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another distorted sound problem

Discussion in 'Amps and Cabs [BG]' started by cronus, Nov 14, 2003.

  1. cronus

    cronus Guest

    Jan 17, 2002
    Romulus, Michigan
    alright, i looked through the search engine and could exactly find my answer...so here it goes :

    i just recently bought an SVT3 pro off of a friend of mine and it works great and everything. but it seems to be whenever i play higher notes it sounds a little distorted. got any idea what the problem could possibly be? im running it bridged with a QSC RMX850 and an Avatar B410 :bassist:
  2. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Could be a bias adjustment. I have not seen one of those for quite a while, and I don't have the info near me now, so I don't remember what's up with that unit.

    But some distortion at highs is typical for that.

    Usually it will be worst at low levels, does that sound right?

    If so its an easy adjustment in most cases.
  3. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    How are your volume controls? Try opening up the master all the way, and adjust your level using the preamp volume. Most of the time distortion means "too hot". Have you tried using the "2" (active) input?
  4. cronus

    cronus Guest

    Jan 17, 2002
    Romulus, Michigan
    do you mean the level on the power amp or the svt? i usually only have the power amp up to about 1/4 way up and then just get the rest of the volume from the head.
  5. Um... correct me if I'm wrong here guys but it sounds like he's overloading the input to the power amp.


    Make sure you have the amp and pre hooked up properly (the pre-amp "out" is plugged into channel A of the power amp) and that you have the proper cable to run your amp bridged into the cabinet.

    Then try this-

    Turn down all the levels on everything (amp and pre) and flatten out your EQ ("center" everything on the EQ). Put your power amp in "bridged" mode, make sure you have the 30hz filter on, and turn the volume up almost all the way (turn it all the way up and then back it off 3 notches).

    On your pre-amp-

    Turn the "master" volume up between 1/2-3/4 (12-3 o'clock). Then adjust the "pre" (or input volume) to get the amount of volume you desire. IT WON'T TAKE MUCH SO GO SLOW!!! Adjust the EQ to your taste.

    If you still hear distortion it might be from some type of problem or something else in the signal chain.
  6. cronus

    cronus Guest

    Jan 17, 2002
    Romulus, Michigan
    i had everything right except that, that acually worked also, thanks alot
  7. Do you guys generally run your poweramps full out and adjust the level going into them as necessary? I usually do it the other way around... no problems with it so no reason to change, just wondering what the standard method is?

    I like my pregain setting for a bit of overdrive, so in my case I'd be running the preamp out as the master volume control if I take this route.
  8. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX

    stop doing what you are doing, you are going to blow a speaker. I blew a 10" speaker in my Berg 322 having my rig setup that way. I did not overdrive my speakers with power. I was sending a clipped signal to my power amp. Although I did not hear any clipping, distortion, or see any clip lights on the power amp, I was still cliping. Having your poweramp all the way up while adjusting the overall volume at the preamp is the easiest way, assuming you know when to say when with the volume. The safest is to find the happy medium between your preamp and your poweramp.
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You will not blow a speaker simply by sending it a clipped signal--only if the clipped signal is too much power for the speaker. But that is true for an unclipped signal as well. For example, 20 watts of a clipped signal can not blow a 250-watt speaker, but 400 watts of a clipped or unclipped signal can.

    The better and safer way is to turn the power amp down, using only as much gain as you need to.
  10. Big String

    Big String Supporting Member

    Apr 22, 2000
    Northwest Indiana
    First let me say I would never disput Bob Lee.
    Thanks from everyone for all your help Bob.
    Further I have never blown a speaker.

    My experience with PLX2402. I tried many different setting on my amp and pre (Demeter 201s) and always went back to these settings on any of my speaker cabs.

    Demeter volumn from 3 to 6 (1-10) internal pot setting (same as master) about 3 o'clock). Comes from Demeter set at 12:00. PlX 2402 Bridged, Gain Full. I always get the best tone and volume this way.

    I tried many times to set the preamp hotter and keep the gain on the amp less than all the way up. It always sounded more "distorted" to me that way and was not as loud as I liked or needed.

    I understand what Bob means to set the gain on the amp as high as one needs. In a gigging situtation, I always needed to have the gain all the way up. That is what worked for me. The only time I would lower my bass setting or pre signal was when I would slap.
  11. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The SVT3PRO has a number of controls that could affect distortion.
    It has a "tube driven mosfet" power amp, meaning that the tubes in the power amp control the power amp gain and the mosfets just "follow" what the tubes do. It does not necessarily respond like fully solid-state power amps.

    For the least preamp distortion, setting the master up as far as possible is best, since this requires the least out of the preamp. If you don't have a wild setting on the EQ, or are not using it, and the peak led isn't flashing much, the preamp should be clean.

    The power amp has a "tube gain" control, that varies the voltage on the driver tubes in the power amp. If that is set down, it can be distorted as well as somewhat compressed. The "compression" really is a sort of distortion. Try turning "tube gain" up more.

    Yes, there is a bias adjustment on the power amp for the mosfets. That could be set wrong, and might make the sound distorted also, with it possibly being more noticeable on highs. Because of the "tube drive", the mosfet bias is a little more critical on this than on some other amplifiers.

    Finally, if your cabinet has a tweeter, any distortion from anywhere in the amp (clipping, tube drive set low, etc) will be more noticeable.

    I would check signal levels, and the "tube gain" first.
    Hope this helps.
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    cronus, I assume you're driving the RMX 850 from a preamp output (or line-level output) on the SVT3?
  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Good point....got in a hurry and forgot that was mentioned, it certainly would let out the internal power amp........

    Assuming you haven't solved it yet...

    Where are you getting the output from? Could be from the balanced out (XLR or phone plug) or from the preamp out.

    The preamp out is "after" the front panel master and the balanced out is "before" it with its own level control.

    The balanced line out isn't the strongest on those units, later ones have better balanced outs. If you are using the balanced and you don't need the transformer balancing, you might try the "preamp out".
  14. Sorry, I should have said I was using my preamp master volume to send as hot as possible to the poweramp without clipping. I can tell when that's happening by listening to it.

    Thanks for the clarification Bob Lee QSC, that's what makes sense to me too.

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