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Making a Active Speaker Passive

Discussion in 'd.i.y.' started by Space is the Place, Nov 2, 2017.

  1. Space is the Place

    Space is the Place pfm Member

    I've got a pair of Dynaudio actives (BM5A Mkii) in which one of the transformers has blown, i've contacted a transformer repairer but he's that busy at the moment and he can't do it till after Xmas at the earliest.
    The amp packs from Dynaudio's are more expensive than a new speaker and individual transformers aren't available.

    So i've hatched an idea to make the speakers passive (or active!), i think on this version of the speaker the active crossover mimics a shallow 6 db first order slope, but i'm not up on the details as yet.

    The bass driver is the same as the one used in the C1's, and the tweeter from the focus range, so they are both quality, obviously i'd like to use the cabinets too, can anybody point me to a place where i could either find some information on how to make a crossover, or somehow implement a digital one, as i have a couple of amps knocking around i could use.

    Cheers, Jon
     
  2. fatmarley

    fatmarley Registered User

    Crossover design Is not easy without all the relevant measuring gear, and even then I'd argue It's still not easy.

    Give ten loudspeaker designers a pair of drivers and ask them to design a crossover, and they will all be different.

    Surely you can find a transformer of the same spec somewhere?
     
  3. Space is the Place

    Space is the Place pfm Member

    System Two-way Active Nearfield Monitor

    Frequency Response (+/- 3 dB) 48 Hz - 21 kHz

    Input level for 85 dB SPL @1m -16dBu RMS @ 0dB setting

    Power consumption Idle: 10 W / Max: 90 W

    Amplifier power Transient power 2x 90W (2x 50W RMS)

    Bass Principle Bass reflex
    Vent tuning frequency 55 Hz

    Internal Cabinet Volume 9 liters

    Crossover Frequency 1500 Hz

    Crossover Slope 6 dB/oct

    Tweeter D-281 - 28 mm soft dome, rear chamber, magnetic fluid 4mm aluminium front Pure aluminium wire voice coil
    Woofer 7 inch moulded aluminium frame One piece thermo formed MSP cone 75 mm pure aluminium wire voice coil
    Weight 8.7 kg / 19.2 lbs

    Dimensions (W x H x D) 186 x 320 x 320 mm / 7.3" x 12.5" x 12.5"
     
  4. Purité Audio

    Purité Audio Trade: Purite Audio

    MiniDSP processor of your choice, 2x4 Hd perhaps, advanced 2x1 plug in, initially copy the passive crossover’s parameters and go from there.
    3100 all in!
    Keith
     
  5. Space is the Place

    Space is the Place pfm Member

    Thanks yes i've looked for a transformer, and found some information on DIY audio about it, the transformer has an SNo number on it and it comes up in a list of the Chinese company that manufacturers it, but other than that i can't find it available anywhere.

    I just thought it'd be easier to make a passive crossover or implement one than me messing around with transformers.
     
  6. fatmarley

    fatmarley Registered User

    Well that's a load of rubbish for a start. There's no way on earth a 28mm tweeter could survive being crossed over 1st order acoustic at 1500hz.
     
  7. Space is the Place

    Space is the Place pfm Member

    When you say 3100 all in, do you mean £ or pence !? :D
     
  8. Space is the Place

    Space is the Place pfm Member

    Ha! I'll look and see what other specs there are, all the later speakers have steeper slopes and higher crossovers... 2.4-6 kHz.

    Looking at Dynaudio speaker with similar volume and drivers, they all have a low crossover spec, many of them are 1800 KHz first order crossovers.
     
  9. demotivated

    demotivated pfm Member

    As everyone says, there is a lot to it. If you wan't a project, you could make a 'good' [ie just like any other brand] passive. It will not sound just like the actives, because passives have limited options due to cost/size/weight, not hurting your amp, wasting power, or ending up with a low sensitivity speaker. As FM says everyone has their own xover compromise.

    Unless you want to do algebra, sell the working bits on ebay, or measure the working transformer and buy a size fit replacement.
     
