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Tried and true crossover upgrade: Tobin Mods for Bozak B302a

Discussion in 'DIY' started by tensleep, Apr 3, 2011.

  1. Steven Ver

    Steven Ver New Member

    Messages:
    37
    I will indeed...I got a great deal of distortion on my first "audition" of my new find, so I will Tobin the x-overs and enclose the midrange drivers. I forgot if the flowers need insulation inside...Will check earlier in the post. Thanks so very much!
     

     

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  2. Steven Ver

    Steven Ver New Member

    Messages:
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    I was unable to find a consensus about the flower pot midrange enclosure...insulation inside the flowerpot around the driver, or insulate over the flower pot (sides and back)...any help appreciated. Ordered my crossover parts....distortion is pretty significant in these,hope the mods help. Cheers!
     
  3. Retrovert

    Retrovert AK Subscriber Subscriber

    Messages:
    3,598
    Location:
    New York City, NY
    Flower pots should be covered, inside and out, with cotton batting to reduce reflections.

    Do you have the paper-cone B-200X tweeters? Identifiable by the silver dust caps. The performance is quite poor compared to the successor aluminum cone B-200Y. Same rise in impedance, but the SPL is much lower and not as clean.

    Like the tweeters, the paper-cone midranges are not as good a driver as the aluminum cone successors. But certainly not to the point you should have considerable distortion.

    If the crossovers are the original PIO then the capacitors are creating significant distortion. The sound will be murky and muddy. No magick there.

    I also suggest you add bypass capacitors, 0.1 uF and 0.01 uF, to each capacitor as this will increase the performance at higher frequencies. Explanations in one of the numerous Bozak threads.
     
  4. Retrovert

    Retrovert AK Subscriber Subscriber

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    3,598
    Location:
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    Biggles has posted photos of his implementation of the flower pot covers, BTW. One of the threads will have this.
     
  5. Steven Ver

    Steven Ver New Member

    Messages:
    37
    Ok thanks Retrovert..I will do the flower pots and rebuild the crossovers first, then may consider changing out drivers but I should notice significant improvement with these first major steps. Wish the cabinets weren't French Provincial but they're solid cherry and like new so I'll save these Bozaks for the next generation
     
  6. Retrovert

    Retrovert AK Subscriber Subscriber

    Messages:
    3,598
    Location:
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    I think you'll hear a great deal of improvement by using new capacitors, moving the crossover points, and shielding the drivers from cross-modulation.

    When that works out, time for new midranges. Remember, no A series. Never, never, never.
     

     

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  7. Steven Ver

    Steven Ver New Member

    Messages:
    37
    Got it..no A series EVER! :) Already ordered 6.5" ID flower pots..biggles used 8.7..didn't think they'd fit in the enclosure...here we go...
    Update...cancelled the 6" pots and got 8" same company...inside diameter is 7.5..close enough...and they're black
     
    Last edited: Sep 26, 2018
  8. Steven Ver

    Steven Ver New Member

    Messages:
    37
    Assembled all my parts and have schematics and flower pots covered in thick white cotton batting. Have tensleep posts and pics in front of me as well as the Bozak crossovers. Now wondering if I should have my soldering genius "patient" friend do the actual operation...thinking...
     
  9. Retrovert

    Retrovert AK Subscriber Subscriber

    Messages:
    3,598
    Location:
    New York City, NY
    A black flowerpot smothers the sonics. You need terracotta flowerpots for the widest possible sound stage! Organic plastic made with unicorn fur molds is even better, of course.

    Don't forget to seal the flowerpot holes and seal the lip to the baffle with caulking or spongy weatherstripping. This is key to driver isolation.
     
