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Soundcraft Live - difference between channels

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  • Soundcraft Live - difference between channels

    Hi,

    I have a Soundcraft Live 8-channel mixer for repair.

    The question I have is about the differences in gain between the channels.

    While testing the unit I noticed that when I put in a constant test signal and set all the controls the same, the gain was more or less the same. I am not doing this scientifically but by ear (play a rom play song) and plug it into each channel.

    But when I start playing with parametric tone controls I can boost a lot more on one channel than on the other. Some minor differences are to be expected due to component tolerances and the age of the unit. But this is really noticeable.

    I am considering fixing this, but I am unsure of what is a good channel to use for reference. Of the 8 channels, 2 exhibit this issue that they can boost a lot more using the EQ than other channels. So are these (2) bad or are all the other channels bad? Is there any way to know a plausible

    Not sure if this is the exacts correct one, but the mixer seems similar enough:
    http://juggernautmusic.com/wp-conten...o_Schems-1.pdf

    The opamps are mainly TL072's for the channels and NE5532's in the master sections.
    I have not measured the electrolitics but non of them leak (physically) or are bulged in any way.

  • #2
    What is the customer's complaint? Is it the EQ or something else?
    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

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    • #3
      Originally posted by eschertron View Post
      What is the customer's complaint? Is it the EQ or something else?
      I buy defect gear and repair it as a hobby the try to sell it of again with a small profit. I just try to get the unit up to a point that I would consider it good.

      Comment


      • #4
        Aren't there insert jacks on each channel up next to the mic and line inputs? Make sure to clean the inserts.
        Education is what you're left with after you have forgotten what you have learned.

        Comment


        • #5
          Originally posted by Enzo View Post
          Aren't there insert jacks on each channel up next to the mic and line inputs? Make sure to clean the inserts.
          Yes, there are inserts on the channels (and the master outputs as well) and I know that is a common issue with old gear and I have not cleaned them yet.
          Although I would be very surprised if that was the cause, especially because the difference in gain is in the EQ specifically.

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          • #6
            it is something you need to do anyway, so why not? Sometimes a dirty normal; on an inset can affect the signl through put, which could affect EQ. A few minutes with cleaner and we will know.

            I have no reason to think any parts have aged out, semiconductors like ICs don't "wear out".

            You can use the inserts another way. You can run your test signal into a channel in, and use the insert send as a measure. Are the channels with differences different on those sends, or are they the same at that point? Likewise, you can inject a signal at the insert to bypass the channel input stages. does the channel differences still exist at that point?
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              What is the actual model? Spirit Live? Live 8 ? Folio?

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              • #8
                A high resistance insert contact, or any contact really can show up as a filter. It's very unusual for res, caps and IC's to wander far off spec sufficiently to produce an audible problem.

                You don't have to rely on your ear. If you have a PC with a sound card you can download, for free, an audio white noise generator and a real time spectrum analyzer. This will allow you to see precisely where the eq differences are and hopefully narrow it down to one area, pretty much in real time.
                Last edited by nickb; 04-25-2017, 05:53 AM.
                Experience is something you get, just after you really needed it.

                Comment


                • #9
                  Originally posted by g1 View Post
                  What is the actual model? Spirit Live? Live 8 ? Folio?
                  Its says Spirit Live but I think it's the old model - if that is possible. I saw pictures on the web of a Spirit Live that were too new.

                  Originally posted by nickb View Post
                  A high resistance insert contact, or nay contact really can show up as a low pass filter. It's very unusual for res, caps and IC's to wander far off spec sufficiently to produce an audible problem.
                  Most noticeable is a profound difference in gain.
                  I would think that caps and resistors might change value over time due to thermal influences...?
                  So if these components don't wear, something is broken that causes the difference in gain?

                  Originally posted by nickb View Post
                  You don't have to rely on your ear. If you have a PC with a sound card you can download, for free, an audio white noise generator and a real time spectrum analyzer. This will allow you to see precisely where the eq differences are and hopefully narrow it down to one area, pretty much in real time.
                  Interesting, do you have a name or a link for that software?

                  I have a old 20MHz analog scope and a cheap (chinese) sound generator. I use that to check the functionality on the bench. But to detect crackling and determine clearness of the sound I always put real music through it al play it back over the speakers and test all the controls and buses etc.

                  I will start with cleaning the inserts.

                  Comment


                  • #10
                    Originally posted by obiwanjacobi View Post
                    Interesting, do you have a name or a link for that software?
                    Try this White noise generator and this Spectrum Analyzer
                    Experience is something you get, just after you really needed it.

                    Comment


                    • #11
                      Cleaned the inserts and that fixed it. I would not have figured that.

                      Thanx everyone.


                      Currently I am waiting on some parts to repair one of the master sections of this unit. After that it'll be ready to be sold.

                      Also started with another Soundcraft Live spirit; a 16 channel one - same vintage (~92) as the previous one. I'm stripping it completely and cleaning off years of grime of all the knobs and the case.

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