Dynaco A-25xl crossover network

[dynaco_dan]

Hi there

I took a few photos of a Dynaco A-25xl crossover board I bought off ebuy a few years ago.

The switch is 3 position and it appears to be from a different manufacturer than the regular A-25.

The open contacts are on the rear of the wafer for all to see and clean, if ever required.

The capacitor on both boards were glued with the identification writing mostly in the glue close to the boards.

The name appears to be Wicon, for crossover, 9 uf 50 volt peak type ECI bipolar capacitor.

The 2 smaller resistors are Modulohm brand, 1 is 2.2 ohm and the 2nd is 3.9 ohm, both are 3 watt rating.

The larger resistor is Modulohm 15 ohms and 5W-A-1 5 watt rating.

The serial numbers are 36-E45004x and 36-E45005x.

The open coil is about 5/8" in diameter and about 7/8" long made of hairlike guage wire and just a bead of goop to hold it in shape.

You can see the yellow insulator sleeving for the coil leads to the rightmost end of the 15 ohm resistor and to the leftmost 2.2 ohm resistor connection.

I presume that the small rectangular sticker inside is the manufacturers part number as they are both identical and both have a red penned inspectors mark.

[Dchristie]

Hi Vern, thanks for posting the A-25 XL crossover photos.

I now have a question for the Dynaco folks regarding the actual crossover components.

Does anyone have access to an actual schematic of the A-25 XL crossover? The caps and resistors are fairly evident as is the layout but to date, I have not been able to find any information about the small air core inductor in the circuit.

I recently picked up a pair of A-25 XL speakers and noticed the very small inductor leads are both broken right at the coil and may not be able to be repaired. Since it looks like the inductor is part of the 2nd order crossover for the tweeter, I would like to replace it if I can't fix the originals.

Thanks

Dean

[dynaco_dan]

Hi Vern, thanks for posting the A-25 XL crossover photos.

I now have a question for the Dynaco folks regarding the actual crossover components.

Does anyone have access to an actual schematic of the A-25 XL crossover? The caps and resistors are fairly evident as is the layout but to date, I have not been able to find any information about the small air core inductor in the circuit.

I recently picked up a pair of A-25 XL speakers and noticed the very small inductor leads are both broken right at the coil and may not be able to be repaired. Since it looks like the inductor is part of the 2nd order crossover for the tweeter, I would like to replace it if I can't fix the originals.

Thanks

Dean

Hi Dean

The Dynaco A-25XL is different in drivers, crossover quantities and values and the grille cloth mounting, for our purposes, from the original A-25 speaker system.

The original A-25 had more resistors and of different values.

The capacitor was a different value as well.

The XL switch had fewer contacts and appears to be made by a different source than the A-25's.

The coil in my photos of the crossover boards that I bought off the net have no identification on them.

I can at a later date check the coil guage with my wire guage.

It is about thread size for certain.

The switch was simple in design and self cleaning, the only problem was knob breakage occassionly.

I never saw a discolored or burnt resistor or capacitor, unlike KLH Five and KLH Twelve.

The 25XL used different drivers which I never serviced.

If the coil wire is broken, carefully, using a magnifier glass or lens, working through the woofer opening, and using an Xacto type knife or razor blade, unwind that end of coil 1 or 2 turns, very carefully.

The coil looks like bare copper wire but it is insulated with a transparent insulation which must be scraped off before soldering it.

A few turns removed is not the end of the world and we have no information on the original wiring schematic.

There is/was an Ebay seller in Victoria BC that had a website with some of the classic Dynaco wiring schematics and cabinets that he drew.

Every time I've looked at his schematic I believe I see an error, but I just can't seem to put my finger on it.

I will work this out eventually, I believe he has drawn a resistor inline without turning the switch.

His name was David Dlugos, I believe.

I had several successful and pleasant business dealings with him.

It was very kind and generous of him to do the drawings and schematic and post them for all the world to see.

Only a person with a coil tester can come up with the coils value.

Unless the coil is burnt up like a crisp it doesn't need replacing.

Surprisingly in over 200 Dynaco A-25's the very most common problem was burnt woofers.

Some were covered by warrantee, even if the woofers voice coil was toasted and I mean toasted.

