Boston Acoustic A400--I'm the original owner!

[FireGuruMN]

Yep, bought these if Fargo, ND for $812.00 at Team Electronics back in 1984 if all those memory cells are still working correctly. I'm sure some are misfiring at this point. They were my main speakers until I purchased a pair of Polk RTIa9's a few years back. Now I've gone speaker crazy so it's hard to say what my main speakers are anymore.

They are in pretty nice shape. I refoamed them 10 years back after I blew out the old foam when I used them for an outdoor movie party for my kids. At least that is when I noticed the foam was gone. It may have been gone long before that. Regardless, they are long over due for a recap. It appears all of the capacitors are electrolytic. I will use film caps where ever it is reasonable. But some caps are 160uf and there is no budge tor room for that sort of film cap.
Here is a schematic I found on the interweb. I put it here for reference because the web link is lost now:

The thing to keep in mind on this one is that there are TWO separate crossovers in each speaker. One for the mid/high and one for the woofers. You get to the crossovers by removing the speaker drivers. It was a bit of an Easter egg hunt for me so I pulled out all the drivers in the end. The upper woofer:

Nothing there except a yellow/black pair leading to the jacks that allow bi-amping with connections to the upper crossover. Keep looking. The lower woofer:

My memory always thought there was one driver and one passive radiator but clearly there are two drivers. Memory updated. It is nice that they used poly fill instead of insulation. After doing AR3a's and Advent Large I've had it with fiberglass insulation. There is the lower crossover after removing the poly fill:

It is possible to replace those capacitors without removing the board from the speaker. The boards are glued in place and not easily removed. I highly recommend replacing the crimp on connectors. I tried to re-tension them and several of them broke.
Continued. . .

 

[FireGuruMN]

Here is my capacitor list (total count for both speakers):
Qty 8 of 80uF 100V Electrolytic Non-Polarized Crossover Capacitor Part # 027-358 (really any combination of capacitor that gets you to 160 will work. Some stock is disappearing due to the current pandemic it would seem)
Qty 6 (or so) of Audiocap PPT Theta 0.10uF 600V Film/Foil Capacitor Part # 027-710 (its your choice what brand of bypass capacitor you want to use or if you even want to use them at all. I'm not getting into that argument)
Qty 2 of Solen 3.9uF 400V Polypropylene Capacitor Part # 027-548 (original is 4uf. close enough.)
Qty 2 of Solen 15uF 400V Polypropylene Capacitor Part # 027-576 (original is 16uf but that was out of stock)
Getting the 60uf capacitor value (any combination of caps that get you to 60 will be fine). You could almost use film's here is you went with some Daytons or something. I think it is in the audio path so there might be some rational reason for it. But not for me. I added a bypass to make myself feel good.
Qty 2 of 12uF 100V Electrolytic Non-Polarized Crossover Capacitor Part # 027-342
Qty 2 of 47uF 100V Electrolytic Non-Polarized Crossover Capacitor Part # 027-352

All the inductors and resistors are fine unless you want to get obsessive about air core inductors (can someone add inductors into the spelling dictionary of this web site!) and super tight tolerance resistors. In which case you should by different speakers and/or seek therapy.

Here is what the lower crossover looks like when I finished. The sanity of a bypass capacitor on a shunt capacitor is doubtful but whatever. I used hot glue to keep everything in place. It is easiest if you assemble and solder the the three capacitors before putting them in the crossover. I just cut the leads on the old capacitors and looped them in to the leads on the new capacitor. I like to have a physical loop in the wiring instead of just solder holding them together.

another view (this is the first one that I removed before I learned how hard it was to remove them)

Hopefully that picture was taker before I soldered them in place and hot glued. It doesn't look there is much solder on the right hand connection! Sorry if some of these pictures are upside-down. My iphone does not understand left handed people so I always hold the phone upside down so I can get to the shutter button. I wonder if I can sue Apple for that. It's soo annoying. I don't think my Android had that problem. . .but I digress.
In case someone has never seen the back of an A400 here is the chance of a lifetime:

This is the only speaker I have seen that has a separate pair of jacks to use when bi-amping. It comes with a factory installed jumper that has never been removed in my case. But this might help explain my previous comment about input jacks for bi-amping.

Continued. . .

 

[yesshows77]

Excellent work on the recap job. I own a pair and they hold their own or best many other vintage floor standers in my man cave.When supplemented with a subwoofer, they are almost perfect sounding to me. Boston Acoustics really knew what they were doing when they developed the A series models.

