[art]

Would that be fine if I use an Allen Bradley 122R 1W on the secondary site of Newava S22083?

Why would you want to? A "few ohms" means "a few ohms", as in 105, 107, 110 ohms max.

That value will certainly not yield 75 ohms. if you cable has more than a few ohms tolerance, then you will have to match the impedance on each end to it.

Which almost no one here can do. I can, and therefore I can tweak the circuit if I have the customer's cable at hand.

All of our cables are either 75 ohms, on the money; or some that have measured 76 ohms. That is well within any reasonable tolerance for a cable of this sort. (The reflection will be down over 40 dB. I consider anything that is 30 dB down or more is sufficient.)

So, for starters, that value is almost certainly too high. It is 1W, and almost certainly too large, in the physical sense. (Think stray inductance, and all that stuff. This is RF, not audio.) And if it is wirewound..........totally unusable.

My digital cable is a Zu Ash with RCA connectors (SB2) and BNC connectors in SB3.

I have no idea what that cable is, whether or not it is really 75 ohms, and what tolerance it is built to. No way I can give a definitive answer. But I can not see a case where 122 ohms would work.

Pat

[multibit16]

Your teaching us a lot on here Pat    problem for most of us especially us in the UK is actually finding a suitable cable

[art]

Hmmm......at one time I could find it at the surplus stores. A  buddy bought a 100' roll a while back, and offered to sell me the rest. Too bad he can't find it now.

If there are enough guys, here and UK, that want some, I can get a 100' roll, and sell it by the foot. Mind you, waiting in the queue at the Post Office will be the snag.

That reminds me......their stamp machine ate $1 in quarters the other night, and I need to fuss at them about it. Sods.

Pat

[Nuuk]

OK, just to help keeps things clear, here is the latest circuit digram.

I had the BGs recommended to me as ideal candidates for the bi-pass cap but nothing for the 100-220UF to ground so I will use a standard (used) BG 100 uF that I have in the box!

I'm also going to buy some Dale non-inductive resistors (if I can make up a worthwhile order).

[tanchiro58]

OK, just to help keeps things clear, here is the latest circuit digram.

I had the BGs recommended to me as ideal candidates for the bi-pass cap but nothing for the 100-220UF to ground so I will use a standard (used) BG 100 uF that I have in the box!

I'm also going to buy some Dale non-inductive resistors (if I can make up a worthwhile order).

Nuuk, Pat and Gary

First thing to say that I am not EE guy and do not know much about RF vs Audio whatsoever. I wonder why there are so many different ways and/or diagrams to modify the SB3/SPDIF output and did you or any of you have tried at least one or two ways but did you listen to compare which diagram is the best sounding one (I know it depends of individual sonic taste). I have tried to modify my SB2 with the first diagram in this thread and now there is another version from Nuuk. To my best sonic taste the first version is already good. However, I will try to do the new one since it sounds interesting to me. Any other new version? Thanks all of your ideas and opinions.

Regards,
Tan

[Nuuk]

Don't worry Tan, I would guess that most of us here are of about the same ability and knowledge! That's why we are here following the Pied Piper of Texas (if Pat will forgive the epithet)! 

The latest circuit I posted merely reflects that the DC blocking cap C1 has been moved from before the transformer primary, to after it, and the value is much larger. I think we can safely assume that this is done for a reason by somebody who doesknow what he is doing.

The latest diagram also details some improvements to the power supply going to the HCU04 chip. Sorry if I have caused you any confusion. 

[tanchiro58]

I have no idea what that cable is, whether or not it is really 75 ohms, and what tolerance it is built to. No way I can give a definitive answer. But I can not see a case where 122 ohms would work.

Pat,

I have listened to you to replace the 122R with a 110R across the secondary site of Newava. It did not have ANY SIGNAL sent to my DAC at all. So my conclusion is your opinion about the digital is totally right. When I reinstated the 122R to it I finally got my wonderful music back. Thanks for your lesson. 

The latest diagram also details some improvements to the power supply going to the HCU04 chip. Sorry if I have caused you any confusion.  Smile

Nuuk,

If you do not mind would you show us some pictures about where to cut the trace of 3.3V and replace with a bead and BG NQ 47uF? So for the primary "cold wire" you definitely choose BG 100-220uF to connect to ground. Thanks in advance.

Tan

[Occam]

I have no idea what that cable is, whether or not it is really 75 ohms, and what tolerance it is built to. No way I can give a definitive answer. But I can not see a case where 122 ohms would work.

Pat,

I have listened to you to replace the 122R with a 110R across the secondary site of Newava. It did not have ANY SIGNAL sent to my DAC at all. So my conclusion is your opinion about the digital is totally right. When I reinstated the 122R to it I finally got my wonderful music back. Thanks for your lesson. 

