I recently asked a question about monitoring two recorders with one pair of headphones. I have been struggling like crazy figuring out a solution that will work in the time frame I have (short as heck).

For the electronic geeks out there... I just ordered a custom cable that works the opposite of a stereo Y-cable. The idea is that two stereo mini-jacks go into each Sound Devices monitor output and get summed into one stereo cable with a female mini-jack to plug in my headphones.

My questions: Will this work? Is it safe for my headphones? Will the quality be okay?



First off - do NOT use a y-cable to combine signals. To quote Dennis Bohn:

Here is the rule: Outputs are low impedance and must only be connected to high impedance inputs -- never, never tie two outputs directly together -- never. If you do, then each output tries to drive the very low impedance of the other, forcing both outputs into current-limit and possible damage. As a minimum, severe signal loss results.

Source: http://www.rane.com/note109.html

Now that that's said and done, what you probably ordered was a summing cable. You basically tie in some resistors and verything works the way it was supposed to. Check the above link for more details and see if this is what you got. (As a side note, these are way easy to build on your own - about $12 worth of materials and a a little soldering skillz).

As for me, I wouldn't want to have both signals firing at me at the same time. There are plenty of nice, cheap passive mixers that should do the job and let you turn down each source if you need to.

Good luck!

EDIT: looked at your previous post and that last one is probably what you want - no battery powere, it's fully passive. Can't attest to the quality - usually anything fully passive will work just fine, but not be the best thing you've ever heard. You could also make a cable that sums each stereo channel to mono and that way you have one recorder in your left ear, one in the right, and can slip your headphones off one ear to monitor just one.

  • @VCProd "You could also make a cable that sums each stereo channel to mono and that way you have one recorder in your left ear, one in the right..." - aren't you then doing the same thing as your quote advises against? Adding two outputs resulting in the possibility that one output attempts to driver the other (though on the same device)? – EMV Nov 20 '10 at 15:12
  • Thanks so much for the warning! Damn, what a pity. I'll see if I have anytime to solder in some resistors prior to leaving but I seriously doubt it. I checked all those mixers you linked to, but none of them work for my needs. That MX28 would be absolutely perfect if it were battery powered. I even phoned Rolls to ask them if they knew a solution to operate it with batteries, they said no. Thanks for the Bohn link. – Andrew Spitz Nov 21 '10 at 9:00
  • @EMV You would make two "Stereo-to-Mono Summing Boxes" per the Rane instructions, and then take the signal of one to left, the other to right in an 1/8" female connector. Ground doesn't matter - you can tie that straight. @Andrew Let me know if you find something good. You could probably use something like the Rolls MX42 - that's completely passive, just need to adapt from 1/8" to RCA. bhphotovideo.com/c/product/331962-REG/Rolls_MX42.html – VCProd Nov 22 '10 at 4:02
  • @Andrew, this might work too. bhphotovideo.com/c/product/155438-REG/Rolls_MX41B.html – VCProd Nov 22 '10 at 4:05

Just by theory you will have a louder signal if the two sum right - so I would guess the only time it could damage your hp's is if you had both recorders turned up to the point where it would be louder than the loudest of monitoring just one. This is if there is no built in limiter somewhere - you might be able to put a pad somewhere in the chain to be safe.

I wouldnt see why it wouldnt work though.

Would a safer bet be a switcher? - You could easily monitor 1 device at a time but A and B between the 2 at the flick of a switch?

  • Thanks for that. The Sound Devices have headphone limiters, but I'll also keep the volume at a safe level. A selector would work great, but I couldn't find one that was battery powered and deliverable by Tuesday... This will have to do (crossing fingers). – Andrew Spitz Nov 19 '10 at 8:20

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