Balanced/un-balanced problems with Protools 192 i/o

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strangeandbouncy

Well-known member
Joined
Aug 8, 2004
Messages
2,112
Location
West Sussex. UK
Hi,

  I have recently started using more and more of my outboard as "inserts" with in Logic and Protools. Makes for lightening fast recall, and I often need to get 2 or 3 tracks up a day. I am also rarely making adjustments to bits of outboard for the same reason. Compromise, but best of both worlds, and an instant recall.

 I have just made a studer/audiox 169-500 eq. It is amazing, but was giving me a 6dB  loss as an insert in 'tools. Fine inserted before a channel of my desk. I have finally had a minute to myself to investigate, and I find that other bits of gear ALSO give me 6dB loss. SOme are unbalanced, but, get this, some AREN'T! To make matters worse, I balanced the input to my new eq with a shiny new Carnhill 10k:10k, and it STILL gives me a 6dB loss! I have checked and checked and checked again .What the f@@k? I am certain it is not the wiring. I have tried many different patchpoints to try to work out. All the same. Inserts that use our Apogee Rosetta send/rtn do NOT lose 6dB running into the same gear.

  Help! can anyone suggest how to connect an unbalanced piece of gear so as NOT to get this loss? I even wired hot and cold to pins 1 and 3 of the input to lunchbox, which surely can't be shorting out one half of the balanced signal?



     Tearing my hair out!



   ANdyP
 
You might say, just use the Apogee sends/rtns . . . .but they give an overall loss of >1dB which is not adjustable like the 192's. This is not acceptable on, say the lead vocal in a mix.
 
What other bits of gear are giving the loss?  Are they also DIY?  Perhaps the equipment itself is not unity in to out?
Good time to link again to the Rane white sheet on interconnects.
I have many people using PT inserts and pro equipment and have never had the issue.  Most everything is balanced, but even stuff like 80's SPX90's, Rev7's, Orban stuff, and API EQ's are no problem. 
I remember that API's hated to be connected to A800's directly and used 600:600 iso transformers to make it work.
Mike
 
Hi Andy,

This may be super obvious but have you tried an analog loop with no gear inserted? - just output to input. Perhaps your input or output trims have been changed (or switched between the A/B options the 192 gives you by some devious guest engineer!).

I'm in the middle of major converter comparisons at the moment so have spent the last few days listening to analog loops in Pro Tools and calibrating and level matching Prisms, Hedd, Benchmark and Digi converters....

Re proper wiring for the 192s when using unbalanced gear I collected some info when I first got my HD rig back in the day, I'm sure you have this info already.  Pasted in below.

Best of luck,
Ruairi

-----------------------------------------

From a post on Digi support forums..
The proper way to drive an unbalanced load from a 192 I/O is to connect the 192's "+" pin to the load's "+" pin, connect the 192's "GND" pin to the load's "GND" pin, and leave the 192's "-" pin unconnected.

Dave Clementson
Digidesign Engineering

-----------------------------------------

From Digi support

http://www.digidesign.com/index.cfm?navid=54&langid=1&itemid=17371

Q - When connecting an unbalanced signal to the 192 I/O interface, and merging the negative and the ground, I'm hearing a lot of hum and buzz.

A - When connecting an unbalanced signal to the 192 I/O, you must first "lift" the negative (-) connection.

When outputting audio from the 192 I/O, the negative must also be "lifted" if sending signal to an unbalanced connection.


Another one
http://www.digidesign.com/index.cfm?navid=54&langid=1&itemid=21765

Q - What is the proper way to bring an unbalanced source into the Analog In of the 192 I/O?

A - It depends several factors. Typically, you would leave the ground side connected to the (-) input in a relatively clean setup. If you had a really noisy ground (an unbalanced output from a computer sound card, for example), you would bond ground to ground, (+) to (+) and leave the (-) input floating.

-----------------------------------------

Interesting thread on REP
http://recforums.prosoundweb.com/index.php/t/13516/0/
 
Hi,

 Guys, as ever, thanks for the replies. Much appreciated.


 yes, a direct balanced cable gives unity, as does most other gear which is balanced. I myself set up my 192 ins and outs, +18dfs on set A , and +15dfs on set B. I usually run my stuff at +15dfs btw. Lossy things are API 553 and 550A, and Helios.  Lifting Pin 3 on the input of Lunchbox will give a 6dB loss too with unbalanced eq.

 

    resigning myself to the fact it is a function of 192's. I am F@@king shocked that something as expensive as this should be effectively useless into unbalanced gear. I find that it is the same with the outboard reverbs I am using that are un-balanced too. I never noticed before, not too surprisingly. At the end of the day, I can compensate for the 1.3dB loss going out/in of the Apogee's( i cannot understand how THEY are not EXACTLY the same in and out. Shocking!) I could, at a pinch, insert a plug-in set to +6dB for inserts out/in of 192. That too me is NOT the point! A professional set-up should just be that. Professional, not +6dB here, -6dB there. I am shocked, frustrated and disappointed. I derive some comfort in finding out I haven't done anything stupid with my build. Scant comfort that is though.


  Hurumph! Another staggering oversight from Avid! Yey! Do they really think that ALL gear is balanced? MotherF@@kers. And Apogee . . . . 1.3dB discrepancy in/out. . . . . Tut Tut Tut!!!!!


     Inexcusable or what?



    ANdyP


 
I'm with u on the avid tip. Had a client who had bad wiring in his studio which lled slow tools to have a few I and o not balanced, imagine his horror when he ran a pair of 1073,s accross a pair of guitar mics and the sound was thin and gross. Once I fixed the wiring not an issue but for a brief moment he was swearing that his 1073's need repair. I squashed that by making a long loop between I and o and getting 6 db loss without any gear inserted.
 
I have not had many interfacing problems with the scores of 192's I've installed over the years.  I just did some patchbay wiring clean-up in a place with 100 foot machine room runs done with the un-jacketed Belden multipair and everything tested OK- unbalanced API's, old DS-201's (why they even had them they could not explain!), and a REV7 were unity.
Now going through the conversions, delays, and 200 feet of cable just to use a REV7 patch, well, that's just wrong to me!
Mike
PS: I guess that instead of designing a replacement for the 192 it will simply be re-packaged and re-branded "AVID" and be good to go for another 10 years?
 

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