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What does a "limiter" do?

Discussion in 'Amps and Cabs [BG]' started by SirGrotius, Feb 16, 2008.

  1. I recently got a used SWR Workingman 15" combo used for some basement jamming, and I have a couple "obvious" questions (I'm a newb):

    I don't know the different between "preamp" and "master" volume. I just set them the same...what should I be doing?

    Also, jamming at about 55% volume today (preamp and master both at 5/6), and when I'd really wail on some high notes I noticed a green light shot on for less than a second and it was called the limiter.

    I'm assuming this is something that knocks out something considered too loud for the range. I'm worried that this means that I can't pump up the volume more so than 55%...i.e., the limiter is indicative of "too loud" to handle.

  2. mntngrown

    mntngrown Supporting Member

    Aug 18, 2007
    Santa Cruz Ca
    I'll give you a guess till the experts answer. My new power amp, which is only an amplifier for a separate source, typically a preamp, says in the manual to put a limiter between the preamp and the power amp so if the preamp signal is too hot it won't clip etc and do bad things to your speakers. I think if you turn down that preamp volume you mention and turn up the main volume it won't happen?
  3. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    A limiter senses the onset of power amp clipping, and temporarily reduces the overall gain. If it is implemented well, then it is relatively unobtrusive, and lets you work closer to the full power of the amp without worrying about distortion.

    With amps that had a limiter, I also used it as a convenient indicator of when I was getting close to the usable power of the amp. If it is doing more than just flashing at the start of each note, then you are close to running out of power.
  4. heytrid


    Feb 12, 2008
    Calgary AB
    fdeck is correct, on most swr's there is 1 of the knobs (i think mine is the master) that you can pull out to defeat the limiter if needed, personnaly i think if you need to defeat the limiter then you just need a more powerful amp.

    as for the difference between the preamp and master in the most untechnical terms would be.

    preamp = volume or "gain" for the preamp (input) section of the amp
    master = overall volume control

    if you like the sound of it with both set the same then that is fine but it is ok to experiment with them at different levels to see what you find sounds best, most will turn the preamp/gain up higher in order to overdrive the input source and gain some "dirty" to the sound. I think if it is the same as my model it will have a red LED to tell you when the preamp is clipping (clipping is what causes distortion)
  5. A good rule of thumb to set the preamp level is: first disengage the limiter if you can. Next look for a "preamp clip" light somewhere near the gain knob. Hit your E string HARD, turn the pre volume up and keep turning up and hitting the string hard until the light flashes a bit, then back the knob off 'til it doesn't. Then you can engage the limiter again and adjust your overall volume with the master.

    This will of course give you a clean sound, no dirt.
  6. heytrid


    Feb 12, 2008
    Calgary AB
    i just checked on mine, the limiter on it is the effects blend knob, so not even sure if your model has the same function.

    Also i should note while using mine the limiter only limits power amp and not preamp, so the way to set the gain would be the same way only you do not have to disengage the limiter, there is a red led to go by.
  7. same. i bought mine used so don't have a manual or anything. i'm unclear what the "effects blend" knob does, but the limiter is just above it (to the left of the "horn" switch).

    thanks for the info.
  8. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    The "effects blend" knob would be for when you have effects units plugged into the effects loop; changing the blend knob changes how much of the effected signal is mixed in with your clean bass signal.

    Aside from the very practical advice given before, a limiter is a type of compressor. You can read what those do in the FAQ linked in my sig.
  9. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    SirGrotius, please read thoroughly here is some info from the owners manual for the WM15...

    Two separate and independent input jacks are provided so that the best signal-to-noise ratio can be obtained without overloading
    the preamp section. The Passive input has over twice the gain than that of the Active input. Both inputs can be used simultaneously
    without affecting the volume or tone of the other. One use of these inputs would be to plug your bass into the
    Passive input and practice along with a drum machine by plugging it into the Active input. A more detailed explanation of these
    inputs follows.

    Passive Input
    This input can and should be used if your instrument has passive electronics (no built-in preamp). Technically speaking, this
    input should be used if your instrument has an output voltage of 1 volt RMS or LESS. Consult the owner’s manual that came
    with your instrument or ask the manufacturer if you are unsure.

    NOTE: Generally speaking, you should try the Passive input jack first. If you hear a small amount of distortion and the
    Preamp Clip LED is not activated, try using the Active input jack. And please note, some passive pickups DO distort.
    Because of the hi-fi nature of all SWR products, even the smallest amount of distortion originating at the source (instrument)
    may be heard.

    Active Input
    The Active input jack should be used with instruments having a built-in (on-board) preamp that will produce signals over 1 volt
    RMS. Some really “hot” pickups installed in your instrument may find the Active input more compatible. The best judge is your
    own ears.

