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Bridging into two cabinets.

Discussion in 'Amps and Cabs [BG]' started by ndjx, Jun 12, 2005.


  1. ndjx

    ndjx

    Oct 26, 2001
    MN
    I'm sure this has been covered before, so if someone has another thread they can link me to that would be fine. I tried the search function, but the thing won't highlight words for me and alot of the topics are not what I'm looking for.

    I have a Behringer EP1500 power amp and I want to bridge into two 8 ohms cabinets. I'm pretty sure this can be done, I'm just not sure how being the bridge output uses a banana plug.
     
  2. ndjx

    ndjx

    Oct 26, 2001
    MN
    HELP? BUMP. :help:
     
  3. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    as long as the amp in question can be run bridged into a 4 ohm load you can do it. If it is capable of running a 2 ohm load per side in stereo it should be able to be bridged into 4 ohms.

    The easiest thing to do is to daisy chain the 2 cabs together with a short speaker cord (the cabs should have parallel inputs/outputs). Then you connect one cab to the amp. Consult your owners manual re: how to set up the amp for bridge mode. you'll probably have to flip a switch from stereo to bridge mono mode. If the amp uses bannana jacks on the back they're probably going to have you bridge it by connecting a bannana plug to the positive terminals of both sides of the amp. Some others have a special speakon jack just for bridge mode, but usually you need a special speakon cable to make it work.
     
  4. ndjx

    ndjx

    Oct 26, 2001
    MN
    I'm bridging into one 4 ohm cabinet right now. So if I use two 8 ohm cabinets and daisy chain them, will I still get the 4 ohms output of the amp?
     
  5. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    yes. for more information read the faq linked in the post above mine.
     
  6. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Take one of THESE and put it here.

    [​IMG]

    :D

    Joe.
     
  7. markfsy

    markfsy

    May 14, 2005
    Suffolk, England
    Put the dip switches into the following positions for monobridged -
    1,2,3 - I think best is - clip limiter on, filter at 30Hz, and filter on
    4,5 -stereo
    6,7 - bridge mode on
    8,9 and 10 * see below
    The outputs are - use the two middle binding posts ONLY(ie as + and -), or use output 1 speakon (upper) +1 and +2 pins As the other guy said, daisy chain the two cabs - 4 Ohms is ok apparently, but don't go below it.Keep the channel 2 vol control down.
    *8,9,10 - read the small label on the rear of the unit (left side if facing rear) which gives you these positions. They are different from the instructions in the manual, so follow the label, not the manual. I didn't notice, and you get some really weird sounds, which I don't think you'd like.As far as I remember, it tells you to keep the channel 2 clip limiter and filter off.
    I tried mine on bridged and it worked fine, but then I realised that I'd get 500 watts each side into the two 8Ohm cabs I've got, and that seemed enough. You only get more out in bridged when you turn the output up past 30db, and those two clicks between "max allowable into my cabs" and "possible blown speakers" seemed too small for comfort!
     
  8. The volume control doesn't limit the max output of the amp at all.

    If you turn the power amp down 50% and turn up the preamp twice as loud, you're right back where you started. Turn it down to 1/4 and turn up the preamp 4x. Bingo. Back to same output level.

    The power amp volume controls are used to match the various preamp outputs for differnt models (turn up for lower output preamps, turn down for high output preamps).

    Kind of works like the input gain. Turn it down for active basses, turn up for passive basses. End result is same signal level.

