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The "Un" Balanced input on an API550b 500 Series EQ\'s
Old 24th June 2007
  #1
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stevetgn's Avatar
The "Un" Balanced input on an API550b

I am just about to buy a 10 slot API rack with some 550b's in there. I've only just realised though that API are still making them with an un-balanced input. Now I know that's how they were originally made because of the architecture of the console they where used in, but I would have thought that in this day and age API would have change the input to a balanced one, even if it was just electronically balanced like the 560 and not full tranny balanaced!

Now I'm probably being over paranoid here because virtually every top engineer in the last 30 years has used them at some point, but will there be any problems interfacing the 550b's with all the balanced gear already connected to my patchbay? Will I come across any problems?
Old 24th June 2007
  #2
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I have a rack of 550A's and B's and when mixing using a manley line mixer, I have to insert a compressor between the API's and the Digidesign 192's, or I get a hum. I haven't had any problems tracking. I have had a tech look at this, and he said he could build me a custom box, or to keep doing what I was doing, compressor before eq.
Old 24th June 2007
  #3
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Quote:
Originally Posted by bforest4 View Post
I have a rack of 550A's and B's and when mixing using a manley line mixer, I have to insert a compressor between the API's and the Digidesign 192's, or I get a hum. I haven't had any problems tracking. I have had a tech look at this, and he said he could build me a custom box, or to keep doing what I was doing, compressor before eq.
Yeah I've heard of that problem before but apparently its to do with the outputs on Digi gear. I don't think they use a floating balancing or something?
Old 25th June 2007
  #4
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Steamy Williams's Avatar
 

What I would suggest is that you double check which, if any, of the electronically balanced outputs that are connected to your patchbay are not 'pseudo floating', and then highlight the label above the points with a particular colour, say red. Then do the same for any unbalanced inputs, such as the 550A/B. Then make a note (mental or physical, which ever works for you) that if you patch red into into red there will be a 6dB level loss. I have a pair of 550A's, and this is what I plan to do if I ever add equipment with that aforementioned type of balanced output to my studio, although I don't have any as of yet. You can then make an informed decision which piece you may or may not want to connect directly to the inputs of your 550B's.

Steve, feel free to PM me a list of the other equipment in your studio, and I'll tell you at a glance the pieces I know that have electroncally balanced outputs that are not 'pseudo floating'.
Old 25th June 2007
  #5
Gear Maniac
 

The 5500 has balanced inputs
Old 25th June 2007
  #6
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Tim Farrant's Avatar
 

The bottom line is;

If the gear feeding the unbalanced input has a transformer on it's output, you will encounter no problems.

If the gear feeding the unbalanced input has a "transformer like" electronic output stage, you will encounter no problems.

If the gear feeding the unbalanced input has an unbalanced output, you will encounter no problems (except if the wiring is wrong).

If the gear feeding the unbalanced input has an electronic output stage that does not act like a transformer, you may encounter problems.

A "transformer like" output stage is one that is designed to act like a transformer (strangely enough) and it will shut down the "leg" that gets short circuited by the unbalanced input and raise the level of the other leg by 6dB.

The 192 interface does not have "transformer like" outputs.



Tim.
Old 25th June 2007
  #7
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stevetgn's Avatar
Quote:
Originally Posted by Steamy Williams View Post
What I would suggest is that you double check which, if any, of the electronically balanced outputs that are connected to your patchbay are not 'pseudo floating', and then highlight the label above the points with a particular colour, say red. Then do the same for any unbalanced inputs, such as the 550A/B. Then make a note (mental or physical, which ever works for you) that if you patch red into into red there will be a 6dB level loss. I have a pair of 550A's, and this is what I plan to do if I ever add equipment with that aforementioned type of balanced output to my studio, although I don't have any as of yet. You can then make an informed decision which piece you may or may not want to connect directly to the inputs of your 550B's.

