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Advice on setup...blowing amp

Discussion in 'Amps and Cabs [BG]' started by Jonesy4fnk, Sep 26, 2003.


  1. Jonesy4fnk

    Jonesy4fnk Supporting Member

    I've managed to blow my Ampeg SVT-4 for the 4th time. The last time it was repaired the tech replaced eveything inside (circuit board too). It runs great in stereo with 4ohm loads on each channel. Its only blown in bridged mono. But I don't notice any major clipping or the limiter led when it blows, it just fries.

    Could it have something to do with my input? Here's my setup. I run my bass, midi bass, loops, and elec. upright into a mixer, then out through a compressor, then through my effects, then to the Ampeg. When I get going with MIDI drum loops and layered bass parts could it be overloading the circuit? I admit when I've got all those things going it draws serious power, I've popped the circuit breaker in my house before.

    My next move is to buy a pre-amp for my bass signal and a separate 2 channnel power amp. Then I can run my MIDI/loops through one side and my clean basses through the other into 2 cabinets.

    That seems like the only option for minimizing the input load.

    Any ideas?
     
  2. This belongs in Amplifiers. Many experts over there.

    Blackbird or Embellisher will move it for you.

    Mike
     
  3. pbd

    pbd Commercial User

    Jul 17, 2003
    Metro Detroit
    owner Procables N Sound
    are you running in bridged at 4 ohms? most amps don't like this.
     
  4. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    Running this amp bridged into 4 ohms should be no problem as its designed to do so. What doesnt make sense is that if each channel works separately then bridged mono should work because it uses both channels added together. Also, running the midi loops through one channel and clean bass on another may be worse because you are driving one channel hard and another not as hard instead of both working together evenly when bridged. Its not your signal at the input. Something is probably wrong with the bridging connection.
     
  5. Jonesy4fnk

    Jonesy4fnk Supporting Member


    No I was running everything through one channel on the Ampeg. I'm considering buying a preamp/poweramp setup to run MIDI/loop and clean bass separately.

    Also, the tech replaced all the outputs each time it blew just to be sure.
     
  6. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    I see what you are saying but you should be able to do the same running separate channels on the Ampeg. The idea is that the bridged amp operation should be able to handle twice as much as separate channels. If the amp cannot handle this bridged then separate channels will not fare any better. If you have a power amp thats more powerful than the Ampeg then youll be better off but bridging channels will still handle more. Something is wrong with your amp sorry I dont have better advice...
     
  7. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Are you trying to bridge the amp into *two* 4 ohm cabs? If you are, you're giving it a 2 ohm load, and I doubt if the amp is rated for that. Bridged into a 2 ohm load is basically like giving each side a 1 ohm load.
     
  8. Jonesy4fnk

    Jonesy4fnk Supporting Member

    no thanks for the input man.

    This thing has me and everyone who has tried to figure it out stumped. I do understand that it should work fine with that kind of input. But that was my last guess at this point.
     
  9. Jonesy4fnk

    Jonesy4fnk Supporting Member

    nope, one 4ohm cab bridged is when it blows. When run in stereo I use two 4ohm cabs.
     
  10. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    Good point Richard. The Ampeg 4-pro is not designed to be bridged into a 2 ohm load and this could damage the amp. The only way it should be setup bridged is into two 8 ohm cabs or into one 8 ohm cab. Good luck jonsey...
     
  11. Jonesy4fnk

    Jonesy4fnk Supporting Member

    METRON - I didn't mean for my response to sound unappreciative at all. It should have read...

    "No....but thanks for the input man"

    I just re-read it and thought it sounded lame. Sorry for fast typing.
     
  12. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    its all good jonsey... hope you find a setup that works for you.
     
  13. Jonesy4fnk

    Jonesy4fnk Supporting Member

    I think I may have to give Ampeg a call or something. Seems odd that its giving me so much trouble and I've explored all the explainations I can think of.
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I googled the specs:-

    RMS Power Output (8 Ohms): 300x2/900 (mono-bridged @ 8 Ohms)

    RMS Power Output (4 Ohms): 490x2/1200 (mono-bridged @ 4 Ohms)

    RMS Power Output (2 Ohms): 600x2

    Seems the amp can take a 2 ohm load and can bridge to 4.

    Mate you're more patient than I am. If I was running an amp within it's specs and it blew, I don't know that I would have given it that many chances.

    I must say the drum loops worry me, but I'm more concerned about the speakers than the amp.

    Sorry, I'm stumped.
     
