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My Boston A400 rebuild

tromba

tromba

Super Member
I've only been on AudioKarma about a month. I can't count the times I've seen a great deal with pickup only and the location has been Michigan or New Jersey or other netherlands of the north. That's quite a distance from down here in Alabama.

Then I visited the Member Classified section and found an ad from someone in northern Alabama!!! A pair of Boston Acoustics A400s free to a good home, and to someone not going to turn them for a quick profit. Since my wife says I NEVER throw ANYTHING away, I qualify for that! A little reading here on the forum found how highly regarded these are by many members.

So due to the generosity of AK member Jim Porter I have a new project. He had already had the drivers all refoamed (one set was still in the shipping boxes) and had already bought new caps. All I have to do is replace the caps, put the drivers back in and they'd be good to go. (or maybe some cabinet work?)

This was very generous of Jim!!! Thank you.

I have some experience making computers from scratch, soldering/rewiring/installing my car stereo, etc. but no experience at all with replacing caps. And while I won't actually be able to start until summer, I'll be looking for information. As an aside I also have AR3a and AR3 speakers to recap also -- for that I found several threads here going through the process as well as an excellent PDF guide from ClassicSpeakerPages.

Is there such a step by step guide for the A400s??

One problem Jim ran into is that the crossovers are mounted on a board that seems to be hot-glued to the back of the cabinet. Anyone think of a safe way to remove it?

While Jim provided new caps, he said I might want to get better ones, and that some values couldn't be found. This is all stuff I'll have to look into.

For now, here's the BEFORE pictures!!

The front with and without grill:
BostonFront1.jpg


BostonFront1.jpg

BostonFront2.jpg



The crossovers in place:
BostonCross1.jpg

BostonCross2.jpg


The Drivers:
BostonDrivers.jpg

BostonDriverBack.jpg



The back and the Caps:
Boston_Back.jpg

BostonCaps.jpg


Boston_Back.jpg

BostonCaps.jpg
 
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Wow! Nice score and project! Replacing the caps is VERY easy. Do one crossover at a time, replace one cap at a time. Use the other crossover for reference.
 
Thinking back when I redid my 400's a couple of years ago I had the same problem of the crossovers being securely glued to the back. I used a claw hammer if memory serves correct and it came out in one piece. I also had to fashion a new board for the bottom crossover because of those big caps. I'm still pretty happy with sound and I used daytons. Good luck to you with those fine old 400's.
 
Great score on those, and with all the parts ready to install. Its a great sounding speaker :) Keep us up to date as you move along
 
OK, I'm ready to start on this. I'd REALLY like to be able to remove the crossover from the cabinet to give me more room to work. They appear to be hot glued in place. Any suggestions on how to remove them?
 
motorstereo said:
Thinking back when I redid my 400's a couple of years ago I had the same problem of the crossovers being securely glued to the back. I used a claw hammer if memory serves correct and it came out in one piece. I also had to fashion a new board for the bottom crossover because of those big caps. I'm still pretty happy with sound and I used daytons. Good luck to you with those fine old 400's.
Click to expand...

Moto had givin his way early on. Good luck :)
 
I'm jealous! One of those rare speakers that I really wanted but never got. They will sound magnificent!
 
A-400s are a wonderful speaker !!!!!
I've refoamed mine, but live with the original crossover.
Apart from being 4 ohms, they are very power hungry ...
I've not bi-amped them, but they are happy at 100 watts a side.
I've fed them less and the bass is not the same.
You'll love them!
Just keep them well fed, they are not the world's most efficient speakers.
 
tromba said:
I know but my claw hammer won't fit in there. I might have a smaller one at the office. I'm still afraid I'll break it.
Click to expand...

Then use a smaller pry bar. Take your time and pry gently and chances are it'll come out in one piece. Don't fret if it does break though. Chances are you're going to have to fashion a new backing board anyways to accomodate the much larger caps.
 
tromba said:
I know but my claw hammer won't fit in there. I might have a smaller one at the office. I'm still afraid I'll break it.
Click to expand...

Try a putty knife or similar with a thin, flexible blade. Work it under very gently and carefully. This has worked for me to remove crossover boards and JBL foilcals with minimal damage.

Good luck with the A400s! I really love the smaller Boston A-series models I've had and would like to get some bigger ones someday.
 
update

I'm going to update this as I go along, so maybe the next person will see what I did right, or wrong.

So I went to Lowe's today and bought a Crossover Remover Tool. They don't know any better and call it something else

Cross_Tool.jpg

which just seems to fit in there fine

Cross_Remove.jpg


As it turns out, there wasn't a lot of glue on the back of the board

Cross_Glue.jpg


Now to the tweeter crossover. It's a much smaller area with a bigger board and my new Crossover Removal Tool can't get under any edges, thus so far haven't budged it....

CrossSmall_Remove2.jpg
 
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Figuring it out

Still working on getting the upper crossover out. In the meantime....

Here's a photo of the lower crossover. (Remember this is new to me.) Am I right that #3 and #4 are the caps? What are #1 and #2?
EDIT: Only #4 are the caps... see post 22 below

caps1.jpg
 
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Cap Wiring

Here's the two ends of the caps.... on one end all 3 are joined, and on the other end the square one goes to #1 & #2 while caps #4 go to the board

joinedCaps.jpg


Can someone explain the electronics of this to me?
 
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