Bnc & rca
Some things I pieced together from my surfings (so you might wanna check!)...
BNC is better than RCA in theory as the socket/plug geometry is designed to maintain impedence through the connection. Change in impedence is bad as it effectively forms an obstruction for the signal, causing reflections which mess with the signal = bad for sound quality.
Much of this benefit of BNC is lost as soon as the path of either conductor is obstructed. So soldering the central conductor is ok, but twisting the outer shielding to solder to a lug is not. So if you are doing this, I guess you may as well stick with RCA.
The best way to make BNC connections is by crimping, which gives a full circle contact for outer shielding. To do this properly you need a proper crimp tool bit. However, each bit is specific to only a few types of cable and they cost £70'ish each. When I found that out I decided just to buy a professionally made cable. I can highly recommend Mark Grant cables. He uses the right Belden cable with the correctly matching plugs & the right tools and he charges a fair price. For those of you over the pond, Blue Jeans cables look like they offer much the same cable.
Regarding impedence matching - if you do use BNC, the cable & socket & plug impedence should be chosen to match. That could be 50 or 75 Ohm or whatever. These DAC boards are set up for 75 Ohm I think, so you would need to change the resistor on the boards if you want to use something else.
One last thing - apparently LONGER cables are better for SPDIF. Something to do with signal reflections and the frequencies involved I think. Over 3m is best!
Some things I pieced together from my surfings (so you might wanna check!)...
BNC is better than RCA in theory as the socket/plug geometry is designed to maintain impedence through the connection. Change in impedence is bad as it effectively forms an obstruction for the signal, causing reflections which mess with the signal = bad for sound quality.
Much of this benefit of BNC is lost as soon as the path of either conductor is obstructed. So soldering the central conductor is ok, but twisting the outer shielding to solder to a lug is not. So if you are doing this, I guess you may as well stick with RCA.
The best way to make BNC connections is by crimping, which gives a full circle contact for outer shielding. To do this properly you need a proper crimp tool bit. However, each bit is specific to only a few types of cable and they cost £70'ish each. When I found that out I decided just to buy a professionally made cable. I can highly recommend Mark Grant cables. He uses the right Belden cable with the correctly matching plugs & the right tools and he charges a fair price. For those of you over the pond, Blue Jeans cables look like they offer much the same cable.
Regarding impedence matching - if you do use BNC, the cable & socket & plug impedence should be chosen to match. That could be 50 or 75 Ohm or whatever. These DAC boards are set up for 75 Ohm I think, so you would need to change the resistor on the boards if you want to use something else.
One last thing - apparently LONGER cables are better for SPDIF. Something to do with signal reflections and the frequencies involved I think. Over 3m is best!
Yes, I have wondered how far it should go - solder coax to the receiver chip legs?!
Yes indeed SPDIF is at 75ohms. Just if your buying connectors its worth checking. I've seen me open the wrong ones from my parts shelf
As said BNC done right is better but one bad bit in the chain nulls the benefits.
I agree 100%
Hi guys, I've been busy turning an old Philips player into a transport. New caps and new low jitter clock and also reclock of the SPDIF and running 2v out of the digital RCA. It has made a meaningful difference in every respect. Next I'm going to try running I2S directly to the CS8421, but I'll get another dac board to experiment with. I'm not messing with my system now, I love it.
Belden 1505F cable is damn good for digital.
Best, Bill
Belden 1505F cable is damn good for digital.
Best, Bill
if you're making your own connections on both ends - Use F connectors ( same as on cable & SAT/TV lines) ;
that way - terminating is easy , and good quality antenna cables are cheap
if they're good for long SAT signal runs , they're certainly good for SPDIF
use F "kuplung" for chassis mount
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Hi Ken
Hopefully Bill will agree but I have ordered these from Cinemag (will take ages to arrive)
CMOQ-2H - $55.74
High nickel - 1:1
Cinemag Audio Output Transformers
Here is a connection diagram that Data very kindly sent me showing resistor and cap loads:
Hopefully Bill will agree but I have ordered these from Cinemag (will take ages to arrive)
CMOQ-2H - $55.74
High nickel - 1:1
Cinemag Audio Output Transformers
Here is a connection diagram that Data very kindly sent me showing resistor and cap loads:
An externally hosted image should be here but it was not working when we last tested it.
