I'm not an electronics expert, although I've wired more than a few patch bays in my time, and there are certain things that I do know.

The main reason is simple - but it's important - and this is signal integrity.

Every time you introduce another "junction" to a signal, or interrupt that direct signal flow in any way, you are increasing the potential for lowering the optimum performance level and overall integrity of the signal.
The result could be problems associated with impedance matching (or mismatching), sufficient or required voltage, grounding issues, etc. And all it takes is just one of those things to occur, to effect the optimal performance of the mic, and the integrity of the signal.

I''m not saying you can't do it... But unless you really know electronics and wiring - and you mentioned that you don't - then you are best-served by getting that signal from the source to the destination in a way that is direct as possible.

Phantom power shouldn't be "patched" - (used in a bay) - because the mic that it is powering needs a certain minimum voltage to operate at its optimum level and efficiency, and there's no guarantee that interrupting that voltage - in any way - won't cause problems. And, if you aren't careful, You can also run the risk of sending that voltage to a device or mic that doesn't require it, and that could even possibly damage the device.

Your best bet - your guarantee to avoiding potential issues - is to run the mic directly to a preamp (or console channel) which can not only allow you to adjust the input gain, but that can also supply the proper voltage required to power the mic with, ( if required.. dynamics and ribbons don't require this type of voltage to operate, although they do require preamps powerful enough to gain them up to optimum performance levels) and to your ultimate destination ( DAW Computer) without being interrupted.

(Side note... there are some mics that come with their own power supplies, because they require a voltage that is different than the "standard" 48v Phantom Power. There are some condensers, generally of the tube-type, that often require a voltage that is higher than 48v.)

For further info, I'm going to page our resident audio electronics wizard for you ( Boswell ) and see if he can give further info, and maybe give other reasons ( or suggestions) that I've perhaps neglected to mention here.

He may tell you that you can do this, he may tell you that it's not difficult... But whatever he does tell you - if he gets the page and weighs in on this post - listen to him ... and not to me.

Past the basics that I've mentioned here, Bos knows a lot more about this stuff than I do. ;)

-d.

At this degree of experience, the one rule to stick to is only put line-level signals through a patchbay. That rules out all microphone signals, whether phantom-powered or not and, at the other end of the scale, loudspeaker signals (don't laugh - I have seen this). Line level signals include all standard pre-amp outputs, mixer inserts (these may be unbalanced) and also, stretching it a bit, outputs from guitars that have built-in pre-amps.

There are many reasons for restricting yourself to this rule, but the main one is to ensure that 48V phantom power does not come anywhere near the patchbay. Unintentional mis-patching is common, so the patchbay must be safe to yourself (electrically), to your ears, and to all the gear that can be plugged into it. In addition, the design of both standard-size and bantam jacks that are used in patchbays short-circuit signals to ground during the mating and de-mating operation, so having any d.c. present on the bay can cause large pops and bangs in monitoring loudspeakers or headphones.

Interesting. Thank you Donny, and Boswell for taking the time to respond, You know your stuff.
I had no idea, but all this makes sense. Running my Mic cord directly to the back of my mic pre is not a hassle, so no issues there. And I think it's probably better to prevent things like ground loops and Independence issues like Donny mentioned. When I bought this patch bay a few years ago I was just thinking it was something to make life easier, but I guess it wasn't practical in my situation.

Just curious on the subject of line level: I run my audio interface at +4db. I know that's line level. So can I assume that a 48V powered mic is also line level, but a much hotter level? And how about a dynamic mic such as a SM57, that's also line level? What about jacks from the back of rack effects such as XLRs coming out my t.c LX M1 effects unit, that would also be +4db I'm assuming?

I guess what I'm getting at is, if all these things are line level, then what do you plug into patch bays?

waveform, post: 430255, member: 49116 wrote: Just curious on the subject of line level: I run my audio interface at +4db. I know that's line level. So can I assume that a 48V powered mic is also line level, but a much hotter level? And how about a dynamic mic such as a SM57, that's also line level? What about jacks from the back of rack effects such as XLRs coming out my t.c LX M1 effects unit, that would also be +4db I'm assuming? I guess what I'm getting at is, if all these things are line level, then what do you plug into patch bays?

