NOS1a BNC > XLR conversion

[rutger21]

Hi Peter,

My NOS1a has 2x BNC stereo sockets.

Q: What is required for reversing 1x BNC stereo sockets back to former XLR sockets (with the intention using solely just the XLR sockets)

Is it simply a matter of replacing 1 pair of the BNC sockets with XLR sockets - pin 2 hot....
Or should the 4x 75ohm resistors also be replaced back to original 33ohm(?) resistors for proper XLR SQ/operation.

Thank you Peter !
Pete

[PeterSt]

Hey man,

Indeed the 33 Ohm was original and intended to be the lowest possible while all still decently working. This was for RCA and XLR the same. However, since BNC is a 75 Ohm official path, those resistors where replaced with 75 Ohm.
Leave that be when changing to XLR ? this is harmless, but the relation with the device at the other end will be slightly worse. Officially, when the other end bears 600 Ohm (a typical pre-amp I think ?) then the 75 is just a tad too high (and the 33 is fine).

Where to put which wire is somewhat harder for me to explain because I don't know how the DAC in question was set up or changed and how "obvious" the wires are visible on their function. However, I suppose that first changing the hot from XLR to "a" pin on XLR is fine always, as long as you apply it the same for both channels. And the other wire (per channel) goes to the other pin. All you could imply is a reverse absolute phase but if you use XXHighEnd, that's settable in there.

Best regards !
Peter

[rutger21]

Yo Peter,

Apologies to bother with such things. It is more curiosity than anything, hopefully no cats are harmed, simply to test former favorite $$ XLR cable which has not been done here yet since NOS1a/G3 version(great sound BTW!!) Once method is understood then should have no worries changing to either socket if/when desired.
So this is helpful information and sounds easy enough so thank you for that!

Again, out of curiosity, and not that there is any `pre-amp` here as always like going direct to Orelo, just wondering why (as you say) 75ohm output would be less than ideal situation for connecting to some preamp with say 600ohm. So does the higher 75ohm output somehow result in higher/hotter voltage signal, vs lower 33ohm, that 600ohm preamp might not like?
Or is there something else going on here i do not understand that would cause more toward incompatibility in such a situation.....

Nice to know things even if useless 

Pete

[rutger21]

DAC output impedance does not effect anything with voltage strength ?
 
Other than that... i am aware with the said rule of thumb being load impedance should be a minimum of 10 times the source impedance to achieve best compatibility/transparency.

But if 75ohm output impedance is bit too high for say 600ohm load (breaking above rule) then conversely would something like 0.5ohm output then become too low for the same (or higher) 600ohm load...
Or is the rule of thumb always valid regardless how low the output.

[acg]

Pete,

There are no penalties for lowering the output impedance of a dac other than that which comes with the internal topology of the dac itself (i.e. the means by which the dac achieved such low output impedance).  Higher output impedance can affect sound should the input impedance of the downstream component, the Orelo in your case, be too low.  I do not know the input impedance of the Orelos, but they are active speakers so I reckon it is going to be in the kilo-ohm region where there is effectively no difference between 75R or 33R at the output of the NOS1a.

Get the wiring recommendations from Peter and you are good to go.

Cheers,

Anthony

[rutger21]

Anthony,

Still learning basic technical aspects but yes i do understand all you explained.
 
Was just curious the relationship between output impedance and output voltage of DAC (if there is any) for future reference more than anything and if ever introducing other components to try or w/e.

Does voltage change at all if impedance is changed or is it always stable/set according to circuit design.... will NOS1 always keep 2.7v output via XLR?

Thanks!

[rutger21]

Ok image of my NOS1 parallel wired channels

Should i leave existing wiring on the remaining stereo BNC sockets or should they now be disconnected and protected after swapping in the XLR sockets...

[rutger21]

In addition after checking Orelo wiring...

Orelo XLR
pin 2 = hot
pin 1 = ground
pin 3 = nothing

Fine to wire up the new 1x stereo NOS1 XLR sockets in same fashion?

