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Amp limiter question

Discussion in 'Amps and Cabs [BG]' started by Erkalump, Jul 12, 2018 at 12:36 AM.


  1. Erkalump

    Erkalump

    Thursday
    New bassist here with new to me gear. Been lurking for a month or so and already learned a bunch.

    I just bought my first bass rig consisting of the following: A used SWR working pro 400 and one Acoustic BN115 neo cab (500 watts @ 8 ohms).

    My question has to do with the built in limiter. The only control for the limiter is a defeat button.

    I just completed my first band audition playing near gig volume. Following the instructions, I set the input gain with the active pad engaged. Eq flat and bass eq flat (active sbmm SUB 4 string). I had the master volume set at 12:00.

    I noticed during the last song that the power amp clip light was nearly constantly illuminated, indicating power amp clipping. I had the limiter engaged and functioning. Based on my limited understanding, the limiter was holding the signal Into the power amp section below a preset threshhold.

    My question is: Is 50% volume level all she's got? Is that as loud as she goes? I didn't have more time to putz with different settings, and I won't have an opportunity for a while (neighbors, etc)

    What do I need to do to crank it and get full power (250 watts at 8 ohms)?
    Any input is appreciated. Thank you.
     
  2. biguglyman

    biguglyman

    Jul 27, 2017
    Rochester, NY
    Not sure how well this applies to your specific issue, but here's how I set my stuff. I also have an active bass and a pad on my amp. My amp also includes a built-in compressor/limiter.
    With the pad engaged, I rather vigorously pluck my E string...about as hard as the hardest I'll play when really digging in while at the same time turning up the gain. I turn it up until the compressor/limiter light is just blinking at the loudest, hardest pluck. I then use the master volume to adjust the level. It sounds to me like you may have the gain up too high.
     
  3. Stumbo

    Stumbo Wherever you go, there you are. Supporting Member Commercial User

    Feb 11, 2008
    Intergalactic Mind Space
    Song Surgeon sofware
    More speakers=more volume.

    With only 1x15, you get what the speaker gives you regardless of amp watts rating, tone control flat, etc.

    Acoustic cabs are not high end therefore not very efficient, don't handle a lot of watts or mechanical excursion.

    Btw, how do you know the amp tone controls were set "flat"?

    Also, with only the 1x15 and 260w, why do you think it should hold up in a loud rock band?

    Try turning the volume to 2 o'clock and start with the gain on zero and adjust upwards. Also cut the bass tone on the amp and your bass.

    I also suggest adding another 1x15 to move more air.

    Still, it may not be loud enough until you step up to higher end cabs that can handle more watts, are more efficient and can move more air(Xmas, mechanical excursion).

    Something like a 2x2x10 or 2x2x12 or 2x2x15 vertical stack with an HPF should do rhe job. With four speakers and an HPF protecting them, you should be able to keep up with a loud rock group.
     
  4. Another cab.

    Best bet is usually another of the same cab but that would be doubling down on the Acoustic relative junk.

    You might be able to afford a better cab stack? It's generally accepted that cabs are the most critical element of the amplification chain.
     
  5. Element Zero

    Element Zero Supporting Member

    Dec 14, 2016
    California
    Not all Master Volume controls on amps are the same so keep that in mind. That being said, if you in fact had all eq flat and you were still getting POWER AMP clipping, then yes. That’s all she’s got. A different and more efficient cab is worth looking into. If that’s not in the cards right now, you may want to look in to setting the cab on a STABLE step stool of some kind to get the cab off the ground so your ears can hear it more than your knees.
     
    Garret Graves, Eric DK and saabfender like this.
  6. saabfender

    saabfender

    Jan 10, 2018
    Indianapolis
    That SWR head and a good 15” speaker should be able to run you out of your rehearsal space. I know my Peavey TNT 115 with a nice JBL 15” can. I have yet to have a rehearsal where it couldn’t keep up or dominate if necessary.

    You’ll need either a new better speaker for the cab or swap the whole cab out. If you go the new speaker route, look to spend a couple hundred on something nice.

    No way to futz with your amp? Take it out to the parking lot. Do it in your building mid-afternoon for a few minutes some weekend. Dude, you gotta be futzing. That’s how you learn to work your rig.