I don't remember replacing a tweeter except in one A-50.

The A-10 was a real dollar value speaker, all things considered.

Available in oiled walnut, no switch but a Seas assembled crossover board less switch.

Same tweeter and a larger than expected magnet assembly was used in their puny woofer.

I always digress but what the heck.

I did have a photocopy a year or so ago of a Dynaco A-25XL speaker system from our local library.

I re-read the review 4 or 5 times trying to make sense of it.

When I find and post it I will be doing a review of that review.

It would not have helped the Dynaco A-25XL sell.

I bought a mint pair of XL's off the net a few years ago and I'm expecting a nice pair of donated XL's next week.

I am accepting these as a charity case and I am well beyond a divorce now.

.

.

[Dchristie]

Hi Vern, thanks for your response. As the A-25XL came out in the mid 70s, I assume that they are more scarce compared to the original A-25. I do not see that many for sale on the used market. Great for you that you have been able to secure a couple of nice pairs.

I actually bought this pair thinking I was buying an A-25 only to find out it was the XL model once I saw the actual speakers - the owner also mistakenly thought they were A-25s. It is interesting to see the renewed interest in these old speakers today. When I was in college, I did not know a single person with Dynaco speakers. It is amazing to me how many were sold but I also lived in a more remote area and did not have access to a lot of dealers. I do remember them being available in all of the mail order centers however. When I was buying speakers back then, I had my sights on the KLH 5s, AR 3as, or ADS 810s. I did consider buying Dynaco A-50s but finally settled on the KLH 5s and then moved on to the ADS 810s.

This pair of A-25 XLs appeared to be OK upon buying them ( quick inspection showed no damage to the drivers) but they actually had some major issues which I discovered after I got them home. In addition to the broken coil in the xover, both had sat in water for an extended amount of time and the cabinets were severely compromised as a result. The miter seams had separated significantly at the joints from the water exposure to both speakers. Of course the veneer on the lower parts of the speakers was also severely discolored as well. In addition, once I got into the speakers, I noticed that someone had broken one of the woofer leads (positive lead from the voice coil attachment to the solder joint on the woofer basket)at the positive terminal. They had just tied picture frame wire to the broken lead and then wrapped it around the solder terminal on the woofer basket - it was a wonder it even worked at all! Also, the positive solder connection for the voice coil lead on the other speaker had broken loose from the woofer basket and was just dangling loose on the basket. I am grateful the voice coil did not short out on the metal woofer basket.

Well, I was able to splice a piece of wire lead from another damaged speaker to the broken lead of the woofer and resolder it back on the terminal. I was also able to epoxy the loose solder terminal back onto the woofer basket of the other speaker and I then reinforced all of the other 3 solder lead terminals with a little epoxy as I have read that these terninals often fail over time and become dislodged as mine did.

I have also resanded both speakers and glued the open joints back together (as well as I could without doing a major cabinetry rebuild) and have reoiled both cabinets with 2 coats of clear danish oil. Once the oiled cabinets are dried, I will add a topcoat finish. And finally, I rebuilt the crossovers with Mundorf oil capacitors and noninductive resistors. Hope to have them up and running within the next week or so.

I also have a review of the Dynaco A-25 XL from the 1976 edition of High Fidelity Test Reports and they concluded that the XL model sounded very similar to the original A-25 with just a little more extension in the highs and perhaps a shade more bass definition. Intersting to read different opinions from owners of both speakers on the different web sites. There seem to be supporters for both models - which is fine. Some prefer the originals and some prefer the XLs. I only listened to my pair breifly before I dismantled them, but I thought they sounded pretty good in spite of their problems at the time. Since I have updated the xovers, I will be listening to a non-original A-25 XL but I look forward to hearing what they can do. For me, the fun is in fixing up these old speakers and hearing them again after 40 years .

[Pete B]

Do you have at least one good tweeter inductor that you can measure for DC resistance?

Then if we can determine the wire gauge the total length can be determined.

It would be easier to just measure one of course but I don't have access to one.

The A-25 woofer had a paper VC former so they did burn out kind of smelling like

toast. The A-25XL version with the ceramic magnet had an aluminum former and

could handle much more power.

