[Kuja]

Hello everybody,

This is my first post here.

I recently posted this question on Logitech Squeezebox forums, but so far I got no answers that I could actually use...

I'm a happy SB3 owner for almost three years.

I use it exclusively through its coax digital out, connected to Pedja Rogic's NOS TDA1541 DAC.
http://www.hifi-forumi.com/forum/viewtopic.php?f=21&t=4846&p=56506

My DAC has the optional reclocker board installed.

Recently I tried Stereovox digital cable instead of my Bandridge Profigold digital IC.
I've got noticeable improvements, especially in bass definition.

For a long time now I had been toying with the idea of improving SPDIF out on my SB3.
If I had such an improvement with a new cable, I might get more of the good thing by tweaking SB's digital out... Right?

The problem is that when I started searching, I got swamped with numerous variations of similar soultions.
It is hard to tell which solutions will actually improve things... Some of them could make them even worse?




You have this (now legendary) thread here that I'm sure everybody knows about:
http://www.audiocircle.com/index.php?topic=45330

Pat (art) did a great job analyzing SB3's digital output with a scope.
He proved that some non competent tweaking can make things worse.
Also, he said that he did not listen to the results of his mods...
There is a big difference on scope screen, but how this translate to actual sound?



He suggested that a simplest and most effective mod is removing two inductors (L8 and L9) and adding a BNC instead of RCA socket.
As I understood those inductors are there for reducing EMI, so that SB can meet some regulations (and that has nothing to do with sound quality).

The big question is: if I remove them, is increased EMI going to do some harm to SPDIF signal going to my DAC?
Osciloscope trace might look flatter, but the resulting sound coming out of my DAC could be worse?

Did anybody here modded SB3 by only removing those inductors?
If yes, can you describe changes in sound in detail?

Pat has suggested that this mod (together with adding BNC socket) might be all that average listener needs to do.
The simplest mod that brings the biggest improvement!
Exactly the thing I'm looking for.



The next modding level would be adding a transformer...
As I understood, the role of transformer is to galvanically isolate SB form DAC by separating their grounds?

Can transformer protect my DAC from EMI polluted SPDIF signal (if there is such a thing) after those inductors are removed?!

Or... the EMI had induced some garbage in a SPDIF signal... since the transformer does not "know" the difference between this garbage and the pure signal, it juss passes them together without any change to DAC, where some bad things happen?



I'm sorry If I'm asking stupid questions!!!
I'm not a modder/tweaker type of person.
I just want get as good results as possible with the minimal ammount of modding.

If removing inductors will bring 80% of improvement and adding transformer will bring additional 20%, I will be more than happy to live with those first 80%, since I'm not sure that in everyday listening I will be always able to appreciate the additional 20% of improvement.


Thanks in advance,

Aleksandar



PS

On Logitech forums I've been told by Logitech engineer that there is no need for BNC connection since it will make NO difference and that it is not needed in this type of application ...and that differences between digital ICs are not likely to be heard...

Check it out here:
http://forums.slimdevices.com/showthread.php?p=460521

It is great news if it is like this - it means that I don't have to change anything in my setup. 


.

[richidoo]

"No component is perfect, and every imperfection is audible."
J. Gordon Holt

Simplest mod that brings the biggest improvement: Get a better DAC.  One that really takes care of the jitter.

Empirical, Buffalo32, Bryston BDA1, etc.

[srb]

Simplest mod that brings the biggest improvement: Get a better DAC.  One that really takes care of the jitter.

Empirical, Buffalo32, Bryston BDA1, etc.

While I would agree that one of those DACs would likely offer a major sonic improvement, Kuja (Aleksandar) would have to change the title of the thread to
 
"SB3 SPDIF out - which expen$ive replacement DAC would bring the biggest improvement?" 
 
Steve

[face]

"No component is perfect, and every imperfection is audible."
J. Gordon Holt

Simplest mod that brings the biggest improvement: Get a better DAC.  One that really takes care of the jitter.

Empirical, Buffalo32, Bryston BDA1, etc.

The DacMagic also handles jitter very well.

[Kuja]

"No component is perfect, and every imperfection is audible."
J. Gordon Holt

Simplest mod that brings the biggest improvement: Get a better DAC.  One that really takes care of the jitter.

Empirical, Buffalo32, Bryston BDA1, etc.

