Testing the SMSL SU-1 DAC with a TEAC VRDS-20 CD player and Squeezebox Touch

Maybe I shouldn't say "testing". It more like a simple listening comparison...

A while back I posted about a video jukebox project that plays music from my media server through a PC connected to my TV and soundbar, and displays trippy visuals synced to the music in 4k resolution at 60 fps. I recently put together a better audio system in the living room and wanted to connect the jukebox to it (and to eventually get rid of the soundbar). The jukebox PC has line outputs that I could connect to the stereo system, but the quality of the audio from the PC is not great, so I bought a USB DAC to connect between the PC and the stereo.

The stereo system currently consists of a 25 year old Krell KAV-300i integrated amp (recently recapped), a 30 year old TEAC VRDS-20 CD player, and a 15 year old Logitech Squeezebox Touch streaming player. Speakers are 20 year old Canton Ergo 22 DC bookshelf type (recently recapped), and there's a new SVS 3000 Micro subwoofer.

The test set-up. The little black box on top center is the SU-1 DAC. The white thing is a wireless router.

The new DAC is an SMSL SU-1, very popular among Youtube reviewers and on audio forums, and cheap, too- $80 via amazon.com. There's a good technical review here. It has USB, TOSLINK optical, and coaxial digital inputs. There is a single button on the front panel to select the input. I plugged the USB cable into the jukebox and analog outputs to the Krell and it started working without any messing around (it's powered by the USB port). It definitely sounded a LOT better than using the computer audio out to connect to the Krell, so I count that as a successful project completion.

This is the SMSL SU-1 DAC guts. 

Then I wondered if the new DAC (and its analog output) would sound any different/better than the DACs (and analog outputs) in the CD player and the Squeezebox.

The TEAC VDRS-20 CD player cost about $2500 new in the early 90s (that's equivalent to $5600 of today's dollars). It might seem ridiculous to compare its DAC/analog output to that of a new, $80 DAC. However, with improvements in technology, I think it's entirely possible that a $80 DAC might get the best of a 30 year old $2500 CD player.

The Squeezebox Touch cost $300 when it was new, in 2010 (that's $433 in today's dollars). It seems more reasonable to compare the new DAC to it, simply based on the similarity of the prices. However, technology has changed a lot- the iPhone was released in 2007 and look how far things have come. Maybe the new DAC will blow the Squeezebox out of the water. Let's see.

Note: I'm not an audio reviewer, and my vocabulary does not include the purple superlatives that audio reviewers often use. I'll tell you if I hear a difference and what I think of it. But that's about it.

Another note: The CD player, DAC, and amplifier are stacked so cables between them are short and identical. I expect no audible differences based on the cables.

First test: CD player balanced analog output vs unbalanced analog output

Balanced I/Os were originally used in stage and recording studio equipment to allow long cable runs without signal degradation. AFAIK they started showing up in hi-fi system components in the 90s, and seem to be becoming more common, even in less expensive gear, at least when the equipment's form factor allows the larger XLR connectors, and the budget allows for their cost. 

I played several CDs and switched between the the balanced and unbalanced outputs. The only difference I noticed was that the balanced output seemed to be at a slightly higher level than the unbalanced outputs. Otherwise I could not hear any difference between them. For the remaining tests, I used the unbalanced analog output from the CD player because the SU-1 DAC only has unbalanced analog outputs.

Second Test: CD player unbalanced analog out vs DAC coax in and unbalanced analog out

The VRDS-20 allows both analog output and digital outputs to be active at the same time, so I connected the unbalanced analog output to the Krell amp and the unbalanced analog output from the SU-1 DAC to another input on the Krell amp. The CD player coax output connected to the SU-1 coax input.

During playback I could instantly switch the inputs on the Krell to compare the sound from the CD player's internal DAC (a Philips TDA1547 bitstream type) and analog stage to the SU-1 (an AKM4493S DAC chip) DAC and analog stage. I could not hear a level difference - they were very closely matched.

After swapping multiple CDs, switching back and forth between the CD player and the DAC,  and careful listening, I could not hear any difference between the two. 

Third Test: CD player unbalanced analog out vs DAC optical input and unbalanced analog out 

I connected a toslink cable between the CD player and SU-1 DAC, switched the DAC input to optical and tried again. Same result. I was unable to hear any difference between the CD player's unbalanced output and the SU-1 DAC. 

Conclusion?

The fact that I couldn't hear any difference between the CD player's analog output and the SU-1 DAC doesn't mean there aren't any differences, only that any differences were too small for me to hear them. My speakers are not especially great, and maybe the room is not set up in an ideal manner for them. The CD player is 30 years old and hasn't been serviced (recapped), so it could be operating at less than ideal performance. Finally, I'm 66 years old and my ears aren't what they used to be (too many ZZ Top concerts and too many hours around high volume dental suction), especially at high frequencies. 

OK, this time with headphones

My speakers aren't so great, so I repeated the both the coaxial and optical input tests using my Koss ESP/950 electrostatic headphones with their companion E90 amplifier plugged into the tape loop on the Krell amp. These headphones are considerably better at sound reproduction that my (or just about any other) speakers, but they won't reveal anything about the soundstage you might hear with properly set-up speakers.

Result

Unchanged. I was not able to hear any differences between the the CD player's DAC and the SU-1 DAC. Maybe the SU-1 is that good. Maybe my ears are that bad. All I know for sure is that there's no point for me to spend any more on a DAC, except to get more or specific I/Os that might be useful in my system.

Squeezebox Touch vs SMSL SU-1

I repeated the coax and optical tests with the SB's unbalanced analog output connected to one input of the amp and the SU-1 DAC. I tried with speakers and with headphones. The squeezebox doesn't allow analog and digital output at the same time, so I couldn't switch back and forth as readily as I could with the CD player. I did the best I could. Result: same. I was unable to hear any differences between the analog output of the SB and the analog output of the SU-1 DAC.

Final notes

I ran into the Audio Science Review of the SU-1 DAC after I wrote most of this post. I also found their VRDS-20 review, posted on the day after I ordered the SU-1 DAC while I was adding links to this post. Stereophile did measurements on the Squeezebox Touch that can be seen here.

Comparing the measurements in the three reviews it is clear that the technology has indeed improved and the SU-1 DAC is much better than the DACs in both the VRDS-20 and the Squeezebox, and the Squeezebox is a bit better than the CD player.

Some people commented that the SU-1 produces popping noises audible during silent passages and between tracks when used as a USB DAC on a Windows 11 PC. I have not had any problems like that in several hours of listening through my Windows 10 PC. In my long experience, problems of any sort on Windows PCs are frequently OS or configuration problems. Maybe my windows configuration is somehow different from others. Maybe SMSL changed the firmware in the DACs coming out of the factory. We'll probably never know. If I start to have any problems with the SU-1 I'll update this post.

For me, the only reason to spend more on a DAC would be to get functions and I/O that the SU-1 doesn't have.