USB interface with S/PDIF and digital XLR output ?

[halman]

Quote:

Then the best cable you can make is a standard coax lead termianted with BNCs. $10

Just make sure you actually get 75R connectors. There are lots of stores who mix 50R/75R connectors at leisure since in most cases it does not really mater much. In this case however it does.

 

[ckunstadt]

hmmm, I might be able to pull that off (connector swap).
thanks guys.

and my apologies to the OP. Thanks for letting me bend the topic.

 

[Daroid]

Quote:

Originally Posted by ckunstadt and my apologies to the OP. Thanks for letting me bend the topic.

Naah.. you're more than welcome

Having read a lot of posts by jocko homo by now, well, i will be staying with S/PDIF only, it is fine for me - actually just wanted to take advantage of the (grrr) AES/EBU interface... sorry Ericj for the earlier "arrogant" reply to your post... had a very bad day.


The USB digital output which someone here made (not sure if it was Guzzler ?) , did this feature the 1:1 pulse transformer on the output ?
If it didn't, what was the reason (other than Jocko Homo doesn't know about this forum yet) ?

 

[ckunstadt]

Quote:

Originally Posted by Daroid Naah.. you're more than welcome Having read a lot of posts by jocko homo by now, well, i will be staying with S/PDIF only, it is fine for me - actually just wanted to take advantage of the (grrr) AES/EBU interface... sorry Ericj for the earlier "arrogant" reply to your post... had a very bad day. The USB digital output which someone here made (not sure if it was Guzzler ?) , did this feature the 1:1 pulse transformer on the output ? If it didn't, what was the reason (other than Jocko Homo doesn't know about this forum yet) ?

Daroid,
Do you think you'll possibly be doing the RCA to BNC connector replacement thing? with your Aqvox?

 

[Daroid]

I'm not sure what these mods require... i have no idea how they made the S7PDIF circuit they currently use, but will open it up one day. So in other words, no, will stick with the standard RCA although it might be less good, if something goes wrong they can see i have tampered with it, not willing to risk it.

 

[Garbz]

The circuit they use is over the top and many not even work. If we are reading the same thread the circuit buffers the signal and then pumps it differentially into the receiver.

As far as the connector swap that requires you to open the chasses, snip or desolder the RCA connectors, unscrew, and if you're lucky the rca connector is the same size as BNC connector. Plug that in and solder it back onto the board.

This will give you a fantastic result, the pulse transformer more so, then you hit the law of deminishing returns so buffering it is all up to you.

 

[Daroid]

The RCA connector looks like it can easily be desoldered, so i'll see if i can find any BNC that fits...

The same thread... this one ? http://www6.head-fi.org/forums/showthread.php?t=105088 , where Guzzler's final was http://www6.head-fi.org/forums/showp...2&postcount=83 ?

One more thing i just saw now: http://www6.head-fi.org/forums/showp...&postcount=120 - someone already thought of this: pulse transformer, bnc, what more can we ask for ?
Don't know how to solder anything SOIC or SMD with just a regular soldering iron however.

About cable for a BNC to BNC cable, should this be 75 Ohm "video" cable too, or is a different type better for this task for less reflections etc ?

 

[Francis_Vaughan]

Quote:

Originally Posted by Daroid Don't know how to solder anything SOIC or SMD with just a regular soldering iron however. About cable for a BNC to BNC cable, should this be 75 Ohm "video" cable too, or is a different type better for this task for less reflections etc ?

Cable must be 75 Ohm. Video cable is a good source of such cable. You can obtain very high spec cables - essentially ones with much better manufacturing tolerances - but starting with a good quality video cable is likely a sensible first step. Boutique cables are mostly junk.

You may find this thread exactly what you want. Especially the later pages where a fully realised output is shown soldered together.

http://www.diyaudio.com/forums/showt...7&pagenumber=1

SMD really only needs a reasonably good iron with a very fine tip. There is nothing magic about SMD components - care and practice is the key.

 

[Daroid]

Ok, but is there any reason why SMDs are used, couldn't it be done with regular components, or is it because the length of the pcb traces will be too long then ?

http://www.diyaudio.com/forums/showt...002#post764002 top post looks like it has what i want, except the "2R???" would be 25 ohms also in order for it to be a H-pad ?