The DacMagic also handles jitter very well.

I also tried my Squeezebox with Cambridge 840C CD player.
http://www.cambridgeaudio.com/set_territory.php?TID=48&Redirect=/summary.php?PID=112
It has digital inputs so it can be used as a DAC.
It's DAC is more advanced than CA DacMagic.

I ripped couple of CDs to my hard drive.
840C's internal CD playback was better compared to playing ripped CDs through Squeezebox feeding 840C's DAC.

Instead of looking for another DAC, I could try first to improve digital out on my SB.
It will be much cheaper.

.

[srb]

I ripped couple of CDs to my hard drive.
840C's internal CD playback was better compared to playing ripped CDs through Squeezebox feeding 840C's DAC.

Well, that test sure seems to point to the jittery output of the SB3, which one of these super-DACs may or may not compensate for.
 
I think you're on the right track - there have been a lot of SB3s that were modified.  There must be someone out there who experienced what you did, got some digital mods, and can attest to the change in sound quality.
 
Steve

[art]

Do you expect them to admit that something as simple and easy as a BNC would make it better? All one has to do is to try it. However, the only way it would make sense is if you have a cable that has a BNC. Adapters are not an improvement.

The "extra" EMI will not do harm to your system. Maybe if you were watching the old analog Ch. 2-5 on your TV, with "rabbit ears" right next to your SB3, you would see interference.

I can not say exactly how the differences would sound, but I have made enough SPDIF products since '92 to have a good idea. Bass will be tighter, top-end will be smoother and cleaner. Those will be the main things that you will hear.

I think that touches on the main points that you have made. Let me know if it doesn't.

Pat

[srb]

Pat,
 
How does the BNC modification maintain the true 75 ohm spec, if the DAC on the other end is not also BNC modified?
 
Thanks,
 
Steve

[art]

All 3 components of the chain contribute reflections: TX end, RX end, and the cable.

On a typical system, with RCAs and poor control of output Z (especially over a wide frequency range), you can easily get 20% reflection from either end. If 20% bounces back from the RX end, and 20% of that bounces back from the TX end as it is re-reflected forward, you are down to 4% total energy ending up at the RX end as an unwanted signal. If you can reduce the TX end's contribution to only 5%, then you will only have 1% unwanted energy arriving at the RX end.

If you can get both ends to reflect only about 4-5% of the signal, you can see how you can get far below 1% total reflection.

(All this ignores the cable; we shall assume it is matched fairly closely.)

Since I have done RF design for a living, I can get below 1% on both ends. You need good test equipment to be able to do this.

Some of you may recall from the data that I posted a few years back that some of my stuff has 4% or so of reflections. That is true, but I am measuring out to over 1 GHz. Over 10 times the BW of the SPDIF signal that you will ever encounter. When you reduce the BW, it drops to 1%.

Hope this helps to clarify things.

Pat

[Kuja]

Pat,

Thanks a lot! 

Do you expect them to admit that something as simple and easy as a BNC would make it better?

Slimdevices (Logitech) forums have changed.
It seems that now, vast number of forum members are saying that everything is fine and that nothing does matter, cables make no difference and that no improvements can be made...
Some are Logitech employees, some are not. It's hard to tell who is who.

The "extra" EMI will not do harm to your system. Maybe if you were watching the old analog Ch. 2-5 on your TV, with "rabbit ears" right next to your SB3, you would see interference.

So if I understand you correctly, EMI will not induce any garbage in SPDIF signal that might confuse my DAC?
This is of highest importance for me, since I don't wach TV that much.

However, the only way it would make sense is if you have a cable that has a BNC. Adapters are not an improvement.

I'm thinking of buying Stereovox XV2 cable. It has BNC connectors and comes with high quality RCA adaptors.
It is quite expensive, but has raving reviews.
I tried it in my setup (with RCA adaptors) and it brought noticeable improvement compared to my present cable, mostly in bass definition.
I don't know why is it so special - I'm wondering if I can get similar performance from some bulk cable that I can terminate myself...
Any deas?

Bass will be tighter, top-end will be smoother and cleaner. Those will be the main things that you will hear.

Great. I already got similar improvements just by trying that Stereovox cable.

I think that touches on the main points that you have made. Let me know if it doesn't.

Will do! Thanks! 

.

