SMSL SU-6 Review (Desktop DAC)

[pieterv1]

Can somebody confirm how this DAC behaves when receiving AC? As much as I love my Topping E30, my main issue with it is the auto stand-by function. I control my listening setup with 1 smart plug, allowing my preamp and amplifier to power-on automatically when I ask Google to turn on the listening setup/tv. The Topping won't however.. it goes into standby and the automatic input detection is pretty buggy in a way that when audio is already playing (optical), it won't go out of standby and I still need to grab the included remote or get out the couch to turn it on manually.

IF the SMSL SU-6 fully powers on when AC is coming in, I'm definitely upgrading. It also needs to remain set to the same input as I'm running everything through a toslink switcher

 

[MRC01]

My SU-6 arrived today and I just finished bench testing it. Good news: the SU-6 does not have the bugs that the EX-5 had. The SU-6 properly displays the current sample rate from all inputs, and the SU-6 does not auto-mute or shut itself off when playing WAV files that have a quiet L channel (such as a REW freq sweep in R channel only). Also, the SU-6 filter measurements match the descriptions & graphs in the manual.

Regarding jitter, DP1 is the setting to use for minimum jitter, if it works. Driving it from my Juli@ sound card, DP1 worked at every rate except 176.4, where it occasionally glitched. DP2 works flawlessly at every sample rate.

The 2 best filters are #3 and #6. Neither is "better" they just make different tradeoffs. #3 fully attenuates by Nyquist, so there is no aliasing. But, it has some passband attenuation, -1.5 dB @ 20 kHz, and 0.1 dB of ripple. #6 has no passband attenuation, -0.2 dB @ 20 kHz, and is perfectly smooth with no ripple. But it doesn't fully attenuate until 24.1 kHz, so it can leak some HF noise, though this should be benign as any aliasing must be > 20 kHz. If you prefer minimum phase / causal / asymmetric impulse filters, #4 is the one to use. It's the minimum phase version of filter #6.

BTW, Bluetooth measures poorly with the SU-6, just as with the EX5. No surprises, BT is a bandwidth limited lossy codec, even when using "high quality". It sounds good enough for casual listening in a noisy environment like a car.

 

[MRC01]

PS: here are my filter measurements at 44.1 kHz. Played REW sweeps and captured the SU-6 output with my Juli@ sound card.

Here's a closeup of the 2 "best" filters, 3 and 6

Summary of filter measurements, highlighting the best.

Num	Name	Stop kHz	20k	measured 19k	measured 20k	measured 22.05	measured phase
1	corrected min phase fast rolloff	22.05		-3.4	-10.4	-39	+18/-260
2	linear phase slow rolloff	28.2		-2.0	-3.6	-14.2	0/+20
3	apodizing fast rolloff	22.05		-0.2	-1.5	-24	0/flat
4	minimum phase fast rolloff	24.1		-0.1	-0.2	-6.5	-6/-210
5	minimum phase slow rolloff	28		-2.8	-5.1	-13	+6/-150
6	linear phase fast rolloff	24.1		-0.1	-0.2	-7.6	0/+6
7	brick wall filter	22.05		-0.4	-3.8	-30.2	0/flat

 

[FOB69]

Hi

Can someone tell me if by default the SU-6 switchs "on", if the rear switch is "on", and then i plug the DAC supply ?
(or does i have to push the "on" button on panel or remote after the rear switch is "on" ?)

(I need it to be "on" when supply is switched on).

thank you

Bernard

 

[pieterv1]

Hi

Can someone tell me if by default the SU-6 switchs "on", if the rear switch is "on", and then i plug the DAC supply ?
(or does i have to push the "on" button on panel or remote after the rear switch is "on" ?)

(I need it to be "on" when supply is switched on).

thank you

Bernard

That's what I'm curious about as well

 

[driveman]

That's what I'm curious about as well

Yes, once power is reapplied, the DAC will turn on and resume the DAC function it was on before power was removed (i.e., once power is reapplied, one does not need to explicitly turn it on via the button or the remote).