I will need to connect this directly to the output of a buffer (eg. 74HC04) which again connects to Dout and Dgnd of the PCM2902, correct ? Is there more to it that than that besides connecting the PCM2902 like TI says ?

 

[halman]

Quote:

Ok, but is there any reason why SMDs are used, couldn't it be done with regular components, or is it because the length of the pcb traces will be too long then ?

Even the way the compoents are layed out will have an effect on the TL:s impedance short traces and smds works best.

Quote:

top post looks like it has what i want, except the "2R???" would be 25 ohms also in order for it to be a H-pad ?

It would still be a H-pad but it would not be set to the proper impedances

1,8R resistors would work well giving the circuit an output impedance of 74,9R

Quote:

I will need to connect this directly to the output of a buffer (eg. 74HC04) which again connects to Dout and Dgnd of the PCM2902, correct ? Is there more to it that than that besides connecting the PCM2902 like TI says ?

You also need to consider the output impedance of the logic device aswell and set the signal amplitude to propper spdif levels.

 

[Daroid]

Ok, wouldn't risk it with non-SMDs then.

With logic device you mean the hex inverter, right ? Couldn't find any info in the datasheet about the output impedance, is there any way to tell (calculate), or is it trial and error ? If the H-pad on the "secondary" side of the transformer is ~75 ohm, the output impedance of the inverter should be the same, i.e. add resistors until it matches up, or ?

The signal amplitude from the PCM2902 is 2.8V, should be 0.5V ? How is sthis done - voltage divider network ? (sorry, i'm a newbie at this)

 

[halman]

Quote:

Ok, wouldn't risk it with non-SMDs then. With logic device you mean the hex inverter, right ? Couldn't find any info in the datasheet about the output impedance, is there any way to tell (calculate), or is it trial and error ? If the H-pad on the "secondary" side of the transformer is ~75 ohm, the output impedance of the inverter should be the same, i.e. add resistors until it matches up, or ? The signal amplitude from the PCM2902 is 2.8V, should be 0.5V ? How is sthis done - voltage divider network ? (sorry, i'm a newbie at this)

Read the thread on diyaudo and all will be revealed

 

[Daroid]

Yes, i can see that now,
But i am unsure why R1 and R2 are said to be in parallel, i see it as a normal voltage divider, so why do i have to do like "hifi" calulates:
"4R7+25R // 4R7 will not give you 75R"

when the 4R7 across the primary side of the transformator is not in parallel compared to the other resistor ? Or is the "coil" in the transformator seen as 0 ohm, so they thereby are in parallel ?

(haven't worked much with transformators yet)

Jocko Homo looks like he guessed the impedance of the SAA7220, to 25 Ohms, how do i make a similar guesstimate ?

 

[halman]

Quote:

But i am unsure why R1 and R2 are said to be in parallel, i see it as a normal voltage divider, so why do i have to do like "hifi" calulates: "4R7+25R // 4R7 will not give you 75R"

Consider the output of the logic device to be a 25R resistor tied to ground.

If memory serves the schematic you refer to has two 4R7 resistors configuered as a voltage divider

""4R7+25R // 4R7 will not give you 75R"

Quote:

Jocko Homo looks like he guessed the impedance of the SAA7220, to 25 Ohms, how do i make a similar guesstimate

Jocko Homos sugests 25R is a good rule of thumb for output impedances of logic ic:s and who am i to argue

(he got a TDR to meassure it precisely)

 

[mark4]

Hi, i'm currently looking into making a digital output on a laptop, so it has to be rather small. Guzzler's design looks good (PCM2902 reference ?), but i', thinking that having a balanced digital output through XLR would be nice.... Does such a design for USB exist ? Does anyone have a hint of what this would take - e.g. what needs to be modified on Guzzler's digital output to allow this ?

tia.

A very good USB to AES interface is the Yellotec PUClite
 
http://www.yellowtec.com/en/products-lp/puc2-lp/puc2-lite.html
 
AES/EBU has one big advantage to S/PDIF. It is transormer balanced and this way you have a galvanic isolation.