    Come to think of it, last time I had an overactive limiter light, it was cleaned up by recapping the power supply. Lower internal voltage means less volume ( possibly a lot. The last recap I did was dramatically louder) and it has to work way harder to get the same loudness as a fresher amp. It also means it can’t deal with transients very well. Those big caps are essentially batteries. They need to keep up with a huge instantaneous demand. If the SWR is 15-20 years old and has been run a lot, they probably need replacement.
     
    Last edited: Jul 12, 2018 at 6:32 AM
    Garret Graves likes this.
  7. Erkalump

    Erkalump

    Thursday
    Great advice. Thanks, all.
     
  8. Wasnex

    Wasnex

    Dec 25, 2011

    The master volume control sets the signal level before the power amp, it does not limit the amount of power the amp can generate. If the amp is producing full power with the controls at 12, it is maxed out.

    IMHO 250 watts at 8 ohms is not a huge amount of power, especially if you don't have a very efficient speaker. If you want the max performance this head is capable of, you need a second 8 ohm speaker. Adding a second identical speaker will increase your volume by almost 6dB for frequencies where spacing between the drivers is close enough for near perfect coupling....basically within 1/4 wavelength.

    Ideally you should use two identical speakers for the best performance. This is because different designs can have significantly different phase and group delay characteristics. Basically, dissimilar speaker systems may be out of phase at one frequency and in phase at another...better to use identical speakers so they are in phase at all frequencies.

    As @saabfender mentioned, worn out filter capacitors may limit the power your amp can produce. Not only do worn capacitors store less energy, they can also develop internal resistance that pulls down the voltage of the power supply. Both of these factors limit power.
     
    Garret Graves and fourstringburn like this.
  9. Erkalump

    Erkalump

    Thursday
    Thanks wasnex for that explanation. At the audition, the volume was good with the band and everyone liked the sound and tones.
    I was suprised to learn that the power section was at the end of its rope though.
    I bought the cab because of a killer deal and a really smooth tone, realizing that I could add a cab when necessary. I didn't realize that could be this soon.

    Actually, if I get the gig, I'll have a great pa to di out to and this cabs volume level should be adequate for the stage according to the other band members.

    Regarding what you said about matching cabs... very interesting... It makes me wonder why amp companies are always talking about different cab combinations...

    Thanks for that great explanation.
     
  10. Wasnex

    Wasnex

    Dec 25, 2011
    With careful design, cabs with different size drivers can work reasonably well together. Unfortunately some of it is pure marketing drivel, so it may be a roll of the dice. Sometimes dissimilar designs from different companies work well together as well...serendipity happens from time to time.

    Good luck!
     
  11. Rip Van Dan

    Rip Van Dan Supporting Member

    Feb 2, 2009
    Duvall, WA
    Two things I can think of off hand. One take the pad back off. Turning the pad on typically drops your signal by 12 to 15db. Second, try turning your gain up until that preamp clip light flashes but doesn't really stay on all the time. That should let you turn your master down a bit leaving you some headroom to go after more volume if needed.

    The other thing is the last I checked with acoustic, they didn't have very good sensitivity levels, which means it takes more watts to make them loud. Perhaps that has changed. I used an acoustic B410 for years and had to write to the company 3 times before I got an SPL rating out of them for it. According to acoustic it was all of 92db. Starting that low it takes 256 watts to hit 115db "IF" everything works perfectly with my B410 cab.

    I just looked for the SPL on your 115 and not only do they not specify the sensitivity, I don't see an acoustic 115 that has power handling of 500-watts. The one they have on their web site handles 350-watts, which is more in line with what I would expect.
     
    Bass_Pounder likes this.
  12. 40Hz

    40Hz Supporting Member

    I have an SWR SM-400 amp.

    SWR suggested set your bass the way you usually do and turn the gain up until the clipping light flashes during your hardest playing monents. That provides the amp with the optimal gain level for you and your instrument. Then you can take it from there. If you want more volume, crank your master knob

    On my SWR I put everything through the normal input jack. I will only use the padded or “active” jack if I’m getting bad distortion with an active bass regardless of what amp I’m using. On my SWR I haven’t had that problem.

    My onboard limiter is a single knob rather than a switch. I leave it off. If you need a limiter or compressor, buy yourself a pedal.

    Same goes for the enhancer. It doesn’t do anything IMO except junk up your sound. If you want an “enhancer” type device, buy a used Aphex Bass Xciter for about $60-$80. Those actually work and sound good.

