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Broken Ultra-Hi on Ampeg SVP-Pro

Discussion in 'Amps and Cabs [BG]' started by magic papa, Oct 12, 2013.

  1. Hi Everybody,

    Got an Ampeg SVP-Pro, works fine, but the Ultra Hi button does nothing. I can hear a slight pop, so I'm assuming the switch engages OK, but there is no change in tone. Everything else seems to be working.

    Has anybody had this problem? What does the Ultra Hi button actually do (in electrical sense)?


  2. mazdah


    Jan 29, 2010
    Kalisz, Poland
    Ultra High adds highs ... is kinda subtle in this preamp (Bright is much more radical - adds high mids) - you won't hear it unless you have fresh round strings and quite bright cab. Using it with my P-bass with flats and PF-115 without tweeeter it does almost nothing - the attack is a little bit better pronounced, the slap and pop technique is more defined. And thats all.
  3. capcom


    Mar 23, 2005
    Hello, I have the same preamp.
    I suggest you open the unit and apply Deoxit to the "Ultra Hi" button, press it 20-30 times successively to spread the fluid to do its job and see if it works. It's contacts are probably rusty/dirty due to not being used for a long time. I don't think it's a serious problem.

    I had a similar problem with the "EQ" button. When the button was pressed, sometimes EQ wasn't engaging and it was also causing the whole unit dead quiet.
    Hopefully the solution was to apply/spray some Deoxit to the EQ switch. I also remember the "popping" sound I hear when I pressed the EQ button, which reminds an unwanted sudden short circuit due to switch being dirty.

    Don't know how Ultra Hi button does electrically but don't also think it does a very complicated job. I assume it just boosts +4k frequency in tube stage rather than in SS eq stage to also take adventage of high frequency responses being colored by the tubes...
  4. I've got an SVT VR with the same feature, so I was assuming it would be similar. On VR the button does add quite a bit of top end, definitely audible. Also my cab has a tweeter, so I'm thinking that something is actually wrong with the preamp.
  5. No worries, that's easy enough to try. Thanks

    That's what I thought. It probably connects a cap, RC or something similar. So that's why I'm thinking there shouldn't be much that could go wrong there. Switch is the prime suspect now.
  6. mazdah


    Jan 29, 2010
    Kalisz, Poland
    VR has old SVT-style preamp, different filters.
    SVP-PRO is from SVT-2PRO, whis is more like SVT-CL than VR.

    It may be problem with your preamp, but as I wrote, with P-bass with single "15 ultra hi does not much.
  7. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Most likely causes...dirty switch, disconnected switch, broken switch. I'd try contact cleaner first.
  8. Turns out all statements were correct. I cleaned up the switch (not easy though, it's pretty much sealed) as it was not engaging properly or at least not each time. Looks like it helped.

    The feature is indeed very subtle and as mazdah mentioned - may appear to have little effect depending on the setup.

    Anyway - looks like it's working as designed now. Thanks a lot for your help.
  9. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Good deal!
  10. Steve Dallman

    Steve Dallman Supporting Member

    On many Ampegs the ultra hi is like the bright switch on a Fender...it engages a treble bypass capacitor on the volume control. The higher you turn the volume, the less effect it has. Dime the volume and it will have no effect.

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