Steve, feel free to PM me a list of the other equipment in your studio, and I'll tell you at a glance the pieces I know that have electroncally balanced outputs that are not 'pseudo floating'.
Cheers dude! I'll post the list here as it might help others too:

MASSIVE PASSIVE
SMART C2
TFPRO P38
2 X FOCUSRITE ISA220
SSL X-RACK DYNAMIC MODULES (LINE INPUT MODULES TOO BUT PROBABLY NOT RELAVENT)
2 X RME FIREFACE 800 (16 X D/A outputs may get patched directly into a 550b from time to time)
SOUNDCRAFT GHOST (ONLY THE GROUP OUTS WOULD POSSIBLY BE USED INTO A 550B)

Thats what I currently have that would or may be connect to the 550b input. Here's a list of "to be added very soon"

API512C ( TO BE PURCHASED WITH THE 550B)
BUZZ AUDIO POTION (MAYBE AN ESSENCE TOO)
PURPLE BIZ

Cheers Steamy!
Old 25th June 2007
  #8
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stevetgn's Avatar
Quote:
Originally Posted by Tim Farrant View Post
The bottom line is;

If the gear feeding the unbalanced input has a transformer on it's output, you will encounter no problems.

If the gear feeding the unbalanced input has a "transformer like" electronic output stage, you will encounter no problems.

If the gear feeding the unbalanced input has an unbalanced output, you will encounter no problems (except if the wiring is wrong).

If the gear feeding the unbalanced input has an electronic output stage that does not act like a transformer, you may encounter problems.

A "transformer like" output stage is one that is designed to act like a transformer (strangely enough) and it will shut down the "leg" that gets short circuited by the unbalanced input and raise the level of the other leg by 6dB.

The 192 interface does not have "transformer like" outputs.



Tim.
Cheers Tim
Old 25th June 2007
  #9
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I'm still kinda concerned about introducing extra noise though. The signal will effectively be travelling down about 40' of unbalanced cable (there and back from the patchbay) is this not why we balance things in the first place for CMR?
Old 25th June 2007
  #10
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Steamy Williams's Avatar
 

Quote:
Originally Posted by Tim Farrant View Post
A "transformer like" output stage is one that is designed to act like a transformer (strangely enough) and it will shut down the "leg" that gets short circuited by the unbalanced input and raise the level of the other leg by 6dB.
This is the 'pseduo floating' type of electronically balanced output that I was referring to.

I would also add to Tim's list:

If the gear feeding the unbalanced input has an 'impedance balanced' output stage, you will encounter no problems.

If the gear feeding the unbalanced input has a grounds compensated output stage, you will encounter no problems. This type of output allows ground voltages to be cancelled out even if the receiving equipment has an unbalanced input - as long as balanced cable is used - therefore making ground-loops innocuous.

So Steve, here is what I know about the outputs from the equipment on your list

MASSIVE PASSIVE - Transformer output plus additional unbalanced output
SMART C2 - Electronic output stage that does NOT act like a transformer
TFPRO P38 - "Transformer like" electronic output stage
2 X FOCUSRITE ISA220 - Electronic output stage, not sure which type
SSL X-RACK DYNAMIC MODULES (LINE INPUT MODULES TOO BUT PROBABLY NOT RELAVENT) - Electronic output stage, not sure which type
2 X RME FIREFACE 800 (16 X D/A outputs may get patched directly into a 550b from time to time) - "Transformer like" electronic output stage
SOUNDCRAFT GHOST (ONLY THE GROUP OUTS WOULD POSSIBLY BE USED INTO A 550B) - I used to have one of these. The group, aux, studio 'A', mix and mix 'B' outputs are all grounds compensated. There is more info on this type of output earlier in this post. All inserts plus the direct, studio 'B', control room and alt outputs are all unbalanced.

API512C ( TO BE PURCHASED WITH THE 550B) - Transformer output
BUZZ AUDIO POTION (MAYBE AN ESSENCE TOO) - Transformer ouptut (not sure what type of output the side chain on either of these has)
PURPLE BIZ - Transformer output

The Alan Smart C2 is the only item on your list that I am sure will exhibit a 6dB drop in signal level when patching directly into the 550B's. It's possible that either the Focusrite or SSL pieces might also do the same.