  15. notanaggie

    notanaggie Guest

    Sep 30, 2003
    I dunno what happened the first time,,,,BUT

    The repair guy maybe didn't get his parts from Ampeg?

    The output devices in that amp are in matched sets. If they are not replaced with matching parts, it won't last two days.

    Also, he maybe didn't find all the bad parts. I have fixed a couple of those, and it can be tricky.

    The good news is that when they are right, its real hard to blow them up. But if the repair job isn't good, it will just keep happening.

    There aren't any special fixes out for that unit that I know about.

    Also, any amp will be *unhappy* if you feed it a lot of crap from a noisy effect like some ADA pieces. They put out some sort of digital garbage that can fry amps.
     
  16. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    .....it's not a real good idea to run synthesizers and samplers through the same kind of compression you'd normally use on a bass. Those signals don't have the big transients that electric bass does, so when you give them the same "squash" factor, you get something very close to a sine wave, which really pushes your amp hard. When fed a normal signal, an amps average output is only 10-20% of its capacity, with the rest used only momentarily for audio peaks. Even with a 1200 watt amp, you'd be surprised if you ever put a meter on the output and saw what you're averaging - probably 200 watts or less. A heavily compressed signal can make an amp average 70% or more of its capacity, which is not considered a normal situation. A lot of amp manufacturers warn against heavily compressed and synthesized signals for this reason. The amp shouldn't have a problem operating at that much output, but you are pushing it to it's absolute capacity. It's kinda like saying your car will go 130 MPH - but you probably shouldn't drive it that hard for 6 hours at a time.

    This may not be what's blowing your amp, but it'd be a good idea to run compression only on your bass, not the drum loops or the MIDI/Synth stuff. Those signals shouldn't really need much compression, if any at all.
     
  17. redneck2wild

    redneck2wild

    Nov 27, 2002
    Memphis, TN
    What type of cabinet are you running when you blow the amp?

    What type of speakers are in the cabinet that you are running?

    Have any of the speakers in the cabinet been replaced? If so, is this replacement different than the other speakers?

    Is the cabinet capable of producing the frequencies that you are giving it?

    Finally, have you measured the cabinet impedance with a meter to see if it might be lower than 4 ohms?
     
  18. Jonesy4fnk

    Jonesy4fnk Supporting Member

    Thanks. I have heard that about using compressors before. I try to set my compressor threshold to barely even activate. Also, I don't run my bass through the same compressor side as my MIDI. I send my bass signals out one side of the mixer to one side of my 2 ch. compressor, then the MIDI signal out from the other side of the mixer into the other side of the compressor (and set it to barely touch the signal, just when a louder patch or sound is used). I turn the compressor on the amp head off when I run the external compressor.

    The other thing is that the first two times it blew, I was just running my bass, through my effects, straight to the amp.

    notanaggie - I know my tech got the parts from Ampeg. He replaced the whole circuit board last time and anything that could have been stressed (even the fan). He's stumped. I've never heard that noise from effects could cause problems, sometimes my Lexicon and my Mesa-Boogie V-twin pre-amp (for dist.) make some serious noise in certain rooms. But its never caused problems with my backup amp.

    Thanks for the advice. I'm sending it to Ampeg and they're going to see if they can help me out. I hope so because I love the amps tone.
     
  19. Jonesy4fnk

    Jonesy4fnk Supporting Member

    I use the Ampeg PR-410hlf (1200watts peak/4ohms)- this cabinet was made for this head.

    The first time it blew I was using 2) 2x10 cabs (400watts/4ohms). I couldn't push these cabs too hard without a distortion. I rolled off the low end and they worked fine for a couple years of gigs. We tested them afterwards and found they were operating fine, though one of the cones looked like it may have tapped the magnet at some point. Which may have caused the initial power amp surge.

    I also use an Aguilar 212 (600watts/4ohms) But its never been blown using this cabinet.


    But the 410hfl should have no problem with this amp, so I'm led to believe.
     
  20. I seriously doubt that you're damaging the amp with input. SVT4 Pro's are VERY unstable after they've developed a problem and there is usually a cascade effect where one fault keeps leading to more successive failures. To get rid of it, you pretty much have to completely rebuild the amp and even then, there are no guarantees. In other words, you've got a lemon.

    It's not noise as in background noise; it's digital garbage like subsonic artifacts and ultrasonic oscillations that wreak havok with amps. You can't hear them, but they can work your amp literally to death reproducing frequencies that you can neither hear, nor can your speakers reproduce.