There are many standards relating to signal levels. The usual figure for an analog line-level is the one you quote: +4dBu. This is a type of average voltage, and it's understood that peaks go appeciably higher, occasionally by a factor of 10 times the voltage, so could reach +24dBu as a peak value. For analog signals going into digital equipment, you need to know what peak level the digital gear can convert without overload, so the signal is referenced to how much below the full-scale value it is. If the signal peaks were half the full-scale, the signal's peak value would be -6dBFS, where FS=full scale. Amalgamating the two measures in these examples where +24dBu = 0dBFS, the analog standard +4dBu would be -20dBFS.

Now your other point: 48V phantom power is not part of the signal when it comes to considering signal levels. Microphone signals, whether they have phantom power riding on top of them or not, are not line levels, and should not be fed into general-purpose patchbays. On the other hand, outputs from effect units are usually considered line level, even if they are unbalanced at -2dBu, so would standardly go into patch bays. I'll skip over the problem of balanced and unbalanced signals on patch bays, but you could refer to other [[url=http://[/URL]="http://recording.or…"]recent threads[/]="http://recording.or…"]recent threads[/] in these forums where there was extensive discussion on this topic.

Waveform, studios usually have Mic Pannels in the recording rooms that are permanently plugged to preamps in the control room (either mixer board or external preamps)
They would plug the mic they want to use to the preamp they want to use.
The pathbays come to play when you want to patch the preamplified signal to the recorder or to an external processing unit.

So, in day by day work, every direct-outs of your mixer and every output of your external preamps would be connected to the patch bay and also every ins and out of outboard gear like compressor, EQs, reverbs, delays etc...

If you only have an audio interface and mics.. you don't need a TRS patch bay, you need an XLR patch pannel. Something like this :

Boswell
I get the idea of what you're saying now. Though I have to admit you lost me on some of your number conversions. Like when you said, "4dBu as being a type of average voltage, then peaks can go higher, occasionally by a factor of 10 times the voltage, so could reach +24dBu" How is 24dBu considered 10 times higher? My lack of knowledge on how the scale increments are converted is the issue and is something I need to spend time on myself I think. When you say things like +24dBu = 0dBFS, you're talking another language to me. Sorry, I'm just being honest. I'm totally green on this subject and very visual in how I learn. I need charts with comparisons or it won't click. Either way, I get the idea of what you're saying with regard to why patch bays should only be line level. Thank you again! And thanks for pointing me to the recent discussion. I'll have a look though it.

pcrecord
you said in your third paragraph that,
"...in day by day work, every direct-outs of your mixer and every output of your external preamps would be connected to the patch bay and also every ins and out of outboard gear like compressor, EQs, reverbs, delays etc..."
You mean external guitar preamps ? My John Hardy M1 is a mic pre amp, but Boswell said no Microphones in the patch bay, so you must mean guitar pre amp. Unless you were referring to the Mic patch bay you displayed below?

By the way, thanks for putting the picture up. Makes sense to use that for mics exclusively.

Man this is simple.. you can't plug a microphone in a TSR (1/4'') patchbay, put it on ebay if you are not gonna use it for what it was made for!!
But there are XLR patchbays that are made exactly to help you plug the mic in front of your rack instead of going behind it if your interface has mic input in the back.
Or you could even make one yourself. Buy a plate, put female xlr connectors in it, run mic cables from the female XLRs to male connectors that will go to your mic inputs.

