sc947-02 group buy

Brian T. · « **Reply #120 on:** 25 Apr 2007, 12:03 pm »

Gosh, been away for a few days, you guys have been busy!

Quote from: GBB on 19 Apr 2007, 02:43 am

Quote from: Brian T. on 18 Apr 2007, 06:52 pm
I think that a fully balanced approach might be better.

I agree with Josh K here - there is no benefit to using XLR and balanced cables. Once you've gone to transformers on the output of the SB3 and the input of the DAC then things are already balanced. The BNC connector is better than the XLR so you'll be moving in the wrong direction.

--- Gary

Gary – I fully agree that the output of the transformer is balanced, but as soon as you connect a coax the balancing is destroyed. Coax is, by its very nature, ‘unbalanced. Once you connect the coax to a balanced output, apart from destroying the CMR, you also have the problem of what to do with the ground/shield. The threads from tanchiro58 is testament to the difficulty in finding a ‘clean’ sound in a mixed digital/analogue environment. Of course you can leave the shield floating but then you might as well use a shielded twisted pair and retain the CMR advantage. (I suggest connecting one end of the shield to ‘technical ground’ via 10nF ceramic disc capacitor.) A floating shield also makes for a great HF antenna and I wonder if the “dry and bright ” effect noted by Tan is down to HF hash mixing in.

Cheers!

Ps – Josh, I have not heard from you regarding payment for the transformers. I will PM.

cft · « **Reply #121 on:** 25 Apr 2007, 12:22 pm »

Will there be a second round of group buy on sc947-02? Or someone ordered extra that could spare two?

tanchiro58 · « **Reply #122 on:** 25 Apr 2007, 06:12 pm »

Quote

The threads from tanchiro58 is testament to the difficulty in finding a ‘clean’ sound in a mixed digital/analogue environment. Of course you can leave the shield floating but then you might as well use a shielded twisted pair and retain the CMR advantage. (I suggest connecting one end of the shield to ‘technical ground’ via 10nF ceramic disc capacitor.) A floating shield also makes for a great HF antenna and I wonder if the “dry and bright ” effect noted by Tan is down to HF hash mixing in.

Brian,

What is the CMR advantage?

Let's assume the 10nF disc capacitor is connected to one end of the shield (either pin 6 or pin 7) so other end will be connected to technical ground (somewhere in the PS chassis?), is that what you meant? Thanks.

Brian T. · « **Reply #123 on:** 25 Apr 2007, 07:05 pm »

Quote from: tanchiro58 on 25 Apr 2007, 06:12 pm

Quote
The threads from tanchiro58 is testament to the difficulty in finding a ‘clean’ sound in a mixed digital/analogue environment. Of course you can leave the shield floating but then you might as well use a shielded twisted pair and retain the CMR advantage. (I suggest connecting one end of the shield to ‘technical ground’ via 10nF ceramic disc capacitor.) A floating shield also makes for a great HF antenna and I wonder if the “dry and bright ” effect noted by Tan is down to HF hash mixing in.

Brian,

What is the CMR advantage?

Let's assume the 10nF disc capacitor is connected to one end of the shield (either pin 6 or pin 7) so other end will be connected to technical ground (somewhere in the PS chassis?), is that what you meant? Thanks.

Sorry Tan, I was just being lazy... CMR is 'Common Mode Rejection'. The concept is that if you employ a twisted pair of conductors the 'airborne' interference/crap will hit both conductors equally but out of phase and therefore cancel themselves out. This doesn't happen with unbalanced connections. Unless the coax shield is well grounded it will, itself, act as an antenna and contribute to injected noise. This is why 'most' professional gear utilise balanced connections via XLRs.

With respect to the capacitor, one end of the coax is left unterminated whilst the other is connected to the technical ground via the 10nF disc. Never connect both ends if you wish to avoid AC loops. Usually it is best to connect the cap to the downstream ground. (i.e. SB3 to Dac, connect at the Dac input.)