 

[FireGuruMN]

Now on to the midrange and tweeter.
I pulled the tweeter out just so I could document it. It is not necessary to remove it to get to the crossover:

I love date codes that are not codes, just dates. 1984, that means this is the only vintage speaker I own that was bought when it was not a vintage speaker.
I apparently do not have picture of the midrange driver. That's awful. Get over it.
Here is the upper crossover. As some sort of cruel joke on people with large hands, they put the large crossover in the small hole. So I personally had to remove this one to do anything with it:

This is my attempt to photograph me using a "cats paw" tool to get some leverage behind the crossover and pry it up. This got enough of an edge that I could pull the rest up with my hands. It is possible to break the masonite so be somewhat gentle. I did not try it but it is possible that heating the entire board up with a heat gun will make this easier. It certainly helped on my Ohm Walsh crossover removal.
Eventually most of it came out:


Did they build these things in a garage? Maybe production quantities were low enough that it did not pay to build a PC board or anything. Hard to say. But I guess the electricity doesn't care. I do respect that all the labels are facing up. That shows that someone cared. And it's all laid out square.

Here is my recapped version:

oops, some labels are not showing. It was a long day at this point.
I don't really have any photos of it but the upper crossover, midrange, tweeter are in a separate enclosed space at the top of the cabinet. So they designed the volume to match the characteristics of midrange. Sweet. This also makes for some narrow vertical spaces on the sides that are part of the volume that the woofers are in. I wonder if that was in the design? And those narrow space were stuffed with fill also. Someone did care. . .
Another view or maybe the other crossover. I can't remember and it doesn't matter. I do find that the second speaker is always easier to do because I know what I am doing. That didn't happen with my kids because I had twins. No option to learn from my mistakes there. But I digress. . .

Slap a huge glob of hot glue on the back and stick it back into the speaker. Remember to replace the space connectors! I had to go back in and do that because the midrange was not making contact.
Everything I removed:

Looks like an Easter Egg basket. . .
They sound very good. They always sounded very good except when the foam was blown out. I've been replacing caps in speakers most of the Winter. My thoughts are that the midrange/voices are always better after the recap. I'm thinking that the shunt capacitors across the woofers are getting leaky and allowing the midrange to leak into the woofers and making those frequencies muddy. It would certainly be a lot cheaper to just have to replace those shunt capacitors. I'm always a bit torn about tearing out film capacitors because theoretically they should not degrade like electrolytics. Some day I should try just doing those caps. But I'm running out of speakers. But never to be one to follow my own advice, I'm recapping my 4435's next. . .

Be safe.

 

[swechsler]

Did they build these things in a garage? Maybe production quantities were low enough that it did not pay to build a PC board or anything. Hard to say. But I guess the electricity doesn't care. I do respect that all the labels are facing up. That shows that someone cared. And it's all laid out square.

You may be surprised to learn that with older speakers, more often than not, crossovers are done point-to-point on a piece of pressboard.

 

[Blue Shadow]

Looking forward to your listening sessions with all these top performers with new caps soldered and glued in place. Will you be doing some comparisons of discuss the sound of the different sets you rebuild?

 

[FireGuruMN]

I always feel like discussing acoustic performance with words is like trying describing colors to a blind person. Smooth, tight, open, forward, flat, mellow are all words I have heard to describe audio performance. But really they seem more like words that belong on a Tinder account.
Then you can always hook up a spectrum analyzer and go all scientific on the measurements. But most manufacturers already publish all that data (if you can believe them).
But I will probably start doing some comparisons at some point. At least I will get into doing some apples to apples comparisons (like L100's to 4312's--there is really a big difference even thought they are similar on paper).

I recently picked up this toy:

It allows connecting 7 pairs of speaker and even switching between two amplifier sources WITH A REMOTE CONTROL! It will certainly make a/b comparisons much easier when I sit down to do some heavy listening. I got it off amazon as an open box. It's an OSD ATM-7 if the numbers don't make it clear in the pictures. It seems to do exactly what the manufacturer claims. There are buttons to allow multiple speakers to be selected at the same time or it will only allow one pair on at a time. There is NO PROTECTION if you put too many speakers on line at once so be careful. Here is the inside. Not sure about the brand of relays but at least it is relays and not some weird triac or something.