    Randy
     
  9. markfsy

    markfsy

    May 14, 2005
    Suffolk, England
    Sorry - I've got the 2500, so the output levels are differentof course, but the switching and connections are all the same
     
  10. markfsy

    markfsy

    May 14, 2005
    Suffolk, England
    I've only just noticed your strange post Randy. I've currently got an Ampeg amp which I use as a pre, and a EP2500. Now the strange thing is that my power amp volume controls DO control the oputput levels - if I turn them fully counter-clockwise, I get no output from my speakers, and if I turn them fully clock-wise, I get full output. Where do you get bthe idea that they are only for matching various preamp output levels? Perhaps other makes do work like this, but I can assure you that in my setup I set the preamp up to a level around/just before clipping, and then I use the volume controls on the EP2500 as, surprisingly, volume controls. They are even marked as 0 to 34db GAIN, which should be a bit of a clue.OK you can run the power amp wide open and control the volume with the pre level control, but I think this gives a gutless sound, and it doesn't mean the volume controls on the power amp are purely for matching to the level of the preamp output.When I said that you only get more in bridged mode than parallel mode past 30db on the controls, I meant just that. You get 500 watts per side in parallel mode at volume setting 34db, and 960 watts in bridged mode at 30db. 32 gives you 1536 and 34 gives you 2400 (all approx and in theory obviously) Please enlighten me as to what you are talking about, as this is the second time you have jumped on my replies to people and contradicted what I have said for no reason at all. Have you got some sort of a problem, or is it a hobby of yours?
     
  11. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Easy there, markfsy.

    Theoretically, technically he's right.

    But as far as practicality goes, you are right.

    Sure. You can use your amps gain controls as a volume control, but you are wrong about the amount of watts you get at given gain settings on the amp.

    IF you set the gain controls on your amp at 9 o'clock and you set the gain on your preamp so that the amp is just under clipping, you have maxed out the amp (1 watt or 2400 watts, it doesn't matter, it's whatever your amp was designed to put out). If you set the gain control at 3 o'clock on the amp and set the preamp so that the power amp is just under clipping you have once again maxed out the amp...at the same level of power (with the same amp, of course).

    I agree that there is a difference in the tone or maybe the feel of the tone depending on how much pre-gain you have compared to how much power gain you have. And I also feel that it is subjective. But as far as POWER PRODUCED goes, once your power amp has hit clipping it has been maxed out (power-wise) no matter where the gain settings are at!

    See?

    I know, just a bunch of hair splitting...but true.

    :D

    Joe.
     
  12. markfsy

    markfsy

    May 14, 2005
    Suffolk, England
    Zero audible output = 0 watts out ok? No-one was talking about getting more watts out at one particular way of setting up the amp rather than another. What I'm talking about is that, on MY amp at least, zero (or fully anticlockwise) results in zero output, or zero gain. Fully clockwise results in max gain, in my case 34db. Now as the max output at 4 ohms bridged is 2400 watts, reducing the gain by each 3db halves the watts out. So if 34 db results in an output of 2400 watts, then 30 db gain results in an output of 960 approx. Stevesucks says that the vol controls on the power amp are just for matching the preamp output to the power amp, which is odd with a range of gains of 0 - 34 db. Those preamps must really vary in their output to require such a vast range. What do you mean technically he is right?. He's not arguing about the same point that you're making. When I talk of setting the pre up to clipping level, I'm talking about the clipping led on the preamp. You seem to think I meant that I set it up till the power amp clips, and that's not what I said. I set up the pre to just at or under clipping of the signal from the preamp as indicated by the led on the preamp, and then use the power amp vol contols as vol controls. I didn't say that having the pre amp right up and the poweramp down gives you more watts than having the preamp right down and the power amp right up, as you would see if you read what I originally wrote. Stevesucks says the vol controls on a power amp are level matching controls, right? Show me somewhere that says that is correct. They are volume controls - they control the volume that comes out of the speakers - they control gain. The reason I am getting shirty with randy is that he has done this before - misinterpreting what I have said, and then arguing against it in a patronising manner. And you have not followed what I was saying either, as you will see if you read what I originally wrote. It seems you can't say anything on this forum without someone trying to shoot you down in flames, which I wouldn't mind if they took the trouble to read what I say in the first place without getting it all upside down ie no-one but you has mentioned power amp clipping, and no-one but you has argued that more watts are produced by on set-up or another. I was saying that there are only two clicks between 960 watts output and 2400 watts out in bridged mode on my amp - quite simple, but not simple enough, apparently. Read what I wrote again, and then you can post that technically I am right, and Randy is talking out of his ear. This should be called "The Cross-purposes" Forum
     
  13. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Yes, we all know zero is zero.



