SDA SRS 1.2 sound goes dull at half volume

briandarf
briandarf Posts: 4
in Technical/Setup
Hello everyone!
Today I was cranking up my stereo, and at @ half volume the Highs and mids dropped completely off, sound becoming very 'dull'. Then, after turning down the volume, the sound quality returned to normal. I JUST got my amp back from being checked out, so I dont think is a amp issue- Its a DBX BX-1, so it has a ton of power- underpowering is definitely not a concern. Does the crossover have some sort of thermal circuit breaker? It seems to be happening fairly easily- not while terribly loud. Is this normal? Does anyone have any info? Id really appreciate any info, fixes, explanations. TIA
-Brian D
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Comments

  • Navy_Goat
    Navy_Goat Posts: 375
    edited February 2022
    There is a polyswitch in the HF signal path to protect the tweeters. Sounds like you are tripping it. My understanding is that each time it is tripped it gets a little weaker making the next trip more likely.

    Not normal, but the circuit is doing what it is designed to do. Sounds like your crossovers could use at least a partial rebuild.
    SDA SRS 2.3tl, SDA 1C, SDA 2B (TL mod), Reserve 200
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  • briandarf
    briandarf Posts: 4
    Thank you for your quick response Navy. Ive never heard of a polyswitch. Is there a way of testing it? Is it one component? is there a fix ? Thanks
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  • Navy_Goat
    Navy_Goat Posts: 375
    It is a single component and essentially what you were guessing anyway. It can be jumped or replaced by a resistor to maintain the circuit. 0 - 0.5 ohms can be used. I think I used 0.5 and 0.47 in the past. Check the vintage section, there is a thread stuck to the top with all the SDA crossover schematics.
    SDA SRS 2.3tl, SDA 1C, SDA 2B (TL mod), Reserve 200
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  • pitdogg2
    pitdogg2 Posts: 25,437
    edited February 2022
    Poly switches are bad.
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  • briandarf
    briandarf Posts: 4
    Perfect thank you. I found the "polyswitches are nasty" post. My 1.2s are really bright, so maybe a new resistor will be the way to go. Thanks guys
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  • nooshinjohn
    nooshinjohn Posts: 25,410
    briandarf wrote: »
    Perfect thank you. I found the "polyswitches are nasty" post. My 1.2s are really bright, so maybe a new resistor will be the way to go. Thanks guys
    RD0-198’s are the way to go, along with TL modded crossovers.
    The Gear... Carver "Statement" Mono-blocks, Mcintosh C2300 Arcam AVR20, Oppo UDP-203 4K Blu-ray player, Sony XBR70x850B 4k, Polk Audio Legend L800 with height modules, L400 Center Channel Polk audio AB800 "in-wall" surrounds. Marantz MM7025 stereo amp. Simaudio Moon 680d DSD

    “When once a Republic is corrupted, there is no possibility of remedying any of the growing evils but by removing the corruption and restoring its lost principles; every other correction is either useless or a new evil.”— Thomas Jefferson
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  • briandarf
    briandarf Posts: 4
    Isnt there a how-to thread with pictures, showing the polyswitch removal without directing me off site?
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  • Gardenstater
    Gardenstater Posts: 4,459
    edited February 2022
    It will be the tiniest component on your PCB. Usually gold/yellow or blue I believe. There is another small component which are the tiny brown silver mica bypass capacitors which are in parallel with the tweeter capacitors so I do not mean those. Desolder it and put a 0.5Ohm resistor in it's place, or whatever those with your speakers say is the proper value. Looking at the schematic would be a good idea.

    https://us.v-cdn.net/5021930/uploads/attachments/1/8/5/1/1/26686.pdf
    Post edited by Gardenstater on
    George / NJ

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