Preamp rack wiring question

[SLS]

Hi all,

I'm going to be putting together a new mobile rig and have been happily reading through posts on setups, splitters, wiring, etc.

Since I am somewhat of a novice in wiring, I do have a quick question on setting up my preamp racks. I am going to have several racks with 8 channels of various pres in each rack. I definitely want an input panel that is easily accessible on the back with XLR(f)s but also would like DSUBs for quick interconnecting with my other gear.
-see picture for what I was thinking-

To wire the inputs, would you just wire both connections to a single xlr? In other words, do you just combine the 3 wires from an xlr(f) and 3 wires from the pins on the dsub connector to one set of connectors on an xlr(m) or does something else need to be in line?

Thanks!
Adam

[grindx]

You can wire it that way as long as both are not live at the same time. In use, the unused path needs to be electrically inactive, or your signal might be split without maintaining impedance.

[SLS]

Ok, that's what I was thinking...thanks for the input. Is there a more elegant way to do this?

[grindx]

A more flexible, and expensive, way would be to use a patchbay with normals. This way you could use a combination of the Dsubs and XLR and you could leave them plugged in. The patching would be accomplished via the bay which would also break normals when appropriate.

[SLS]

I was considering patchbays. I still may have some patch situation when I figure out all the components (and points) I am going to need. Thanks for the input.

[NorseHorse]

Splitting the signal would result in a 3db drop and the change in impedance (can someone post the math?) rarely seems to be an issue.

At least that's what I hear. A number of folks on this board use passive splits (which is what we're talking about) regularly without issue.

[grindx]

You can have a passive transformer split. Passive, meaning that there is no power and amp in the split. Impedance is still maintained via the transformer and yes there is likely at least a 3db (half) power drop.

[SLS]

There would be a 3dB drop even if there was nothing else in the other input? I understand that if you split one signal to two sources there is an impedance change, but I guess I'm unclear as to why there is one if you have 2 sources to one input...given that only one source would be connected at a time...i.e., xlrs or dsub.

Thanks!

[mixedupsteve]

Parallel: ZT = (Z1Z2)/(Z1 + Z2)

It doesn't matter if its hardwired or has a iso transformer. The impedance calculation is the same.

[mixedupsteve]

Originally Posted by AdamONE

There would be a 3dB drop even if there was nothing else in the other input? I understand that if you split one signal to two sources there is an impedance change, but I guess I'm unclear as to why there is one if you have 2 sources to one input...given that only one source would be connected at a time...i.e., xlrs or dsub.

Thanks!

If only one is connected at a time then there wouldn't be any change. If everything is powered off when the connection is made then a hardwired split connection like you described would be fine.

[Remoteness]

We daisy chain the connectors in our I/O panels all the time with good results.

ELCO, EDAC, XLR, DSUB are have been wired together for connection convenience.

[Rick Sutton]

Adam,
what you propose is the best way to do it (IMO). Stay away from normals on patchbays as they are a likely source of trouble on remotes.

[Remoteness]

I think it's more about which patch bays you use for remote recording than the patch bays themselves.

We have small, medium and large patch bays in use.
The one common factor is that they are all Audio Accessories bays.
We've had excellent results with Audio Accessories Jack fields on location.
IMO, they are the best in so many ways.
For one, their normalising jacks are the strongest around.
I have never had one fail to date and I've been using them since the 80s.