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Saffire Pro 40 - unbalanced inputs

Discussion in 'Recording' started by Unregistered, Apr 17, 2011.

  1. Unregistered

    Unregistered Guest

    I bought a refurbished Focusrite Saffire Pro 40 (with full manufacturer's warranty), and I'm running into a problem (maybe with my brain). Here goes:

    When I insert an XLR cable into any of the 8 inputs, the signal is fine...and angels fly. However, when I insert an unbalanced 1/4" cable (either a mic cable or from a preamp), the signal is so low it's unusable.

    Now, if the instrument switch (which only exists on channels 1 & 2) is on, then the 1/4" unbalanced sound is at a regular level again. So, it seems that there is something wrong with the way it handles my standard unbalanced inputs (without the Inst switch).

    Am I missing something here? Am I insane? Any suggestions would be much appreciated.

    Thanks,
    Jim
     
  2. TheJackAttack

    TheJackAttack Distinguished Member

    Why are you using an unbalanced cable from a preamp? Why aren't you using a balanced TRS cable?
     
  3. Big K

    Big K Well-Known Member

    Well you missed to read the manual more thorroughly.. ;-)

    As far as I can remember there are no unbalanced inputs in this device other than the 2 combi sockets on the front, but only for HiZ jack plugs instruments input.
    With XLRs they switch to balanced. If you plug in an unbalanced jack plug ( or XLR ) in the balanced mic/line combi sockets you get less signal strength.
    Btw, what unbalanced preamp do you use?
     
  4. Boswell

    Boswell Moderator Distinguished Member

    It's fine to plug an unbalanced TS jack cable into the balanced TRS inputs of the Saffire Pro40. There will be no loss of signal at the Pro40 end, although depending on the source of the signal, you could lose 6dB by taking an unbalanced feed out of the balanced output of an external pre-amp, for example. If you have this condition, just use a balanced TRS jack cable, as Jack suggested. He knows how jacks behave.

    Now as for signal level, the line inputs of the Pro40 are high level and not microphone level. You would not expect a microphone to work correctly plugged into the line-level inputs, let alone using a TS jack cable.

    So the only issue is why a pre-amp output does not give a good level when connected to the Pro40's line-level inputs. This may have more to do with the use of a TS cable than with anything at the Pro40 end. It could be that whichever pre-amp you are using does not react well to having one half of its output shorted to ground by the TS cable, and as soon as you switch to a TRS cable, it will spring to life again.
     
  5. Unregistered

    Unregistered Guest

    The particular preamp is a Presonus Bluetube. It actually has an XLR out as well, but my issue is that the level of the Saffire 40 line in. I actually used to record with a Roland VS-840, and that only had 1/4" line inputs. Using the same preamp, I got a nice signal going out of the Blue Tube with a 1/4" cable. When I do this with the Saffire Pro 40 (on any of the 8 inputs), the signal doesn't come through properly. The signal only works at a good level on the front two jacks if the Inst button has been pressed.

    The loss of signal is in the Pro 40. That is my concern. It should be able to accept unbalance inputs without a loss of signal (according to the manual), but that doesn't seem to be the case. Is there a special (digital) way to specify unbalanced? I couldn't find anything like that.

    It's not so much that I want to use unbalanced; I just want to make sure I do not have a defective unit....and I actually may be short of XLR cables as of right now..though I'll probably buy some soon..I just wanted to test what I have.

    On a happier note, I was able to record 8 inputs at once at 96khz in Audition with no problems.
     
  6. Unregistered

    Unregistered Guest

    saffire 40 unbalanced input issue

    I guess I just find it weird that the unbalanced cable from the preamp keeps a solid level on my Roland unbalanced inputs but drops in the Saffire 40. So, plainly put, that would mean that the Saffire Pro does not accept unbalanced inputs in a usable fashion. It doesn't really matter to me...I'm just trying to get the right understanding of it. I'll most likely be using xlr only for inputs anyways...and I pretty much mic everything....and route through external preamps. I just thought it should handle a regular quarter inch unbalanced cable without cutting the signal.
     
  7. TheJackAttack

    TheJackAttack Distinguished Member

    You aren't listening. The OUT of the Presonus IS balanced. You are shorting HALF of that signal out by using the WRONG cable. You need a TRS cable period. The inputs on many of the Roland units are NOT balanced inputs so of course an unbalanced cable would work.

    Short version: two balanced connectors need to be connected with a balanced cable.
     
  8. Unregistered

    Unregistered Guest

    saffire 40 unbalanced input issue

    TheJackAttack,

    My preamp is using an unbalanced output (labeled right under the jack), and based upon my previous post, you can tell that it works with my unbalanced inputs on my Roland recorder. Therefore, the setup is as follows:

    mic -> preamp -> unbalanced output from preamp -> unbalanced cable -> roland ====== this works
    mic -> preamp -> unbalanced output from preamp -> unbalanced cable -> saffire pro 40 ====== this cuts the signal

    Does that make more sense?
     
  9. TheJackAttack

    TheJackAttack Distinguished Member

    Mea culpa. I forgot the Bluetube was one of their low end preamps. Ok here is the deal. The balanced XLR outputs of the Bluetube are at a nominal +4dB pro level. The unbalanced outputs (TS) of the Bluetube are at a nominal -10dB level. The consumer -10dB level matched the consumer inputs of the Roland VS 840 (page 10 of the Bluetube manual). Everything is copacetic. Everything matches up.

