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Thread: Tweeter not working with acoustic 405 cab

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    Tweeter not working with acoustic 405 cab

    https://imgur.com/a/a1QEXky

    The tweeters on my acoustic 405 stopped working, this is the crossover. Any advice on troubleshooting what part is broken and what good replacements would be? Any advice would be appreciated, thanks.

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    Supporting Member The Dude's Avatar
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    The most likely suspect is dirty switch contacts on the high level selector switch. I'd first check continuity on the switch from the input to each output. Try cleaning the switch with some contact cleaner. It could also be open drivers- again check with meter. Then, on to crossover caps- they could have dried out. if everything else checks good either check or replace caps. Resistors could be open, but it's unlikely.

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    Thanks for the response! i was able to pinpoint it to one of the capacitors being dead. Im going to swap them both. Is this fine https://www.taydaelectronics.com/10u...or-6x11mm.html or should i go for an exact replacement https://www.alliedelec.com/product/v...407/70079235/?

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    Supporting Member TomCarlos's Avatar
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    It is recommended to get "Non-Polarized" capacitors. Look at the ones you have. Do you see a Plus or Minus symbol? If not, that is a good sign it is a Non-Polar cap. Did you confirm that your caps 10 microfarad? And the voltage rating?

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    It has a positve sign and although i cant find an exact model later models with the marking "1407" are 100v. Im going to go for https://www.alliedelec.com/product/v...1407/70079235/ as they are the closest ive found.

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    Supporting Member The Dude's Avatar
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    I agree with Tom. You should use a bipolar cap in crossover applications. Here are some, but I'm sure there are plenty of other places that have them. They are not Axial, but that doesn't matter.

    https://www.digikey.com/product-deta...141-ND/2539603

    Edit: Also, your link says you need to order a minimum quantity of 510. It could get quite expensive.

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    Ok great good to know, so as long as they are 100v and 10uf ill be good?

    Edit: ill probably just get them off tayda or ebay

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    Supporting Member TomCarlos's Avatar
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    There are two things you need to consider. One is the "value" of the cap. So if it shows 10uf, that means it is a 10 microfarad. You want that value. The second is the voltage rating. So if it says 100v, that is the minimum you want.

    Parts Express - 10uF 100V Electrolytic Non-Polarized Crossover Capacitor

    These caps should not be expensive. While you are at it, replace them both.

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    Here it is in schematic form. I'm not sure we know the value of the caps yet. Whatever they are, the bipolar cap should be half the value marked on one of the originals Or just use 2 caps back-to-back like it is now.

    https://music-electronics-forum.com/...1&d=1580830072
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Acoustic 405.gif 
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    Supporting Member TomCarlos's Avatar
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    Interesting configuration... I guess Acoustic got a great deal on caps so they used two +- -+ to create a non-polar cap?

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    Maybe Bipolars were more expensive. The thing to remember is that two caps in series of equal value will become half the value of one. The voltage rating will be unchanged.
    Somehow there must be a better way to express this but I can't think of it right now. C + C in series = 1/2 C ?

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    Impedances add in series wiring. The impedance of a cap is proportional to 1/C. So 1/Cseries = 1/C + 1/C = 2/C or Cseries = C/2.

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    Last edited by Helmholtz; 02-04-2020 at 06:01 PM.
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    Yes, that's a more accurate way to put it. My equation only applies when both capacitors are the same value as they are in this case.

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    My equation only applies when both capacitors are the same value as they are in this case.
    So does mine .
    With 2 different caps the formula is slightly more complicated. But the principle is the same:

    1/Cser = 1/C1 +1/C2 = (C1 +C2)/ C1*C2 and Cser = C1*C2/( C1 +C2).

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    Last edited by Helmholtz; 02-04-2020 at 06:50 PM.
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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by dmeek View Post
    Whatever they are, the bipolar cap should be half the value marked on one of the originals Or just use 2 caps back-to-back like it is now.
    Even though "theoretically" one can create a non polar cap by running two electrolytics in series, "back to back," I find it a cheap and nasty solution. You can get hi quality film caps rated 250V - a rating which would never fail in any reasonable circumstance - from Parts Express, for coffee break money. I've found their house brand "Dayton" to be perfectly functional. Why not skip the potential hazards of using electrolytics in this application. Install reliability instead.

    Disclaimer: I have no business interest in Parts Express. Just a very satisfied user of their Dayton film caps.

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    Quote Originally Posted by Leo_Gnardo View Post
    Even though "theoretically" one can create a non polar cap by running two electrolytics in series, "back to back," I find it a cheap and nasty solution. You can get hi quality film caps rated 250V - a rating which would never fail in any reasonable circumstance - from Parts Express, for coffee break money. I've found their house brand "Dayton" to be perfectly functional. Why not skip the potential hazards of using electrolytics in this application. Install reliability instead.
    Disclaimer: I have no business interest in Parts Express. Just a very satisfied user of their Dayton film caps.
    I’ve had very good experiences using Express Parts. I’ve gotten great deals on big L Pads, horn drivers, knockoff speakers (mostly for stereo or PA use), and usually pick up crossover caps, etc at the same time. Very fast processing and shipping too.

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    I couldn't find any 5uf caps, should i get two of these https://www.parts-express.com/dayton...itor--027-428?

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    Quote Originally Posted by andvgeo42 View Post
    I couldn't find any 5uf caps, should i get two of these https://www.parts-express.com/dayton...itor--027-428?
    You can use 5.1µF or 4.7µF.

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    Thanks, ill end up getting one of these https://www.parts-express.com/dayton...citor--027-423

    I appreciate all the responses!

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    Supporting Member The Dude's Avatar
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    I'm with Leo on using a film cap. Here's a good example. And, as mentioned and since the caps are in series, just use one to replace both.

    https://www.digikey.com/product-deta...F2475-ND/56516

    Edit: I was typing while you replied. The one you linked is good, too.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by andvgeo42 View Post
    I couldn't find any 5uf caps, should i get two of these https://www.parts-express.com/dayton...itor--027-428?
    What Helmholtz said ^^^. Also keep in mind, these are thumb-size caps, not rinky-dink miniatures. They will need some sort of support when mounting them. A large cable clamp or a big glob of RTV,, epoxy, or similar adhesive will do.

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