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Safe to *defeat* Ampeg B2RE limiter?

Discussion in 'Amps and Cabs [BG]' started by jwaugh, Mar 10, 2006.


  1. jwaugh

    jwaugh

    Feb 26, 2006
    West Virginia
    I'm trying out an Ampeg B2RE (SS, 450 watts @ 4 ohms) with Ampeg SVT 410-HLF (apparently could absorb a blast from an M1 main gun) .. passive Fender J Bass .. gain up to about 3 o'clock, master volume past 4 .. limiter light does flash from time to time ...

    To get *more* volume out of this rig .. how safe is it to turn off the 'octocoupler' limiter? Thinking I need a more powerful amp to drive the SVT 410's ...
     
  2. Lync

    Lync Supporting Member

    Apr 13, 2004
    NY
    Trying putting the master on 10 and controlling your volume with the gain...if it is like the B2R, the amp pretty much maintains its tone whenever the gain has a decent signal.
     
  3. Skel

    Skel

    Jun 19, 2005
    Boulder, Colorado
    The limiter is to protect the speakers, not the amp. You have a 450 watt amp driving a 500 watt cab, so I can't see how it could hurt anything.

    Skel
     
  4. leelove

    leelove

    Oct 26, 2007
    Isthis definately right yeah? Im not too good with this stuff but i have just bought a B2RE head and am rather worried that its way too quiet?!...If you turn the limiter on it does start to flash at what id consider a rather low volume... Im a bit worried ive only had it two weeks and should have just bought something louder-although i love the tone it throws out?
     
  5. Lync

    Lync Supporting Member

    Apr 13, 2004
    NY
    Are you running it with a speaker (or combo of) at 4 ohms? It seems this amp really likes 4 ohms. It is louder and just has more life.

    Oddly enough, this is also the case with my all tube V4BH. At 8ohms it is quiet and kinda weak. Run it at 4 and you have that concert bass tone.
     
  6. John Wentzien

    John Wentzien

    Jun 25, 2007
    Elberta, AL
    Artist:TC Electronic RH450 bass system (original test-pilot)
    I always have it turned off on mine. Seems to suck some of the tone out, and engages too quickly for my taste. I've run it this way for about 6 years with no problems.
    Run it at 4 ohms---plenty loud (I have the older 350watt)
     
  7. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX
    Correct in that it protects the speakers, but you can still easily damage a 500 watt cab with 450 watts. The limiter does not reduce power, what it does is reduce the signal so the peaks are not clipped. When extreme clipping occurs, the signal begins to act like DC, with large flat spots at the peaks. Hold a 9 volt to your speakers, then imagine what will happen with 450 watts.

    I would NEVER defeat the limiter. I don't even know why they make them defeatable, to be honest. If you need to routinely defeat a limiter to get the volume you want, you need a bigger head.
     
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Almost all untrue......

    Clipping does NOT act like DC.

    A 450W cabinet will have a very hard time damaging a true 500W cabinet. Mostly because there is no way you can play through it "musically" and use all 450W, let alone more. Not unless your definition of "musical" is a lot different from most anyone else's.

    The limiter WILL reduce peaks until they are not clipped much.

    Therefore, defeating it can allow you to play more dynamically without having the limiter hold you back to a low level. The limiter can make a powerful amp sound like a much weaker one, so the point of defeating it is to allow a "peaky, dynamic playing style" to use all the amp power available.

    If you defeat the limiter, you DO need to listen for excess distortion, because "you" are the limiter now.
     
  9. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX
    It is true. Long periods of flat voltage on a waveform act like DC, forcing the voice coil out for longer than it was designed to do. This can cause heat build up in the speaker, even if the amp is rated less than the speaker is. It is called DC Burn. Sure, you can play dynamically, but it does not chance the fact that with a severely overdriven signal, you can damage a speaker below its rated power.
     
  10. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Still not true.......

    The only ways it can happen as you suggest is that:

    1) The frequency is far lower than the audio range the speaker is designed for.

    or

    2) The amplifier misbehaves in a way that causes a DC offset during clipping. This CAN happen, especially if the power supply is not symmetrical, but is bad design.

