not a bad score, but amplifiers over 30 years ago were already achieving scores of 88-89.

My 1987 NAD 2200's SINAD score (first a few other things but then the [stunning for the time: SINAD]):
It is power measurements where the magic of this amplifier comes to life so let's look at that with 4 ohm load first:

We can see a kink in distortion when we hit 200 watts as the unit sails past that to produce whopping 337 watts per channel, both driven! Per design characteristics, you can have much more during momentary peaks:

Wow, we have one kilowatt of power coming out of this amp in short duration!

Switching to 8 ohm we see similar results as 4 ohm:

Sweeping the power test at 4 ohm with different frequencies shows a well-behaved amplifier:

You do loose power in higher frequencies but that is fine since music spectrum has lower energy there anyway.

Due to the long duration of this test, the protection circuit likely backed off the high voltage rail, producing lower output levels.

EDIT: adding Lab Input Measurements
Lab Input Measurements
I was surprised that the frequency response was not flat but was relieved to see later in the thread that this is due to insertion of low and high pass filters. So here is the frequency response with Lab input that doesn't have such a filter:

Response now (in green) as it should be, ruler flat to below 10 Hz, and well extending past the 40 kHz limit of this measurement.

I figured the filters may be adding some noise/distortion so re-ran the dashboard again:

Distortion doesn't change but if you look at the noise floor at 20 Hz, it is down by some 10 dB. That improves SINAD a couple of dBs, making the amplifier stand out even more!
Zoomed:

And signal to noise ratio:

Conclusions
Nice to see innovation like this from equipment that is over 30 years old! Shame on manufacturers that produce amplifiers for much less power, more distortion and higher prices these days. No, you don't get a fancy case here and sheet metal is strictly budget category. But you are not going to sit on the amp. The guts are where it matters and NAD 2200 delivers.

NOTE: the output relay on stock 2200 gets corroded and fails over time. There are videos and DIY threads on how to upgrade the relay there to fix the problem. The unit tested here has that fix. Other than that, there are not reports of many other reliability issues even though NAD products are often said to be less reliable than other brands.

Overall, I am happy to recommend the NAD 2200. I almost gave it the highest honors but given the upgraded nature of the test unit, and the fact that used amps may have issues, I avoided that. But you could have easily pushed me to give it the golfing panther.

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Last edited: Jun 10, 2020
Amir
Founder, Audio Science Review
Founder, Madrona Digital
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[JSmith]

The PFFB implementation details are not publicly disclosed.

SMSL Just replied to me via FB and told me there's no PFFB in this amp...

"Implementation details" sounds like it has PFFB, but they don't want to go into the specifics... then this email saying no PFFB.

So which is it? To me a TPA3255 based amp without PFFB or implemented pooly is not competitive in 2025/26 market.


JSmith

 

[Roland68]

"Implementation details" sounds like it has PFFB, but they don't want to go into the specifics... then this email saying no PFFB.

So which is it? To me a TPA3255 based amp without PFFB or implemented pooly is not competitive in 2025/26 market.


JSmith

SMSL has never provided open and clear answers and statements here in the forum. Whether it's about problems, firmware updates, etc., they've always been vague and uncommunicative.

What can you expect from a manufacturer that still waves the MQA flag with every new device and promotes it as a great feature, even though there isn't even any streaming content available in MQA anymore?

 

[JSmith]

still waves the MQA flag

Agree, I wish they would let it go already.

I mean I like to have multi-format compatibility, but nothing is MQA anymore anyway.

Although, I do believe in some parts of the world, MQA CD's are still a thing, so maybe they're still providing for that market.


JSmith

 

[Kitty (S.M.S.L Marketing)]

"Implementation details" sounds like it has PFFB, but they don't want to go into the specifics... then this email saying no PFFB.

So which is it? To me a TPA3255 based amp without PFFB or implemented pooly is not competitive in 2025/26 market.


JSmith

It does not include PFFB, because our engineering team evaluated it and found that it had a slight negative impact on the sound performance in this design.
We wanted to maintain the tuning and overall sound character of the product.
(And we may introduce amplifiers with PFFB in future models.)

 

[Roland68]

I'm having déjà vu.
I got this exact answer from SMSL once when I asked why they only used half of the AK4499 DAC chip in the M400 DAC, i.e., only 2 of the 4 channels.
They had simply wired up half the AK4499 and only connected 2 channels; the remaining components were missing. In the end, it was a crippled AK4499, reduced to an AK4497 .

 

[EJ3]

I'm having déjà vu.

Sometimes I feel like I am having Déjà Vu all over again, too!

 

[Bleib]

Please click the link for details.

Why is as400 described as smooth and al400 isnt? Is the al400 frequency response flatter?

 

[Kitty (S.M.S.L Marketing)]

Why is as400 described as smooth and al400 isnt? Is the al400 frequency response flatter?

Each has its own merits; it's best to experience them yourself.