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Problem with Output Levels - SWR 750x

Discussion in 'Amps and Cabs [BG]' started by tpmiller08, Apr 30, 2009.

  1. tpmiller08


    Mar 15, 2009
    Boston, MA
    Hope I posted this in the right place.

    This is my set up :

    BW 1X18" with 2x8" horns, 8 ohms I believe.
    Ampeg 4x12 Cab, think its 4 ohms, been told it was 8, but the specs online say 4

    Those go directly into my SWR 750X

    Now heres where my problem lies. 750 watts at 4 ohms should be plenty of power. But I still find myself turning up to almost 3/4 (3 O'clock) on BOTH my Gain and Master Volume just to be heard over the drums.

    The wierd thing is. I have a Bass Pod Pro pre-amp effects rackmount. When I had this plugged into the INPUT of the 750X, my Output Levels / Volume was through the roof.

    Now that I set it up the proper way with effects send / return with two 3 ft speaker cables, I have to turn up again. I don't want to push my SWR 750x this hard if I don't have to.

    Why is this? Anyone have any ideas?

    I was thinking of just plugging the Bass Pod back into the INPUT on the SWR 750X. But then I lose my crisp SWR tone it seems.

    Thanks for reading about my fiasco of a set up.

  2. I have an SWR Mo bass head, (check the mo bass thread for more info) It's rated at 900w but in normal settings it only puts out around 400... The input needs a lot of gain, and the "scooped" eq setting that is the SWR sound looses a LOT of power. Try the passive input, and cranking the input gain. That and try boosting mids...
    Good luck!
  3. tpmiller08


    Mar 15, 2009
    Boston, MA
    What do you mean by "scooped"?
    I've been using the passive ( I believe it has 5 times the gain or something crazy like that), and my mids level are at 3 o'clock. Should I boost the frequnecy to about that or higher? I have the frequency at aroung 1 o'clock, so it probaly could use a bit more.

    I keep my treble at about 9 o'clock, think I should boost them as well?

    Thanks man. I just don't get why 750 watts doesn't blow away the room at 3 o'clock. But if your only getting 400 watts at 4 ohms, I'm probaly getting around 300 if that! eep! :crying:

    Whats the pluses to having an SWR if you lose so much power?

    Sorry for the bombardment of questions, curiousity runs abound :cool:

  4. Here goes the quote:
    Well all I can say is I'm shocked! and not suprised.

    Dyno'd the mo the other day. (The "Dyno" measures power drawn from the powerpoint, and the total power produced at the speaker out (through a dummy load) and then with some fancy calculations, including the amount of signal fed into the amp, we have an answer on wattage.)

    Dynoing cars can lead to them blowing up as you are measuring it's maximum output, and the same with amps, DO NOT TRY TO MAKE YOUR OWN AMP DYNO!

    Well the results. As the dyno is only setup for mono that's the only measurement we did. We set a 4 ohm load, and ran exactly 240 volts (Australia) off a variac so we were getting accurate readings.
    Then with a sine wave at 1khz (the industry standard pitch) at -20db into the passive input, we fired up the Mo'!
    Setting the input gain to just as the red light thinks about coming on, and with the eq flat, aural enhancer off, all fx off, limiter off and the master to maximum. The dyno soared all the way up to....


    I know where did all the other watts go?

    We saw the output wave (on the cathode ray osciloscope) was still quite smooth with no signs of clipping, and so, we cranked up the test tone to -10db and then cranked the amps input gain.
    The silly red light was now steady red and the dyno now read 880watts! Still with a smooth sine wave! Only 20watts to find
    Next we grabbed the mid and treble eq controls and boosted around 1khz (the test tone freq) and lo and behold, 902watts at 4ohms.

    There are a couple of things this made me realize. I have to dyno more big amps more often! and I'm back to thinking SWR treat all their customers like morons! That stupid red light comes on way before the input clips! I'm sure it's just so idiots don't blow up the amp, but I would hazard a guess that you could safely run the amp for hours with that red light on... I'm thinking of trying the mo' as a power amp for a gig sometime, just running another pre into the fx return.
    But now we all know. Yes they are 900watts, but if you follow the manual you'll never find them...

    Here endeth the quote.
    Hopefully this helps...
    I don't know if this helps, but I reckon it'll be the input gain.
    Does the 750 have an input light? If so make sure it's on on loud notes...
    Good luck!!
    I personally don't use my SWR much, there are other heads I prefer, but I know people who run 750s with great sucess!
  5. tpmiller08


    Mar 15, 2009
    Boston, MA
    Yup, it has an input clip light. I set it a notch or two below the input clip level. But reading that I'm sure I can turn it up.

    Maybe I'm being a big wuss about it, but I'm really afraid of this thing over heating and dying on me. Thing gets relatively hot.

    Still doesn't explain why I get a HUGE gain boost when I plug my pre-efx into the input instead of the effects loop. But, from what I gather, it's safe to get the red light to blink when I play loud, or dig in deep right? I thought it was like a the red light of doom, and if it blinked it was causing damage to the amp heh.
    Can you hear pre-amp clipping? Or is it silent?

    Thanks for the help man. I got a few shows comin up, and it'll definatly come in handy!