Tan,

I'm not Pat, but as someone who has made their own fair share of mistakes in modding (and continues to do so, just different ones), I'll comment. I assume that bowdown smiley was a facetious/sarcastic comment. If not, I apologize in advance. Personally, when I follow someones advice and I find it not to work, human nature makes me blame the adviser. But when I think about it, I find it a good idea to check my work.
In this specific situation, I would hazard to guess on a number of different possibilities -
1. There was an error in soldering and you inadvertently cause a solder bridge shorting the output.
2. You mis-read the resistor value and the shunt was actually 11 or 1.1 ohms or it was simply faulty.

There is simply no way that if you did as Pat suggested, error free, that you'd have gotten no output.
First, I'd have measured the resistance across the transformers output with the shunt resistor in place, and if I got a near 0 reading, I'd know I'd mucked something up. Ideally, I'd have been prescient enough to have measured the secondary's resistance prior to the mods (I never am that prescient  ). That would have allowed me to back calculate the actually resistor value. Better yet, sometimes I even remember to measure a resistor prior to soldering it, as my memory of banding codes isn't what it used to be.

Frankly, you made an error (we all do so occasionally), and the problem is not in Pat's guidance.

FWIW

[tanchiro58]

Frankly, you made an error (we all do so occasionally), and the problem is not in Pat's guidance.

Occam,

I did not and never intent to blame Pat or anyone who really wants to help us in this thread as he was wrong or told me to do something not right based on his knowledge. I have already accepted Pat's inputs or guidance as a fact. Therefore, I gave a try to modify my SB2. Besides I am really not a professional modder but I know what I am doing and trust my ears. I have also learned experiences since I have known how to modify stuffs. If there is misunderstanding please accept my apology. As always I honestly respect everyone who is willing to spend time and effort not only in this thread but also other.

Regards,
Tan

[Occam]

Tan,

Sorry for my misunderstanding... Regardless, there isn't any way as far as I know that simply paralleling a marginally different resistance to adjust the impedance should (as far as I know) result in the total lack of output. Possibly, if one goes in the wrong direction, an intermittant lock, possibly. Did you check for an actual output with something like an oscilloscope, or simply not get an output from the dac and assume it was due to no spdif output? If there were no errors in your mod, your dac should have locked onto the signal.  Make sure that 110 Ohm resistor actually is what you assume it is.
As my shop teacher impressed upon me 40+ yrs ago, measure twice, cut once. This from a man missing a thumb he'd cut off on a bandsaw.
Its quite frustrating spending 6+ hours looking for an error, only to find you'd accidentally nudged a lead shorting out the whole damn thing. Been there, done that.

Regards,
Paul

[Nuuk]

If you do not mind would you show us some pictures about where to cut the trace of 3.3V and replace with a bead and BG NQ 47uF? So for the primary "cold wire" you definitely choose BG 100-220uF to connect to ground.

I haven't done that part of the mod Tan so obviously no pictures yet. The bypass cap should be attached to pin 14 of the HCU04, that's the one on the lower right corner in the picture below. Immediately to the right of that pin is the existing bypass cap. The other end of the new bypass cap can be soldered to the via immediately above the existing SMD cap. I expect it is necessary to remove that crystal to make room for the new cap!

And the choice of the 100uF BG is just that - my choice as an enthusiastic tweaker so don't take it as gospel! 

Until I dismantle my SB3 again and have a look at the PSU, I can't point you to where to cut the 3.3v line.

[art]

Excuse me, but where did I say to stick in a 47 uF cap?????????????

I didn't.

I suppose that you could. It would have a "+" lead that would have to be at least 5 mm long, which is not a lot of good at RF. Sure, it might help at the lower frequencies, in which case the added length won't be a problem. Expecting it to clean up the RF garbage.......ain't gonna happen.

Unless you can live without the PCB that houses the "Wi-Fi" card (and a bunch of other stuff). Either that, or get a cap that is very small.

Mr New UK:

That 300 ohm resistor should be 249 ohms......just as in the original circuit. Your level will be too low at that value. It would work if you were running on +5 V. You are not.

The trace to get cut is under the chip! Why do you guys think that there are no pictures of it???? (It is just to the left of the via on Mr. UK's photo. Nice photos, btw. Wish I could do ones that nice.)

Speaking of which: what is "new" in the UK?  A former business associate (who is from there) liked to say that the reason it is now called the "UK" instead of Great Britain is because nothing is great about it any longer. (His words, not mine.) (He sounds more like Enoch Powell every day, which is funny because he is the sort that Powell ranted against.)

Pat

[tanchiro58]

Did you check for an actual output with something like an oscilloscope, or simply not get an output from the dac and assume it was due to no spdif output? If there were no errors in your mod, your dac should have locked onto the signal.  Make sure that 110 Ohm resistor actually is what you assume it is.

