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    Trouble shooting Dynaco A40XL Speakers

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    Mad Dog Cycles

    Posts : 2
    Join date : 2017-08-07

    Trouble shooting Dynaco A40XL Speakers

    Post by Mad Dog Cycles on Mon Aug 07, 2017 9:00 pm

    New to the forum and electronics, so if I ask some dumb questions, try an go easy on me! I'm just getting my system together. I'm driving these with a rebuilt SCA-35 containing Dave's Lab components. I picked the speakers up little while ago and when I bought them the seller admitted that one of the tweeters wasn't working. I took it a apart and jumped out the tweeter (1" H-086) and found that I got sound. I tested continuity on the old capacitor and didn't get any. Found a cheap replacement JE 10MFD 50VD Axial Non Polar and installed it. The tweeter still isn't working. I'm thinking that the switching for the resistors is shot. I couldn't find schematics for this crossover, and from what I've searched, it's set up a little differently from the other Dynaco Speakers

    I read through this thread and got some insight an older forum post entitled "World Designs speaker KIT based on the Dynaco A-25 "aperiodic" speaker - link:"

    I also studied the crossover design for the A26 build on the MadiSound website. The MadiSound crossover seems pretty straight forward. Could I use their suggested capacitor and then just install a simple 3 way toggle switch for the resistors? Are there better suggestions? I'm a big fan of KISS method!

    Thanks
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    arledgsc

    Posts : 457
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Trouble shooting Dynaco A40XL Speakers

    Post by arledgsc on Tue Aug 08, 2017 5:50 am

    Without a schematic I would check the tweeter selector switch circuit continuity and the associated resistors with that switch. It may be as simple as a failed resistor, bad switch, or a wire has fallen off. But I would thoroughly inspect before ripping out and installing something else.
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    Peter W.

    Posts : 436
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Trouble shooting Dynaco A40XL Speakers

    Post by Peter W. on Tue Aug 08, 2017 6:55 am

    It is a set of series resistors and series capacitors. You have the option of jumping them out - that is, pick your combination and hard-wire it - or fixing the switch. But I would test for continuity across all resistors and all switch positions first. Also the wires from the switch to the speaker.

    There are several web-pages dedicated to theses speakers, start there for a schematic, and let that information lead you through your choices.

    wildiowa

    Posts : 163
    Join date : 2012-03-19

    Re: Trouble shooting Dynaco A40XL Speakers

    Post by wildiowa on Tue Aug 08, 2017 9:37 am

    I went through a similar hassle with a Carvin PA speaker a few months ago..no high end, usually always a diaphragm...but it did work straight up without the crossover. I've replaced a million diaphragms but this was different. After pondering resistors and coils and this and that I just tried to find a similar replacement online at Parts Express and DigiKey etc.

    Not as easy as it sounded. I found that every single component must match or the crossover point gets all messed up. I could not find a matching impedance and i guess that impacts the crossover point bigtime. So many other hassles, you just can't be certain where you're crossing the thing...I wanted about 8k who knows what i got...It works, sounds OK, but probably not matching the other cab. This is OK for live performance, as probably not noticeable...but if your playing tunes in your listening room and one crosses at a different point you got issues.

    In the end, if i had more time, and I gave a crap more, i would have tried to rebuild the crossover...the original was cheap, cheap, garbage...the one I bought was far superior, handled more watts, had a bigger coil. but who knows where the heck it crossed.....just a caution, the best way is to rebuild it but finding the faulty component or what the heck is wrong can be maddening even though there are very few things that can go wrong.

    Mad Dog Cycles

    Posts : 2
    Join date : 2017-08-07

    Re: Trouble shooting Dynaco A40XL Speakers

    Post by Mad Dog Cycles on Tue Aug 08, 2017 11:10 am

    Thanks for the advice. I don't have a problem rebuilding it. I realize these are 40 year old speakers, and from what I've gathered on researching older components, they should be rebuilt anyway. I'd just like to get guidance on a simple crossover (if there is such a thing) schematic. That's why I was leaning towards the MadiSound design for their A26. When I do this I'll do both speakers.
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    Peter W.

    Posts : 436
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Trouble shooting Dynaco A40XL Speakers

    Post by Peter W. on Tue Aug 08, 2017 12:12 pm

    Mad Dog Cycles wrote:Thanks for the advice. I don't have a problem rebuilding it. I realize these are 40 year old speakers, and from what I've gathered on researching older components, they should be rebuilt anyway. I'd just like to get guidance on a simple crossover (if there is such a thing) schematic. That's why I was leaning towards the MadiSound design for their A26. When I do this I'll do both speakers.

    Keeping it simple: If you decide to keep the existing drivers (a good thing, if they are good), then use the original-design-but-rebuilt crossover. If the resistors are good and the switch is good, replace only the caps. Do not try introducing another crossover unless it closely mirrors the OEM design. Look up Greg Dunn's Dynaco page, which will list the Dynaco speakers and other useful information.

    There was nothing particularly magical about Dynaco speakers back in the day. However, 30 - 50 years later, in the world of tiny woofers and stupidly expensive speakers, a decent speaker with decent bass response *is* remarkable. Enjoy them!
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    deepee99

    Posts : 1646
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Here's a pretty handy history on the Dynaco speaker line

    Post by deepee99 on Wed Aug 16, 2017 11:18 am

    Never had any of the XL series, but I think, space considered, the A-35s were the creme de la creme.
    http://home.indy.net/~gregdunn/dynaco/components/speakers/

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