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Boston A-150 repair


Guest tonedeaf

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Guest tonedeaf

Hello all, I got to my refoam project, and I wanted to share some observations/questions. I bought new foam rings from Looneytoon2001 on Ebay. When I was installing the foam rings, I noticed that the woofers (Aug. 1985) have a 16mm hole thru the magnet center pole from the rear of the magnet extending into the area covered by the dustcap. Whats that for? cooling, tuneing? Anyhow the foam replacement went ok and the speakers sound fine.

I did check the nonpolarized 50v caps used in the crossover for value. All values for the caps were very close, that was a suprise because they looked like the metal can axial type that I have seen dry out. I disconected one end of each cap to measure the value (esr was not checked). I also meaured the unmarked inducturs while the speakers and caps were still unhooked. See crossover schematic.

Boston_A150.bmp

Next are the large Advents with masonite ring woofer. Anyone know how well the caps hold up in them? The Advents use pink fiberglass insulation for stuffing. Is it necessary to keep the fiberglass out of the woofer? If necessary, then how is that done?

Thanks

Tonedeaf (what)

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Next are the large Advents with masonite ring woofer. Anyone know how well the caps hold up in them? The Advents use pink fiberglass insulation for stuffing. Is it necessary to keep the fiberglass out of the woofer? If necessary, then how is that done?

Thanks

Tonedeaf (what)

You may be interested in this thread:

http://www.classicspeakerpages.net/IP.Boar...?showtopic=4919

I haven't started the refoam yet, but I think replacing the caps is always a good idea. I used inexpensive Carlis and also replaced the resistors. Pete B recommends replacing the inductors as well, but that can run into a bit of money :blink:

Could you weigh the amount of fiberglass in each speaker and post it here? Mine used foam rubber--like a cut up cheap mattress ;) I'd like to replace that with fiberglass.

Good luck.

Kent

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Guest tonedeaf
You may be interested in this thread:

http://www.classicspeakerpages.net/IP.Boar...?showtopic=4919

I haven't started the refoam yet, but I think replacing the caps is always a good idea. I used inexpensive Carlis and also replaced the resistors. Pete B recommends replacing the inductors as well, but that can run into a bit of money :blink:

Could you weigh the amount of fiberglass in each speaker and post it here? Mine used foam rubber--like a cut up cheap mattress ;) I'd like to replace that with fiberglass.

Good luck.

Kent

Hello Kent

I am new to working with speakers and crossovers, its been much fun so far. I think my next move will be to install 0.1 caps and resistors in parallel with the np caps. Its interisting that others have replaced the inductors as well. An inductor would not change value in time, but will have different Q values (series resistance).

Thanks for the link also Kent.

Tonedeaf

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  • 1 month later...

Thanks for the schematic, tonedeaf.

I can't help you with the 16mm hole question.

I can tell you from many years of experience as a maintenance electrician that capacitors can test well, but behave differently when passing current in application as I've remedied some vexing problems in older equipment by replacing electrolytic cap.s that tested well for capacitance value. I follow the advice I've seen many times in various forums regarding cap. replacement. If it tests bad, replace it. If cap.s test ok, but you don't think your (older) speakers sound as good as they should. replacement of electrolytic cap.s should be tried. If the new cap.s alter the voicing unacceptably, put the old ones back in. I'm not trying to say there is no value in bench testing cap.s, but it's not always completely definitive.

Woofers in stuffed enclosures usually have some type of barrier between the speaker cone and the stuffing. I copycat the method of cutting pieces of window screen mesh (I recommend the non-conductive type) and glueing them over the openings in the basket as I've seen on several OEM woofers. Another alternative would be to wrap some coarse woven fabric around the basket like I saw in my AR2a's.

Turning back to A-150s about stuffing, mine have a white polyfill similar to the "Acoustistuff" sold by Partsexpress in them, is that what y'all found in yours?

Are Boston Acoustics A-150s worth the trouble to get working right? My answer is not only "Yes", but "H-ll yes!" In my opinion they are among the best in all of vintage speakerdom.

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Guest tonedeaf
Thanks for the schematic, tonedeaf.

I can't help you with the 16mm hole question.

I can tell you from many years of experience as a maintenance electrician that capacitors can test well, but behave differently when passing current in application as I've remedied some vexing problems in older equipment by replacing electrolytic cap.s that tested well for capacitance value. I follow the advice I've seen many times in various forums regarding cap. replacement. If it tests bad, replace it. If cap.s test ok, but you don't think your (older) speakers sound as good as they should. replacement of electrolytic cap.s should be tried. If the new cap.s alter the voicing unacceptably, put the old ones back in. I'm not trying to say there is no value in bench testing cap.s, but it's not always completely definitive.

Woofers in stuffed enclosures usually have some type of barrier between the speaker cone and the stuffing. I copycat the method of cutting pieces of window screen mesh (I recommend the non-conductive type) and glueing them over the openings in the basket as I've seen on several OEM woofers. Another alternative would be to wrap some coarse woven fabric around the basket like I saw in my AR2a's.

Turning back to A-150s about stuffing, mine have a white polyfill similar to the "Acoustistuff" sold by Partsexpress in them, is that what y'all found in yours?

Are Boston Acoustics A-150s worth the trouble to get working right? My answer is not only "Yes", but "H-ll yes!" In my opinion they are among the best in all of vintage speakerdom.

Thanks Mazeppa for the tip on the screen to keep the fiberglass out of the voice coil.

