Tweeter not working with acoustic 405 cab

[andvgeo42]

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.

[The Dude]

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.

[andvgeo42]

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/?

[TomCarlos]

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?

[andvgeo42]

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.

[The Dude]

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.

[andvgeo42]

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

[TomCarlos]

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.

[dmeek]

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

[TomCarlos]

Interesting configuration... I guess Acoustic got a great deal on caps so they used two +- -+ to create a non-polar cap?

[dmeek]

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 ?

[Helmholtz]

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.

[dmeek]

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.

[Helmholtz]

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).

[Leo_Gnardo]

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.