$100 ESS AMT3 rock monitors

Discussion in 'Speakers' started by Jer, Sep 9, 2017.

  1. Porkloin

    Porkloin Oscar Heil Groupie Subscriber

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    Spoken like a man afraid to piss off the little lady by filling one of her caserole dishes with ferric chloride. :banana:

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  2. Jer

    Jer New Member

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    Honestly, I'm not highly experienced with this type of tech. I'm fully capable of replacing components/ soldering etc. I
    Here's the other cabinet.
     

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  3. Porkloin

    Porkloin Oscar Heil Groupie Subscriber

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    That has got to be the most popular volt-ohm-meter of all time. It commonly measures and ohm and a half too high, which can be confirmed by touching the leads together and seeing what you get - it should be 0.
    That method of measurement will only give you the DC resistance of the woofer(s) and their associated filter inductor. It can't take into account the tweeter or midrange legs of the crossover/driver combination as there's a capacitor in line with each. Capacitors won't pass the DC output of the meter.
    The DC resistance of a pair of 8 ohm (impedence, not resistance) woofers should read about 3.6 ohms (resistance, not impedence) on an ohm meter. The resistance is always a little lower than impedence, impedence being the resistance to alternating current, which is what is squirting out of your amp. Two inductors/resistors in parallel are generally half of their average impedence/resistance. The official formula (for two inductors/resistors) is R1 X R2 divided by R1 + R2. (8 X 8) divided by (8 + 8) = 4 ohms.
    In series, you simply sum the values.
    Capacitors are the other way around.
    Glassy eyed yet? There'll be a test on this on Friday.

    PCBoard_With_Old_Crossover_REDUCERD.jpg
     
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  4. MarZutra

    MarZutra Super Member

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    Just stopping bye. Fabulous find! Kudos to you. Total restoration back to original is the way...
     
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  5. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Ok.. well I didn't notice that the other coil had fallen off
    This is like my second pair... it also had the peerless mid range.
    However my woofers were four ohms.
    Mine had a circuit board
    I can count the resistors in my crossover when I get a chance.
    As I recall there were 8 for the woofer circuit.
    So if this amounts to being the same, you're going to have to use 4 ohm woofers... if you want to use the original crossover.
    Cactus Bill had the same set up as well
    He used some Polk 4 ohm woofers from Electro Mavin... but they don't have them anymore
    This is the earlier version and uses the larger mid tube.
     
    Last edited: Sep 11, 2017
  6. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    IMG_1668.JPG Here's a picture I use the switches the nameplate for another project
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  7. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Somewhere I have the picture of the intact crossover and wiring
    I'm assuming those four ohm woofers Musta had a peak in their response accounting for stiff inductance and Zobel. My set up actually had better bass then the three coil set up.
    I just wanted to go a different route with both sets.
     
  8. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Sure... i'll stick with the hardwiring!!
    Except for one pair of crossovers, all the other AMT three crossovers I've had all showed heat related problems,
    And lifting of the crossover traces.
    Obviously they weren't the best printed circuit boards, but traces are notorious for not flowing enough current.
     
  9. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Ok... looking closely I see you have eight total resistors in the woofer Zobel.
    That makes complete sense now.
    So you need to find yourself some nice 4 ohm woofers,
    otherwise you're going to end up having the wrong crossover point, basically moving it up one octave.
    Not good.
    Just replace resistors, and caps with the same value.
    And glue your loose inductor coil back on the board!!
     
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  10. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    That Peerless mid is nice... I kept mine.
     
  11. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Personally, I would look
    to the Eminence BP102-4, 4 ohm version of what I'm currently using.
    Should sound awesome!!
    Even when pushed, they sound clean and powerful.
    I would just stick with the same set up, and port, and fill your cabinet up fully with stuffing.
    Make sure you pull it apart, and not just stuff it in there so it's not clumped up anywhere.
    It really makes a difference.
    These weigh about the same as the O.E.... but you might want to add some hurricane nuts.
    I would just mount the Peerless mid as stock... use a thin bead of silicone.
    You shouldn't ever have to take it out anyway.
    The surface is thin, and the driver won't stay in with just the stock screws, without the aid of silicone.
    Or you could add a couple screws and try using a gasket the sealing surface as mentioned is very thin
     