The back panel and the brains:

Not the highest quality banana jacks but at least they are banana jacks and not spring connectors. I will end up using bare wires and screwing them down on this end. Banana jacks on the other ends so I can easily swap out speaker pairs. It would have been nice to have the hex shaped plastic screw downs so I could use a nut driver. It is hard to get my big hands in those tight spaces. Maybe I can find one that will fit. I think it came in at $160.00 with tax so that is quite a bargain in my book for such a toy.

But I have a few more speakers to get through first:

yep, at some point it becomes hoarding.

 

[FireGuruMN]

You may be surprised to learn that with older speakers, more often than not, crossovers are done point-to-point on a piece of pressboard.

Yep, been there (AR3a, Advent and several others). But in 1984 I was thinking I would find a PC board. I have a pair of electro-voice speakers (pictured above on the end) that have all the capacitors POTTED in TAR. And I cannot find any documentation on what is inside the tar. And to make things worse one of the "presence" or "brilliance" l-pads is potted in there with them. I know the caps need to be replace but I'm just dredding going in there. I might design a crossover from scratch instead of figuring out what was done previously. That would be a new adventure for me also. New is good.

 

[LinderK]

A literal wall of sound!

 

[Qtronic]

I lived in Fargo from 1989-1997, my hometown is Jamestown.
Nice work on the Bostons!

 

[rongoe]

Thanks for sharing your A400 recap experience!
I'm picking up a pair tomorrow so this info may be very helpful if I decide to do the same.
Did you happen to test the old capacitors you replaced? If so, how'd they do?

 

[FireGuruMN]

First: I'm not an expert, I only play one on the internet.

I tested the old capacitors for capacitance only. They were within specifications. Often specifications are 20% tolerance so that's not saying much. I did not test for ESR (equivalent series resistance). That is often the killer. The resistance increases as the electrolytic in the capacitors dries up. The resistance then sucks up some of the audio signal causing loss of high end and such. It also creates heat which further degrades the capacitors. Its a nasty cycle of failure. Film capacitors do not have electrolytic fluid so they never dry up. Most people film caps sound better also. but possibly that's just because they paid way more for film caps than for electrolytic capacitors. I know I fall into that category of people. .

Different capacitors also behave differently at different frequencies. Some capacitors are designed for power filtering and are not good with audio signals. Feel free to go down the rabbit hole googling all about capacitor design and application. Its a dark science.

Its good to see that some people actually read these posts.

Stay safe.

 

[Dain Bramige]

Thanks for taking the time to document your rebuild process. I recently picked up a set o A400. Currently in refoam stage. I'll have to debate recapping. But so nice to see the process in action. And a great reference for others going forward. Thanks again for you work and sharing it.

 

[qert]

Thanks for taking the time to document this process. Just acquired a pair of these, but taking them to be professionally refoamed and recapped. They'd been sitting in a government warehouse for a while. So far I've had one tech say to not even hook them up until they're serviced.

Probably a $1200 repair by a pro all in at any rate. That's canuck bucks. Seeing these a400 repair threads is making me question doing it myself during the summer, however.

 

[drbranch]