[art]

Pat,

Thanks a lot! 

The "extra" EMI will not do harm to your system. Maybe if you were watching the old analog Ch. 2-5 on your TV, with "rabbit ears" right next to your SB3, you would see interference.

So if I understand you correctly, EMI will not induce any garbage in SPDIF signal that might confuse my DAC?
This is of highest importance for me, since I don't wach TV that much.

The EMI results from a signal that has a faster rise time, which increases the number of harmonics. That is all there is to it.

I'm wondering if I can get similar performance from some bulk cable that I can terminate myself...

Look at our website for some hints. Not sure where exactly it is buried, though.

Pat

[Kuja]

The EMI results from a signal that has a faster rise time, which increases the number of harmonics. That is all there is to it.

Aaaahhh!  That makes it much clearer!!!

I thought that EMI is the product of some other SB inner electronics like internal switching voltage adaptors, WiFi and other stuff,
and that those inductors are there to suppress their infuence to the SPDIF signal.

Now I understand that SPDIF signal without those inductors will be just "sharper", which will result in increased EMI from it.
I.e. the sharper SPDIF signal is the source of increased EMI.

So additional "garbage" actually does not exist, in the sense that removal of the inductors will inject something that is not SPDIF in my DAC.


Thanks for the clarification!   





Some practical questions:

I would like to hack my SB as little as possible.
It would be nice if I could revert all changes if needed (for any reason)...

Do those inductors have to be physically removed, or I can just bypass them with short pieces of wire on the back of the PCB?
If yes, will bypassing the inductors have exactly the same beneficial results as their removal?





I'm wondering if this solution could give better results: http://www.pinkfishmedia.net/forum/showthread.php?t=57212

This guy bypassed the PCB track going from the digital output resistor (R67), thus bypassing the offending inductors.
He did run a new 75 ohm cable directly from R67 to the output BNC adapter and he cut the track at the output side of R67.

If I go this route, do I really have to cut the PCB trace going from R67?
I would like to avoid doing irreversible changes... but if they have to be done, they will be done.


In theory, using 75 ohm cable directly from digital output resistor seems to be better (in terms of impedance matching).

Am I going to have audibly better results by doing it this way, compared to just removing/bypassing L8 and L9 inductors and sticking BNC in place of RCA?


I understand that soldering 75 ohm cable to BNC socket is not such a simple thing.
Some impedance mismatching will occur at solder joints. If not done properly it could get worse.




Thanks again!!! 

I almost abandoned the idea of improving my SB.

Thanks to you I'll do it.

[art]

Some practical questions:

I would like to hack my SB as little as possible.
It would be nice if I could revert all changes if needed (for any reason)...

Do those inductors have to be physically removed, or I can just bypass them with short pieces of wire on the back of the PCB?
If yes, will bypassing the inductors have exactly the same beneficial results as their removal?

If you scrape them off, you may lose them! Yes, you can put a wire or big nasty glob of solder over them just to see if it works and sounds better. (It should.)

I'm wondering if this solution could give better results: http://www.pinkfishmedia.net/forum/showthread.php?t=57212

If you have the right coax (75 ohms!) and can work with it, then yes.

If I go this route, do I really have to cut the PCB trace going from R67?
I would like to avoid doing irreversible changes... but if they have to be done, they will be done.

Once you get the hang of it, you should cut that trace, all the rest of the extraneous stuff.

In theory, using 75 ohm cable directly from digital output resistor seems to be better (in terms of impedance matching).

Yes.

Am I going to have audibly better results by doing it this way, compared to just removing/bypassing L8 and L9 inductors and sticking BNC in place of RCA?

Might not be as big an improvement as getting rid of the ferrite beads. Will depend on a lot of other things.

I understand that soldering 75 ohm cable to BNC socket is not such a simple thing.

Depends on the cable, the connector, and how much experience you have.

Some impedance mismatching will occur at solder joints. If not done properly it could get worse.

Yes, but why is that? (Homework question.)

Thanks again!!! 

I almost abandoned the idea of improving my SB.

Thanks to you I'll do it.

It isn't that hard. Yes, it can look intimidating if you have never tried any of this. And yes, you can mess one up. I have seen a few. A good soldering iron, steady hand, attention to detail, and some self-confidence should do you well.

Pat

[Kuja]

Pat,

thanks a lot!!!