  10. Shadders

    Shadders Member

    Hi,

    Someone else had the same issue - wanted to replace the transformer :

    https://www.gearslutz.com/board/gee...itor-power-transformer-replacement-query.html

    The last post links to the manufacturer :

    http://www.americantoppower.com/toroidaltransformers.htm

    They state that the transformer wanted is derived from :
    XUZHOU GLORIA ELECTRONICS CO LTD
    MODEL: TD-230-0050H
    DYN769

    The issue is that the output voltage is not stated for the transformer. If you know this, and that it is a 50VA transformer, you can purchase a replacement, which will cost a lot less than implementing a new active setup, or time wise (possibly money too) by going passive.

    Regards,
    Shadders.
     
  11. Arkless Repairs

    Arkless Repairs Trade: Arkless Repairs

    Replacing transformer is easy. Redesigning crossover VERY difficult.
     
  12. Space is the Place

    Space is the Place pfm Member

    Thanks all for the advice just thought they'd be some way of implementing a crossover using the drivers and cabinets i have, i realise that a passive crossover could be done a number of ways, perhaps if i have no luck with the transformer.

    Thanks Shadders have contacted them previously but never got any reply so i've sent them another email. Perhaps one of the dsp boxes i'll have a a mess around with, as i've used ATP systems to implemented target curves/crossovers when i've been using the Tact stuff, i can understand a frequency plot/graph better than algebra!

    Is there not a program where you input the parameters of the drivers the cabinet type and volume and get a ballpark crossover? i was thinking i could implement the crossover outside the cabinet for easier value changes, although as i have no cossover parts at all it could end up pricey.
     
  13. fatmarley

    fatmarley Registered User

    Yes there are programs but unfortunately they don't work very well.

    Here's a link that's worth reading - LINK
     
  14. Space is the Place

    Space is the Place pfm Member

    Smashing, will have a read!
     
  15. david ellwood

    david ellwood Kirabosi Kognoscente

    given that the transformer is only 50W its safe to assume that its only supplying the active crossover.

    If you post detailed pictures of the active crossover so we can see the regulation and PSU im guessing we will find that its got dual rail 15V supplies and a 20-0-20 transformer is likely to be sufficient.
     
  16. Space is the Place

    Space is the Place pfm Member

    Hi David, no the 50VA transformer is supplying everything! Not just the crossover amazing how they get 50Ws for the bass driver and the tweeter eh!?

    Will post some pics in a bit.
     
  17. Space is the Place

    Space is the Place pfm Member

    With a bit of digging i've also found a fair few crossover schematics for various kit Dynaudio speakers (i remember listening to them at Wilmslow audio back in the day) the drivers in the kits are close to the ones used in the BM5 Mkii's, the plans show the cabinet of a larger volume though, so might get someone to make me some cabinets yet, as well if i can't source a transformer!


    Some images of the amp pack.


    [​IMG]
     
  18. david ellwood

    david ellwood Kirabosi Kognoscente

    it might be worth taking off the outer layer of tape from the toroid and seeing if there is an
    in line temperature cutout.

    if there is you can short it out to temporarily determine the voltage of the secondaries.
     
  19. Space is the Place

    Space is the Place pfm Member

    Hi David, yes the transformer shown is the one that has burnt out, in fact you can see through the main windings that underneath them its the secondaries that have shorted out. I've been reading through a thread on DIY audio about the transformer and i think it's 18 V on the secondaries.

    It's the transformer that is the weak link in the monitor, as this is the second one thats failed, Dynaudio eventually sent me a later set of monitors free of charge (with Class D amps with no transformer!) because i had such a saga with them. They let me keep the old monitors but it seems a shame that some good drivers and cabinets are just laying idle.

    This is one reason for my thoughts on making them passive or an active outboard DSP crossover as i feel the transformer may fail again. Again thanks for the input.
     
  20. hp1

    hp1 pfm Member

    If you have a good transformer in the other speaker then it would be best measure that one and have a new one made to those specs by someone like Canterbury windings.

    If its a common problem then you could have 2 upspecced ones made.
     

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