Those have no electronic parts but the connectors and cables, so no danger with phantom power.

waveform, post: 430283, member: 49116 wrote: I get the idea of what you're saying now. Though I have to admit you lost me on some of your number conversions. Like when you said, "4dBu as being a type of average voltage, then peaks can go higher, occasionally by a factor of 10 times the voltage, so could reach +24dBu" How is 24dBu considered 10 times higher? My lack of knowledge on how the scale increments are converted is the issue and is something I need to spend time on myself I think. When you say things like +24dBu = 0dBFS, you're talking another language to me. Sorry, I'm just being honest. I'm totally green on this subject and very visual in how I learn. I need charts with comparisons or it won't click. Either way, I get the idea of what you're saying with regard to why patch bays should only be line level. Thank you again! And thanks for pointing me to the recent discussion. I'll have a look though it.

Sorry, I didn't mean to bamboozle you - it's hard to judge first-time posters' technical knowledge. In addition, these forums are read by thousands of engineers of all levels of experience around the world, and the more that accepted professional practice is laid out, the more that sites with misleading or incorrect information are shunted down the search engine lists of results.

Really the only thing to remember from these figures is that when you are working in the analog world, you tend to work at standard levels (+4dBu in this case) with a known allowance for peaks above that level. Compared with the cramped dynamics of studio tape machines, we have the luxury these days of having a large dynamic range and being able to allow, for example, a factor of 10 in amplitude (20dB) for peaks, hence the peak figure of +24dBu.

The digital revolution has re-focussed signal levels away from standards such as +4dBu towards peak values, as exceeding the specified peak levels produces extremely unpleasant-sounding clipping, quite unlike the soft saturation of tape machines. Thus for inputting to digital gear, signal peaks are specified as what level they are below full-scale (dBFS), hence the need to know what your equivalent analog levels are in the digital domain. I should emphasise that each piece of gear has its own full-scale values, so you either have to check the data sheets carefully, or you purposely choose lower values knowing that almost any gear you use will accept them without overload. You may well see experienced contributers to this forum suggesting that operators keep peaks at something like -12dBFS, as this both allows for unexpected transients that go higher than this and also affords some "headroom" to work with at the later stages of processing.

Interesting stuff Boswell.
I never realized that there were variations of peak level capability's in different types of equipment. Like you said, guess that's where one has to dig into the data sheets. I know what you mean about analog tapes, the days when you could push the meters into the red and it would produce fantastic secondary harmonics, warm punchy drums. Some of the old Steely Dan comes to mind.

But, I'm glad you through out some of these figures, because it made me think about some things that would be healthy to learn. Right now I'm looking over these topics.
http://www.soundonsound.com/sos/1994_articles/feb94/decibels.html

http://www.ovnilab.com/articles/linelevel.shtml

http://www.sweetwater.com/sweetcare/articles/whats-the-difference-between-mic-instrument-line-and-speaker-level-signals/

pcrecord
Yes you can (physically) plug a TRS Mic cord into a line level Pbay, it just wouldn't be wise I guess. I get it.
But there are people out there who have both XLR and TRS jacks for their mics in their possession. I think it's important to dig deep and understand the fundamentals of signal levels and how things are referenced. Too often you get people saying, "don't do this", and others saying "do it this way", but unless you get down to the technicality's, you never really understand how it all works. I like to dig. It just happens that this is a subject I've never explored till recently. Anyway, I got what you said about the Mic Patch panel, but I was looking a little more under the hood as to the reasons.

Good responses everyone. Thank you! I know what I need to do.

When I said you can't, I ment it was not advisable. Like jumping off a bridge...
I know that some walmart microphones come with a TRS connection but those are not getting in my studio, EVER ! ;)

True, my more expensive blue mics (all my mics actually) come with XLR connections, but you can buy cords that have TRS on one end and XLR on the other end (I know you know that already, just saying). There is no difference in signal. They're both balanced, just different connections. Some mic pre amps take both types. But regarding what you said about a mallmart mic with a TRS getting in your studio: Even if a Mics did come with a TRS jack as it's connector, That wouldn't necessarily make it a wallmart microphone. They're both balanced Tip-Ring-Sleeve signals. But I know what you meant with regard to not using a TRS with a line level patch bay as a general rule.