2-way mic/line splitter questions..

Hi everyone. My first post, not counting all the "I'll take two of those please" and thank yous. A very simple project compared to anything else here, but I have some simple questions, which were not answered in the other splitter topics, and I hope someone can help.

This all started because I needed to build a 4 channel, 2-way mic splitter. I bought 4 Jensen JT-MB-C transformers, and planned to use them with a direct out as the data sheet shows:
http://jensentransformers.com/datashts/mbc.pdf

Then, I saw this:
http://jensentransformers.com/as/as015.pdf

and thought I'd combine the two. Except I will need DC blocking caps, right(?), in case someone (not me, of course :wink: ) sends phantom to my line source? The guy at Jensen also told me I should use bleed resistors if I use a switch for the pad, so I don~t get any crazy thumps flipping the switch. OK... so there is a schematic at the bottom, frankensteined from the ones on jensens site. It's cleaner than it would be if I did it by hand. I put dots where I think the caps might go and put a question mark at the "signal ground" from the original Jensen mic/line schematic (do I need this?)

My questions I would be forever grateful to have answered are:
1. Are the caps supposed to go where the green dots are or the red, or somewhere else? What value should I use?
2. Do the bleed resistors just connect the caps to ground? Again, what value?
3. Do I need the "signal ground"?
4. Anything else glaringly wrong with this idea??

Thank you!
dimitri

my schematic:

[img=http://img180.imageshack.us/img180/9964/splitterschem2np6.th.jpg]

[quote author="mitsos"]Hi everyone. My first post, not counting all the "I'll take two of those please" and thank yous. A very simple project compared to anything else here, but I have some simple questions, which were not answered in the other splitter topics, and I hope someone can help.

This all started because I needed to build a 4 channel, 2-way mic splitter. I bought 4 Jensen JT-MB-C transformers, and planned to use them with a direct out as the data sheet shows:
http://jensentransformers.com/datashts/mbc.pdf[/quote]

Any particular reason why you need transformers?

-a

well, I am building it for live recording of a touring musician I work with. In all the places we've been to, I have to say I have come to not trust the PA equipment .. and don't want it to contaminate the signal in any way. It is rare, and I know that a Y-cable would suffice most of the time, but I don't want to get caught with a "dirty signal" at the one perfect gig.. I bit the bullet and bought the trannys, so I could take an isolated signal from the stage.

Dimitri, I find your posted schematic too hard to read. Can you re-host it but larger?

In the Jensen schematic, the phantomis only connected to the mic section and is isolated form the line input due to the switch, so in this configuration, no caps would be necessary.

I see what you're saying...Sorry.... I guess the schematic isnt exactly how I will have mine wired... I am going to use a combo XLR/TRS for input, but with both XLR and TRS wired together, then to the pad switch. This way I think I could use either jack for either mic or line. Not that I'll ever use the TRS for a mic, but I am likely to use the XLR for a line signal, so that's why I want to be careful with phantom... Does this make sense?

Thanks for taking a look..

I hope this image works:

Forget about the second schematic. Keep it as simple as possible if you want it to work in various situations. You should not need the line in pad, this is easily accomplished with a pad that can be built into an XLR barrel if you don't have some allready (a few -20 db pads, phase reverses, and in line iso trannys /DIs are essential parts of the remote recording toolkit). The other thing I suggest is to eliminate the resistor and cap by the ground lift switch, tie all ground/shields at the tranny, and have a true ground lift at the iso out (or just leave it lifted, you will never use it grounded anyways).
It's always best to use the direct for the record side, if you can get away with it, but most mixers will bitch about the minor level drop from the iso out.

Thanks Niels,
So you're saying to just keep it simple right? I am kind of leaning towards doing it that way so I make this usable quickly... but I like the idea of a built in pad, so I don't have to use separate ones. Don't know if I will go that route or your way yet, but leaning away from complications right now.

About grounding, I was planning to ground to my case, which will (probably) always be in a rack with other grounded (through 3-prong AC cable) equip. In this case, are you suggesting to tie all grounds together, through a lift switch and then to the case? Should I do all channels together and have just one switch or do 4 switches?

thanks
dimitri

you need to consider what you are isolating. the idea of a iso split is that inputs of different systems can be fed the same source without interaction. Given that most likely you will need to have the iso out, so you are not required to provide phantom power or change levels to the house system, you should wire it as follows:
the input feed should pass directly to the direct output, and to the transformer primary. Connect pin 1 of input to pin 1 of direct out. Do not tie to your rack or case. Mount the transformer with isolation hardware, a rubber covered cap clamp works well for this, and provides shockmounting as well. Connect pin 1 of the input to the faraday shields and core of the transformer. Connect the secondaries of the transformer to pins 2 & 3 of the iso out. If you want to put ground lift (better to call them "tie", as you will always use it lifted) switches, use 1 switch for each output, from pin 1 of the input to pin 1 of the iso out. Tie the case or box the trannies are in to your system ground.
You can try the scheme shown in the Jensen doc, but I have not found this to work well in all circumstances.
The problem with many little switches for pads and the like is they get broken in the field, or accidentally thrown. Not bulletproof......A XLR barrel is almost indestructabe, but easily lost, as when you lend it to someone to solve their problem and never see it again

Thanks for that Niels. I think I will skip the pad etc, and just do it simply. Thanks also for the grounding explanation.

-dimitri