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Source of squishy attack??

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Phil Divine, May 20, 2011.

  1. Phil Divine

    Phil Divine Member

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    I have a Traynor YGL Mark 3 head. It was modded to sound a litte more Marshally on one channel a few years ago. Kind of has a JMP thing going on. The reverb was sacrificed for a paralell effects loop.

    The amp sounded incredibly tight when it was first modded, and was my all time fave amp for a couple of years. Then one day, something went in it, and since that time, the attack of the notes is not as tight or clear. It's a little blurry and squishy.

    I have taken it back to the tech, but he can't find it, or rather won't try. There is a serious shortage of techs in my area, and I have a friend who helps me out, but major mods are a little out of his comfort zone and we could use a nudge in the right direction.

    Without going over the entire history of what I have replaced in this thing, here is what I can verify are NOT the source of the problem, as all of these components have been changed, A/B'd individually one at a time, with mutliple options in each. None of these addressed the problem.

    Anything to do with the Guitar signal
    Speakers
    Tubes
    All Coupling Caps

    The filter caps in the preamp and PI are the original Mallory mustard looking things at 40 mf. I tried replacing them, but it didn't fix the problem. I also played with a few values, but while it did make the amp sound more and less "tight" it didn't fix the blurred, squishy attack.

    The caps in the power section are the JJ black cans with 2 100 mfs. I even ordered more E caps to try replacing these, in case they have gone bad.

    I have also ordered Electrolytics to replace everything in the amp. I assumed that would be another good place to start. My intent is to keep replacing every one of these items one at a time, listening before and after. This is taking hours, but I am learning a ton.

    I will also add that the trem circuit oscilates. I pulled the tube out, which I think takes it out of the circuit. The oscilation stops, but the squish remains.

    Anyone have experience with anything like this? Any advice on where you would start your search?
    My tech did not give me a schematic of the work he did, but it the layout did not change from tight to squish.
     
    Last edited: May 20, 2011
  2. TweeDLX

    TweeDLX Member

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    Look at resistor values to see if any have drifted significantly. Plate load resistors in particular.
     
  3. Phil Divine

    Phil Divine Member

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    Thanks. Will do. I should have mentioned that many of the resistors were changed to new ones, but not all. THere are quite a few carbon comp ones left in there. I should also have mentioned that the problem exists in either channel, the original clean side,and the new modded side. So I assume that it must be beyond those 2.
     
  4. TweeDLX

    TweeDLX Member

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    Can you elaborate on "squishy" a bit more? Is it a distorted squish? After you replace the filter caps, you can narrow things down a bit more. If you have 20+ year old caps in there, that's a likely suspect as well.
    Trem "oscillation"- do you mean high pitched howl? Replace the tube in the trem slot with a known "good" tube. Yours may be microphonic.
     
  5. dazco

    dazco Member

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    I'd suspect those carbon comps. I have spent several years TRYING to get lots of squish in the amps i built and the #1 factor in getting that to happen has been resistor values in certain places, and we all know CC's are known to sometimes drift a lot. Look for drift in the CC's, especially any grid stoppers. A grid stopper thats drifted much higher can do just that. Plates too. Also, if it has NFB check to see the NFB resistor hasn't drifted and gotten lower if it's a CC. A 100k resistor there that drifts down to 50k or less will create a huge amount of squishy sag and loss of clarity especially in the lows.
     
  6. Phil Divine

    Phil Divine Member

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    Awesome tips. I know what I am doing this weekend!

    As for the trem, I have replaced the tube numerous times. It still sounds like a young crocodile calling for its mother.

    The filter caps are new in the power section, and in the preamp section I already replaced them, but it didn't do the trick. I am still going to do them again anyway, because I usually check everything 6 times. One of those guys.
     
  7. dazco

    dazco Member

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    Oh, also if either of the PI plate resistors is cabon comp, that would also ne a highly suspect part, as throwing the PI/PA balance off does what you described too.
     
  8. gght

    gght Member

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    Clips please!!!! Great new effect!:love:
     
  9. VaughnC

    VaughnC Supporting Member

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    With a heavily modded amp, a lot of things could be going on. The obvious place to start would be the tubes themselves...they can lose gain but still work creating all sorts of issues.

    Beyond that, you really need to go through the amp with an oscilloscope to see what's going on in the circuit. But that appears to be beyond your abilities so changing parts one at a time is about the only thing left. Checking resistor values with a DVM might tell you something. However, "squish" might be caused by too much negative feedback...you could open the NFB loop to see what happens or just add a switch to turn it off or on. Some amps sound cool with no NFB. Good luck.
     
  10. CaptainJake

    CaptainJake Member

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    Might be worth trying to replace the diodes with UF4007s, but I agree with those saying to check the resistor values
     
  11. Tone_Terrific

    Tone_Terrific Supporting Member

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  12. Keyser Soze

    Keyser Soze Member

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    What bypass caps are in there? The life span of electrolytic caps (already short) is shortened when they are used well below their rated voltage. Over time they can begin to exhibit distortion at lower frequencies.

    This is more common with 'full bypass' values like 22 uf. If the caps are more Marhshall value, or non-electrolytic this is probably not the source of your problem.
     

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