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Vox Escort Mains/Battery Powered Amp Humming help.

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  • Vox Escort Mains/Battery Powered Amp Humming help.

    Hi, just picked up a Vox Escort amp, tried it out when i got home and the thing works, but theres this pretty loud hum along side it. the louder you turn up the tone/volume, the louder the humm.

    Any suggestions?

    Vox Escort Mains/Battery Amplifier - late 1970's Schematic
    Schematic is there.

    Thanks.

  • #2
    I would check the 0.1 uf caps for leaking Vdc.

    Comment


    • #3
      what will i need to do this? a digital multi meter? long time since i did electronics...

      Comment


      • #4
        A DVM is what you need.

        Comment


        • #5
          Originally posted by Jazz P Bass View Post
          I would check the 0.1 uf caps for leaking Vdc.
          I hope You don't mind if I jump onto this thread ...

          I have the same problem with my "Vox Escort Mains/Battery" amp.

          My "Vox Escort Mains/Battery" is presenting noise/humming in both mains and battery mode.

          I've already renewed the 0.1 uf caps mentioned above , but the humming is still there.

          Jazz P Bass:
          Should I now go for the rest of the capacitors or do You have some other recommendations for me?

          thanks in advance
          benilo

          Comment


          • #6
            What happens if you set volume to "0"?
            What happens if you short to ground the node 220K/220K/.1/2n2 which is on the left of the transistor?
            A node is where two or more parts touch each other.
            What happens if you put a shorted plug in either input jack?
            What happens if you plug a guitar there, with a known good cable, and put its volume and tone on "0"?
            Juan Manuel Fahey

            Comment


            • #7
              Originally posted by J M Fahey View Post
              What happens if you set volume to "0"?
              What happens if you short to ground the node 220K/220K/.1/2n2 which is on the left of the transistor?
              A node is where two or more parts touch each other.
              What happens if you put a shorted plug in either input jack?
              What happens if you plug a guitar there, with a known good cable, and put its volume and tone on "0"?
              Hello "J M Fahey", thanks for Your reply,

              Unfortunately, it may take some time to make the tests You suggested, because I don't have access to the amp at the moment. But I'll try it out.

              I've also replaced the 220 uF Cap at the very right of the board and both the volume and the tone potis.

              Some more comments:
              - the noise is there without having a guitar cable plugged in.
              - when I plug in a guitar cable and short circuit the input, the noise is still there.
              (I haven't tried this with both inputs simultaneously)

              Thanks in advance
              benilo

              Comment


              • #8
                Originally posted by J M Fahey View Post
                What happens if you set volume to "0"?
                The noise is still there but it gets louder at 70%.
                What happens if you short to ground *the node 220K/220K/.1/2n2 which is on the left of the transistor?
                A node is where two or more parts touch each other.
                The noise is still there.
                What happens if you put a shorted plug in either input jack?
                The noise is still there. I've tested this with both input jacks simultaneously.
                What happens if you plug a guitar there, with a known good cable, and put its volume and tone on "0"? * * * *
                *
                The noise is still there.

                I think with the tests above, the noise source seems to be on the right side of the TBA810, do You agree?
                Could the TBA810 itself be the problem?
                Or should I now go for the rest of the capacitors?

                Best regards benilo

                Comment


                • #9
                  You have to systematically identify where the hum is originating from.
                  Yes, the TBA810 could be at fault.
                  I would look at all of the pins of the TBA IC.
                  Specifically looking for volts ac ripple on any pins.
                  If every input pin is stable, it points to the ic being faulty.

                  Comment


                  • #10
                    Solder a 1000uF or 2200uF x 25V electrolytic capacitor in parallel with the 220uF one filtering the + rail.
                    If you *still* have hum, the only other component there is the TBA810S itself, obsolete for ages.
                    You *may* use a TDA2030 there, after some brain surgery.
                    Post some pictures of your Escort, both external and internal.
                    Juan Manuel Fahey

                    Comment


                    • #11
                      Originally posted by Jazz P Bass View Post
                      Hello Jazz P Bass,
                      You have to systematically identify where the hum is originating from.
                      Yes, the TBA810 could be at fault.
                      I would look at all of the pins of the TBA IC.

                      Specifically looking for volts ac ripple on any pins.

                      If every input pin is stable, it points to the ic being faulty.
                      Unfortunately, I only own a Digital Voltmeter, no oscilloscope.
                      What do You mean with "input pin", do You mean every pin or only the pins
                      that transport the input signals for the ic?

                      Best regards benilo

                      p.s. Im from germany, although I had a education in electronics some 30 years ago,
                      maybe I don't understand every technical term in english.

                      Comment


                      • #12
                        Try taking the amp outside to the garden, running on batteries, does it still hum there?

                        There are plenty of TBA810 ICs available on Ebay, but I don't think the IC is the problem.
                        "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

                        Comment


                        • #13
                          Hello J M Fahey
                          Solder a 1000uF or 2200uF x 25V electrolytic capacitor in parallel with the 220uF one filtering the + rail.
                          I've already replaced the 220uF with a 20 year old 220uF cap that I've found in my toolbox,
                          it had no leaking current.
                          Shall I addtionally add another 1000uF cap?
                          If you *still* have hum, the only other component there is the TBA810S itself, obsolete for ages.
                          You *may* use a TDA2030 there, after some brain surgery.
                          What do You mean withbrain surgery?
                          As I wrote above, I'm from germany and therefor I'm not a native english speaker.
                          Post some pictures of your Escort, both external and internal.
                          Here are the pics and a sample of the noise.
                          (It starts with 0 volume, where the noise gets louder, I've changed the volume to 100%)

                          greetings benilo
                          Attached Files

                          Comment


                          • #14
                            Hello Steve,
                            thanks for Your reply,
                            Try taking the amp outside to the garden, running on batteries, does it still hum there?
                            I've alredy checked this with my stabilized power unit, the noise was still there.

                            There are plenty of TBA810 ICs available on Ebay, but I don't think the IC is the problem.
                            In my opinion, this was the last thing to try, I thought it would be easier first to
                            check the other parts ot the amp.

                            greetings from germany,
                            benilo

                            Comment


                            • #15
                              Originally posted by benilo View Post
                              Hello Jazz P Bass,

                              Unfortunately, I only own a Digital Voltmeter, no oscilloscope.
                              What do You mean with "input pin", do You mean every pin or only the pins
                              that transport the input signals for the ic?

                              Best regards benilo

                              p.s. Im from germany, although I had a education in electronics some 30 years ago,
                              maybe I don't understand every technical term in english.
                              A DVM is fine to use.
                              What I suggested was looking at all of the pins of the IC for Vac ripple.
                              Set your DVM to read volts ac.

                              Comment

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