VT-Bass Output Mod attempt... Fail...

Discussion in 'Amps and Cabs [BG]' started by silky smoove, Feb 24, 2010.


  1. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    After developing concerns that my VT-Bass would not be able to properly drive a Crown XLS Drivecore power amp properly (1.4V input sensitivity) I took the advice of TB'er rpsands and looked into doing an output mod to boost the output level of the VT.

    I took my VT down to Condor Electronics in Seattle, which is a place I've never dealt with before, but my stepdad had nothing but wonderful things to say about them. I dropped off the VT yesterday and got a call back today.

    "Hey Chris, I talked to the guys at Tech 21 and they won't release a schematic for your pre, so I'm not going to be able to do any kind of output increase for you. The engineer did say he was shocked that there would be any problem driving a power amp with one of these as most of their complaints are for additional attenuation rather than a higher output.

    One thing you might try is converting the output of the pre, which is unbalanced, to a balanced signal. Since the 1/4" input of your power amp is looking for a balanced signal, this will give you a 6db increase.


    I'm mainly interested in the second paragraph of our conversation. I'm in over my head when it comes to this sort of thing, so if someone can chime in and answer these questions it would be super helpful:

    1. Will sending a balanced signal really net me a 6db increase when it reaches the power amp?

    2. I've got a Radial JDI that I use frequently. If I send the 'thru' output from the JDI into the power amp's 1/4" in, will that be giving me a balanced signal, or does the 'thru' output of the JDI not go through the Jensen transformer and remain unbalanced?

    3. If the 'thru' output of the JDI won't do the trick, would I be able to run the balanced (DI) output of the JDI into the XLR input of the power amp, or will the DI output of the JDI be down at mic level rather than line level?
     
  2. KramerBassFan

    KramerBassFan

    Jan 3, 2009
    Did you actually try driving your Power amp with your VT pedal?

    Why bother taking it to people to pay money for them to "mod" it, when you havent even tried it? :meh:

    Not trying to be a SmartA$$ or anything, but i'm just curious. ;)
     
  3. stflbn

    stflbn

    May 10, 2007
    Nashville
    Boost the output of the VT????

    Almost everyone gripes that the output is to ridiculously high on the VT-bass. It's designed to be able to push a PowerAmp.


    Seriously.


    .
     
  4. uaudio

    uaudio

    Apr 11, 2008
    Arizona
    Yeah, +100. It runs my poweramps just fine. Its almost TOO hot to use in my chain as an effect. If i have the drive at noon, I usually end up with the level at 8 oclock - barely on. That's with a passive P bass!
     
  5. stflbn

    stflbn

    May 10, 2007
    Nashville
    Ya, when I had several different VT pedals I'd always end up using them on about 1 or 2.
     
  6. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    The issue is that the power amp I want to use (Crown XLS Drivecore series) has a rather high input sensitivity at 1.4V.

    I've ran my VT into two different power amps and had no problem driving them, but after digging into some specs after the fact, I found that both of the power amps used previously had input sensitivities of 1.0V and 0.8V respectively. I don't want to order the XLS Drivecore (currently the only power amp I can find that meets ALL of my requirements for features and form factor) and have it be a bust because of the 1.4V input sensitivity.
     
  7. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    IMO, it shouldn't have any problem driving the drivecore series amps.
     
  8. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    I just found the block diagram for my Radial JDI on the Radial website. It looks like the 'thru' output does not go through the transformer unless you engage the 'merge' button, which (and please correct me if I'm wrong) effectively turns the 'thru' output into a stereo input with the 'input' jack allowing you to merge stereo sources and send a mono output through the DI. Basically a way to save real estate on a mixer... Looks like the 'thru' route is a bust.
     
  9. KramerBassFan

    KramerBassFan

    Jan 3, 2009
    Just try it.

    You can always turn the pedal down. :)
     
  10. Bardley

    Bardley

    Nov 16, 2007
    Louisville, KY
    I honestly don't think you will have much of an issue. The VT is super hot.
     
  11. TL5

    TL5

    Jun 27, 2005
    Nashville
    I just run a small mic preamp (m-audio, audio-buddy) between VT (pedals) and my Yamaha poweramp.

    It's clean and effective and I keep unity gain through the pedal board.
     
  12. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    The problem would be not being able to turn the pedal up far enough.
     
  13. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    how do you know until you've tried it? those pedals are known for having a TON of output.
     
  14. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    -10db unbalanced according to the engineers at Tech 21.

    I've looked locally (Seattle) and can not find anyone that has the XLS Drivecore amps in stock to try. At this point, if I want to try that power amp I would have to pull the trigger and order one, presumably from RMC Audio. They have a good enough return policy that it wouldn't be too much hassle, but a hassle none the less.
     
  15. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    I'm by no means an expert on any of this, so please correct me if I'm wrong, but if line level is 0dBV (1.0Vrms) and the output of the VT-Bass is -10dBV, while the input sensitivity of the Drivecore XLS is 1.4Vrms, how could there NOT be an issue?
     
  16. stflbn

    stflbn

    May 10, 2007
    Nashville
    IMHO - stop worrying about published numbers until you've witnessed how hot the pedal outputs.

    No one has EVER complained that the VT will not push their poweramp, or that it doesn't have enough gain. All complaints (as mentioned by others) are that it's way to hot... and the general response is 'it's designed that way so that it can push poweramps'.
     
  17. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    If I could find one to try, I would absolutely stop worrying about numbers, but until then, the only thing I have to rely on other than speculation are the numbers. Being an engineer (albeit civil engineering, not electrical/electronics/audio engineering) I tend to lean pretty heavily on the numbers side of any discussion, so you'll have to excuse my predisposition.
     
  18. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    just get a power amp with the numbers you like.
     
  19. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    It's true that you will gain 6dB of output level by sending the power amp a balanced signal instead of unbalanced. Unfortunately, the JDI (as well as every other passive DI) drops your signal level about 12dB as it crosses the transformer. Net loss. So you'd want an active balancing device like a small mic preamp with DI input.

    That said, used VT's show up in the TB classifieds regularly, and they sell quickly. So in your shoes, I would buy the next one that pops up used; try it out in person; and if it doesn't work, then either re-sell it at little to no loss, or get a small balancing preamp to boost and balance it.

    I suspect Tech21's site says the output is -10dBu because that is a normal level expected for home recording devices, not because it's the actual maximum gain possible from the pedal.
     
  20. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    Buy a drivecore, buy the VT bass, if it doesn't do it for you, send the VT to Putnam or Guttermouth and have a balanced out added with an output boost :)
     
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