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SSL balancing (balancing in general too)

Discussion in 'Electronic Repair Modifications DIY' started by toothpastefordinner, Feb 24, 2004.

  1. So I have the SSL boards, parts, and I'm going to start putting it together today, but I have to ask: What's the best way to go about unbalancing the SSL inputs/outputs?

    On some devices I have, you must float the cold pin, and on others, connect it to ground. This has been mostly trial-and-error to me so far, except in cases where it's clearly marked "FLOAT UNUSED OUTPUT PINS" or similar.

    In a nutshell: Should I ground, or float, the SSL "cold" inputs and outputs? I know that I could probably dodge this bullet by using transformers on the inputs and outputs, but I don't wanna buy expensive parts just cause I don't know what to do! smile.gif

    thanks!

    drew
    http://www.toothpastefordinner.com
     
  2. ssltech

    ssltech Guest

    On the SSL comp output look at the cold leg generation. Float it. There's no cross-coupled feedback to increase the gain of the other leg and turn that one down, so leave it unterminated.

    In the input for that circuit I recommend taking the cold leg to ground, but mu preference is to lift the ground at the local end and take it to ground at the far end for noise rejection.

    Keith
     
  3. thanks keith!

    In looking at the schematic it almost seemed like I could leave off the cold inputs and outputs... but I wanted to get the stamp of approval from someone who actually knew!

    So would you suggest actually tying the cold inputs to ground (well, ok, you just did), or are those input caps redundant given that the non-inverting input of the input opamp is tied to ground w/ a 33p cap and a 22k resistor? Or does the 22k-in-series-with-input-caps setup on the cold input need to be tied to ground to bias the opamp correctly? (Please pardon me if I am using the wrong terms here, I am not an EE! smile.gif )


    drew
    http://www.toothpastefordinner.com
     
  4. ssltech

    ssltech Guest

    well, they refer it to ground, but they're a pretty high-impedance referral.

    Tying it to ground at the far end, any common-mode noise (i.e. noise which also comes up the groud line) is fed to the opposite-pole input, where it helps to cancel out the noise on the 'hot' signal line.

    -Does that help explain? -Also it works really well with "star-grounding at the patchbay" philosophies.

    Keith
     
  5. Got it! Thanks! smile.gif

    drew
    http://www.toothpastefordinner.com
     
  6. oneno

    oneno Active Member

    Hi folks. The back of my distressor says "Float unused output pins!" next to the output jacks (it has a balanced xlr output which i use, and an unbalanced 1/4" output which i don't use), so what am i supposed to do? Plug something into the unbalanced 1/4" output that i never use?

    Thanks
     
  7. Boswell

    Boswell Moderator Distinguished Member

    Yes, that's about it. You could find suitably distressed plugs and stick them into the unused output connectors. However, make sure there is nothing connected to the plug terminals.
     
  8. oneno

    oneno Active Member

    What do you mean by "distressed" plugs? And by "nothing connected to the plug terminals" you mean no cable running out of the plug?

    Thanks for the help, Boswell!
     
  9. Boswell

    Boswell Moderator Distinguished Member

    What it's trying to say in a round-about way is that you should only use one of the types of output at a time. So if you taking a balanced XLR output, don't try taking an unbalanced jack output from the same channel at the same time.
     
  10. MrEase

    MrEase Active Member

    I'm smiling at Boswell's humour here! Maybe because I'm English as well....

    To clarify further, what the "Float unused outputs" really means is, as Boswell has clarified, that you should only use one output socket at a time. That means that, in your situation, the unbalanced output should not be used while using the balanced output. Further to that, it also means that if you are using the balanced output for an unbalanced connection, you should not ground the unused (cold) output but leave it unconnected.

    The reason for this clarification on the box is that balanced outputs can have several different types of circuit driving them. Some of these circuits can be used with the "cold" pin grounded which will increase the unbalanced output but there are various other options. When using any balanced output to drive an unbalanced load, it is useful to know how it can or can't be connected due to this variation in driving circuits - hence the comment on your distressor box.

    EDIT: Maybe the previous owner of KROK's Calrec's (see the other thread) took a "float" comment too literally! :<)
     
  11. oneno

    oneno Active Member

    Thanks!

    Thanks, Boswell! It should just say that on the device. Not all of us have that level of knowledge when it comes to electrical connections and such. I wish I did, but I have to decide whether to dedicate time improving my musical/compositional skills or my tech skills. These days, dedicating time to the intricacies of using DAWs and plugins is enough to limit any time potentially dedicated to other tech areas. I guess when you have the income to be able to hire a personal engineer then that problem disappears, in the meantime forums save the day time and again. Thanks again!!
     

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