Quote:
Originally Posted by stevetgn View Post
I'm still kinda concerned about introducing extra noise though. The signal will effectively be travelling down about 40' of unbalanced cable (there and back from the patchbay) is this not why we balance things in the first place for CMR?
The grounds-compensated outputs on the Ghost will offer some advantages with the 550B in this respect, but there will be no CMRR as such.
Old 25th June 2007
  #11
Dan
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informative posts. Thanks guys!
Old 26th June 2007
  #12
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666666's Avatar
Quote:
Originally Posted by bforest4 View Post
I have a rack of 550A's and B's and when mixing using a manley line mixer, I have to insert a compressor between the API's and the Digidesign 192's, or I get a hum.
FWIW, I've connected 550Bs after a Digi-001 and into a Manley mixer (while mixing) and no hum problems. Perhaps it IS the 192 that is causing the issue.
Old 26th June 2007
  #13
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Quote:
Originally Posted by Steamy Williams View Post
This is the 'pseduo floating' type of electronically balanced output that I was referring to.

I would also add to Tim's list:

If the gear feeding the unbalanced input has an 'impedance balanced' output stage, you will encounter no problems.

If the gear feeding the unbalanced input has a grounds compensated output stage, you will encounter no problems. This type of output allows ground voltages to be cancelled out even if the receiving equipment has an unbalanced input - as long as balanced cable is used - therefore making ground-loops innocuous.

So Steve, here is what I know about the outputs from the equipment on your list

MASSIVE PASSIVE - Transformer output plus additional unbalanced output
SMART C2 - Electronic output stage that does NOT act like a transformer
TFPRO P38 - "Transformer like" electronic output stage
2 X FOCUSRITE ISA220 - Electronic output stage, not sure which type
SSL X-RACK DYNAMIC MODULES (LINE INPUT MODULES TOO BUT PROBABLY NOT RELAVENT) - Electronic output stage, not sure which type
2 X RME FIREFACE 800 (16 X D/A outputs may get patched directly into a 550b from time to time) - "Transformer like" electronic output stage
SOUNDCRAFT GHOST (ONLY THE GROUP OUTS WOULD POSSIBLY BE USED INTO A 550B) - I used to have one of these. The group, aux, studio 'A', mix and mix 'B' outputs are all grounds compensated. There is more info on this type of output earlier in this post. All inserts plus the direct, studio 'B', control room and alt outputs are all unbalanced.

API512C ( TO BE PURCHASED WITH THE 550B) - Transformer output
BUZZ AUDIO POTION (MAYBE AN ESSENCE TOO) - Transformer ouptut (not sure what type of output the side chain on either of these has)
PURPLE BIZ - Transformer output

The Alan Smart C2 is the only item on your list that I am sure will exhibit a 6dB drop in signal level when patching directly into the 550B's. It's possible that either the Focusrite or SSL pieces might also do the same.



The grounds-compensated outputs on the Ghost will offer some advantages with the 550B in this respect, but there will be no CMRR as such.
Great info Steamy thank you!

I'm not liking the idea of this so far, which is a shame because I really want the 550A & 550B tone. I would quite often becoming out of the SSL X-Rack modules into the EQ so I need to find out what kind of balanced output SSL use.

I'm stating to wonder if I should look at a pair of Avedis E27 instead though?
Transformer balanced input AND output that will connect to anything!

COME ON API SORT OUT THE BALANCING ON THE 500 SERIES EQs
Old 26th June 2007
  #14
Quote:
Originally Posted by stevetgn View Post

COME ON API SORT OUT THE BALANCING ON THE 500 SERIES EQs
The fault is not really the API.

Its the Digi 192 interface.

Most components inside a console run unbalanced anyway.
Old 26th June 2007
  #15
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.Originally Posted by stevetgn
I'm still kinda concerned about introducing extra noise though. The signal will effectively be travelling down about 40' of unbalanced cable (there and back from the patchbay) is this not why we balance things in the first place for CMR?