    NOTE: Using the Active input with passive basses may result in a loss of high-end transients. Players who roll off their
    high-end starting at around 2kto 3kHz may find this input more to their liking.

    If your hear some distortion from your active bass and are using the Active input jack, check your battery. Also, make sure the
    Preamp Clip LED is not lighting.

    The Preamp Clip LED will light whenever the Preamp, Tone section or output buffer reach clipping (that is, run out of headroom).
    In the event the Preamp clip indicator lights, turn down the Gain control. Since the Preamp Clip also monitors the Tone
    section, boosting any one of the tone controls can cause the LED to activate. Again, turn down the Gain control if this happens.

    NOTE: Constant clipping of the preamp will not harm the electronics in your Workingman’s 15. However, damage can
    occur to speakers due to near-DC content present in a clipped waveform.

    The gain control adjusts the volume of the preamp section. After the Tone controls, Aural Enhancer and any effects you may be
    using have been set to your liking, the Gain control should be set to where the Preamp Clip LED barely flashes upon hitting
    your loudest note. After setting the Gain, use the Master Volume to set the desired volume level. Using these controls in this
    manner assures the maximum signal-to-noise ratio with no distortion caused by the preamp circuits clipping. Since the Gain
    control is similar to a “pad,” a small amount of signal will get through with the Gain control turned all the way down. The Gain
    also adjusts the level sent to the Effects send jack. If your effect is being overdriven, turn down the Gain control.

    The Master Volume adjusts the signal level going to the power amplifier. It DOES NOT control the output of the effects send
    jack or Balanced Direct Record XLR output. It DOES affect the output of the internal speakers, headphones, and extension
    speaker jack. Losses caused by effects units can be recovered by increasing the Master Volume.

    NOTE: If you need more volume than the Workingman’s single 15” can provide, add an extension speaker cabinet. The
    extension cabinet should have an impedance of no less than 8 ohms.

    The Workingman’s 15 Limiter Circuit is a soft knee type limiter that prevents distortion of attack transients or peaks. The
    Limiter can be used as an effect and is also helpful in preventing speaker damage. The circuit is located after (post) the master
    volume and before (pre) the power amplifier; it is driven by the Master Volume Control. Its threshold (starting point) is preset
    by the factory so that the user can get maximum overall apparent volume without unduly overdriving the power amplifier.

    The Limiter LED lights when your signal has reached the Limiter threshold, letting you know that the Limiter circuit has been

    NOTE: No harm is being done to your amplifier when this LED lights or stays lit.


    I would assume if you use too much bass on your guitar or combo it will set off you limiter earlier and lower your volume when you might need to be heard...

    good luck

  10. Mike thanks so much for that info! I actually did a google search last night for my amp's owner's manual, since I purchased it used but came up empty handed.

    It seems that my 5/5 method isn't optimal--I'll try boosting my pre and adjusting my master afterward. It's good to hear that I'm not damaging anything when that limiter light did flash!

    Now I need to search out adding that extension speaker cabinet. I suppose it's kind of cool that I can add an extension to this "combo" amp, but I doubt the extension speaker cabinet can add much gusto.
  11. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    actually if you add a 8ohm speaker cab you could DOUBLE your total acoustical energy, although it results in a 3db volume boost it doesn't seem like double. but it will cause an increase!

    from the owners manual, found at http://www.swrsound.com/support/manuals/pdfs/wm10_12_15_om.PDF
    see page 19...

    Use an unshielded 2-conductor cable (NOT A GUITAR CORD!) to connect an additional speaker cabinet. Use a high quality,
    heavy gauge cable of at least 18 gauge (the lower the gauge, the heavier the cable). The impedance of the speaker should be
    8 Ohms or greater. If you wish to connect two additional cabinets be sure their combined load impedance is not less than 8
    ohms (equivalent to two 16 ohms speaker cabinets in parallel)."
  12. Great stuff. Thanks again for linking. I'm a little surprised that this COMBO amp has such extension capabilities. I usually assumed that the sole purview of the $800 head and $1000 cabinet territory, but getting used SWR 2X10Ts might add some punch?
  13. StringThing


    Dec 6, 2007
    San Diego
    I thought a 2 10 would work, but I needed bottom. Go figure, I tough a 15 would need the opposite, but they are not "shaping" amps that color your signal. I run a 18 sometimes with mine. Moves more air than hurricane Katrina.

    Notable on this amp is that the XLR out bypasses the EQ, so stage adjustments do not effect the house board.

    I believe i have the manual in PDF if you want to contact me. Good reading!!!

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