    Yes, see above.


    This is where you are getting off track. Please re-read my post. Your total output (2400w) totally depends on the COMBINATION of input signal strength AND input signal gain. Not JUST the position of the knob.


    More or less, yes, that is correct.


    They ALL do.


    O.k....


    There's absolutely nothing wrong with doing it that way.


    In your original statement you said that you only get more output in bridged mode after turning your amp past 30db. IF your are speaking SPECIFICALLY of your rig and how YOU have it set up, then o.k. But IF you meant that you only get that extra power in bridged mode when you turn up past 30db then you are wrong. Which I belive is what steve was responding to and what I (may have misread) was responding to.

    Maybe take a second and clear this up. Thast way no-ones panties get in an uproar.

    I don't know about your past with this guy and it is irrelevant to how you conduct yourself in these forums. And as I tried to imply earler, I thought you were both right but possibly talking about different things.

    Now it turns out that you MAY have been meaning something else from what I originally understood. Lt's just chill and get this figured out.

    See my above responses.


    You are way too defensive...and what I said is true.

     
  14. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Sorry I messed up the quotes at the end of my last response but I think it is still clear what I meant.

    :D

    Joe.
     
  15. Common misconception, but you couldn't be more wrong.
    You're confusing max output with the current volume.

    Turning down the power amp gain from 34 dB to 31dB just means you have 3 dB less GAIN, the available power out is still 2400 watts. It just takes a 3dB hotter signal to produce 2400 Watts output. You can get the extra 3dB gain by turning up your guitar, your preamp, the EQ, anything that results in 3dB more signal. But you always have the full 2400W available, provided you give it enough input signal.

    I thought you were under the misconception that the only way to get full output out of your amp is to run the power amp volume all the way up. And reading the followup, I think I was right.

    That's a very common misconception, meaning you have lots of other people believing it, and therefore you are not stupid, I'm not calling you stupid, so chill??? It came up, so this was a good time to dispel that urban legend.

    The power amp volume control is identical to all the others. If your guitar knob was labeled in dB instead of 1-10, turning the guitar down 3dB would have exactly the same effect as turning the power amp volume down 3dB.

    As you noticed, the power amp output goes to zero when you turn the power amp input to zero. Same thing happens when you turn the guitar all the way down. You aren't suggesting the guitar controls the power amp output? Of course not... you can see its obvious that's not whats happening. Its not what's happening with the power amp volume control either, but its not obvious cause you're thinking its part of the power amp, it could be actually limitiing the power amp output. A logical conclusion, simply incorrect. It just chokes off the input signal to the poweramp by varying degrees. Probably the total gain of the internalpower amp stages is fixed at 34dB. Full volume up=0dB loss from the volume knob, total system gain = 34dB. Turn the volume down, it trims the input signal 3dB per click. Internal gain stages are still 34dB, include the -3dB loss from the volume knob, now you're at 31dB. Turn the volume to 0, the power amp still has 34dB of gain internally, but the volume control results in the input signal being attenuated infinity dB, total system gain=34dB minus infinity=0.

    If you put a strong mag field near the power amp, so that the internal circuit picked up the noise, if it was powerful enough (think linear amp CB in the bar parking lot) it could result in 2400 W of "Hey good buddy, what' your 20" signal going to your speakers, even with the volume knob set to 0.

    Just as turning the guitar all the way down chokes off the signal to the preamp, the power amp volume control chokes off the input signal to the "internal" power amp gain stages.

    Make sense?

    Randy
     
  16. Marksf, I don't remember drilling you about any posts, if I came off as demeaning, I apologize.

    I often resort to humorous, albeit sarcastic responses in an attempt to be entertaining, generally not intended to belittle people.