    Last edited: Sep 11, 2017
  12. Porkloin

    Porkloin Oscar Heil Groupie Subscriber

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    [
    That's assuming a lot from what little information there is available. A simple drawing with the values of the caps and coils would make relatively accurate reverse engineering with an online or software based crossover calculator pretty easy, as opposed to haphazardly throwing stuff in based a quick perusal of a photograph. The difference between crossover components for 4 and 8 ohm driver/driver combinations would become plain as a Bulgarian pinup with the smallest amount of diligence.
    Someone put in all 8 ohm drivers in the cabinet at one time. Were they using the former drivers for reference or were they settling for the correct physical dimensions from a Radio Shack close-out bin?
     
  13. Porkloin

    Porkloin Oscar Heil Groupie Subscriber

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    Nobody builds PC boards for speaker crossovers. Drawing and etching them yourself to get the wide traces on thick copper clad is too damn much work. The pictured board was customized to fit the oversized, overpriced polycaps in place of electrolytics and axial in place of radial caps and still slide out of the hole in the back of the speaker when you pulled the terminal plate off. It was another "learning experience" that I'd be hard pressed to repeat, and I'd never claim sonic superiority of either PC board or hard wiring. It's hard to fathom skimping on boards that would burn up like that with such a comparatively light load, unlike power supply boards which spend generations unscathed. If one were to calculate the given working area of a stranded cable, it would take a pretty good sized cable to match the working area of a trace on a crossover board. Do you think the burning is bad board design or bad materials?
     
  14. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Ok... well from the information I have from my own speakers, cactus Bob , and one other member .. all the 4 coil speakers originally came with 4ohm woofers
    I don't think I'm haphazardly saying anything that I haven't figured out from my past experiences.
    Im not assuming anything, but its quite obvious you are if you think about it!!!
    If you have an association of three speakers that have the same type of crossovers, and mine were one owner speakers the others also had four ohm woofers.. well that would lead you to think that they came from the factory with four ohm woofers.
    I don't need to decide for the crossover to know if you know a little bit about Zobels, it becomes clear.
    All that other stuff is just theory and garbage talk, and has nothing to do with the reality of the situation!!
    Anyway...
    You can't put an eight ohm woofer in a speaker that originally came with a four ohm unit it doesn't work that way.
    Unless you can find some other information out there, I'm sticking with what I know.
    As far as the PC goes go with whatever works for you.
    Copper traces are thin, they might be wide but they're pretty thin.
    I don't think they dissipate heat very well.
    In the posters speakers, I don't think I'd worry too much about a circuit board as to getting them up to snuff.
    I'm assuming that's what he's looking for.
    The guy that put the RadioShack speakers in there probably didn't realize that he had 4 ohm woofers, they aren't to common.
    You either have to measure them or deciphered the part number because they're not stamped 4ohm
     
    Last edited: Sep 12, 2017
  15. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Sure..
    I can post some pictures..
     
  16. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Mr B bought my four ohm woofers he might be willing to part with them
     
  17. Jer

    Jer New Member

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    That

    I had to go open the other cabinet.
    Here's a look inside.

    So the conclusion is 4ohm drivers.
    Is this what I'm looking for?
    https://www.parts-express.com/eminence-legend-bp102-4-10-bass-guitar-driver-200w-4-ohm--290-470

    I've got hurricane nuts on the way.
     

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    Last edited: Sep 12, 2017
  18. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    Sure.. i'm assuming there is another coil lurking?
    Because the crossover looks essentially the same.
    That's what I would go with, and just make sure you stuff the cabinets full with damping material.
    At some point you might want to experiment with different venting, but I think you'll be happy with the way it is.
     
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  19. automojo

    automojo OurBandCouldBeYourLife Subscriber

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    By the way I think it's great about the circuitboard, I'm not really trying to knock it.
    It would make life easier to recap,
    And perhaps understand the circuit better.
    At some point I'll try to break down the 4 coil circuit board and write out a rough schematic and get some help from some of the members here and maybe we can post it, for people to understand better I think that will be awesome!
     
  20. Jer

    Jer New Member

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    Are the 4ohm drivers are wired in parallel?
     
    Last edited: Sep 12, 2017

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