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Help with Yorkville YSM1p studio monitors

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  • Help with Yorkville YSM1p studio monitors

    I've got a pair of Yorkville YSM1p studio monitors and they both started to hiss after a couple of second/minutes. I tried ground lifts but nothing changes.
    the hiss will progressively fade in after around a minute and it will get really loud. This happens when no audio cables are plugged in and the volume knob doesn't affect the hiss at all.
    Here's the schematics:

    I would really appreciate it if someone could help me out! Thanks!!

  • #2
    Nobody has a clue? I can make a video if it helps understanding what it does. Thank you!!


    • #3
      Itīs weird and unlikely that both develop the same problem, at the same time, so that strongly hints at an *external* cause, some interference may be getting into both , maybe through mains cables, maybe straight through the air.

      Try them somewhere else, preferrably outside that house.

      What mains supply are they getting?

      If too high or too low the supply might be working improperly.

      WHERE-ARE-YOU ??????????????????????????????

      Iīm thinking about suggesting Forum Moderators to make that answer an obbligation for any member.

      That monitor has stupid high voltages for a poor LM3886, crazy +/- 45V ; datashet suggests +/- 35V .

      IF you are in an actually 240/245V mains Country but monitor is set to 220V, he extra voltage may be pushing those poor chipamps into "Zenering", a fancy name for breakdown.

      On the contrary, on a 220V Country, setting selector to 245V might solve the problem.

      Of course, we donīt know.
      Juan Manuel Fahey


      • #4
        Thanks for helping! I'm in America so it's 120V and I tried another power outlet from another room and the same thing happens. 1 Speaker started doing it 2 weeks before the other and now they are both doing it so I'm guessing there's a problem with that outlet that broke something in both speakers over time but what do I know :S Maybe I should test the voltage and see if the ground is actually working there? Where is the "Selector" located on the speakers? Thanks again!!


        • #5
          Ok, now we may focus a little better.
          As of a "selector" , 2 transformer taps are shown on the schematic, 230 and 245V, no mention on how to switch from one to the other, you might have one soldered and the other taped out, or jumpers, or different spade terminals on the PCB, all equivalent.

          In any case, the 120V version (now we know ) does not seem to have taps, so my suggestion does not apply.

          Itīs also good to know that they didnīt start atthe same time.

          Those details seem irrelevant but point different ways, so they are useful.

          You may try to do some audio tracing to detect at least in what section is the problem, an important first step.

          Use its own speakers and power amp as an audio probe , better than nothing, although it forces you to work backwards, from output to input.
          Solder a short piece of wire to ground (say 30 or 40 cm), bare and tin the other end and use it to selectivly ground certain sensitive points, the check which does, which does not, kill the annoying hiss:

          1) turn amp on, test wire already soldered to ground, wait until annoying hiss starts.

          2) Definition: a node is electrically a specific connection between some elements, where they are joined , there is continuity and voltage is the same on all points involved.
          Example: the right leg of R47, the top leg of R48, the left leg of C27 are all the same node, called R47/R48/C27 .
          If we are in a hurry, mentioning just 2 parts identifies a node even if it has another 50 parts also connected to it, just follow the continuous line.

          Now we start trying to find which grounding kills noise, which does not.

          3) ground the node R47/R48 . Does the hiss disappear? Y/N

          4) now C31/R21

          5) now C33/R13

          6) now R22/R113 . This one might pop o click loud. No big deal, Iīm trying to find the stage were hiss *starts* .

          7) now R112/R28

          8) now R10/R11 and we are already before the volume control, which you say does not affect hiss.

          We "should" have found one stage which kills noise and an earlier which has no or minimal effect.

          Ok, now itīs your turn.

          NOTE: IF not even R47/R48 kills it, then we have power amp trouble-
          Juan Manuel Fahey


          • #6
            Hey, sorry for the delay .... Thank you so much for your help it's really appreciated.
            I finally found the problem .. it was Capacitor C5 ... I just removed it and put a wire on both speakers and it works like a charm now
            Thx again for your help!!


            • #7
              I have 2 Yorkville YSM1p monitors with the exact same problem described above. I also noticed a slowly rising DC voltage on U2 pin 8 up to about 6v when the hiss would start.

              What I found is that the gain control circuit is not as shown on the schematic. Notice there is no DC reference for U1.

              The solution is to add a 22K resistor to ground. DC problem fixed and no hiss.

              Attached Files