Sc2 v1.07 rear output knob V1

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Home Forums Ask Ted Sc2 v1.07 rear output knob V1

Viewing 15 posts - 1 through 15 (of 31 total)
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  • #15293
    Avatarsupafuzz
    Participant

      I’m sure you’ve been asked this but is there a fix for the extreme imbalance between left and right signal.

      There is easily a 9db difference.

      How does this get repaired????

      This is way too extreme.

      I may like to sell this piece eventually and want it working right.

      Thanks

      Harley

      http://www.facebook.com/Super70Studio” class=”bbcode_url”>http://www.facebook.com/Super70Studio

      #15862
      Ted FletcherTed Fletcher
      Keymaster

        As you can imagine, I take a dim view of your comment about wanting to sell it!! 😯

        As for a 9dB difference, the usual reason for L/R level difference is the linearity of the input and output potentiometers…. they are never perfect and when new they are often as much as 1dB adrift at certain parts of the scale. However, a 9dB difference is virtually impossible and I would look elsewhere for the reason. The most likely cause is an incorrect connection on the input…. For balanced connections 2 is +ve, 3 is -ve and 1 is ground. All must be connected. For unbalanced connection 2 is hot and both 3 and 1 must be grounded…… if pin 3 is left hanging then the level will be at least 6dB low.

        So check both input and output connections!

        On the earlier V1.05 versions, we sometimes had problems with the output stage going ‘one legged’, but the later V1.07 versions did not suffer from this.

        If there is a real electronic fault, I’m happy to let you have the circuit information for that model, or if you would like me to fix it, the deal is that I charge US$50 plus the cost of returning it to you. (I’m assuming you are in the US.)

        BTW, when sending equipment to me for fixing, be sure to give it a low value for customs….. the risk of getting it impounded is much higher than the risk of losing it; a $25 valuation ensures it gets here without problems! :(

        #15861
        Avatarsupafuzz
        Participant

          I said “MAY WANT TO SELL”….just leaving my options open..lol.

          Hi Ted I took it out of the rack and will test it more thoroughly and get back to you with the results.

          I’m going to see my tech guy on wed and he can take care of repairs…Philadelphia is a little closer to NYC than England.

          So I could use the circuit info.

          thanks!

          Harley

          #15860
          Ted FletcherTed Fletcher
          Keymaster

            Hi Harley,

            I was just winding you up!! :D

            I have emailed the circuits to your ‘studio’ address.

            #15859
            Avatarsupafuzz
            Participant

              Yes I realized and that’s why I wound you right back!!!

              thanks for the info got your e-mail

              Going to check the outputs…could be the problem there.

              When running a test tone in and just looking at the meter it seems it’s compressing exactly the same left and right

              I’ll have to listen to the output now both xlr and 1/4″

              H

              #15858
              Avatarsupafuzz
              Participant

                Ok testing done and It seems to be the wiring on the xlr output. The volume is lower on one side and then intermittently comes back. So we will have that checked out and all should be well.

                #15857
                Ted FletcherTed Fletcher
                Keymaster

                  That’s good! I do get numbers of engineers with those JM compressors worried about level differences and it’s often a wiring or connector problem. I’m glad yours is OK again. That’s quite a rare piece you have; the very early ones had no output gain control, then I added a control on the back as a temporary measure while we redesigned the fronts to take the new layout. There were probably only about 10 units made like yours. :)

                  #15856
                  Avatarsupafuzz
                  Participant

                    Rare?? I thought the v1.07 with the rear output gain knob was common. If so that’s very good news. Thanks

                    #15855
                    Avatarsupafuzz
                    Participant

                      Hey Ted

                      I know Jim Kay has been in touch but he said you sent him a flow chart for the sc2 and not the full schematic and it’s still not fixed

                      one side is compressing more than the other and it’s not the input knob and the chips aren’t over heating

                      Really need your help on this.

                      #15854
                      Ted FletcherTed Fletcher
                      Keymaster

                        Ah! So the problem is over-compression on one side….. That is always caused by one of the opto resistors being more sensitive than the other, it can be an ‘ageing ‘ problem.

                        Under the lightproof box there are two light cells (type ORP12) and a pair of LEDs. Physically moving the light cells will give different compression results.

                        Pls email me separately at ted@tfpro.com and I will be sure that you have the schematic.

                        #15851
                        Avatarsupafuzz
                        Participant

                          Hi Ted it’s many months later and still no joy. My tech guy hasn’t been able to figure out why one side is compressing more than the other.

                          So in a last ditch attempt to get this back in service I think i want to send it off to you.

                          Unless you think there’s some one in the USA who can fix it…

                          thanks

                          harley

                          #15852
                          Ted FletcherTed Fletcher
                          Keymaster

                            OK, send it to me at the Sound House, Hunsdon Road, Torquay TQ1 1QB, UK, and I will fix it…. The fault is bound to be a faulty compression cell and I do have stocks of the original cells. :)

                            #15853
                            Avatarsupafuzz
                            Participant

                              Many thanks in advance!!

                              #15863
                              Avatarsupafuzz
                              Participant

                                Hi Ted

                                I’m getting closer to sending this unit back to you…it’s still 6 db lower on the left side. Could there be any other reason we’ve over looked??

                                I am going to ask some questions of my new tech to see if there’s anything else he can check out

                                Are you planning a trip to the states any time soon?

                                thanks

                                Harley

                                #15864
                                Ted FletcherTed Fletcher
                                Keymaster

                                  I don’t have any trips planned at the moment….

                                  Looking back over this thread, if the compressor is working at all on both channels then the problem is certain to be either one of the gain cells is faulty, or, more likely, that it has taken a knock and the relationship between the LEDs and the gain cells has been changed…. one of the gain cells has moved away from the LEDs.

                                  It’s worth removing the plastic covers (on the gain cells); one plastic cover is over a single cell and LED, that one controls the compression meter.

                                  The other cover is over 2 gain cells which are set close to the pair of orange LEDs (you will see when you get the cover off) The gain cells should be close to the LEDs , the closeness controls the amount of compression so compression imbalance can be corrected by moving the cells.

                                  If you are sure you have a faulty cell, I can supply replacement gain cells as they are difficult to get. The price is $5.50 each plus $5 for shipping. (I need to confirm that shipping cost)

                                  It’s worth giving the above a try as sending it back to the UK will take time and effort and shipping is expensive.

                                  If you do decide to send it to me be sure to mark it clearly as being sent for repair otherwise we do get problems with customs. :(

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