SP1200, 1700, or 2500 Crossover Diagrams

Discussion in 'Exclusively Sansui' started by Culpeper, May 17, 2017.

  1. Culpeper

    Culpeper Active Member

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    Yep, it is sort of daunting. I keep running into road blocks.
     

     

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  2. Culpeper

    Culpeper Active Member

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    Ragan, when you get back on xsim tinker with a zobels on the mid and tweets. Brings down -3dB and flattens FR at high freq after raising the cap value on the tweeter. Looks like another possible tweak.
     
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  3. Culpeper

    Culpeper Active Member

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    185
    So, got tired of working with the whole band pass and HF filters. I have a couple of MCM $19 woofers with just 1.0 mH inductors on them that have pretty good specs for some reason. For the tweeters I started out with just the 2.2 uF capacitor but the tweeters are pretty sensitive and was about 12dB too high. So, I swapped out the capacitor with 1.2 uF and a 30R shunt resistor. This got everything into line. Since the bass and tweeters are 1st order we don't have to worry about phase alignment. This really opens the door to the tweeters with plenty of protection. Bass is very nice and holds its own like a Heresy III. I left the ports as is. The midranges are left at the Natural (1.062 mH setting). I used SPL Copy to put together a FRD and ZMA file. Those got me started using Xsim to get a good idea of the electrical response. Polarity on the band pass is reversed. Frequency response graph below was measured in the cabinet and the listening room at near field. So, it is an acoustic response. Sort of ironic that this is so simple and yet so good. I'm thinking on bypassing the parallel midrange cap and transformer and make it a full 1st order. That will need a different cap on the tweeter.

    Woofers:
    http://www.newark.com/mcm-audio-select/55-2952/12-woofer-with-paper-conecloth/dp/80R7003
     

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    Last edited: Mar 20, 2018
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  4. Culpeper

    Culpeper Active Member

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    figured out why the midrange and tweeter driver sections are reversed polairty from the factory. When set to Clear it is coming out normal polarity from the crossover and reversed on the drivers. When on Natural or Soft the polarity is reversed from the crossover. Something to remember when modeling in Xsim. Also, explains the advertised 750Hz crossover frequency. It is based on the system response crossover with the woofer and not the actual crossover between the midrange and woofer. Here is another example of a 1st order modification with the same MCM woofer. One with the -180/+180 vertical line is reverse polarity on the midrange with a very acceptable flat system frequency response. Regular polarity has the near linear system phase. Very nice. Hard to decide but easy to determine by listening in the room. No noticeable HF bleeding into the LF or LF breakup. Converting to 1st order on the tweeter and midrange is really simple. Remove the 16R resistor. Disconnect the transformers and keep the switches on Clear or solder the switch just to keep it there.
     

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    Last edited: Mar 23, 2018
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  5. Culpeper

    Culpeper Active Member

    Messages:
    185
    At the end of the day I settled on using the MCM with a 2.0mH inductor and regular 22uF cap before the midranges. Basically, a two way 1st order. The midranges have an L-Pad consisting of 2R/12.5R. There is no need for the tweeters. Frequency response is less than +/- 3dB between 170-17,000 Hz using ERB. To complement this set I have a pair of HUMAN Model 81. My second set of SP-2500 has a 100W Dayton subwoofer amp in the rear and a GRS subwoofer in the other box. They connect together using the original speaker inputs. The sub crossover is 80Hz and the gain is set -5dB below the MCM woofer. MCM woofer is sold by Newark and the rest came from Parts Express. Total cost was about $60 for the drivers and $100 for the sub amp. The inductors was one of their factory buyout specials and the resistors were Dayton. The capacitor is the regular $1 variety. I decided the OEM crossover is obsolete and only using it for the inputs and to mount the capacitor. The transformer switches need to be set/solder to Clear and the resistor disconnected. All the inductors disconnected and jumper to replace the series 351. This is so the squaker outputs can still be used. Same thing for the tweeters if used with 1st order capacitor. Woofer inductor is mounted inside the box. The L-Pads are connected inline.

    As a result I have plenty of spare parts. Also, these boxes are a good candidate for the Two Pi speaker kit. Came close to going this route and may eventually go there :)
     

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    Last edited: Apr 26, 2018
  6. vha

    vha New Member

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    6
    I brought back and connected my very old speakers SP1200.
    except that one of the 2" 50mm tweeters cone is damaged (not completely) they seem to work ok.
    I will have to replace it..
    I read most of the interesting full of information discussions from start and I noticed if not mistaken that most of them are based in replacing the woofer.
    I was thinking why not keeping the old woofer and replace all mid-rage and tweeters with a mid-high or even with two 4inch drivers of 30w 8Ωms each and cut the woofer lower somewhere between 300 and 700Hz.
    I guess that just a lowpass filter is needed in that case by using one of the original coils in series and add a bipolar capacitor on the new fullrange/tweeter driver?
     
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  7. Culpeper

    Culpeper Active Member

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    10_Jun_2018_12_50_06.jpg I used the original network board bypassing the inductors. Set the tone control to Clear and soldered in place. One series capacitor for the midranges and one for the tweeters on the board. A single separate coil for MCM woofer mounted in the cabinet. Disconnected the original midrange resistor and added a -3dB L-Pad after the network board for the midrange. The tweeters just utilize the existing parallel resistor on the network board. I have a nice FR between 170-15khz. Use Xsim to simulate to make a determination on your best combination. Main thing is the original network super chocked up the tweeters and midranges so they are normally well preserved for a little hot-rod changes. Also, boxes are bettered sealed if not using original woofers with no inductor. You'll need to do the math.
     
    Last edited: Jun 10, 2018
  8. vha

    vha New Member

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    6
    thank you for all the detailed description
    I will try to be more familiar with this technical terms and get back to you.
    As a first approach I was thinking the keep the woofer and replace the rest with two 4" med/high drivers.
    But first I will make some tests by connecting the speakers several different
    amps (one 70s Sansui and one 90's Luxman vintage among them) and class D amps too.
    and make some frequency measurements too before of (or if.. ) any changes.
    If we change the woofer we get something completely different, will have to change the other drivers too.
    The idea of a more powerful new speaker system in the old beautiful enclosure..
    Then the Sansui SP1200 will probably lose its value?
    Ill get back to you with sharing this
    Thank you
     
  9. Culpeper

    Culpeper Active Member

    Messages:
    185
    Yes, I came close to a complete rebuild inside myself. Something like the Two Pi loudspeakers with a single port tuned for the Sansui box.
     
  10. vha

    vha New Member

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    do you have a picture to share?
     
  11. Culpeper

    Culpeper Active Member

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    Last edited: Jun 14, 2018 at 4:22 PM

     

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  12. vha

    vha New Member

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    Yes this is another speaker with 2 drivers and a port and with about the same size box.
    Maybe I misunderstood I thought you had SP Sansui speakers that you upgraded??
     
  13. Culpeper

    Culpeper Active Member

    Messages:
    185
    Yes, mine our SP 2500s. Your 1200s would be a good box for the Two Pi kit. It is just an idea I was throwing out there. There is nothing wrong with your idea to upgrade the sound. As for losing value. I wouldn't worry about it. You're creating a sound for yourself.
     

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