Suggestion on potential DAC upgrade

[Giulios86]

Hello everybody,

as in object I'd love some suggestions on a DAC upgrade I'm planning.

Current system:
Rpi4 (Volumio/MoOde) -> KTB -> Hypex NC500 dual mono --> Beatclub Base DIY Speaker (https://www.lautsprecherbau.de/?serie=901449)
Rpi4 and KTB powered with LPS
I noticed that I do most of my listening in the 40% to 60% volume when regulating with hardware volume control on the Rpi4

These are the reasons why I'm considering to change DAC and replace my Khadas Tone Board.
1) The Hypex modules have balanced input and I'm currently feeding unbalanced line into them. Am I potentially losing something here?
2) I recently bought an android based projector that I'm running with Kodi and it has toslink output, which means that I would need an additional Optical/Coax converter in order to use the SPIDF input in the KTB. On the other hand the capability of the KTB to switch automatically between USB and SPIDF can be quite handy
3) A friend of mine recently bought a AlloBoss2 Streamer/DAC and "subjectively" I really think I could listen to better details in some music tracks we played as b2b on my system

The main products I've been looking at are the Soncoz LA-qxd1, Schiit Modius and SMSL A300mkii.

The question is, do you think buying one of these modules in the 200EUR price range is a worthy upgrade or should I just buy the Optical/Coax converter and stay with the KTB?
Moreover, the Soncoz/SMSL have volume control. When acting on the volume buttons on the unit is it actually the same as changing volume with Hardware volume control from the Rpi4?
Any other suggestion on system improvements/optimization that might be even more relevant than the DAC is obviously more than welcome

Thanks a lot for your help!

 

[AnalogSteph]

I noticed that I do most of my listening in the 40% to 60% volume when regulating with hardware volume control on the Rpi4

Any clue how these numbers relate to dB ref. full-scale output? Is 100% just moderately louder or are you afraid to go anywhere near it in fear of tearing down the building?

1) The Hypex modules have balanced input and I'm currently feeding unbalanced line into them. Am I potentially losing something here?

Depends on how the adapter cable is wired. If you're not getting any ground loop noise you're probably fine. Speaking of noise, do you hear any?

Does your amp have an input buffer to bring the total gain up to around 26 dB? Then you should have plenty of output for a 2 Vrms input. Otherwise it would be a little tight at under 9 W into 8 ohms.

If the KTB is getting the job done as-is, a Toslink-coax converter would be a worthwhile investment. Make sure it supports up to 24/192, not all optical transmitters / receivers will do that (you need >18 Mbit/s).

Any other suggestion on system improvements/optimization that might be even more relevant than the DAC is obviously more than welcome

It's good that you'd be writing that - hooking up a pair of speakers would be a dramatic, night-and day improvement.

 

[Giulios86]

Any clue how these numbers relate to dB ref. full-scale output? Is 100% just moderately louder or are you afraid to go anywhere near it in fear of tearing down the building?

I don't dare going over 80% and tbh I'm afraid I actually damaged the tweeters listening at that level.
Maybe off topic, but is there a clear way to check if a speaker is damaged?
I'm plannig to buy a UMIK-1 to do some DRC in the Rpi4, would that show a problem if there is any?

Depends on how the adapter cable is wired. If you're not getting any ground loop noise you're probably fine. Speaking of noise, do you hear any?

I did that cable myself, but I'm not too convinced about it.
It's basically this RCA design https://www.tnt-audio.com/clinica/shoestrings_e.html
On the XLR side I just bridged the ground and negative signal pins

Regarding noise, when I was powering with the switching pi power supply there was some noise but I really had to get with my ear close to the tweeter to hear it.
When I plugged the LPS this increased significantly.
As a check I used a cable without ground on the power amp and the noise went close to completely disappear, so I guess some work around ground loops wouldn't hurt.

Does your amp have an input buffer to bring the total gain up to around 26 dB? Then you should have plenty of output for a 2 Vrms input. Otherwise it would be a little tight at under 9 W into 8 ohms.

As far as I know the NC500 and NC502 already have a built-in input buffer with a set gain (25.5 on datasheet) and can't be changed. I can dig-in a bit more but as you said I never felt lack of power.
Different story if you think this can influence the quality of the signal.

It's good that you'd be writing that - hooking up a pair of speakers would be a dramatic, night-and day improvement.

You are right, just went to the store and bought a pair and added to the 1st post

 

[Matias]

Maybe an EX5? Balanced XLR outputs, volume and input control with remote, USB and Toslink, plus headphone amp and does it all measuring great and costing 350 usd.
https://www.audiosciencereview.com/...ex5-review-dac-and-headphone-amplifier.24341/

 

[Trell]

I don't dare going over 80% and tbh I'm afraid I actually damaged the tweeters listening at that level.
Maybe off topic, but is there a clear way to check if a speaker is damaged?
I'm plannig to buy a UMIK-1 to do some DRC in the Rpi4, would that show a problem if there is any?
[snip]

With the UMIK-1 and using REW (Room EQ Wizard, excellent freeware) you can do so.