  6. chadds


    Mar 18, 2000
    How loud is your 750x on one cab?
    I think you've just got too much cab going on there.
    You might want to check the efficiency of those cabs vs. say a GIII.
    You might have power hungry cabs there.
    If so they may need a lot more watts and they seem to make the 750x seem weak.
    We discussed this elsewhere. In a cars if you have a 300 hp engine in a 6000lb car you can claim you've got hp but if won't beat a 200 hp engine in a 2500lb. car.
    Some cabs will scream with 100watts some won't even open up til you give them 500w.
  7. tpmiller08


    Mar 15, 2009
    Boston, MA
    I'll try that out at the practice spot tomorrow for sure. You think I'd be better off going with the 4x12 or the 1x18 with 2x10 horns? I know its a matter of taste, but I love the lows from the 1x18 and the punchy-ness of the 4x12. So I'm torn :help:

  8. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    Shouldn't be using speaker cables in your effects loop. Instrument cables are correct, speaker cable is only for speakers. And, if it sounded better going in the front end, why not put it back in that way?
  9. tpmiller08


    Mar 15, 2009
    Boston, MA
    I might be wrong, I think the SWR manual said to use speaker cables. I'll have to look that up.

    It had more volume, and the effects sounded the same. But I lost the SWR "tone". That crisp, clean sounding thinger :p I lose some functions setting it up that way. The main thing being the effects knob. Using the effects loop, I can move it from dry to wet. Going through the input, the knob doesn't have a function. I like a small seasoning of effects, while the SWR tone comes out on top, if ya know what I mean.

    Also, when recording, it's easier to just plug a XLR cable into my SWR 750X and go right into the board. Again, keeping the tone.

    The tone boss! the tone!

    I'm going to play around with it tomorrow before practice. Maybe using the RIGHT cables might help, using one cab, or just plugging back into the input if all else fails.

    I'm just glad our big show at the end of May has a sound mixer, and an engineer. So I wont have to worry about all this :bassist:

    Thanks again guys!

  10. DWBass

    DWBass The Funkfather

    Could just be the efficiency of the cabs. They just won't get any louder when more watts are added. I had that issue with a SWR Goliath Jr. It was actually louder with less wattage. I pumped 330w into it and I had the volume at 12 noon and no matter what I did, it would not get any louder.
  11. I recall having to really crank the input of my old SWR 350, definitely to the point of clip light, to get a decent amount of power out of it.
  12. Bongolation


    Nov 9, 2001
    No Bogus Endorsements
    The scooped mids are the issue here, as has been pointed out many times.

    My question -- and I know someone has the answer -- is what knob settings on the X series compensate for the tone stack and gives a more or less flat EQ?

    Thanks for any useful info on this.
  13. Bongolation


    Nov 9, 2001
    No Bogus Endorsements
    I wouldn't put it past them, but it's wrong to use speaker cables for an effects chain.

    There's a gross error in my 750X manual about how the limiter works (correct for different models, but not the 750X), and it went uncorrected for ages...and might still be there.
  14. tpmiller08


    Mar 15, 2009
    Boston, MA
    Out of curiousity, whats the misprint about the limiter?

  15. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    You've got one cab with an 18 and two 8's, plus a 4x12 running off a 750X and you're having output issues? I know I'm beating a dead horse here, but its time to rethink your global EQ!
  16. tpmiller08


    Mar 15, 2009
    Boston, MA
    How so? I have ultra high mids ( both mids on the amp itself, and my bass pod pro are set really high), bass boosted, and treble down to 7 o'clock - 8 o'clock.

    What would you recommend for EQ settings?

  17. chadds


    Mar 18, 2000
    Flat on the amp and whatever on the pro.
    How loud is your rig w/o the pro?
    It still might be cab efficiency.
    Can you get your sound without the pro?
    Can you get your sound without one cab?
    Your cabs are so different that I can see why it is hard to choose.
    Is it possible they are out of phase with each other?

    But reread your first post.
    How about Pod with line cord from Pod line out into effects return only of the 750x. That would use the Pod as your pre and the 750x as a pwr amp. Won't hurt anything. Pod is now your pre. The controls of the SWR pre won't affect anything. The Master will work.
    If the 4x12 is really 4 ohms it should be way louder than the 18" cab. If it's 8 ohms they should be similar in output.
  18. guermo


    Dec 4, 2004

    Wondering if anyone has the info on this?
  19. David1234


    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    You can't really flatten an SWR amp's response with EQ. The response curve is really wide, shallow stuff and boosts and cuts that the EQ would add are relatively skinny. Just don't turn the enhancer up past the point where you're hearing it start to get quieter again, that's an extra notch that kicks in at about noon on some amps and 2pm on others, which is skinny and deep at 200Hz.

    As for the POD seeming quieter in the effects loop, I suspect it's because you're using distortion and the effects loop is line level but you've set up your patches for instrument level. If this is happening the distortion will cut things down to an instrument level, so you'll have a volume problem.

    But there's some tests to do first, if you have 10 minutes.

    1. Test your 3 foot leads for phase reversal. Plug one straight from the effects send to effects return and play with the loop set Dry all the way to Wet. If it's "backwards wired" you'll be earthing the signal instead of passing and you'll get practically no volume. Repeat with the other lead.

    2. Bypass the SWR preamp and test the effects return with the POD as the pre. So plug the bass into the POD and the POD's output into the effects return. Chances are you'll still be pretty quiet as the amp is looking for a hot return signal.

    You'll know enough now to fix your problem! Oh and +1 for only using speaker leads for speakers and instrument leads for instrument signals!

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