Cheers!

tanchiro58 · « **Reply #124 on:** 25 Apr 2007, 07:22 pm »

Quote

Usually it is best to connect the cap to the downstream ground. (i.e. SB3 to Dac, connect at the Dac input.)

Brian,

Thanks for your infos. But I am still confused with the connection between SB3 and DAC via 10nF cap (I got a Rifa .001uF/250V secure cap, is this okay?). So you mean the connection begins at (-) of the RCA digital input via 10nF cap then to pin 4 (ground) of the SC947-02. Please correct me if I am wrong at this point. Thanks again.

Regards,
Tan

GBB · « **Reply #125 on:** 25 Apr 2007, 09:05 pm »

Quote from: JoshK on 21 Apr 2007, 07:22 pm

OK, update 4/21/07 3:20pm

I got the transformers today. Most have paid already (thanks!) and I have packaged up the transformers of those gentlemen to go out Monday.

Josh,
I got my transformers in today's mail - many thanks. Pretty good transit time from NY to Ca.

---Gary

crooner · « **Reply #126 on:** 25 Apr 2007, 09:32 pm »

Ditto here. Thanks again to Josh!

They are tiny though!
I'll need to a get a fine tip for my soldering iron.

Since I'll have plenty of space in my custom enclosure, I'm thinking about placing the transformer in a DIY small PCB. And bring the leads out from there. The PCB will be enclosed in a metal or ABS box treated with ERS sheets to prevent RFI/EMI energy from affecting the signal. I might add ferrite beads to the leads as well.

Brian T. · « **Reply #127 on:** 25 Apr 2007, 11:22 pm »

Quote from: tanchiro58 on 25 Apr 2007, 07:22 pm

Quote
Usually it is best to connect the cap to the downstream ground. (i.e. SB3 to Dac, connect at the Dac input.)

Brian,

Thanks for your infos. But I am still confused with the connection between SB3 and DAC via 10nF cap (I got a Rifa .001uF/250V secure cap, is this okay?). So you mean the connection begins at (-) of the RCA digital input via 10nF cap then to pin 4 (ground) of the SC947-02. Please correct me if I am wrong at this point. Thanks again.

Regards,
Tan

Hi Tan,

It would be easiest if you download the AES paper previously referenced by Josh; http://www.scientificonversion.com/AES2003.pdf

Open up the document and look at Fig 35 on page 30. The left-hand transformer labelled “OUTPUT TRANSF” is the one that you have wired in to your SB3. Both of the output connections of this transformer are wired to your new BNC connector. Ignore the dotted ‘Chassis Earth’ connection underneath the BNC as the transformer output should be connected to the BNC, and the BNC only. You then have a coax interconnect cable wired between the BNC on your SB3 and the BNC on your DAC. The latter BNC will connect to the second SC947-02 transformer that you are undoubtedly fitting, or have fitted, to the DAC. This second transformer is labelled “INPUT TRSF.” in Fig. 35. You will notice that there is also a dotted ‘Chassis Earth’ connection under the right-hand BNC. What I am recommending is that you connect the 10nF capacitor in place of this dotted ‘Chassis Earth’ connection. (i.e. between the main body of the BNC connector and ‘Chassis Earth’ or ‘receiver (RX) ground’). You will have to check that any existing BNC connector on the DAC is not already grounded by virtue of being screwed onto a chassis plate. If you buy a BNC connector from a reputable vendor, it will come with a PTFE insulation washer and a solder tag that fits under the securing nut. The aforementioned washer will isolate the connector from the chassis and you can solder one side of your capacitor to the tag.

I don’t recognise the capacitor type, is it one of Rifa’s Metallised Polypropylene types? If it is, it will have the wrong impedance characteristics at HF. You should buy a ceramic disc which is perfect for this application.

I hope this helps.