    Steven Ver likes this.
  10. Steven Ver

    Steven Ver New Member

    Messages:
    37
    Well...dug in with the info and pics that I had, and got out the safe old Weller trigger soldering gun. Routed the big caps no problem...resistors a little harder...kept studying the graphic schematic that someone posted and was pretty confident they would work. Left everything temporary and applied signal...all four drivers worked without hum or buzzing...sweet. Installed my 12% Unicorn fluff covered black plastic flower pots and sealed them around the mids, lowered the mid blanket and sealed up cabinet one. Ran a quick test before reassemble of can two. Sounded so much cleaner and fuller than before the rebuild...as promised! Pretty much a whole day but they sure sound huge...dialing in the highs but not expecting horn tweeter SPL's. I lost a poster off the wall upstairs so the punch is definitely there..playing mp3 files through a 90's Pioneer home theater receiver...pretty efficient I guess...my 16 ohm JBL cabinet from the 50's needs a lot less power than the Bozaks. I'll change out the tweeters someday, very pleased with the sound....now about those french provincial cabinets ;) Thank you Retrovert and mrbiggles and everyone else that gave consistent advice...knew I could figure these odd old speakers out with your help!
     
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  11. Retrovert

    Retrovert AK Subscriber Subscriber

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    Location:
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    Glad it worked out for you.

    No Bozak Left Behind.
     
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  12. Steven Ver

    Steven Ver New Member

    Messages:
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    After a few days of listening...new tweeters are definitely in order...mine may be blown even...noticeable distortion on vocals and horns..hi-hat symbols have no presence...just not crisp and clean, fatigue sets in quickly. They seem to improve with higher volumes. I'll watch for some B200Y sets or maybe just go with another brand and hang onto the originals in case I trade these off. The French Provincial cabinets aren't really my style, but I could make them work if they sounded like they should. Anyone substitute another tweeter for the Bozak paper cones with good luck? I found this photo...
     

    Attached Files:

  13. Retrovert

    Retrovert AK Subscriber Subscriber

    Messages:
    3,598
    Location:
    New York City, NY
    Biggles has described his Audax soft-dome experiments in other threads. Search will turn it up.

    The B-200Y has problem above about 10k Hz, so the desired air won't be forthcoming. Supertweeters are required at some point. So either band-pass the B-200Y to remove the high-end distortion and bandpass the supertweeter to ensure HF oscillation won't cook it, or just go with a soft-dome and use a capacitor as one normally would.

    Bozaks show up in most markets and generally end up stripped for drivers. So you can ask the seller if you can purchase the cabinets. Might work out.
     
    Steven Ver likes this.
  14. Steven Ver

    Steven Ver New Member

    Messages:
    37
    Good advice....heard about Phase Technology soft domes...sound great in my Fried Beta IV bookshelf speakers. What value cap would I use? Thanks Retrovert
     
  15. Retrovert

    Retrovert AK Subscriber Subscriber

    Messages:
    3,598
    Location:
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    If replacing the existing tweeter, same value as before.

    If extending the existing tweeter, you need to pick up where the existing tweeter begins to both drop off and become spikey. This requires a band-pass for the existing tweeter so you remove the distortion at the end of the range. Basically the same approach as a midrange. So you are making a four-way.

    Frequency for a high-pass filter is:
    f = 1 / (2 x Pi x R x C)
    where R is the nominal impedance of the driver (16 Ω || 16 Ω = 8 Ω) and C is the known capacitance in Farads (divide by one million to yield uF). Given f and rearranging for an unknown C, yields:
    C = 1 / (2 x Pi x R x f)
     
  16. Steven Ver

    Steven Ver New Member

    Messages:
    37
    I plan on replacing them with a nice single silk dome 8 ohm tweeter so I'll just disconnect the existing ones while I look for suitable B200y Bozaks at a reasonable price...thanks Retrovert
     
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  17. Retrovert

    Retrovert AK Subscriber Subscriber

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    3,598
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    That works. Leave the compensation network and use an L-pad to adjust the volume.

    The B-200Y surfaces at regular intervals, and the price considerably varies. Patience may save you some cash.
     
  18. Steven Ver

    Steven Ver New Member

    Messages:
    37
    Patience is fine...the dozen or so on that auction site that are all wrinkled and creased and not at all what I'm looking for I will leave for someone else :)
     
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  19. Retrovert

    Retrovert AK Subscriber Subscriber

    Messages:
    3,598
    Location:
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    Yeah, that.

    I further suggest avoiding any B-200Y with severely flaking latex as that indicates poor storage conditions.
     
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