 

[MRC01]

Here's what my computer desktop audio stack looks like now, with the JDS Atom amp and the Subjective 3 EQ that I built from the kit. The audio source is the SPDIF coax output from the Juli@ card in my Linux PC. I'm also using the SPDIF toslink input from a second computer, and the USB input from my phone. The SU-6 is showing the current sample rate, as it does by default (you can disable its screen to go dark). You can see the bass boost which I use to compensate for the bass attenuation of the HD-580 headphones.

Also: I tested the SU-6 digital volume control. It has 100 steps. Going down from full volume, the first 70 steps are 1/2 dB each, so the -70 setting is -35 dB; then the steps slowly get progressively bigger. The -98 setting is -70 dB, the lowest setting (-99) is -infinity, or muted.

 

[pieterv1]

Yes, once power is reapplied, the DAC will turn on and resume the DAC function it was on before power was removed (i.e., once power is reapplied, one does not need to explicitly turn it on via the button or the remote).

Awesome!

... so anybody here interested in a Topping E30 + Linear psu?

 

[driveman]

One area that is a bit disappointing is the level of background noise. Not sure I'm using accurate terminology, so more specifically: When there's no signal and the amplifier volume is over 80%, I can hear a 60Hz mains hum, and some higher frequency noise (around 3KHz, I think).

My setup is MacBook Pro --> SMSL SU-6 (over USB) --> RCA --> Audio Engine 5+ --> SVS SB-1000 Pro. The speakers are near field, on the desk.

The volume control of the AudioEngine speakers is at ~80%, and I'm using the Mac to control the volume. The DAC is at maximum volume.

Here are some tests and comparisons I've made (all at 80% volume):

• When the DAC is powered on, USB is connected, and there's no signal: Audible hum from my sitting position.
• When the DAC is powered on, but on standby: Can't hear the hum from my sitting position, but can hear a very faint hum only when I put my ear to the woofer (this hum is generated by the AudioEngine amplifier).
• When I'm not using the DAC, and connecting the MacBook Pro directly to the line-in of the AudioEngine, I cannot hear the hum at 80% volume, but can hear a hum only at close to 100% volume.
• I also have a LOXJIE d30 here, and when I'm using it I can also hear the hum only at a volume that is close to 100%. For what its worth, the LOXJIE power supply has an earth connector, while the SMSL does not.

Given the tests above, and that the only variable is the DAC, it looks like my SMSL SU-6 unit is generating that noise.

The workaround is to reduce the volume below 70%, but this is not ideal as sometimes I do want to listen in a higher volume without fiddling back and forth with two volume controls.

I wonder if there's anything that can be done about this. Otherwise, I might keep the LOXJIE and return the SMSL.

 

[MRC01]

Sounds like a grounding issue, or interaction between the SU-6 and another device. This is the bane of single-ended (instead of balanced). The SU-6 SNR of 120+ dB that Amir measured is high enough that there should be no audible hum or noise. I keep my SU-6 at 100% volume driving a JDS Atom. It's dead silent in my HD-580 headphones even when the Atom is at full volume and high gain.

The OEM power cord for my SU-6 has a separate ground wire that comes out near where it connects to the device. Does yours? If so, can you try connecting it to the ground or frame of another device?

 

[MRC01]

When the SU-6 fails to sync with the source when playing SPDIF, the result is not subtle. The glitches are easily audible.

Below is the frequency response sweeps at 176,400 rate.

At first I got the green line and wondered what the heck was wrong. All other sample rates were perfectly smooth. After fiddling with a few things that didn't fix it, I remembered Amir's review, bumped the SU-6 "dP" setting from 1 to 2, then got the pink line which is smooth like it is at all the other sample rates.

Here's what the distortion looks like with those glitches. The frequencies for each blast of distortion match the glitches in the above sweep.

Here's the distortion after I switched the "dP" setting from 1 to 2. It's only the residual distortion from my sound card:

 

[driveman]

Sounds like a grounding issue, or interaction between the SU-6 and another device. This is the bane of single-ended (instead of balanced). The SU-6 SNR of 120+ dB that Amir measured is high enough that there should be no audible hum or noise. I keep my SU-6 at 100% volume driving a JDS Atom. It's dead silent in my HD-580 headphones even when the Atom is at full volume and high gain.

The OEM power cord for my SU-6 has a separate ground wire that comes out near where it connects to the device. Does yours? If so, can you try connecting it to the ground or frame of another device?

