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RCF 325A - LF Amp Circuit Issue

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  • RCF 325A - LF Amp Circuit Issue


    I've got an ART325A, It had a blown LF Driver when i got it.

    I'm getting signal out of the HF, but the LF has just a low buzz that is consistent, volume and input don't have no effect.

    Board looks clean, any ideas?

    • I have replaced the LF 15" Driver and there is an audible low buzz, not altered by volume
    • Main Board PST355D
    • Filter Board PST360C


  • #2
    That LF buzz could be DC. You should not hook up a speaker until you verify that there is no DC on the amp's output. You may end up blowing another LF driver. When components go bad, there aren't visible signs most of the time. Visual inspection should always be one of the first steps, but because everything "looks clean" doesn't mean much.

    Got a schematic you can upload?
    "Yeah, well, you know, that's just, like, your opinion, man."


    • #3
      The Board numbers are the same for ART310-A & ART325-A
      Attached Files


      • #4
        I'd first check the LF amp output and see if the hum is AC or DC. Again, leave the speaker disconnected until you determine there is no DC.
        "Yeah, well, you know, that's just, like, your opinion, man."


        • #5
          Ok, just tested: i am now getting nothing on my multimeter in AC or DC out of LF & HF.


          • #6
            Then you will have to scope it to check whether hum is still there or not.
            Momentarily connect the HF horn, or any 8 ohm old speaker you have nearby to HF out: what do you hear if you inject some music? All treble of coures but does it seem to work normally?

            Now connect woofer.
            Do you hear a strong pop/thump or strong Hum?
            Does cone move forward or backward and stay there?

            If you inject Music, do you hear it normally through woofer?
            Juan Manuel Fahey


            • #7
              Ok, so getting the hum through both HF & LF, no music coming through either HF or LF


              • #8
                We go on step by step.

                With woofer and tweeter connected as last test:
                IF you hear hum, then you must be able to measure it.

                Please turn amp on briefly, set meter scale to 200VDC, measure across Tweeter terminals and across woofer terminals , post values .
                If zero say so, no "no measurement".

                Repeat with meter set to 20V DC.

                Now set meter to 20V AC , repeat.

                Now to 2VAC: repeat.

                IF available: to 200mV AC, repeat.

                After we get those results, we go on with "audio" testings, but we first need these basic measurements.
                Juan Manuel Fahey


                • #9
                  Ok, so quick update:

                  Multimeter set to 20V DC

                  HF: 0.10
                  LF: 0.26

                  Also to note: the DC power level was slowly rising to that measurement over a minute
                  Last edited by tpmusic; 09-25-2020, 07:11 AM.