Trouble shooting Dynaco A40XL Speakers

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

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.

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.

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.

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.

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!

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/

Hi Mad Dog, I had a pair of Dyna A-40XL's. An inch wider than the A-35 and the better tweeter, the 86 which gave them a better high frequency response. They were my favorite speakers that now belong to a friend because I was broke at the time. I now have restored a speaker made after the A-40XL called the Dynaco A-25 Mark2, 1977. It uses the same drivers as the A-40XL only in a nice walnut A-25 enclosure with a brown cloth grill with 4 plastic snaps. The crossover was made simpler by using an L-pad instead of the ring of resistors and switch. I have a picture of the crossover before I re-assembled them. I would love to share some info with you so you can get those A-40's going.....Mark Korda (kordamark@gmail.com)

I have recently acquired a pair of A-40XLs. The seller thought they were A-35s until I got them home and compared them against the chart on the Greg Dunn page.

They are in pretty good shape. One of the cabinets has been mashed along a rear-facing edge, otherwise they look pretty good. One of the tweeters doesn't play and the other seems weak, but I tested the drivers and they are OK. So looks like I've got a crossover rebuild project on deck.

daveshel wrote:I have recently acquired a pair of A-40XLs. The seller thought they were A-35s until I got them home and compared them against the chart on the Greg Dunn page.

They are in pretty good shape. One of the cabinets has been mashed along a rear-facing edge, otherwise they look pretty good. One of the tweeters doesn't play and the other seems weak, but I tested the drivers and they are OK. So looks like I've got a crossover rebuild project on deck.

You do - very common. Bit of advice based on having just gone through my recently acquired A35s:

What you do to one, do to the other.
Match your components (caps and resistors) between speakers ahead of time so that the results will also match.
If you save the rotary switch, clean it thoroughly.

It is well worth the effort.

Peter, I have a pair of speakers from Dynaco 1977 that I rebuilt. I had a smunched corner too. They are the A-25 Mark 2's. They use the same tweeter and woofer as the A-40XL in a nice finished walnut cabinet . The tweeter is right above the woofer and not off set to the right. The crossover is better in my opinion as it uses a real nice L-pad instead of 4 or 5 resistors in a switch. I have a nice picture I took of it but can't send it because of this forums image sending ability. I'm too stupid too remember Photobucket's rules. If you send me an e-mail I'll forward it right over to you. I have found schematics of all the other classic Dyna crossovers but not this one. I think this would help you.....Mark Korda. (kordamark@gmail.com) 207-632-1648.......take care Peter.

Mark Korda wrote:I have found schematics of all the other classic Dyna crossovers but not this one.

I haven't been able to locate a schematic for the A-40XL. I'd be grateful if you could point me toward one.

daveshel wrote:

Mark Korda wrote:I have found schematics of all the other classic Dyna crossovers but not this one.

I haven't been able to locate a schematic for the A-40XL. I'd be grateful if you could point me toward one.

Mark has kindly offered to send me a picture. I will try to reverse-engineer a schematic and share it via dropbox.

Reviving this thread. Peter, did you ever reverse engineer this schematic and get a photo by chance?

Peter hasn't posted in a long while.

cci1492 wrote:Peter hasn't posted in a long while.

He's in a place equivalent known at Facebook Jail. I hope he is released soon. Think every guy deserves a second chance, eh?

Well I was hoping it was something like that and not the other thing.

Yikes! Can't imagine that happening here. The limited lurking and posts I've read all seem to be very cordial. Anyhow, I sent an e-mail to Mike, hopefully he responds.

I have PeterW's contact info out in Google-land. PM me if you need or want his advice, or a good chat. (Be sitting somewhere comfortable if you get him going on something.

Ha, ha!... OK I'll keep that in mind