Announcement

Collapse
No announcement yet.

Eden VT.40 Distorting

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    It would be helpful to know what volts/division those shots are taken at. Can you tell us what the p-p voltage is of those waveforms or where your scope was set? Also, try it without a load. Do the waveforms look the same without a load? And, one more thing: Be sure not to overdrive the input of the amp with whatever you are using for a generator.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

    Comment


    • #17
      the scope was set at .2v/div
      I used my computer as the generator, with the volume set at full.
      the amp preamp volume was at 1/4 and the master was at 1/4.

      attached are pics with the volume set at 1/2 on the computer.
      same settings on amp as before.

      Click image for larger version

Name:	100hz_-_no_load[1].jpg
Views:	1
Size:	1.82 MB
ID:	840640Click image for larger version

Name:	250_hz_load[1].jpg
Views:	1
Size:	1.71 MB
ID:	840641Click image for larger version

Name:	250_hz_load[1].jpg
Views:	1
Size:	1.71 MB
ID:	840641Click image for larger version

Name:	250hz_no_load[1].jpg
Views:	1
Size:	1.80 MB
ID:	840642Click image for larger version

Name:	250hz_no_load[1].jpg
Views:	1
Size:	1.80 MB
ID:	840642

      I turned the master up to 1/2 and got similar pics to the earlier ones with the little hitch. I could not take any more pics because my phn died.

      Comment


      • #18
        Thse 250Hz waveforms look *perfect* .
        The 100Hz ones too but in general I avoid them because they are too close to mains and exactly match ripple (in 50Hz Countries) so they may produce *weird* waveforms by beating where there is no real problem.

        If you wish also try 400 or 440Hz but they should also work flawlessly.

        The earlier kink could be attributed to preamp clipping or driving the PC soundboard to its limit.

        I suggest you inject 100 mV at the preamp input, set all tone controls to 5 (flat) , Master volume to 10 , and slowly rise preamp gain/volume until power amp starts to clip.

        You should get around 35V RMS on a load , and just for testing purposes, over 40V RMS without.
        Juan Manuel Fahey

        Comment


        • #19
          Yes, those waveforms look pretty good. I suspect you were clipping the input if you had your computer volume at full. Remember this amp wants to see an instrument level input (low) and you are feeding it line level (high). You will have to keep the computer volume down substantially to avoid clipping the input. Do as Juan says regarding volume staging (Master at 10, etc.). Also, using the Active input will attenuate the signal a bit making it easier to adjust.
          "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

          Comment


          • #20
            I set up the PC and the amplifier as you suggested Juan. I was getting 41vac rms with no load and 50vac rms with a load when it started clipping using the 100hz,250hz, and 440hz tones. I set up the amp with pre and master volume at half and hooked up my bass guitar and was getting clipping only when I had heavy attack on the low E string. It was clipping about at 35vac p-p.

            I am so confused right now.
            I have used three different speaker cabinets, 2 diff 1x15 cabs and a 4x10 and they all had that slight distortion that I have just started hearing lately.
            It doesn't seem to be the amplifier.
            Do I really have three bad speakers?
            Is there other adjustments that may need tweaking? I set the Power amp bias as I said above as written on the schematic.(7mv between TP-A and TP-B)

            Comment


            • #21
              Originally posted by Hankbass View Post
              I set up the PC and the amplifier as you suggested Juan. I was getting 41vac rms with no load and 50vac rms with a load when it started clipping
              I think it's the other way round, voltage unloaded is higher.
              That said, 41V RMS unclipped means 210W RMS into 8 ohms, twice that into 4 ohms, a very healthy and powerful amp.

              using the 100hz,250hz, and 440hz tones. I set up the amp with pre and master volume at half and hooked up my bass guitar and was getting clipping only when I had heavy attack on the low E string. It was clipping about at 35vac p-p.
              AC? (RMS) or PP? (peak to peak).
              Not the same by a Country mile.

              Just to keep one doubt away, use Master volume on 10 , all the time, until we clear this.

              I am so confused right now.
              I have used three different speaker cabinets, 2 diff 1x15 cabs and a 4x10 and they all had that slight distortion that I have just started hearing lately.
              It doesn't seem to be the amplifier.
              Do I really have three bad speakers?
              Is there other adjustments that may need tweaking? I set the Power amp bias as I said above as written on the schematic.(7mv between TP-A and TP-B)
              repeat with Master volume on 10.

              I suggest this:

              a) with a sinewave , drive power amp to clipping, then note on screen where the visible clipping is (grease pencil or a little piece of tape) or rise sensitivity until said peaks reach almost the screen top and bottom edges, we are not *measuring* here (you already did) but *comparing* .

              b) play your Bass. Signal should clip at essentially the same level as before.

              If so, we have a healthy amp and a properly set preamp and you must look elsewhere.
              If not, some earlier stage is clipping, as simple as that.

              Sorry if some tests look repetitive or annoying, but working by "remote control" it's EASY to ignore small details, so the idea is to sweep them away and concentrate on the basics.

              IF the amp is fine (which I guess) , we'll test the speakers, but so far I suspect you may be slightly clipping some preamp stage.

              That said, and a personal experience about chasing ghosts: a customer had one of my early 400W RMS, 2 x 4x12" speakers, a LOUD wall shaking setup, which developed an annoying buzz.

              I instantly recognized it as unmistakeable speaker buzz, so set my ear by speakers, one by one, marked the suspect ones with a piece of tape attached to the cone and later replaced them.

              Lost a week replacing speakers which outside the cab turned to work perfectly

              The real culprit?

              He had replaced the cheapo original bridge in his Jazz Bass with a fancy *heavy* Badass one ... some unfinished sharp edge nicked and eventually cut the wrapping around one of his Rotosound roundwound strings and I guess it "unrolled" a little, yet not enough to make the string unusable.

              That vibration which only appeared playing a couple notes kept me chasing ghosts for a week
              Juan Manuel Fahey

              Comment


              • #22
                well I did as you suggested Juan and as expected the clipping was at the same level with the bass as it was with the 100hz signal. I tried to set the bass guitar as best as i could at around 100mv as you suggested before with the test tones.
                I put my ear up to each speaker in the 4x10 cab and did hear a buzz in one of the speakers. So the 4x10 definitely has an issue. i will check the other cabs the same way when i get a chance

                Comment


                • #23
                  Good to know your amp is fine
                  You might set it up bad, but that's something else

                  Now let's see what we find on the speakers.

                  Get a software generator or a sweep tone, 20-20000Hz is available but way too wide for our purposes, some car speaker vendrs offer more restricted low band sweeps, say 20-350Hz or similar.

                  Best is a hand controlled oscillatir of course: sweep fronm 30 to 300Hz slllooooowwwwwllllyyyyy , atn least bthe first couple times, then go back to suspect frequencies, you'll soon find some very annoying ones, usually meaning loose dustcaps, tinsel wires flapping against cone or frame, etc.

                  When culprit found, proceed as needed, either vregluing bthe loose part if possible or plain reconing/replacing.

                  Mind you, there's lots of buzzing things around there: label badges, grill cloth, **metallic grills** , loose front or back panels, handles, wheels, you name it.
                  Juan Manuel Fahey

                  Comment


                  • #24
                    Update
                    I tested all the speakers as you suggested Juan. I found two of that had some issues. They have been reconed and everything sounds fine now in that cabinet.
                    I also cleaned the hell out of both the amp and the speaker connectors. which i suspect may have been my issue with all the other cabinets i was trying.

                    Comment

                    Working...
                    X