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SMSL SP400 Review (headphone amp)
- Thread starter amirm
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Roland68
Major Contributor
Unfortunately, the display can only be dimmed, it does not turn off.
Bleib
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Ah too bad. Basic features that should be easy to add into any product, even setting the time for display off on your own.
Roland68
Major Contributor
But we are talking about SMSL here.
Firmware, firmware maintenance/updates and well-thought-out functionality are definitely not their strengths.
But that's not just the case with SMSL.
The question I'm currently asking myself is why the management/development management at these companies has a fixed catalog for basic functions, which also specifies points such as various presets, display controls, etc. for all devices.
These companies don't have to reinvent the wheel with every device, especially not with functions that have been taken for granted for 20-30 years.
Roland68
Major Contributor
@Bleib
If you get the amplifier cheaply, I would ignore it.
You could put a piece of special display film in front of it, then you can only see the display directly from the front, but not a few degrees from the side.
Or do you have DIY skills? For example, without soldering anything on the circuit board, you could hack the ribbon cable and turn off the display from the outside using a small reed switch and a mini magnet.
If you get the amplifier cheaply, I would ignore it.
You could put a piece of special display film in front of it, then you can only see the display directly from the front, but not a few degrees from the side.
Or do you have DIY skills? For example, without soldering anything on the circuit board, you could hack the ribbon cable and turn off the display from the outside using a small reed switch and a mini magnet.
Bleib
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I checked the manual, it might be enough to have it at the dimmest setting. We'll see if I purchase, I'm not sure I actually need it..
I keep it at the dimmest setting and you barely notice it unless I'm checking for volume, really unobtrusive. With a 5 volt DAC like the SMSL D-6s I use it just sounds flawless. I've got the matching DAC coming Thursday for it. It's worth getting if the price is right. Doesn't even get warm, unlike my A30Pro.
Bleib
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I ended up with an even cheaper Topping A70 Pro... fits more together with my E70 DAC..
I've got a silver one of those too, with a 5 volt DAC it's really end game. I like the warning it gives on the menu before going into high gain. On balanced the power really feels limitless, even with a big preamp reduction. An amplifier with so many options there's an "advanced" sub menu, they really threw everything at it. If they do an A90Pro I can't imagine anything else they can do/add from there.
So, the screws at the bottom plate release the top shiny plate? Only 6 screws down and then top plate?
I want to open is SMSL put 470ohm series resistance for each XLR phase at the back panel. I really don't understand why putting so high resistance, even for safety reasons it is too much. I want to decrease this resistance to about 20ohm. I am using the SP400 as preamp, not as headphones amplifier..
You can measure the output impedance of (back) XLR either by computing of voltage drop over resistor or by just measuring the resistance between headphone XLR to back XLR
Roland68
Major Contributor
Exactly, loosen 6 screws and then lift the top plate with a suction cup. For the bottom plate you need to remove another 6 screws from the board.
Remember that the XLR preamp outputs are fed directly from the THX circuit with the TI OPA564.
Thanks. Yes, I know directly except 470ohm resistor! Really it is too much.
About volume control. I didn't open it but you did. From measurements it looks like the hot and cold of the XLR input are sum by gain 1/2 differential amplifier to convert to SE. Then volume then convert back to balance and then amplified by the 4 channels amplifier.
I am little disappointed from that as it is a kind of cheating. It is not a real fully differential amplifier
Best
By the way, the rubbers are glued?
You removed them by a Japanese knife or something like that ?
Thanks
Roland68
Major Contributor
You will find this solution even with the most expensive and absolutely high-end devices, which is OK. Because it only makes sense for cable routes.
Most people don't realize that symmetrical small signal processing in devices would have to be absolutely precise in order to prevent cancellations or changes in the music signal due to component tolerances. Not only would very precise, identical and therefore very expensive components have to be used, but the circuit would also have to work perfectly on both sides for the next 10-20 years, without any component deviations.
It's just contact glue or double-sided tape, I just peeled off these rubber feet. No knife necessary.
You can stick them with double-sided adhesive tape or transfer film.
Thanks for all answers.
I agree that most amplifiers (PA) on the market convert the BAL to SE. At least at the VAS stage they are SE after differential pair.
I am not sure that a small mismatch between hot and cold will introduce so much distortions. Maybe because of the differential pair branches are not seeing the same amplitude so no exact cancellation of common mode.
Gustard H16 has full balance R2R volume, I think. It is cheaper but measures not as good as SP400 from published reviews
I agree that most amplifiers (PA) on the market convert the BAL to SE. At least at the VAS stage they are SE after differential pair.
I am not sure that a small mismatch between hot and cold will introduce so much distortions. Maybe because of the differential pair branches are not seeing the same amplitude so no exact cancellation of common mode.
Gustard H16 has full balance R2R volume, I think. It is cheaper but measures not as good as SP400 from published reviews
Hi,
I wonder if you know examples of true balance volume control (R2R).
I think the Gustard H16 is but I am not sure. I am not sure Topping pre90 or A90pro are fully balance R2R. It is just by looking on pictures.
Thanks
Roland68
Major Contributor
You're getting lost in something. There are no advantages to symmetrical small signal processing or volume control, but you have to spend an x times larger budget so that the disadvantages are not too great.
The most important question is, what is the advantage of symmetrical small signal processing/volume control?
Second question, what would be the advantage over normal SE small signal processing/volume control?
First, answer these two questions.
Mostly is reduction of common mode noise (including 50/60Hz). It might reduce even order distortions (but might not improve sound quality ).
Anyway, what is disturbing me is the over processing. Bal > SE >Bal.
Each step might harm transparency, even if you don't see it too much in normal specs (usually, FFT, slew rate, BW).
Maybe it is better to stay all the way SE and not doing these conversions.
I understand the SP400 can drive headphones in a balance way (BTL) but we can ask also here for what reason.
Anyway, what is disturbing me is the over processing. Bal > SE >Bal.
Each step might harm transparency, even if you don't see it too much in normal specs (usually, FFT, slew rate, BW).
Maybe it is better to stay all the way SE and not doing these conversions.
I understand the SP400 can drive headphones in a balance way (BTL) but we can ask also here for what reason.
50hz/60hz distortion in a SMPS?
No, 50/60hz is just an example of something that could be cancelled.
Of course the SMSL SP400 itself has SMPS, but 50/60hz could comes externally from source or by EMI from other instruments.
Anyway, the main issue is that it is over processing. If you are balance the do it fully balance and if SE then SE.
I am not arguing with you, I agree that benefits are marginal, especially when my amplifier is SE by construction.
Of course the SMSL SP400 itself has SMPS, but 50/60hz could comes externally from source or by EMI from other instruments.
Anyway, the main issue is that it is over processing. If you are balance the do it fully balance and if SE then SE.
I am not arguing with you, I agree that benefits are marginal, especially when my amplifier is SE by construction.
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