Seeking advice on vintage speaker repair

[Garyf52]

I have a nice pair of 70's era Dynaco Phase III speakers. They were used for a long time with disintegrated foam surrounds on the mid range drivers. Otherwise they are in very good shape. My goal is to put them back into service if possible. These are 3-way speakers that were only produced in last few years of Dynaco's existance.

Pictures describe them better than words.

Here are the drivers

Woofer: Seas 25F - EWX H-108

Midrange: Seas 11 F-M I've cleaned off the old foam surrounds.

Tweeter: Seas H-086

Crossover:


My plan is to refoam the mids, reassemble, and see how they sound. I don't know if they are ruined or not. I've played them at low volume in their current condition and I can hear noticeable distortion coming from the mids, especially on strong piano notes. Otherwise, they sound pretty good. Tweeter and woofer seem to be fine.

Any advice from the many experts out here would be most welcome.

[Kevin P]

Sounds like a good tactic to me. Refoaming the mids should restore their performance. The cones themselves look good (speakers can be reconed as well).

Interesting that the woofer surrounds still look pristine. Maybe they're a different material?

[Garyf52]

Sounds like a good tactic to me. Refoaming the mids should restore their performance. The cones themselves look good (speakers can be reconed as well).

Interesting that the woofer surrounds still look pristine. Maybe they're a different material?

Yes, different material. The woofers have rubber surrounds.

[---k---]

Very interesting. I would love to hear more of the backstory and about the desire to restore these. There are good reasons to restore old speakers. The stories are fun and interesting. I'm of the generation that wouldn't give these a second look and if I were to restore them would have a hard time not breaking out the router to flush trim the edge and round it over. And I would be moving the switch to the back. Bracing the boxes and who knows what else. Keep us posted.

[Garyf52]

Very interesting. I would love to hear more of the backstory and about the desire to restore these. There are good reasons to restore old speakers. The stories are fun and interesting. I'm of the generation that wouldn't give these a second look and if I were to restore them would have a hard time not breaking out the router to flush trim the edge and round it over. And I would be moving the switch to the back. Bracing the boxes and who knows what else. Keep us posted.

Not much of a back story to this project. I’ve had these speakers for years and noticed the quality deteriorating but I was ignorant as to why. I started building my own speakers last year and it became obvious to me what the problem was.

I’ve replaced the Dynacos with Core 2-way’s, which I am very happy with. Now I’d like to make use of my old speakers so I’m going to attempt to refoam the mids and see what happens. If it works, I’ll have a nice set of speakers, if not, I’ll have some decent woofers and tweeters to use for a future endeavor. I look at it as an educational experiment.

[john trials]

Those speakers are old enough where you should replace the electrolytic capacitors in the crossover. It looks like there are three of them in each crossover circuit. See if you can get new replacements of the same value (capacitance). You can always go for a larger voltage rating, but never go lower. That should help with the sound quality. Electrolytics go bad with age, especially after 40 years.

Pay attention to the orientation (polarity) of the capacitors (I can't tell from the photos if they are non-polarized). Make notes or take good photos before you disassemble the crossovers.

Have fun with the surround replacement. I did this a few years ago with some Infinity and Acoustic Research speakers, and it was a fun project, with great results. It looks like you did a good job cleaning the surrounds already.

[Garyf52]

Success….I’ve completed the refoam job on the midranges and reinstalled everything. I’m happy to report that the speakers are sounding great. I’ll continue to audition them for a few more days to see if any other issues crop up, but at this point I think the problem is solved.

In regards to the capacitors; I may go ahead and replace them but I want to be sure that the drivers are working properly before I do so. The values of the 3 capacitors are 16uf, 2.5uf and 0.5uf (top to bottom in the photo). One question I have is the bottom two are wired in parallel; is that equal to a single capacitor of 3uf ?

[---k---]

The values of the 3 capacitors are 16uf, 2.5uf and 0.5uf (top to bottom in the photo). One question I have is the bottom two are wired in parallel; is that equal to a single capacitor of 3uf ?

Yes. Parallel caps add. (but resistors are 1/x) Based on color, it looks like the 0.5uf is a different brand or type. They might be trying to use a fancier cap as a by-pass cap to improve the sound of the other. But both say 50v. The small black one says NP. (Non-Polar). The 2.5 and 16 are labeled as audio crossovers. So, who knows. The all look small enough that they are probable NPE caps and probably could use to be replaced or will in a few more years.

Now show us a photo of the refoam job. We want to admire your handy-work.

[Garyf52]

Yes. Parallel caps add. (but resistors are 1/x) Based on color, it looks like the 0.5uf is a different brand or type. They might be trying to use a fancier cap as a by-pass cap to improve the sound of the other. But both say 50v. The small black one says NP. (Non-Polar). The 2.5 and 16 are labeled as audio crossovers. So, who knows. The all look small enough that they are probable NPE caps and probably could use to be replaced or will in a few more years.

Now show us a photo of the refoam job. We want to admire your handy-work.

Thanks, Ryan for the capacitor info. I've ordered replacements. Will perform a transplant in the near future.

I said the refoam job was a success, but I didn't say it was pretty. Here you go.

[---k---]

They weren't a real sexy driver before the refoaming. I don't think you hurt the appearance. :T

[Garyf52]

Update....I've replaced the capacitors with new Solen Polypropylene capacitors and I'm truly surprised at the improvement. Treble is much clearer and more detailed. Horns, cymbals, and drums are noticeably improved. Tracks that I used to play with the treble at -6 sound great at -2 or 0.

This was well worth the effort. The swap was very easy to do and less than $30.
New caps are much larger. Here are before and after pics.

[---k---]

I wonder if the old caps were going bad, as NPE caps can do. You wouldn't have a way of measuring them? I'm just curious.

[5th element]

Well if an NPE dries out (some caps can do this over even 5 years although this is unusual and premature ageing is normally the result of increased temperature) then it's performance deviates significantly from what it should be, the ESR shoots up and the caps value goes down. This would raise crossover frequencies and reduce the signal level reaching the driver. NPEs are usually used in places where very large cap values are needed in cost sensitive applications, otherwise using a film cap solves this issue completely.

The speaker in this thread is clearly a design that should have used film caps right from the start.