Hi Ken,
I've never personally tried the Cinemags. I've heard that their opinion is, the lower nickel content units have a warmer sound than the high nickel. Regarding bifilar or quad, I haven't a clue. You can always email them for suggestions, they do respond.
It's just like stepping into a new world when you hear your first set of trafos, dont sweat the choice too much.
I've never personally tried the Cinemags. I've heard that their opinion is, the lower nickel content units have a warmer sound than the high nickel. Regarding bifilar or quad, I haven't a clue. You can always email them for suggestions, they do respond.
It's just like stepping into a new world when you hear your first set of trafos, dont sweat the choice too much.
Hey Bill,
Sounds interesting.
I'm still trying to figure out this I2S thing, which appears to be a significant step up, and hoping someday to be able to use it with my SB3. K & K Audio are offering an I2S interface adapter but I have no idea on how to implement it. As they state:we strongly recommend that the I2S Interface Adapter Send board be used only by someone who has the necessary knowledge and skills to undertake the project without guidance.
I've been using inexpensive BJC with Belden 1505F for a while and have found it to be quite good also. Especially when I look at the price that some cable manufacturers are asking for their "revolutionary new design" stuff.
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I connected my Cinemags as in the diagram after looking at how Bill was using some of his 
MacCrackers? you said that somebody at Cinemag suggested the low Nickel ones, less detail but smoother was how you put it wasn't it?
David never suggested otherwise to me when I told him what I was using them with, so I'm guessing It's a personal preference regarding the resulting sound?
Edit:Listening to a Jazz CD by Malissa Forbes ATM and It sounds just superb
Edit:Come to think of it...when I ordered, I asked for Quadfilars and mentioned that I didn't want colouration from the transformers and David suggested the CMOQ-2H
MacCrackers? you said that somebody at Cinemag suggested the low Nickel ones, less detail but smoother was how you put it wasn't it?
David never suggested otherwise to me when I told him what I was using them with, so I'm guessing It's a personal preference regarding the resulting sound?
Edit:Listening to a Jazz CD by Malissa Forbes ATM and It sounds just superb
Edit:Come to think of it...when I ordered, I asked for Quadfilars and mentioned that I didn't want colouration from the transformers and David suggested the CMOQ-2H
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Data
Exactly. After discussing the technical aspects and pros/cons of 80% nickel vs 50% nickel and quadfilar vs bifilar I justed asked him - What do YOU prefer? His answer was 50% nickel. As for quadfilar vs bifilar he didn't seem to have a preference and responded with some technical stuff that I didn't quite understand.
Like Bill said - I wouldn't think the trafo thing over too much. Easier said than done.
Personally for my second board I'm considering the JENSEN JT11P-1 that Ciu and GerardA seem to be really happy with. So please - If anybody has any objections speak now or forever hold your peace.
Exactly. After discussing the technical aspects and pros/cons of 80% nickel vs 50% nickel and quadfilar vs bifilar I justed asked him - What do YOU prefer? His answer was 50% nickel. As for quadfilar vs bifilar he didn't seem to have a preference and responded with some technical stuff that I didn't quite understand.
Like Bill said - I wouldn't think the trafo thing over too much. Easier said than done.
Personally for my second board I'm considering the JENSEN JT11P-1 that Ciu and GerardA seem to be really happy with. So please - If anybody has any objections speak now or forever hold your peace.
SPDIF cables etc
Coaxial SPDIF out of machines is 75R impedance and as such needs the correct cable and BNC connector. To my knowledge it has never been 50R impedance.