Cheers!

tanchiro58 · « **Reply #128 on:** 25 Apr 2007, 11:43 pm »

Quote

You will have to check that any existing BNC connector on the DAC is not already grounded by virtue of being screwed onto a chassis plate.

Brian,

Thanks again for your time.

I have a MHDT Renaissance II DAC (just like Paradisea) enclosed in a acrylic case. Therefore, it does not have metal chassis. The only I can think of is connected to somewhere outside the DAC. The shortest way is the AC plug (IEC) but based on some DAC experts said that I will ever never connect to AC plug ground (AC too noisy). I have also tried to find a "real ground" to avoid RFI/EMI in around the DAC

Regards,
Tan

PS: I have read Jon Paul papers several times and tried to figure it out his concepts

JoshK · « **Reply #129 on:** 25 Apr 2007, 11:51 pm »

Just a note...the first wave of tx's went out Monday and as some reported they are starting to arrive. There were a handful or less number of gents whose pmt's didn't reach me in time for first shipment that will go in the second shipment, which I plan for tomorrow or Friday. Work tomorrow is going to be busy, so that is why I am unsure whether I will make it to the PO tomorrow.

Overall, I will say its been a great group buy experience (wood is being knocked). Its up to the rest of you to organize a second round. A number of gents have asked about it, just missing the cut off. I am sure there is probably enough of you to make another decent sized order. However, Anthony mentioned to me (he is probably going to hate me for this) that this is no min order with him. You are probably not going to get the free o/n postage that we got though, nor do I know his pricing for one or twosies.

If anyone steps up to organize a second round, contact me and I'll fill you in on some details that may make it slightly easier to manage. My coming week is a bit too busy, plus I want to play with projects some, to organize another round.

mgalusha · « **Reply #130 on:** 26 Apr 2007, 02:21 am »

Mine arrived today as well, many thanks to Josh for putting forth the effort to make this happen.

Mike

krikor · « **Reply #131 on:** 26 Apr 2007, 01:54 pm »

Josh ... got my transformers. Thanks to you (and Anthony at MauiMods) for the lightning fast execution of this group buy!

BTW: In considering how I might alternately use the SC961-04 transformer to convert the Squeezebox's SPDIF to balanced AES/EBU, I came across the following article that some of you may find helpful (it sure clarified a few things for a digital DIY newbie like me). I found it on Rane's website:

http://www.rane.com/note149.html

Now I've just got to take the lid off my Cary 306/200 and see how the digital inputs are handled.

hanguy · « **Reply #132 on:** 27 Apr 2007, 02:13 am »

Josh,

Got the transformers in the mail today. Thanks again for organizing this group buy.

Mike

MarkM · « **Reply #133 on:** 27 Apr 2007, 02:18 am »

Thanks Josh, got them yesterday, now I have to find the time to take things apart.

JoshK · « **Reply #134 on:** 27 Apr 2007, 02:24 am »

I have recieved payment by all, to date. I didn't get time to go to the PO today, for the 4 remaining shipments, but plan to tomorrow morn'. Was a nice GB to organize, all were well behaved...

F-100 · « **Reply #135 on:** 27 Apr 2007, 11:42 pm »

I haven't received mine yet so they must be in the last shipment.

JoshK · « **Reply #136 on:** 28 Apr 2007, 12:20 am »

F100...no yours went out with the first round. Sometimes it takes longer some routes then others.

F-100 · « **Reply #137 on:** 29 Apr 2007, 04:42 am »

Got them today, thanks Josh.

viperrabbit · « **Reply #138 on:** 29 Apr 2007, 10:49 am »

Hi Josh

I received mine today. Thanks very much for making the arrangement.

Regards
Edmund

crooner · « **Reply #139 on:** 3 May 2007, 12:35 am »

Bump!
I was wondering if somebody has a pinout diagram for the SC947-02. Can't find it anywhere online. I'm about to start modding my gear and a diagram would be extremely helpful.
Thanks!