[Dchristie]

Pete, thanks for your advice. I actually was able to work enough of the broken lead off the coil to splice it to some additional fine copper wire and it works OK. So, I have the speakers up and running and am very pleased with the sound. These are my 1st experience to Dynacos in the A-25 family and I can see why so many folks like them !

[dynaco_dan]

Hi Vern, thanks for your response. As the A-25XL came out in the mid 70s, I assume that they are more scarce compared to the original A-25. I do not see that many for sale on the used market. Great for you that you have been able to secure a couple of nice pairs.

I actually bought this pair thinking I was buying an A-25 only to find out it was the XL model once I saw the actual speakers - the owner also mistakenly thought they were A-25s. It is interesting to see the renewed interest in these old speakers today. When I was in college, I did not know a single person with Dynaco speakers. It is amazing to me how many were sold but I also lived in a more remote area and did not have access to a lot of dealers. I do remember them being available in all of the mail order centers however. When I was buying speakers back then, I had my sights on the KLH 5s, AR 3as, or ADS 810s. I did consider buying Dynaco A-50s but finally settled on the KLH 5s and then moved on to the ADS 810s.

This pair of A-25 XLs appeared to be OK upon buying them ( quick inspection showed no damage to the drivers) but they actually had some major issues which I discovered after I got them home. In addition to the broken coil in the xover, both had sat in water for an extended amount of time and the cabinets were severely compromised as a result. The miter seams had separated significantly at the joints from the water exposure to both speakers. Of course the veneer on the lower parts of the speakers was also severely discolored as well. In addition, once I got into the speakers, I noticed that someone had broken one of the woofer leads (positive lead from the voice coil attachment to the solder joint on the woofer basket)at the positive terminal. They had just tied picture frame wire to the broken lead and then wrapped it around the solder terminal on the woofer basket - it was a wonder it even worked at all! Also, the positive solder connection for the voice coil lead on the other speaker had broken loose from the woofer basket and was just dangling loose on the basket. I am grateful the voice coil did not short out on the metal woofer basket.

Well, I was able to splice a piece of wire lead from another damaged speaker to the broken lead of the woofer and resolder it back on the terminal. I was also able to epoxy the loose solder terminal back onto the woofer basket of the other speaker and I then reinforced all of the other 3 solder lead terminals with a little epoxy as I have read that these terninals often fail over time and become dislodged as mine did.

I have also resanded both speakers and glued the open joints back together (as well as I could without doing a major cabinetry rebuild) and have reoiled both cabinets with 2 coats of clear danish oil. Once the oiled cabinets are dried, I will add a topcoat finish. And finally, I rebuilt the crossovers with Mundorf oil capacitors and noninductive resistors. Hope to have them up and running within the next week or so.

I also have a review of the Dynaco A-25 XL from the 1976 edition of High Fidelity Test Reports and they concluded that the XL model sounded very similar to the original A-25 with just a little more extension in the highs and perhaps a shade more bass definition. Intersting to read different opinions from owners of both speakers on the different web sites. There seem to be supporters for both models - which is fine. Some prefer the originals and some prefer the XLs. I only listened to my pair breifly before I dismantled them, but I thought they sounded pretty good in spite of their problems at the time. Since I have updated the xovers, I will be listening to a non-original A-25 XL but I look forward to hearing what they can do. For me, the fun is in fixing up these old speakers and hearing them again after 40 years .

Hi there

Is it possible for you to post your speaker review here please.

My comment regarding a A-25XL review I read was from an old Audio magazine

[Dchristie]

OK - here is a scan of the review as a pdf file.

Dynaco A-25 XL High Fidelity 1976.pdf

[dynaco_dan]

OK - here is a scan of the review as a pdf file.

Hi again

Thank you for posting your copy of the Dynaco A-25XL speaker review.

I used to really bug Mark a lot for a Dynaco section, thank you again Mark.

He set up one and here we have some more historical documentation from the distant, 37 years later, past.

[dynaco_dan]

Hi there

I need to scan and post the Audio Magazine review I have found of the A-25XL speaker system.

I read it 3 or 4 times to try to digest it's contents.

Will try to post it soon.

The owner that gave them to me also found one broken coil wire. Strange!