 

[AnalogSteph]

I don't dare going over 80% and tbh I'm afraid I actually damaged the tweeters listening at that level.

OK, so clearly that's pretty much a % --> dB mapping.

I had a look at the Beatclub Base articles (an Intertechnik design), and while they are going into great detail when it comes to woodworking and drivers, there is precious little being written about the crossover. Supposedly it's a 2-way - with two 6.5" midwoofers in a tower I'd rather want to be seeing a 2.5-way design. There should be relatively little risk of damaging a tweeter in a competent, modern design, but there is no telling whether this one qualifies as either. Without a waveguide helping out the tweeter towards the bottom end, a low-order crossover and/or lowish crossover frequency may in fact make the tweeter susceptible to overloading - doesn't look like there's any ferrofluid business going on, so you can assume actual power handling of <10 W.

I did that cable myself, but I'm not too convinced about it.
It's basically this RCA design https://www.tnt-audio.com/clinica/shoestrings_e.html
On the XLR side I just bridged the ground and negative signal pins

Yeah, I think that's a problem. You're throwing away any advantages of a balanced input like that. (The method described also makes for a lot of work and IMHO only a so-so cable - shield coverage is not all that great. Hard to beat some decent medium diameter coax for unbalanced leads, like RG-59. More flexible types of coax are available if so desired.)

What you want is the wiring suggested in this Hypex appnote (bottom right), i.e. with RCA ground being split between cold and shield. If your network cable is just UTP you may have to repurpose some spare wires to make the shield. The construction method suggested on the above page would also work if you were to replace the single inner conductor by an intact twisted pair. (Frugal studio types are using Cat.6 cable to make "snakes" for 4 balanced channels each - the individual shielding and different pitches of the 4 twisted pairs will keep crosstalk to a minimum.)

 

[Giulios86]

Thanks a lot for all the helpful answers gents!

@Matias the EX5 looks pretty amazing indeed. I don't do much headphone listening but it would actually add something while being not too much more expensive. Remote and things like auto-standby are quite interesting too and not present in the other products I was looking at. I'll definitely consider this if I actually go for the upgrade

@Trell thanks that's what I thought, fingers crossed then for them to measure well eheheh

@AnalogSteph
The cross-over is indeed a 2.5 ways. I did actually have its scheme but lost it due to a Hard-Disk damage. I feel quite stupid about it but can always reopen the boxes and take one out if absolutely necessary in the future...
I do have a picture of it but it's from the top and it's not enough to "retrieve" the circuit.

I understand what Hypex suggests for the cables. if I understood well is what they tend to call "semi-balanced" and can't be achieved with a standard coax since you want a twisted pair, plus a shield.
Regarding the CAT6, I'm not sure I understood. Are they using a single CAT6 for 4 channels while sharing the shield (1 channel per twisted pair)?
Would it work if I use a single CAT6 per channel having RCA ground attached to the shield and all the "whites" of the 4 twisted pairs, while the signal would be connected to the 4 "coloured" wires of the 4 twisted pairs?
I'm asking because these interconnects are relatively short and splitting the shield, plus separating the twisted pairs between the 2 channels seems more effort than just doing 2 separate cables.

Again thanks a lot for all these suggestions, it's very helpful

 

[AnalogSteph]

The cross-over is indeed a 2.5 ways. I did actually have its scheme but lost it due to a Hard-Disk damage.

*missing backup

Would have been interesting to see the filter order.

I understand what Hypex suggests for the cables. if I understood well is what they tend to call "semi-balanced" and can't be achieved with a standard coax since you want a twisted pair, plus a shield.

Correct.

Regarding the CAT6, I'm not sure I understood. Are they using a single CAT6 for 4 channels while sharing the shield (1 channel per twisted pair)?

AFAIR Cat.6 has individual shielding per pair as well. When using AES48 compliant devices the whole shield business will be tied to chassis ground at both ends anyway.

Would it work if I use a single CAT6 per channel having RCA ground attached to the shield and all the "whites" of the 4 twisted pairs, while the signal would be connected to the 4 "coloured" wires of the 4 twisted pairs?

I mean, you're effectively about quadrupling the cable capacitance, but on a short run it probably wouldn't be such a big deal.

 

[Giulios86]

@AnalogSteph
Ok all understood.

Regarding the interconnects (RCA -> XLR), I actually found a pair of them based on "Canare L-4E6S" at 15Euro which is quite attractive and should respect the semi-balanced scheme that Hypex suggested. Do you think it's a good option?

I found as well a Toslink/Coax spidf converter for something like 11Euro which it's stated to support 192kHz.

I think I might try this setup first since it's really cheap to implement it.
The topping EX5 looks very good but I'd wait for some customer experience first.

P.S.
This is the picture I have from the crossover. The part I put in the blue square I'm pretty sure is all tweeter related.
I am personally not able to derive anything from it, but I uploaded it for interest.