I strongly suggest either 75R BNC or "F' types with preferably double screened cable either Satellite cable plus 'F' types, or preferably UK Broadcast cable type SD01 with matching BNC plugs.
SDO1 is good up to about 360Mb/S so should be OK for SPDIF
Phono plugs are a compromise as they are neither 75R or 50R impedance nor are they constant impedance with frequency. The main reason for use is naturally cheapness.
I am not quite sure where this idea of long cables for SPDIF comes from (Snake oil?). As long as:
a) It comes from a 75R source
b) It is terminated in 75R at the destination and
c) You use the correct cable/plugs as above
It will not matter whether it is 5 cm or 20 Metres long.
The 110R impedance spoken of is generally reserved for AES/EBU balanced cables, using XLR type connectors, for sending digital audio signals around mainly professional audio and broadcast studios.
John Caswell
Coaxial SPDIF out of machines is 75R impedance and as such needs the correct cable and BNC connector. To my knowledge it has never been 50R impedance.
I strongly suggest either 75R BNC or "F' types with preferably double screened cable either Satellite cable plus 'F' types, or preferably UK Broadcast cable type SD01 with matching BNC plugs.
SDO1 is good up to about 360Mb/S so should be OK for SPDIF
Phono plugs are a compromise as they are neither 75R or 50R impedance nor are they constant impedance with frequency. The main reason for use is naturally cheapness.
I am not quite sure where this idea of long cables for SPDIF comes from (Snake oil?). As long as:
a) It comes from a 75R source
b) It is terminated in 75R at the destination and
c) You use the correct cable/plugs as above
It will not matter whether it is 5 cm or 20 Metres long.
The 110R impedance spoken of is generally reserved for AES/EBU balanced cables, using XLR type connectors, for sending digital audio signals around mainly professional audio and broadcast studios.
John Caswell
And what do we do between chassispart and printboard?
A small piece of coax or is this less important (I hope so).
And the circuitboard itself, maybe connect directly to the 75R or to the chip...
And inside the PC...
What is the exact effect if some parts are not 75 ohm?
Reflections of coarse but what more can be said about this?
A small piece of coax or is this less important (I hope so).
And the circuitboard itself, maybe connect directly to the 75R or to the chip...
And inside the PC...
What is the exact effect if some parts are not 75 ohm?
Reflections of coarse but what more can be said about this?
Hi Gerard et al
Ideally between the PCB and the chassis socket a piece of 75R coax is the correct/ideal thing to use although a lot of companies use two wires twisted together, which in some cases can approximate a 75R impedance cable, but it is not a good idea and certainly not good engineering practice.
If there is a 75R resistor on the PCB in the output stage that usually means that some effort has been made to provide a 75R send impedance so the cable should be wired between the output and earth on the PCB.
For instance a lot of integrated circuits (IC) used to send SPDIF out to the real world have very low output impedances so you would need to add a resistor in series with the IC to make the output/send impedance up to 75R to match the cable.
If some of the circuit is not 75R you will get an impedance mismatch which will cause reflections of the signal which may show up as distortion and in some cases completely cancel the signal itself.
John Caswell
Ideally between the PCB and the chassis socket a piece of 75R coax is the correct/ideal thing to use although a lot of companies use two wires twisted together, which in some cases can approximate a 75R impedance cable, but it is not a good idea and certainly not good engineering practice.
If there is a 75R resistor on the PCB in the output stage that usually means that some effort has been made to provide a 75R send impedance so the cable should be wired between the output and earth on the PCB.
For instance a lot of integrated circuits (IC) used to send SPDIF out to the real world have very low output impedances so you would need to add a resistor in series with the IC to make the output/send impedance up to 75R to match the cable.
If some of the circuit is not 75R you will get an impedance mismatch which will cause reflections of the signal which may show up as distortion and in some cases completely cancel the signal itself.
John Caswell