    If its a real obvious point, I can get over the line sometimes, but this issue is common misconception, heck, there may be MORE people that believe as you do than who understand how it really works.

    I've got the advantage of playing with electronics since I was a boy, I built a few preamps/mixers, even designed/built an electronic strobe tuner, plus 3 1/2 years of electrical engineering at college. University of Michigan.

    What's obvious to me because of my background isn't obvious to "laymen", so I have no business being scornful to people who have less background in this than I do. If I came off as such I apologize.

    I try to only go off on people when they go off on me, and even then only when I feel the point should be, or has been explained to the point of being obvious. Even then I try to hold back some, cause maybe I just did a bad job of explaining it. And flame wars are ultimately wastes of time.

    Randy
     
  17. Good point, logically deduced. There's no flaw in your logic. But ultimately not correct...

    The reason they do it is because the tool used to vary the range (a potentiometer) hooked up the way they do allows you to vary the gain all the way to zero. They don't really need that much of a range to adjust for preamps. The only way to avoid allowing it to go to zero would be to add a piece to block the knob. Extra piece = extra cost, so they don't bother.

    I do make a habit to turn them all the way down when not in use, just in case somebody turns off the preamp or mixing board/effects first. That can generate BIG signal spikes that could blow speakers if they get through the power amp.

    Randy
     
  18. This time I'm on Markfsy's side.... whoever said

    I'm not disagreeing, but that's like saying "there's nothing wrong with stopping for a red light".

    I'd go one step further and say Markfsy sets his preamp levels, and power amp levels exactly the correct way. I wouldn't be so picky normally, but I want to make a point of supporting Mark when he's earned it, and he nailed this one right on the money.... :D :hyper:

    Getting the preamp and all stages just short of clipping, then using the power amp volume control to control your volume minimizes noise or maximize S/N ratio of the preamp.

    Mark gets extra points if his bass is at max volume also (unless the intermal active preamp clips, my SR5 doesn't seem to like full volume, even with fresh battery. Maybe my pickups are too high, but they're at the specs listed on ernie ball's website).

    Randy

    PS, I'm not here to pick on people, everyone has expertise in different areas, and when something pops up in mine, I try to correct any misconceptions. I dont' even remember who I try to correct, I don't go looking for those people to harass....
     
  19. markfsy

    markfsy

    May 14, 2005
    Suffolk, England
    If you look at your last quote of mine you'll see I speak of max output =2400w, and each reduction of 3 db reducing the power out by half, which fully complies with the not very difficult notion that the gain control actually works by attenuating the feed voltage to the fet's So, full power out at max vol, and 3db less at 3db less on the control is wrong? How so? And it's meaningless to say that the full 2400 watts is available whatever the gain setting on the power amp because not many preamps put out an infinitely variable level, and power amps have a range of inputs at which they're happy( i doubt you could compensate for a 30 db decrease in gain by a 30 db increase in input to the power amp, or don't you think fet's have a limit to the voltage they'll accept?) By the way, do you run your power amp flat out, your preamp flat out, and control your volume with your guitar vol control? Because surely by your logic the preamp gain isn't a volume control either(a preamp is after all an amplifier, albiet with a smaller output) You said the gain control on a power amp is a matching device to compensate for differing output levels on different preamps, and that is plain wrong. And you do have a patronising tone, and I'm not being defensive, just amazed at the nit-picking querulous attitude of youself and some others. And to the last guy, OF COURSE I was talking about one particular amp - the one the post was about. And yes I was talking about my setup - where did I say anything else? What a waste of time this whole deal is. And (the other guy)you prove you still don't follow what I'm saying when you talk about "that's where you start to go off track" - I think you can assume a normal input level to the power amp without having to state the obvious each time - of course if you decrease the input the output goes down. It doesn't matter in the least how a gain control works, it's still a gain control.
    Just to test your own theory, turn your poweramp gain down to 3db, and put 50 volts into it. Will it sound the same as normal? I can't wait to find out.