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[Dusk Bennett]

Hi folks....quick question:

I'm doing a gig this week where I need to split 4 x SM58's. One signal will go to a monitor board the other signal to Pro Tools (x4). Rather than rent a huge expensive multi channel split for 4 mics I like to try something different. I'd like the veterans to comment on my ideas.

1. Build 4 passive XLR splits 6' long. (F XLR - M XLR x 2)
2. Rent a whirlwind 24 channel passive split
3. Patch the 4 mics into the record input of Pro Tools and route the summed output(s) into a line amp on the Mon board.

I know passive mic splitting is frowned on but some tech's I respect do it anyways. What are the consequences of doing passive splits on mic level signals?  

Also I've used the passive Whirlwind split (I refer to above) before and it works great. I have not had any problems with it. What makes the passive spliters I build any different than the Whirlwind (aside from the obvious box)? I need to educate myself on the consequences of passive splits so I understand exactly what I'm getting into.

Thanks in advance for your expertise.

Dusk


(Crossposted in REP)

[Andy Peters]

Dusk Bennett wrote on Tue, 09 January 2007 15:26

I'm doing a gig this week where I need to split 4 x SM58's. One signal will go to a monitor board the other signal to Pro Tools (x4). Rather than rent a huge expensive multi channel split for 4 mics I like to try something different. I'd like the veterans to comment on my ideas. 1. Build 4 passive XLR splits 6' long. (F XLR - M XLR x 2) 2. Rent a whirlwind 24 channel passive split 3. Patch the 4 mics into the record input of Pro Tools and route the summed output(s) into a line amp on the Mon board. I know passive mic splitting is frowned on but some tech's (sic) I respect do it anyways. What are the consequences of doing passive splits on mic level signals?

Do the passive split.  You shouldn't have any problems.  Passive splits are used all the time.

You'll use your splits often.

Quote:

Also I've used the passive Whirlwind split (I refer to above) before and it works great. I have not had any problems with it. What makes the passive spliters I build any different than the Whirlwind (aside from the obvious box)?

Nothing!

(re: crossposting to REP: Good fuckin' luck getting a straight answer outta those people!)

-a

[Dusk Bennett]

[quote title=Andy Peters wrote on Tue, 09 January 2007 22:39]

Dusk Bennett wrote on Tue, 09 January 2007 15:26

(re: crossposting to REP: Good fuckin' luck getting a straight answer outta those people!) -a

very funny....LOL. That's why I posted here first. : )

Thanks Dusk

[Tony "T" Tissot]

I split hardwired all the time. You should be OK - I split to a Digi 002 or an HD24 without difficulty.

There are a number of detailed threads on this topic-

example: http://srforums.prosoundweb.com/index.php/m/95091/11099/0/// 15490/#msg_95091

The "correct" way however is with a transformer isolated split.

[Emil Barnabas]

The problem with a hard-wired split is that fader adjustments on the monitor board will raise and lower the signal at your Pro Tools rig. Having a transformer-isolated split will eliminate this problem. If the levels on the monitor board are not adjusted much, it will not be a problem.

Can you use the insert jacks on the monitor board? A mono 1/4? plug inserted halfway will usually pick up the signal and keep it going to the monitor board as well.

I made up some cables with a TRS connector at one end to plug into the insert jack. The TRS plug had the tip and ring connected together. This tip/ring combo and the shield gives you an unbalanced signal at the other end of the cable to connect to your Pro Tools rig. Shorting the tip and ring together allows the signal to stay in the monitor board as well.

[Gabe Nahshon]

Sorry, dude, but that is completely wrong.  "Hard-wire" split?  As opposed to a wireless split?

The guy needs 4 Y cables. Transformers have nothing to do with the split out being post fader.

Check yourself,

Gabe

[Tony "T" Tissot]

Emil;

That's incorrect. While the impedance does change a bit - it does not affect the levels to any degree. The fader does not affect the level to the other part of the split in any way that is detrimental to your purpose.

Many of us run monitors the exact same way.

To the OP - just try it. Cheap splits are available from audiopile.net for 7 bucks US each - probably much cheaper than you can buy the 2 M and F XLRs.

edit - add that I also find it useful to run the splits to unused channels - or another board and then DO to the Digi or the HD24 so I can easily keep levels where they need to be.

- and again - because of course it's 2 M and 1 F Dooh!

[Andy Peters]

Emil Barnabas wrote on Tue, 09 January 2007 22:55

The problem with a hard-wired split is that fader adjustments on the monitor board will raise and lower the signal at your Pro Tools rig.

BZZZZT!  Wrong.  The preamp's a buffer (with gain) so there's no way the fader can possibly affect the signal at the input.  If it did, then the thousands of shows done each day with passive splits would have real problems.

Quote:

Having a transformer-isolated split will eliminate this problem. If the levels on the monitor board are not adjusted much, it will not be a problem.

BZZZT!  Also wrong.  A transformer will not eliminate this non-existant problem.

-a

[Andy Peters]

Tony Tissot wrote on Wed, 10 January 2007 00:06

That's incorrect. While the impedance does change a bit - it does not affect the levels to any degree.

Not exactly true ... when split, the source sees both loads (in this case, the console and the ProTools rig) in parallel.  So if both the console and the ProTools rig have 2K input impedances, the source will see a 1K load.

But assuming low source impedance, you're right; the levels should not be significantly affected, and if need be, you can simply bump the input trims up a couple of dB.

One thing to note, though, is that source impedance and drive capability are not related.   The reason for the "load impedance > 10 times the source impedance" rule of thumb is simply to reduce voltage-divider effects.  

Now consider that some active output drivers can't drive low-impedance loads.   By our rule-of-thumb, an output impedance of 50 ohms shouldn't mind a load impedance of 500 ohms, but the driver itself may not like such a low impedance, and distortion will increase with desired output level and maximum output swing will be reduced.

-a

[John Roberts {JR}]

Emil Barnabas wrote on Tue, 09 January 2007 23:55

The problem with a hard-wired split is that fader adjustments on the monitor board will raise and lower the signal at your Pro Tools rig. Having a transformer-isolated split will eliminate this problem. If the levels on the monitor board are not adjusted much, it will not be a problem. Can you use the insert jacks on the monitor board? A mono 1/4? plug inserted halfway will usually pick up the signal and keep it going to the monitor board as well. I made up some cables with a TRS connector at one end to plug into the insert jack. The TRS plug had the tip and ring connected together. This tip/ring combo and the shield gives you an unbalanced signal at the other end of the cable to connect to your Pro Tools rig. Shorting the tip and ring together allows the signal to stay in the monitor board as well.

There is a possibility for interaction if one mic preamp is allowed to clip as that could cause a change in input impedance with some topologies. Transformer splits will not prevent this, only true active splits.

Hardwire splits are commonly used with good results as long as everybody keeps it between the ditches.

JR

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