Wiring XLR ins and outs...

Had to replace a meter lamp in my SSL tonight.

When I built it I was confused about how to connect the in and outs.

Its a couple of years ago now, I think I just futzed around till it worked, however it dosent look right to me...

I have NOTHING connected to pin 1 on both my output XLR's...

The ONLY wire going to my chasiis earth point is from the mains IEC...

It passes audio on both channels, it SEEMS ok...

However, I figure its about high time I actually understand how its done, and correct what I have done on the SSL. Anyone kind enough to share some info?

I have tried searching but havent turned up anything substantial...

thanking you . :grin:

Depends what you're connecting it to.

If you send it to a transformer balanced destination, connecting pin 1 doesn;t do anything other than terminate the shield at the SSL end. If it's terminated at the other end and both pieces of gear are grounded to th power, that's NOT what you want...

If it's going to a piece of unbalanced gear and that piece of gear connects pin 3 (low) to ground, then again, you don't want a 0V connection on the SSL because the Gyraf version of the SSL isn't a cross-compensated output.

...So there's no simple universal fits-all answer...

You need to consider what you're connecting it to, and what the story is at it's input, also what's feeding the comp and what the plan is at it's output. Then you can say what to do.

..If it's worked for two years with no hum and no buzz, then you possibly have the ideal setup. Sometimes you need to lift the connection at pin 1 to solve problems.

Keith

Thanks Keith.

Shouldnt I be running earth from the XLR's at some point to star ground though?

This is good practice for inputs. 10 pf caps to ground and ferrite beads:

What do the caps actually do CJ? Is that 2 pins I see tied together there ?

RF supression. Nor necessary but good insurance.
The two caps are tied to ground, which is pin 1 in this case.

I read somewhere (some mic pre manufacturer's paper) that in mike preamp inputs those ferrite beads are critical because they can saturate and produce distortion in the audio signal. Anyone have info about this? There is any special criteria in chosing those ferrite beads to not produce distortion? Or this is bogus.

chrissugar

Ferrites, like other magentic cores, will definitely distort with enough current. It's another design tradeoff. Typically the higher permeablility material is going to be the worse.

At mic-sized currents it's a pretty tiny effect in general.

Many times what we need is a common-mode choke to suppress RF, and properly constructed the differential signal currents cancel each other and don't perturb the core.

[quote author="bcarso"]
At mic-sized currents it's a pretty tiny effect in general.
[/quote]

That is what I was thinking but i remember in that paper they said it has an audible effect in transparent mic preamps. That is why i was curious about the order of magnitude of the fenomenon.

chrissugar

What I remember is that a Jensen paper writes about distortion in line out application. There is much more current flowing, of course.

What about phantom power? Could be a few mA with some mics...

Samuel