Now on to the midrange and tweeter.
I pulled the tweeter out just so I could document it. It is not necessary to remove it to get to the crossover:
View attachment 1826800
I love date codes that are not codes, just dates. 1984, that means this is the only vintage speaker I own that was bought when it was not a vintage speaker.
I apparently do not have picture of the midrange driver. That's awful. Get over it.
Here is the upper crossover. As some sort of cruel joke on people with large hands, they put the large crossover in the small hole. So I personally had to remove this one to do anything with it:
View attachment 1826825
This is my attempt to photograph me using a "cats paw" tool to get some leverage behind the crossover and pry it up. This got enough of an edge that I could pull the rest up with my hands. It is possible to break the masonite so be somewhat gentle. I did not try it but it is possible that heating the entire board up with a heat gun will make this easier. It certainly helped on my Ohm Walsh crossover removal.
Eventually most of it came out:
View attachment 1826828
View attachment 1826829
Did they build these things in a garage? Maybe production quantities were low enough that it did not pay to build a PC board or anything. Hard to say. But I guess the electricity doesn't care. I do respect that all the labels are facing up. That shows that someone cared. And it's all laid out square.
View attachment 1826831
Here is my recapped version:
View attachment 1826835
oops, some labels are not showing. It was a long day at this point.
I don't really have any photos of it but the upper crossover, midrange, tweeter are in a separate enclosed space at the top of the cabinet. So they designed the volume to match the characteristics of midrange. Sweet. This also makes for some narrow vertical spaces on the sides that are part of the volume that the woofers are in. I wonder if that was in the design? And those narrow space were stuffed with fill also. Someone did care. . .
Another view or maybe the other crossover. I can't remember and it doesn't matter. I do find that the second speaker is always easier to do because I know what I am doing. That didn't happen with my kids because I had twins. No option to learn from my mistakes there. But I digress. . .
View attachment 1826837
Slap a huge glob of hot glue on the back and stick it back into the speaker. Remember to replace the space connectors! I had to go back in and do that because the midrange was not making contact.
Everything I removed:
View attachment 1826846
Looks like an Easter Egg basket. . .
They sound very good. They always sounded very good except when the foam was blown out. I've been replacing caps in speakers most of the Winter. My thoughts are that the midrange/voices are always better after the recap. I'm thinking that the shunt capacitors across the woofers are getting leaky and allowing the midrange to leak into the woofers and making those frequencies muddy. It would certainly be a lot cheaper to just have to replace those shunt capacitors. I'm always a bit torn about tearing out film capacitors because theoretically they should not degrade like electrolytics. Some day I should try just doing those caps. But I'm running out of speakers. But never to be one to follow my own advice, I'm recapping my 4435's next. . .

Be safe.

Most likely they built them in a garage or garage equivalent having lived in Boston and Cambridge in the 80s through the 90s.
In the early 80s I came upon a pair of the original A-100s in a store and they were discounted! Loved the sound and snatched them up. Used those for the next 15 years until the foam disintegrated and gave them to my brother as a project. Even had the original boxes.
A few years ago I asked him about them hoping to snag them back. Nope. Gone. He doesn’t even remember what he did with them. Ah, another piece of history lost.

 

[Goggle1824]

Thanks for taking the time to document this process. Just acquired a pair of these, but taking them to be professionally refoamed and recapped. They'd been sitting in a government warehouse for a while. So far I've had one tech say to not even hook them up until they're serviced.

Probably a $1200 repair by a pro all in at any rate. That's canuck bucks. Seeing these a400 repair threads is making me question doing it myself during the summer, however.

Yikes! $1200!!!

I STRONGLY encourage you to hold off and do more reading on this and other sites. Everything you would need to learn, know and do, IS HERE!!!

I haven’t reconditioned this specific set myself but from everything I’ve read, it really is VERY straightforward. In addition, I can nearly guarantee you will actually enjoy them MORE by the doing the reading, learning and repairs yourself!!!

You CAN DO IT! There are tons of here ready, willing and able to help!

 

[Doug G.]

Ah, good ol' Team Electronics. I used to buy stuff at the Rochester, MN Apache Mall store back in the seventies/eighties. I remember a replacement stylus for my Empire 2000 E/III cartridge was $24.95.

Also, I used to sell Boston speakers at the Rochester Mountain Electronics store in the Eighties.

Doug

 

[Tim D]

Thanks for taking the time to document this process. Just acquired a pair of these, but taking them to be professionally refoamed and recapped. They'd been sitting in a government warehouse for a while. So far I've had one tech say to not even hook them up until they're serviced.

Probably a $1200 repair by a pro all in at any rate. That's canuck bucks. Seeing these a400 repair threads is making me question doing it myself during the summer, however.

Double Yikes! Where are you getting $1200CAD quotes????

With a handful of capacitors and replacement surrounds and surround glue you can have those done yourself for less than $100CAD (maybe much less) in an afternoon.

 

[katana1100]

I think I spent around $70 on poly caps and mag fluid on my a400’s when I went through them four years ago.
A few caps were out of spec so I replaced all. One tweeter had tarred up Ferris fluid , the other looked fine so I redid both.
Currently , all crossovers are disconnected, I ran speakers off analog crossover abd triamped them - sounded much better.

 

[rollupp]

I think I spent around $70 on poly caps and mag fluid on my a400’s when I went through them four years ago.
A few caps were out of spec so I replaced all. One tweeter had tarred up Ferris fluid , the other looked fine so I redid both.
Currently , all crossovers are disconnected, I ran speakers off analog crossover abd triamped them - sounded much better.

Interesting. What analog crossover did you hook up to triamp them? -Also what amp(s) did you power them with? Thanks.