Ad Widget

Collapse

Announcement

Collapse
No announcement yet.

Peavey KB60 tweeter issue

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
  • #1

    Peavey KB60 tweeter issue

    So the tweeter sounds like garbage if the amp is turned up...even to a lowish gig level volume. There is no crossover in here. So first, I tried a new sub tweeter. No change. Then I inserted my bench crossover. No change. Disconnecting the tweeter, woofer sounds mostly good. If pushed it does begin to have a similar, yet darker, issue. So...I'm thinking it's the amp not the tweeter.

    Suggestions? I will check the output transistor bias. And report back with some realworld numbers on Vac and wattage at breakup. It really happens on transients...when the string is picked. Now realizing I should've taken more measurements before posting.
    Tags: None
  • #2
    OK, the tweeter with no crossover would be a piezo. I think they sound crappy myself. If you subbed in a tweeter that was not a piezo with no crossover, well that is doomed from the start.

    String dynamics are probably clipping the amp. Run a 100Hz sine through the amp up to clip and see if the DDT circuit comes in to prevent clipping. Go in through the power amp in jack to eliminate the preamp contribution. Scope the output at the speaker jack to see if the peaks are clipping.
    Education is what you're left with after you have forgotten what you have learned.

    Comment

    • #3
      Is U7, peavey cross ref #87478, the DDT limiter? Just curious. The peavey cross reference shows no field part #.

      I'll scope it tomorrow when I'm at the bench.

      Comment

      • #4
        Before losing your mind try putting a 2.2uf bipolar cap in series with the positive terminal of the piezo tweeter. If you like put a pot in series with that. A cheap and effective mod.

        Comment

        • #5
          I tried that. It did help... a little. But... this musta sounded much better from the factory without that mod. So, I'm curious, and interested in diagnosing it nonetheless. Thanks and good suggestion.

          Comment

          • #6
            Originally posted by lowell View Post
            I tried that. It did help... a little. But... this musta sounded much better from the factory without that mod. So, I'm curious, and interested in diagnosing it nonetheless. Thanks and good suggestion.
            Btw... ANY distortion is going to sound bad through a tweeter. Especially a piezo. If you notice, this tweeter thing pretty much disappeared in most all guitar/bass amps after about 1970. It's a fairly recent thing they are doing again. In most cases, for bass, an extension cab with a pair of 10" will get you better results for high end presence imho.

            Comment

            • #7
              You didn't respond, was the tweeter you subbed in also a piezo? Piezos don't sound the best to start, but they are crystals, and they can crack, so it is possible your original piezo tweeter is bad and needs a replacement piezo. To use a real tweeter, yu would need to add a crossover.

              yes, the 87478 is the DDT active element. You can pull that IC to see if it is causing issues. Normally it prevents clipping, so if the amp clips - which I thought you might be hearing - then that IC is not working.

              The cross ref shows it as a CA3094, which is also obsolete. I don't know that you need one, but if you do, I would call PV parts department and ask if they still have them available. We call them an 87478, but the full part number is 70487478. They used just TONS of these, and if they are not available, PV may well have made a little workaround for them.

              For reference:
              http://www.experimentalistsanonymous...ets/CA3094.pdf

              It has a tweeter because it is a keyboard amp.
              Education is what you're left with after you have forgotten what you have learned.

              Comment

              • #8
                It has a tweeter because it is a keyboard amp.
                Thatīs the point.

                Electric guitars donīt like them, so if you used one to test the amp, now you know.

                In any case , tweeters are often unjustly acused when in fact thy only *reproduce* distortion being fed them.
                Harsh tinny Piezo response does not certainly help.

                I suggest you feed 1kHz into your amp and scope output, it sould give you between 16 and 19V RMS into a load and, at least in theory, it "should" not clip, or at most barely sinewave tops, definitely never ever a square wave nor anything approaching that.
                Juan Manuel Fahey

                Comment

                • #9
                  Enzo it was a magnetic tweeter. I had a crossover in circuit and still sounded bad. I realize now after talking with the customer...a bassist...that he's playing with the volume on 3 max. I had it up around 6 and it sounded bad. I also scoped the output and it never clipped even with my signal generator at max. So the DDT is working.

                  I think you all are right in that the amp was not meant for guitar.

                  Comment

                  Previous template Next
                  Working...
                  X