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Dynaco A25 woofer buzz


Guest sake

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Hello,

I just picked up a pair of these great sounding speakers. My only problem is that one woofer seems to buzz if the volume is turned up past low. I noticed some distortion when playing the pair not loud at all. I then sent a 100hz sine wave from my computer to my amp using SigJenny software and compared the two speakers using the balance dial on my amp. One speaker reproduces the tone as it should, the other tries to but actually makes a low frequency kazoo sounding tone. I then turned the volume all the way down and brought it up real slow. BOTH speakers will produce the same tone at a very low volume, but once I take it up a bit, the one changes it's tone to a buzz.

I removed the bad woofer from the cabinet and measured it on a volt-meter, it shows 6.3 ohm and does not make a scraping sound when I manually press down on the cone, it flexes as it should. Is this speaker ok, or is it blown? Can it be repaired? Could this be a vibration from somewhere withing the cabinet?

Any help or tips would be appreciated.

Thanks,

sake

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Well, It's not the crossover or cabinet. I removed the woofer and sent the 100hz tone to it all by itself, still a buzz on anything past 8 o'clock on the volume dial. Looks like I need a woofer...

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Hello,

I just picked up a pair of these great sounding speakers. My only problem is that one woofer seems to buzz if the volume is turned up past low. I noticed some distortion when playing the pair not loud at all. I then sent a 100hz sine wave from my computer to my amp using SigJenny software and compared the two speakers using the balance dial on my amp. One speaker reproduces the tone as it should, the other tries to but actually makes a low frequency kazoo sounding tone. I then turned the volume all the way down and brought it up real slow. BOTH speakers will produce the same tone at a very low volume, but once I take it up a bit, the one changes it's tone to a buzz.

I removed the bad woofer from the cabinet and measured it on a volt-meter, it shows 6.3 ohm and does not make a scraping sound when I manually press down on the cone, it flexes as it should. Is this speaker ok, or is it blown? Can it be repaired? Could this be a vibration from somewhere withing the cabinet?

Any help or tips would be appreciated.

Thanks,

sake

Hi there;

I will assume that I have the most working experience on the Dynaco A-25's here, if not a long time ago.

I have written several topics on the Dynaco A-25 woofers in particular.

To make a long story, short, the woofer is a most certain case of in it's death throw.

I am joking of course.

Any attempt to repair the woofer is in need of a steady and careful hand.

Even skilled and experienced service persons can damage them.

The buzzing can be caused by several means.

The glue has separated from the coil and the former, possibly repairable.

The insulation on the outer coil winding has over-heated and bubbled, small chance of a repair.

The coil was overheated and burnt the coil insulation and/or the former, no chance of repair.

With no previous speaker driver repair experience you can proceed with little expectations of success.

I just do not want to build up your enthusiasm past what you have described here.

After saying that, proceed with due caution.

The leads must be carefully un-soldered from the 2 clips on the frame.

With the Seas woofers, polarity is straight forward and not reversible.

The outer rubber suspension ring needs to be gently pried from the basket frame around the outer rim, not from the cone material.

With the rubber surround detached, the cone facing upwards, from the frame.

A very small amount of lacquer thinner or acetone, used outdoors and use extreme ventilation.

Run a small bead around the spiders perimeter to soften the glue.

The cone should lift up and out after a short period.

Now cover the woofers gap with masking tape or such so that nothing can fall into the magnetic gap.

At that point write your results, please and a photo or two or more would be great.

There is always lot's of woofers on eBay at around $20.00 +/- each as a last resort.

Good luck.

Vern

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Hi Vern,

WOW! You sound like you know what your talking about.

My experience level with speakers involves refinishing, recapping. & refoaming. I have never worked on an actual driver before. I am looking foreward to getting my feet wet. At this point, I will at least learn something new and hopefully repair it.

One thing I did notice when I was desoldering the + / - terminals to remove the woofer, was that the lead wires got pretty hot. I read somewhere once that wasn't good. When you say "carefully" desolder them, do you mean in regards to them getting real hot? If so, how do I keep that from happening as they seem like they will conduct the heat from the iron.

Hopefully this weekend I will have time to get this underway. I will post some pictures of this project as I progress.

Thanks,

sake

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Hi Vern,

WOW! You sound like you know what your talking about.

FOOLED YOU, FOOLED YOU. LOL LOL

Actually I worked at the local Dynaco, and others, warantee depot here in Vancouver for about 2 years part-time in the early '70's.

I saw 100's of A-25's, sadly, usually burnt woofers.

My experience level with speakers involves refinishing, recapping. & refoaming. I have never worked on an actual driver before. I am looking foreward to getting my feet wet. At this point, I will at least learn something new and hopefully repair it.

I just want to be sure that your expectations are not built up to be able to do a repair on the woofer.

