Longframe/Bantam Patchbays and phantom power...

[Steve Anderson]

Hi All,

Doing an install in a school at present, and they have requested a patchbay for stage to desk patching.

If we go this way, some of it will be normalled, and to that end I have sourced a patchbay (ADC BJF403-4MKIVSN) with sleeve normals bought out as well as the tip and ring... but my real question is, what happens when phantom power is turned on and something gets patched?

If it were a quarter inch plug with the diameter of T R and S the same, a mic could get 48V across pins 2 and 3 as the plug is inserted. I don't have one to test, but does the narrower (smaller diameter) tip and ring on the Bantam/Longframe style plugs inhibit this from happening? And what happens to a condensor, electret or oherwise, if this does happen?

Cheers,
Steve.

 

[Craig Hauber]

Re: Longframe/Bantam Patchbays and phantom power...

Generally good practice "back in the day" was to not apply phantom -or even open-up pre-amps, until the patch was complete. Even then I remember some nice pops and explosions as someone messed with the patchbay while things were live. Classic example of something that seems like a really good thing to experienced professionals utterly fails when confronted with amateur users!
Even with all that going on for years (churches, schools with patchbays) I've never seen a failed mic or preamp due to it.
-and how about those well-wishing system designers that had process-out/amp ins points on the bay -guess what happens when a line-level source signal gets inserted into the main PA amps that are on with attenuators wide-open? (not a good idea to even have those points)

 

[Caleb Dueck]

Re: Longframe/Bantam Patchbays and phantom power...

... they have requested a patchbay for stage to desk patching.

Do they really need a patch bay? Are they being stuck with an old analog console? Or is this a bid where details are set in stone, right or wrong? We've only done one patch bay recently (XLR only, for the subsnakes), and that was only because the client specifically wanted to go a certain route.

 

[Brad Weber]

Re: Longframe/Bantam Patchbays and phantom power...

Do they really need a patch bay? Are they being stuck with an old analog console? Or is this a bid where details are set in stone, right or wrong? We've only done one patch bay recently (XLR only, for the subsnakes), and that was only because the client specifically wanted to go a certain route.

I've had theatre and performance venue projects, including schools, with a large number of microphone inputs, in some cases hundreds, spread around the venue but only a fraction of them used for any single show. Similar with tie lines, many terminations at the stage with a limited number in use at any time. Patching is a very practical, and common, solution for those situations even if digital consoles are used and especially if you are also splitting to address broadcast/recording or groups bringing in their own FOH and/or monitor consoles. In fact, I'd say in some situations patching may be how a venue can support the number of physical connections they have and be able to afford a new digital console.

I agree with Craig that standard practice is to patch with the phantom off and preferably with the console and even system off. The patching is usually used for preconfiguring the system before an event and isn't something you should plan on using too much during a performance, so patching with everything turned off is typically quite practical.

I do try to use XLR patching for microphones if at all possible and have always managed to avoid using bantam patching for mics, although I have, due to the rack space available, had to use 1/4" longframe patching for mics and bantam patchbays for tie lines. XLR patching addresses several issues such as making ground contact first, avoiding shorting during insertion and removal and being a locking connection. Another advantage of XLR patching is that you can use standard cables as a common issue with longframe and bantam patchbays is that the patchcords are not something one can necessarily buy at every local music store. This is particularly a concern with B-gauge longframe bays as people may try to use standard A-gauge 1/4" TRS jacks and due to their larger tip and ring width those can bend or even break the spring terminals inside the bay.

 

[Geoff Doane]

Re: Longframe/Bantam Patchbays and phantom power...

Bantam or Longframe patchbays can work for mic level patching, and sometimes they can be a source of continuous grief.

I've seen both. You definitely want to avoid brass plugs (like the old ADC). Once they tarnish, they don't conduct line level signals very well, let alone mic level. On the other hand, we have a Moses & Mitchell bantam patchbay in an SSL console that has been in service since 1998, and the only issues have been mechanical, not electrical. BTW, we use Neutrik and Mogami plated patch cables in this studio. Full, rather than half normaling, is usually used for mic level patching. On the SSL, all the grounds (screens) are bused at the patchbay. There's no attempt to change the path of the grounds when patching.

If I was making all the decisions, I'd prefer an XLR mic scrambler panel, but that may not be possible due to size considerations (an 80 channel panel in a recording truck used 12 rack spaces). For an installation, it is possible to parallel wire more than one female XLR on each input line. If you plan carefully, you can cover most setups without any patches in the path. I'd gladly trade the extra wire for the lack of non-soldered connections (patches).

GTD

 

[Mike Brown]

Re: Longframe/Bantam Patchbays and phantom power...

Nothing wrong with mic lines hitting a patchbay. I see them and wire them myself all the time.

As far as what happens when you patch with live phantom.... check out this informative video: ShinyBox

I HAVE seen damaged ribbon microphones from shorting phantom power, but you have to train people not to do that... or don't use microphones that can be easily damaged by such behavior.