Wire it balanced regardless, shield connected on one end only.
Old 29th June 2007
  #16
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Steamy Williams's Avatar
 

One reason some Digi 192 users may have had issues is because of the fact that pin 3 on the inputs of 500 Series racks/lunchboxes is usually routed to ground on the edge connector of API 550A/B's. This causes problems for electronically balanced outputs that are not "transformer-like", such as those on the 192. It is my understanding that this is because the inverting op-amp may then spend most of its time in current-limiting, injecting unpleasant distortion into the grounding system of the outputting device, and possibly suffering unreliability. However, I could be completely wrong about this. Anyway, so in this scenario pin 3 ought to be disconnected at the output of the 192. However, I supsect many 550A/B owners, specifically those with 192's, are not aware of this. Conversely, pin 3 is supposed to be tied to ground when a transformer or "transformer-like" ouput is connected to an unbalanced input, so I don't think you need to worry too much about doing anything to the wiring when connecting those type of outputs to the 550A/B, as you can just treat the input as balanced.
Old 30th June 2007
  #17
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Does anyone know if using an Apogee DA16X instead of a Digi 192 would solve the hum problem that the Digi 192 causes when going directly out of it's D/A into an API 550?
Old 1st July 2007
  #18
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Radio Design Labs STA-2

If you are having problems with your 550x series. I have had problems due to digital gear, then use these. They fix the problem.
Old 2nd July 2007
  #19
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Tim Farrant's Avatar
 

To avoid issues with the 192 output, you will need to make special leads leaving pin 3 disconnected. But, you will loose 6dB.

Tim
Old 2nd July 2007
  #20
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Hi
If it hums, get the system wired up properly.
See all the zillions of threads about hum loops and star earthing either here or Sound on Sound magazine and many others. There is no excuse for humming interconnects.
Interesting comment about 192 not being tolerant of one leg grounded, I've just never looked at it and the last couple I wired in just worked (into balanced inputs, as they should be).
Matt S
Old 15th July 2007
  #21
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Just got my 10 slot API rack with a 512c and some 560 & 550b.
No problems what so ever with the 550b input and [email protected]#k does it sound good! Can't believe I've taken so long to get one these. Its a superb sounding EQ. I want another rack full of them.. NOW!

On the cable going from my patchbay to the 550b I wired pins 1 & 3 together on the XLR seems to work fine and I'm not noticing a 6dB drop or any hum
Old 16th July 2007
  #22
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Steamy Williams's Avatar
 

Quote:
Originally Posted by stevetgn View Post
On the cable going from my patchbay to the 550b I wired pins 1 & 3 together on the XLR seems to work fine and I'm not noticing a 6dB drop or any hum
I don't think you actually needed to tie the pins in the XLR, as pin 3 goes to ground on the edge connector in the 550B anyway. I presume you tied the pins at the 550B end and not at the patchbay end? AFAIK, normally with unbalanced inputs it doesn't matter too much where the cold is tied to ground. However, if you're still using the Soundcraft Ghost, then you may not experience the full benefits that its ground compensated outputs provide even when connected to unbalanced inputs (see my post on the subject earlier in this thread for more info) unless the cold is tied to ground at the receiving device, and not before.
Old 16th July 2007
  #23
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Quote:
Originally Posted by Steamy Williams View Post
I don't think you actually needed to tie the pins in the XLR, as pin 3 goes to ground on the edge connector in the 550B anyway. I presume you tied the pins at the 550B end and not at the patchbay end? AFAIK, normally with unbalanced inputs it doesn't matter too much where the cold is tied to ground. However, if you're still using the Soundcraft Ghost, then you may not experience the full benefits that its ground compensated outputs provide even when connected to unbalanced inputs (see my post on the subject earlier in this thread for more info) unless the cold is tied to ground at the receiving device, and not before.
Cheers again Steamy!
Old 4th June 2014
  #24
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just got pair of api 550a original… i have apogee symphony IO, anyone know if I will encounter the issue that some reported with the 192s?
Old 5th June 2014
  #25
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Hi
Call Apogee for the definitive answer on running into an unbalanced input (assuming the manual does not say (tut tut)).
The ground compensated output used on some of Soundcraft's gear WILL act like a balanced interconnect if plugged into an unbalanced input when the cold goes to ground at the unbalanced INPUT connection.
The principle uses subtraction at the SENDING end (the output driver) rather than at the receiving end of a more 'traditional' balanced input.
It is for this reason that all studio wiring should be made using balanced cabling and connectors right up until you get to a device with an unbalanced connection, and you should generally 'unbalance' your cabling at this point.
Matt S
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