We had saved several huge boxes of old baskets for re-coning, which never did happen.

One thing I did notice when I was desoldering the + / - terminals to remove the woofer, was that the lead wires got pretty hot. I read somewhere once that wasn't good. When you say "carefully" desolder them, do you mean in regards to them getting real hot? If so, how do I keep that from happening as they seem like they will conduct the heat from the iron.

You really should have a controlled element type soldering station to do a professional job.

That being said, a gun or pencil type will also work, just watch the hand motion control.

You should apply heat to the terminal strip for about 5 or so seconds to soften the solder at the junction of the terminal connector and the tinsel lead.

Using a needle nose plier try to unwind the end of the lead as carefully as possible.

Over doing it can pull the lead from the cone connection if you are too strenuous.

More than 10 seconds and you are not doing something right or too small of a soldering iron.

Use 60/40 or equal Rosin core solder, NOT ACID CORE.

You want to try to not shorten the tinsel by cutting it as this would restrict the cones forward movement.

Hopefully this weekend I will have time to get this underway. I will post some pictures of this project as I progress.

Thanks,

sake

Good luck again.

Vern

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Vern,

Ok, just a quick update.

Whew, I was able to succesfully desolder the tinsel wires with the help of some solder braid & needle nose pliers. The outer portion of the surround lifted off the frame nicely, using the rounded tip of a non serated butter knife; going slowly & carefully. I still need to get some acetone to disolve the glue on the spider, I will do that tomorrow and report back. Once I get the cone removed from the frame, what should I be taking pictures of?

Thanks,

sake

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Vern,

Ok, just a quick update.

Whew, I was able to succesfully desolder the tinsel wires with the help of some solder braid & needle nose pliers. The outer portion of the surround lifted off the frame nicely, using the rounded tip of a non serated butter knife; going slowly & carefully. I still need to get some acetone to disolve the glue on the spider, I will do that tomorrow and report back. Once I get the cone removed from the frame, what should I be taking pictures of?

Thanks,

sake

Hi again;

When you lift the cone straight up, photograph the underside where you will see the copper wire coil.

Side and angle views would be great, please.

Vern

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Well, I got the acetone tonight and followed the instructions. No go. This glue is TOUGH. Tried several times to even disolve a small patch. The acetone evaporates and the glue stays intact. Gave it some time and went at it with the equivelent of a strong dental pick type of tool, trying to at least srape some off the frame near the spider and it just won't budge. Should I go for the lacquer thinner?

And thanks again Vern for attemping to walk me throught this procedure. I am fully aware that this woofer could turn out to be un-fixable, but it would be cool as hell if this is. I got nothing to lose at this point, the woofer was no good as it was.

sake

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It's highly unlikely the VC can be fixed. I suggest you cut the spider, pull the cone assembly out of the frame and visually confirm that is the case. Visit the link below to see my experience with repair of a Snell Model A woofer with a buzz at a particular frequency that had a burned VC . I had to salvage the very special cone and replace the VC and spider.

http://www.classicspeakerpages.net/IP.Boar...?showtopic=4762

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Well, I got the acetone tonight and followed the instructions. No go. This glue is TOUGH. Tried several times to even disolve a small patch. The acetone evaporates and the glue stays intact. Gave it some time and went at it with the equivelent of a strong dental pick type of tool, trying to at least srape some off the frame near the spider and it just won't budge. Should I go for the lacquer thinner?

And thanks again Vern for attemping to walk me throught this procedure. I am fully aware that this woofer could turn out to be un-fixable, but it would be cool as hell if this is. I got nothing to lose at this point, the woofer was no good as it was.

sake

This is what I used as a kid when repairing drivers. My dad is a Chem Eng and he suggested it:

http://www.starbronze.com/720.html

It is powerful stuff, be very careful and use as little as possible.

I wound a replacement voice coil for an A-25 woofer over 20 years ago.

Here's another that I hand wound, back then:

HAND_VC_WEB.jpg

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  • 2 years later...

Hi, i'm hoping vern can help me on a question i have, I have 2 pairs of A25s one i like more then the other pair, unfortunately as of last week my favorite pair have a problem. Buzzing on heavy bass and slight distortion before silence when powering on. When pushing on woofer with no power on it seems fine, unless you push on it right after speaker was used, then you get a slight scratchy sound that shouldn't be there. I took woofer out didn't notice any rips or imperfections, i'm not a tech so i hope i didn't ruin the wires going to the woofer as i seemed to slightly mess one up. I want to take this to a shop and have it repaired. The woofers from my other pair don't match the drivers on the pair i like, yes the differences are slight. I'm hoping to save the original driver, only one of them is bad, any chance this one bad woofer can be salvaged ? It's has me a little depressed i have some BW speakers i never use, i like the A25s more.

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