Paul,

Like I said I am not EE so I do not need any equipments like oscilloscope... I checked before and after swapping the resistors everything was fine (solder joint, wires and caps...) and intact but no good results until I put back the 122R to the circuit and voila it works again. I actually used Allen Bradley resistors which have 20% tolerance. They are not almost accurate like AN Tants and Rikens (1-5%). Therefore, the margin is right there if you do a simple math between 110R and 122R. Maybe I thought the Promitheus DAC and/or Zu Ash digital cable were/was so picky they did not pick up any signal output between 88R-110R but 98R-122R from secondary of the pulse transformer. Sorry for not using any technical terms professionally.

Here is the link that I found Peter Daniels used 121R parallel to the SPDIF output:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=3282&perpage=30&highlight=&pagenumber=3

Tan

[Nuuk]

Excuse me, but where did I say to stick in a 47 uF cap?????????????

Where did I say that you did? 

Unless you can live without the PCB that houses the "Wi-Fi" card (and a bunch of other stuff). Either that, or get a cap that is very small.

The NXQ is about as small as you can get for an electrolytic and should be able to go right on the pin. If not, I reckon the corner of the daughter-board could be cut away to accommodate it!

Nice photos, btw. Wish I could do ones that nice.)

I 'pinched' that one off Gary! 

So here is today's version of the circuit:



If anybody knows just cause or impediment why the above circuit is not correct let him speak now or forever hold his peace! 

[multibit16]

Those yellow caps look very big, won't the inductance be too high  ?

[Occam]

I 'pinched' that one off Gary! 

So here is today's version of the circuit:



If anybody knows just cause or impediment why the above circuit is not correct let him speak now or forever hold his peace! 

Horses for courses.....
No, that is not Gary's schematic! It is your improved circuit.....
Would everyone STOP trying to improve upon the circuits offered by real electrical engineers prior to getting them to work as suggested by Gary (and ART).
The engineering term for this is called throwing shit up against the wall and seeing what sticks.
It might serve you well subjectlively in audio frequency circuitry, but it sure as heck ain't gonna work in RF/Digital.
Stop with the frigg'n BlackGates! If you must decouple a digital ps rail with an electrolytic, then use an OSCON.
For the spdif coupling cap use a film cap and the values recommended. No audiophile axials or electrolytics. A larger value, or physical size gets you nothing but higher ESL (inductance) which is going round off your expected squared pulses. NO la-de-da resistors. 1% or even 0.1% accurate are available in both smt and thru hole from all of the distibutors, Allied, Newark, Digikey, Mouser, etc... for chump change.

FWIW

[Grumpy_Git]

Occam

Chill!

Also as i read it the "pinched" comment was refering to the picture NUUK used/re-posted.

I happily agree about things to the professionals.

Nick.

[GBB]

No, that is not Gary's schematic! It is your improved circuit.....

Paul,
I think Nuuk was giving me credit for the photograph of the board - not the schematic.  And he's right - I did take that picture showing where one connects the transformer.  For those interested in how to take pictures like this, it's quite easy with modern digital cameras.  I got a new Olympus Stylus 820 for my birthday and it has a very good macro mode.  I made sure the board was well lighted and then just took the photo in macro mode holding it my hands - nothing too difficult.  Just takes steady hands.

Regarding the rest of your post, I agree completely.  These are high frequency circuits and capacitors that sound good at audio frequencies don't necessarily work well here.  A couple of pages back I recommended just reusing the 0.1uf ceramic capacitor that was originally used in the SB3.  That's still good advice.  Pat has suggested one gets a little bit of tilt in the square wave and it might be worth increasing this slightly.  Adding a bigger ceramic cap would be fine but I'm not sure it's really worth the effort.

People also seem convinced that it makes a difference whether the capacitor is on the hot or cold side of the transformer.  It doesn't.  A compact layout with short wires and physically smaller components is more important.

---Gary

[Occam]

Nuuk - Sorry about my mis-interpretation of the picture credit. 

Perhaps Grumpy Git and I should swap monikers?

[Nuuk]

Nuuk - Sorry about my mis-interpretation of the picture credit.  Embarassed

Don't worry, I am very thick-skinned these days! 

And I am far from trying to suggest any new tweaks in the presence of those obviously much more skilled than I am. I have merely been trying to get a finalised circuit posted to clear up any confusion. My first attempt showed a 300R and nobody said that it was wrong so that's what I continued with.

As regards the BG cap, this is not the whim of a star-truck bodger, but something recommended me to a highly respected designer, with a very good track-record in hi-fi design! As such, I suggested it here, particularly because that 47 uF NXQ is physically quite small, and is particularly suitable inside the small SB3 case. I agree (and so did my contact) that a small OSCON would do as well but he preferred the NXQ and as I said, who am I to question experienced electronics designers! 

NO la-de-da resistors.

You don't go along with the suggestion to use non magnetic non-inductive resistors then?