    The Saffire is looking for the professional +4dB balanced input of the +4dB XLR Presonus outputs. By using the -10dB unbalanced TS cable you are already lowering the output of the Bluetube. Then you are shorting some of that out by plugging it into a balanced connector which is also looking for a +4 balanced signal. You are mismatching output to input.

    What you need to do to optimize is to purchase a cable that is XLR-female on one end and TRS phone plug on the other. Conversely you can by an adapter to do the same to a normal mic cable. Then you have professional +4dB to +4dB. Easy sneezy.
     
  10. TheJackAttack

    TheJackAttack Distinguished Member

    Just to clarify, the Roland does NOT operate at professional +4dB signal levels. It is a consumer -10dB device. You actually would have overloaded the Rolands inputs by using the XLR +4 outputs of the Bluetube.
     
  11. Boswell

    Boswell Moderator Distinguished Member

    The Pro40 should be quite capable of dealing with unbalanced signals presenting via a TS jack cable on its line inputs. The spec shows that up to 36dB of gain is available on these inputs, so there should be no problem in getting acceptable recording levels from a -10dBV level input. It does, however, mean adjusting the Pro40's front panel gain control that corresponds to the line input in use.
     
  12. TheJackAttack

    TheJackAttack Distinguished Member

    Definitely agreed. I wouldn't worry about perceived audio level differences and turn up the gain knob of the Pro40.
     
  13. Unregistered

    Unregistered Guest

    I really appreciate all of your feedback. My BlueTube preamp actually sounds pretty good for a cheaper preamp and does have a balanced XLR output as well....but I'm just using it to present my issue.

    I have the same problem when I plug a microphone from XLR -> 1/4" directly into the unit...I could boost the Pro 40 preamp all the way, and I wouldn't get a usable signal....unless the instrument switch was on (which is only for 1 & 2)....with the inst switch, it acts appropriately.

    I just do not understand why the signal on the Pro 40 is being cut....unless the Pro 40 doesn't truly handle a -10dBV unbalanced input. I shouldn't have to add additional gain (via the Pro 40 preamps) to a signal that already has plenty of gain....that causes distortion because the signal has already been boosted by the preamp. Also, I find it peculiar that the INST switch allows the same exact signal to flow and sound correct. Could this possibly be a defect?

    What I really don't understand is the technical reason that the Roland and the Pro 40 would not both accept the signal just the same...if the Pro 40 supposedly handles a consumer-level unbalanced signal. I don't know if it's worth whining and dining about...but it certainly would be frustrating if I needed to do that for some reason and couldn't.

    Thanks again for all of your feedback...You're much more helpful than the folks at Focusrite....who never even replied to my support email.
     
  14. TheJackAttack

    TheJackAttack Distinguished Member

    The 1/4" input is not at a mic level period. It isn't designed for mic's and no one would/should plug a mic into the 1/4". Why would you be doing that in the first place? You're subverting the designed intent of the device without understanding the concepts of signal flow.

    There are roughly three basic level types of audio signal. Line level, mic level, and instrument level. A 1/4" input is designed to be either line level or instrument level. An XLR input could be mic level or line level depending on the designer but primarily mic level. Now you could go out and find me exceptions to this rough guide easily enough. Labels are labels and connectors are just connectors and wire doesn't care what signal is flowing on it nor what direction, but these are the primary uses. Each of these types of inputs are designed to amplify the signal to a usable level without overloading the input circuit. Therefore a line input boosts the signal very little or preferably not at all. A mic input boosts the signal an appropriate amount make a microphone usable-low gain. An instrument input boosts the signal a lot hence high gain as a label.

    You need to find and read the book by Yamaha called Sound Reinforcement Handbook, Gary Davis. It will help straighten out a lot of your questions and fuzziness on these things.
     
  15. TheJackAttack

    TheJackAttack Distinguished Member

    One of the others might nit pick this post but this is a highly simplified sketch.

    Also, let me explain a balanced signal. Audio signal is conducted electrically by voltage (dBV). In a balanced signal there is two wires with audio (let's call them red and blue) and one common ground wire (black). The colors I assigned are irrelevant other than as designators. The signal is sent equally down the red and blue wires except one wire is 180 degrees out of phase. At the other end the signal is again switched 180 degrees and combined with it's companion. So if the red wire has 10dBV and the blue wire has 10dBV on the far side you end up with 20dBV. The black wire is just the common ground.

    Now if you intentionally short out the connector with a TS cable you have only half of the signal in the first place so only 10dBV because the other 10dBV is shorted to ground. Now if you are presenting a balanced line input with half of a line level signal you should still be able to make it work fine on quality equipment. If you present a balanced line input with an unbalanced mic level signal it is no wonder you are having problems.

    Balanced (+,-,ground) ---> converts at the hardware to (+, +, ground)
    Unbalanced (+, ground) ----> remains at the hardware (+, ground)
     
  16. Boswell

    Boswell Moderator Distinguished Member

    The Roland that you used to use had TRS jacks as inputs. These would accept mic and line levels. Because of the need for a workable phantom power arrangement, using TRS jacks for microphone inputs is not a pro audio industry standard, so most gear has XLR inputs for microphones with appropriate gain and then TRS jacks with much lower gain for line level inputs. You cannot expect a microphone with a cable that ends in a TRS plug to work correctly with most pro-level gear. Use an XLR-XLR cable and your mic will work fine.

    This is a totally separate matter from the balanced vs. unbalanced connection between the two pieces of equipment.
     
  17. Unregistered

    Unregistered Guest

    Thanks to all for your comments. Hope that wasn't too frustrating; I really appreciate the detail. I finally understand.

    Jim
     

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