    FWIW despite all the bells & whistles on my SWR, I’ve found it sounds best the less of them I use. In my case I use the gain, treble, bass, and master knobs and that’s about it. YMMV.

    I think what you need is maybe just a better cab. My SM-400 into a Goliath Junior II (2x10) cab will shake the room and rattle windows without breaking a sweat.
     
    Last edited: Jul 12, 2018 at 8:23 PM
    Rip Van Dan likes this.
  13. nbsipics

    nbsipics Had to Cry Today Gold Supporting Member

    Apr 8, 2016
    You’re not possibly using an instrument cable to your cab?

    Welcome to TB, and don’t listen to me :)
     
  14. Erkalump

    Erkalump

    Thursday
    Good question, but no.
     
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Ahhhh, the mysterious and awesome urban myth of a recap job, one of the biggest and most profitable farces in the business. Also one of the most common miracle fix-all in the DIY repair industry. In fact, probably 95% of all caps replaced in such "placing of the hands" miracle cap jobs are not bad and have more than plenty of service life left.

    I have also seen plenty of otherwise fully functional amps and especially consoles ruined by ham fisted attempts.

    In general, a bad idea.
     
    Garret Graves, ak56 and BadExample like this.
  16. saabfender

    saabfender

    Jan 10, 2018
    Indianapolis
    Ahhh, the mysterious and awesome urban myth of the all-knowing guru. I like how you know so much about other people's experiences. The story I recounted didn't happen? You are so wise and I am so foolish. It's funny, you hear all the same arguments concerning people repairing their own modern automobiles. I've been in the automotive repair industry long enough to have often heard similar spiels concerning cars. It's mostly BS with a dash of truth thrown in for plausibility. Amps are certainly not more complex than cars.

    I don't think the paper caps in my Hammond and Leslie would have responded to a "placing of the hands." Is that the way you guys work in your shop?

    Are the rated service life figures printed on the caps meaningless and printed for decoration? A scam by the capacitor industry?

    I don't have fists made of ham (a good heated solder sucker is preferable) and all the recapping I've ever done, I want to say about 50 pieces lifetime, has turned out fine. Even the 32x16x2 console. Where was a Prophet of Doom to forecast my downfall then?
     
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    All the power to you then, "Vlad the Healer"

    I'm sure the cap industry thanks you mightily ;)

    I stand by by statement that 95% of all caps replaced are in fact perfectly fine.

    Especially since we are taking about an amp that's not very old here (on practical terms)
     
    Last edited: Jul 13, 2018 at 1:16 PM
  18. Wasnex

    Wasnex

    Dec 25, 2011
    I didn't say the amp needed a cap job. However, I do believe if the amp is not making good power, faulty power supply capacitors can be the source of the problem for the reasons I described in post #8. However, if the amp is suspected of not working properly, my advice would be to send the amp to a reputable shop for a checkup, rather than randomly replacing components.

    I would expect capacitor problems more in an amp that has not been operated for an extremely long period of time, than an amp that has been regularly operated on proper line voltage.

    I am sure I have replaced a few capacitors that didn't need it. If I find a couple of bad electrolytics or suspect a cap failure because the amp hasn't been powered up for 20 years, or because the amp has been exposed to overvoltage, I may take a shotgun approach.

    I have pulled capacitors measuring above their capacitance rating on my meters, that significantly pull down the voltage when placed in a circuit. Obviously that's a bad capacitor...also capacitors that measure below their capacitance rating are obviously bad. But as I only own cheap DVM and LCR meters, I don't have the means to further evaluate capacitors that measure at or above their rated capacitance.

    I would greatly appreciate if you would give a brief description of how a reputable shop would assess the health of a suspect electrolytic capacitor. Then I will have to evaluate the cost of procuring the necessary test equipment against the cost of replacing a few good capacitors.
     
    saabfender likes this.
  19. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    One easy thing is measuring a cap's performance in the circuit it is being used in.
     
  20. Erkalump

    Erkalump

    Thursday
    FWIW, I never mentioned a volume or performance issue. I was really just curious to know why the limiter was being triggered at 50% on the master volume knob.

    My amp would have been made between 2005 and 2013. Not too old in my book. It's in excellent condition.

    I understand the point of other posters that adding a cab or upgrading to a different cab will be needed when more volume is required. For the circumstances, volume level was just fine.
     
    saabfender and Wasnex like this.

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