[acg]

Change output impedance and output voltage will not change, but current will change.  Do you need more current from the NOS1a?  Nope, not into the Orelos nor into just about every preamp or amplifier on the planet.

[PeterSt]

All what Anthony said is correct.
Input impedance of the Orelo is IIRC around 80K Ohm.

Fine to wire up the new 1x stereo NOS1 XLR sockets in same fashion?

Pete, this depends on what you actually are going to do with it. You suggest to try another fine (XLR) cable. But if this is really so - and nothing else, then this obviously won't work because your Orelo does not have balanced inputs.
If this is, however, about a 2nd NOS1 you possess and this is to be connected to something very else with balanced inputs, then fine in itself. But I am not so sure about this, and thus :

The answer is No. In whatever event you can't hope for anything good with a cable made for balanced purpose (your XLR) to behave in any good fashion if it is used as an RCA cable with a wrong impedance on top of it (not that RCA bears a formal impedance but alas).

I see another combination : you do have that 2nd NOS1 and want to try this with your fine XLR on your Orelos ... 
... forget it.
In that case you can leave the old BNC connection be - which you BTW can do anyway, but it will be a total mess electrically. Not that things will explode (all voltages will remain fine) but it will sound like a drag; The half of the XLR you will be using will be worse than a pair of shoe lashes as nothing in that cable will be made / be shielded etc. etc. for single ended operation.

The upside of this all will be that - also with your own original NOS1 you could do this, besides your BNC connection (this is what you asked about too). Thus, no harm done to anything for the BNC connection. But ...

Now this puzzle is pieced together somewhat for me, you won't even had the additionally required wires for a proper XLR connection (they are not hanging loose somewhere in there).
Lastly, electrically such a "faulty" connection has never been tried by me, and again I say the same : it will sound like a drag.
Side note (or not) : I recall a most simple desired combination of two pairs of outputs chosen from RCA, BNC and XLR (but I forgot which), and there was no way I could make that sounding right. The customer in order received an "impossible" from me. But that was judged with my ears and such. What you seem to head for is similar. Thus, what I am saying here is that because of your "illegal" XLR connection, your BNC will sound wrong too. "Will" ? I can't guarantee it.

Do notice please, that all what is impedance "draws" on the output. In this case this is quite directly D/A converter chips (with only one tiny resistor in the path) which have a relation among hem as well (2x 2 for one channel). Thus, draw on this wrongly (or untested) and the one will tear down the other (read : your half-XLR will draw on the other BNC, whether XLR is used or not (not used : means : open ended AKA not terminated). This is fine when it sounds fine. And if you really paid attention, you noticed that this drawing could be on the same chip- half, or the other (of one channel). With Single Ended one half is used for both outputs (like BNC + RCA). With XLR, both halves are used. With half-XLR maybe the other half should be used. LOL.

Try it and let us know ?
And have fun of course !

Peter

[rutger21]

> Not that things will explode
Hahah, but Peter, you know i like things exploding.....   

There`s no 2nd NOS1 but i believe Anthony is keeping 1 or 2 spare NOS1`s in his attic for me just in case all goes up in smoke over here.

Since finally getting NOS1`a G3` going (special shout out to Ramesh and Anthony!) i simply had another silly thought - maybe try former fav Palladium cable again.

It`s ok the idea is scr*pped already. Forget it. Thank you (and for all!)

Meanwhile M3/L3/NOS1a/G3/Blaxius/top AC delivery - sounds KILLA man! 

[PeterSt]

[Erwin]

Hi Peter, i also have a related XLR question. My G3 has RCA and XLR outputs, i plan to use the XLR but i was wondering about the pin-out, can you specify these? To use on a differential input of course.

Thanks

Erwin

Edit: i guess i just want to double check if the XLR connection is wired like most other XLR gear, so pin 1 as shield/chassis, And pin 2 and 3 as 'hot' and 'cold'?

[PeterSt]

Hi Erwin,

Apologies about a late reply.

Of course you don't need to worry about the pinout, or else numerous people would have problems with the connection (which theoretically would be about Absolute Phase only, which can be inversed in software anyway).

Best regards,
Peter