    What IS true is that the RMS output of a true square wave is 2X that of a sine of the same peak amplitude.

    if you can get a true square wave from your amp for enough time to damage a speaker, when speaker is rated same as amp, your ears are tin, or you just don't care..... It will sound really bad.

    This HAS been covered before................
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
  12. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX
    You can also find just as many articles on line about the damage potential by seriously clipped signals. The gist being as you had described. A clipped signal can still supply more than its rated RMS power. I thought that falls into the "you can still damage a speaker by using an amp rated below the speaker" category.

    Why then, are limiters almost exclusively described as having the purpose of speaker protection? Including by Ampeg. (from the SVT-4 PRO manual)

    If overpowering was the only thing that killed a speaker, a limiter would not even be necessary.

    Me, being neither an engineer or designer, have to take my info where I can get it, and since I don't have resources to replace cabs, tend to err on the side of caution.
     
  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Oh, you can cook the speaker with a more powerful amp...... but it's very difficult with a "matched" power amp.

    Bill is correct, the excursion is one big issue, and it interacts with power both due to mechanical and electrical factors.

    It's just the "DC clipping" deal that is very much NOT true. That and over-emphasis on exact matching of powers.
     
  14. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX
    Sure, I never was a believer in matching an amp and cabinet, and have played an SVT-4 PRO through various cabs for a long time.

    I think the problem is that why then are limiters billed as protecting speakers? How does a limiter protect against "speaker damaging distortion"? You guys seem to be saying there is no such thing.
     
  15. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The amp designer has no idea what will be connected to the amp. The only protections that can be put in for an unknown speaker are:

    1) Possibly a power limiting circuit to allow the amp to emulate any lower power amp. But why buy 1200W and turn it down to 200? So this isn't done much, unless for other purposes (deliberate overdrive).

    2) A clipping preventer/reducer. This doesn't do much for a 10" or whatever, but DOES do plenty for a tweeter/HF driver. Even a relatively low amount of clipping on a 1200W amp can put a lot of power (100W or so) into the tweeter range. Since they are normally rated for 15 or 25W, that can be a problem.

    So call it a tweeter saver if you want.

    Also, clipping sounds bad, and a limiter can prevent a person from getting really bad sound. A sort-of "anti-suck" button.....
     
  16. quail

    quail

    Aug 4, 2007
    fwiw ive had no problems blowing 100 watt rms car speakers with 20 watt rms head units the distortion from an overworked amp can damage speakers that arent powered adequately
     
  17. Dmetalbass69

    Dmetalbass69

    Aug 15, 2007
    Mohnton, PA
    i have the same setup as you
    but the amp could still fry since its underpowered by a little and would use more energy than it could handle to try and match the cabs wattage rating

    if that makes any sense... lol
     
  18. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX

    That makes more sense, I suppose. Too bad is is never explained that way, or in a less misleading manner. To me, there is a world of difference between speaker protection, and tweeter protection...As I said, not being an engineer, I choose to err on the side of caution.

    Dmetalbass69, I am not aware of any amp on the market that will try to match the speakers power handling.
     
  19. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    I'd bet new Euros against old moldy scones that the POWER isn't what gets those, but rather the flabby undercontrolled speakers that are overdriven at a low frequency below what passes for an enclosure can handle. It's the excursion.....

    Oh, yeah.... A car stereo watt is about a loud cockroach sneeze in reality, at least when it comes to car audio speaker ratings....... You really can't believe ANYTHING you read as "specs" in that biz......
     
  20. leelove

    leelove

    Oct 26, 2007
    Thanks very much guys..and everyone with their far superior to mine technical know-how!:)
    yeah ive been running it with the 'partner' b115e 1 x15 cab which is rated at 8ohms...so guess i need to stick perhaps a 2 x 10 of another 8 on top to really get something out of it then?

    ...Haha...if youve always had it off then ill trust ya man...i give you a sout if it blows up on me! haha. Like you say...the limiter does come in really damn early and hardly makes the point of it allegedly being 250w into 8 worthwhile!