Thank you @MRC01, it does sound like a ground loop indeed - and I expect a certain level of ground loop, but it does seem rather high, especially compared to the LOXJIE d30, which seems to exhibit something like 20% of the noise I'm getting from the SU-6 at a given level. Both the speakers and the DAC are connected to the same power strip.

As for the power cord I've received with the SU-6. It looks like a standard non-polarized, 2 prong power cable, without a separate ground on neither end of the cable. I don't think that a separate ground wire is compatible with the U.S. power code, perhaps with other countries where there is a separate terminal for earth. In any case, I don't think that this would help address the issue, since the earth terminal is strictly used for safety.

 

[MRC01]

... As for the power cord I've received with the SU-6. It looks like a standard non-polarized, 2 prong power cable, without a separate ground on neither end of the cable. ...

Strange. Mine came with a cord that has 3 prongs to the power outlet with 2 prongs that plug into the SU-6 end, and an extra green wire sticking out to attach to a separate ground. I'm in the USA (WA State).

 

[FOB69]

Yes, once power is reapplied, the DAC will turn on and resume the DAC function it was on before power was removed (i.e., once power is reapplied, one does not need to explicitly turn it on via the button or the remote).

Thank you !

 

[pieterv1]

got mine today, placebo tells me the stereo might be narrower and harsher, otherwise no difference to su-9n

Is it possible the audible difference is there just because the SU-9N was connected with its balanced outputs?

I'm really torn between the SU-6 or SU-9N... I don't need balanced outputs in my vintage setup (Rotel RC-06, modded out Quad 405-2 & JBL 4312A), but the SU-9N took 3rd place overall with measurements. And SU-6 has the 3db SINAD difference between channels...

 

[Jerderv]

Strange. Mine came with a cord that has 3 prongs to the power outlet with 2 prongs that plug into the SU-6 end, and an extra green wire sticking out to attach to a separate ground. I'm in the USA (WA State).

Odd, I received my unit with a 2 prong cable. Also USA WA State. I purchased from SHENZHENAUDIO through Amazon.

 

[MRC01]

Odd, I received my unit with a 2 prong cable. Also USA WA State. I purchased from SHENZHENAUDIO through Amazon.

I bought mine the same way.

 

[pwn87]

Is it possible the audible difference is there just because the SU-9N was connected with its balanced outputs?

I'm really torn between the SU-6 or SU-9N... I don't need balanced outputs in my vintage setup (Rotel RC-06, modded out Quad 405-2 & JBL 4312A), but the SU-9N took 3rd place overall with measurements. And SU-6 has the 3db SINAD difference between channels...

yes that's exactly how i tested so it's possible.
but i think there's slightly more to audio than what you can measure with these methods.
i wish i hadn't heard the su-9n, it had saved me a ton of money and i had never known
and lets be honest, the su-6 looks damn sick, especially with it's useful power led (which the su-9n doesn't have.. while the display is off)
bear in mind that the price difference was really small for me as i got the su-9n on sale and overpaid for the su-6 (190€ vs 305€). if it was 180€ vs 400€ i had chosen the su-6

 

[pieterv1]

yes that's exactly how i tested so it's possible.
but i think there's slightly more to audio than what you can measure with these methods.
i wish i hadn't heard the su-9n, it had saved me a ton of money and i had never known
and lets be honest, the su-6 looks damn sick, especially with it's useful power led (which the su-9n doesn't have.. while the display is off)
bear in mind that the price difference was really small for me as i got the su-9n on sale and overpaid for the su-6 (190€ vs 305€). if it was 180€ vs 400€ i had chosen the su-6

Seems like currently I can get the SU-9N on Amazon for €329.. That's why I'm tempted..

I'm not going to let a standby LED be the deciding factor haha. Can the screen of the SU-9N be completely dimmed?

 

[pwn87]

Seems like currently I can get the SU-9N on Amazon for €329.. That's why I'm tempted..

I'm not going to let a standby LED be the deciding factor haha. Can the screen of the SU-9N be completely dimmed?

yeah you can change brightness and screen timeout.
the su-6 has a brightness setting, but i'm not sure if the screen timeout can be turned off. (which is unfortunate because that white text looks damn cool)