Unbalanced Cabling Confusions

[t_tangent]

Hi chaps,

I have a question about cabling external unbalanced synths to A16 Ultra, and would appreciate some help if possible. I usually try and make my own cables and for the most part this is fairly straight forward to do, if a bit time consuming. I have 2 A16 Ultra's, one of which is set for balanced gear such as Hardware Reverb & Compressor, i.e. set to +4db on the back switches of the A16U, and the other A16U is set to -10db, for unbalanced gear such as synths & drum machines.

For the balanced A16U the connections are simply TRS (Tip Ring Sleeve) jacks to TRS jacks or XLR connectors, on a "2 conductor shielded cable", and these are connected from the outboard gear to a patchbay, then from the patchbay to A16U and vice versa, another short Balanced TRS to TRS patch cable is used. So no problem there

But for the unbalanced A16U connections it is a little more complicated, so I would like to confirm that the following method is sound.

For outputs from unbalanced gear to the patchbay Inputs I am using a TS (Tip Sleeve) jack and then on the other end of the cable I have a TRS jack, wired as follows

JACK Cable
==== =====

Unbalanced Output (from external synth Output)

Tip = + (Hot) Red
Sleeve = - (Cold) Blue
Shield (Unconnected)

Balanced Input (to A16U input)

Tip = + (Hot) Red
Ring = - (Cold) Blue
Sleeve = Ground Shield

Again, the same as for the earlier A16U, from Patchbay to A16U I just have balanced TRS cables for all connections, both for inputs and outputs. Then, for Outputs from patchbay to unbalanced gear Inputs (used for processing audio through synth filters, etc) I have the cables connected as follows

JACK Cable
==== =====

Balanced Output (from A16U Output)

Tip = + (Hot) Red
Ring = - (Cold) Blue
Sleeve = (Cross Coupled Ground Shield connected to both Sleeve & Ring)


Unbalanced Input (to external synth Input)


Tip = + (Hot) Red
Sleeve = - (Cold) Blue
Shield (Unconnected)


I have read various sources on this subject but my main reference's have been the Scope manual A16 Ultra Section, and

http://www.rane.com/note110.html

See 'Figure 4. Interconnect chart for locating correct cable assemblies.' in particular Cabling configuration 11 and 14


Would this way of connecting mean that I can also set this A16 Ultra used for unbalanced gear to Balanced mode, i.e. jumper setting on back of A16U set to +4db) or is it still better to keep this A16U at jumper setting -10db

If anyone could check over this when they have a moment and see if this cabling configuration sounds correct, or if they have any better ideas then I would appreciate any help. Thanks very much

[valis]

Unfortunately there is no 'one'way to make a cable for all installations. There are both significant differences in the way various balanced outputs are designed (floating & differential balanced being the 2 I know of) and in some cases (notably with a balanced to ground output) it is best to use single conductor shielded cable where in other cases it may prove necessary to cut the shield at the end of the cable.

As long as you're ok with your s/n you're getting from your synth>a16 cable run (no extranious buzz/hum picked up) then your cabling looks right there. The a16 back to the synth I'm not sure about as I don't know the way that the a16 is balanced, but in most cases when a balanced output is driving an unbalanced input (on the synth) it is best to use a dual-conductor shielded cable, connecting the shield at both ends and allowing the low side of the cable to joint he shield at the unbalanced input end of the cable. This seems opposite of what you've done here and just how I'm familiar with doing it in live situations, so what you did may be just fine (and if you're not getting extra noise perhaps is?)

As for -10 or +4, if all of your synths are line-level (-10 dBV) I would just leave it set to that. When +4dBu is important is when gear is sensitive to power rather than voltage (ie, impedence makes a big difference), this is typically the case in older gear with XLR connectors (think Mics, preamps etc) and so won't matter to synths, though it may make your apparent levels change.

A 3rd option (especially if you have a transformer whose 'colour' you prefer over the 'straight' sound) is to use DI boxes to convert to +4. With synths this is done both to facilitate longer cable runs (on stage) and to get the coloration that some DI units may impart.

(Feel free to add to this or correct me where I'm misstating something.)

[garyb]

this looks fine, but you can just use a regular instrument cable. as Valis says, unless there's some horrible noise, it's probably ok. nothing will explode anyway. with a regular instrument cable, the signal remains unbalanced and the cold and ground are shorted together, no big deal unless there's a ground loop between the two devices. this is unlikely, especially if both are connected to the same outlet, or atleast the same breaker. most synths aren't grounded anyway. if you do have problems(60hz hum), you can use your trick cable.

the +4, -20 info is right on with one exception. a direct box won't give you a +4 output. a buffer amp would, but that's in the A16 anyway(it accepts a -20 input. that's what the dip switches are for!). a direct box's xlr output is mic level, it IS low impedance...

[valis]

You're correct there, using +4 shorthand was wrong. The impedence difference & the fact that I tend to then use my my board's mic pre's are the main reason I have liked DI's, at least in this decade. There's actually no reason I couldn't go XLR in from TS phono out of the synth and use the pre's, I just find I prefer using a DI as well.

[t_tangent]

Thanks for the advice chaps. I will try what you suggest and see how it works out. I have connected a couple of synths already amd so far things have been running fine with little to no hum or noise, but thought I would check up on this and ask before I got too far down the line and had to start from scratch again

Thanks again, and I'll let you know how I got on in due course. Cheers