I have not replaced any caps yet (got in a hurry to hear them), but I plan to replace them soon.

My A-150's had the white acoutistuff looking stuffing.

I am planning to use the screen or cloth around the driver on my large Advents.

My a-150 refoam project was very rewarding. They seemed to have a wide gap at the voice coil, so I did not remove the dust cover for shims.

Tonedeaf

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  • 5 weeks later...
Guest tonedeaf
Hello Kent

I am new to working with speakers and crossovers, its been much fun so far. I think my next move will be to install 0.1 caps and resistors in parallel with the np caps. Its interisting that others have replaced the inductors as well. An inductor would not change value in time, but will have different Q values (series resistance).

Thanks for the link also Kent.

Tonedeaf

Hello Kent, sorry for the long delay. I did start on my large advent project. The weight of the fibergass in each speaker will probably not mean much because this pair of speakers had been apart many times. The amount of fiberglass was different in them, one was very full, and the other not so much.

These also had radio shack crossovers, so went to work and wound the inductors on empty plastic wire rolls (1.6mh and .44mh). There were parts of the origional crossover in one speaker with exploded cap and burnt spot where the small round inductor was. Maybe this systems amp shorted? I will be using fuses.

The speakers ended sounding fine now whit the fiberglass loosly filling the boxes (I had to add some) I endedup with tweeters from a nla, the highs are fine for my 61year old ears.

Tonedeaf

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  • 4 weeks later...
Could you weigh the amount of fiberglass in each speaker and post it here? Mine used foam rubber--like a cut up cheap mattress ;) I'd like to replace that with fiberglass.

Good luck.

Kent

I've not been in his game for very long, but I've done a lot of reading and never heard of foam blocks for cabinet stuffing.

My A150's have the round SEAS tweeters in them. Do yours have the older round, or newer square tweeters in them?

When I had my woofers out for refoaming it appeared the cab.s were equally full of white polyfill type stuffing. I hope to get back in for a recap soon and will weigh stuffing at that time and post the result.

Turn it up!

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Sorry for muddying the waters by going off on an Advent tangent in the Boston section. Yes Mazeppa, Advents did use foam. The Advent 400 (radio) speakers had foam stuffing and my Original Large Advents did as well. PeteB has recommended replacing the foam with fiberglass or poly so I was wondering how much to use. Will continue this discussion in the Advent area though.

Kent

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  • 1 month later...

I'm finally getting around to recapping my A150s. Refer to the attached schematic, please. I'm fishing for confirmation that the 6.8uf and the 60uf are bypass cap.s in the mid and woofer circuits respectively.

I plan to use less expensive bipolar electrolytics for bypass cap.s is the reason for my question.

Also, is the attached schematic typical for all A150s or should I open mine up to verify cap. values?

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I plan to use less expensive bipolar electrolytics for bypass cap.s is the reason for my question.

Just a suggestion:

Looks like each speaker requires a 60uF, 20uF and 6.8uF and 4.7uF

If you go to Madisound, you can get:

4.7uF Carli Mylar for $1.25

6.8uF Carli mylar for $1.70

20uF Carli for $5.00 OR use two 10.0 mfd Polypropylene “surplus caps” in parallel, at $0.60 ea ($1.20 per speaker)

65uF Bennic NPE for $1.90 OR—if there is room—use 6 of those 10uF surplus caps. $3.60 per speaker. Pretty economical! :rolleyes:

Too bad they sold out of the 5uF GE caps—they were a bargain at .75 ea, but the Carlis are bargains, too. CSP member RoyC turned me on to them, and he knows crossovers!

Good luck

Kent

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Just a suggestion:

Looks like each speaker requires a 60uF, 20uF and 6.8uF and 4.7uF

If you go to Madisound, you can get:

4.7uF Carli Mylar for $1.25

6.8uF Carli mylar for $1.70

20uF Carli for $5.00 OR use two 10.0 mfd Polypropylene “surplus caps” in parallel, at $0.60 ea ($1.20 per speaker)

65uF Bennic NPE for $1.90 OR—if there is room—use 6 of those 10uF surplus caps. $3.60 per speaker. Pretty economical! :rolleyes:

Too bad they sold out of the 5uF GE caps—they were a bargain at .75 ea, but the Carlis are bargains, too. CSP member RoyC turned me on to them, and he knows crossovers!

Good luck

Kent

Thanks for the quick reply and good tip. I'm off to the Madisound wesite.

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I'm finally getting around to recapping my A150s. Refer to the attached schematic, please. I'm fishing for confirmation that the 6.8uf and the 60uf are bypass cap.s in the mid and woofer circuits respectively.

I plan to use less expensive bipolar electrolytics for bypass cap.s is the reason for my question.

Also, is the attached schematic typical for all A150s or should I open mine up to verify cap. values?

I believe there are 3 slightly different versions. Open yours up and verify your cap values before you run off and buy anything.

Attached is a schematic I drew of a version III. However, yours may be different.

The link below is a place to start regarding which series you have. Do more searches here and at AK to determine which you have just to nail it down.

http://www.audiokarma.org/forums/showthrea...coustics+series

Boston_Acoustics_A150_series_III_schematic.doc

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I believe there are 3 slightly different versions. Open yours up and verify your cap values before you run off and buy anything.

Attached is a schematic I drew of a version III. However, yours may be different.

The link below is a place to start regarding which series you have. Do more searches here and at AK to determine which you have just to nail it down.

http://www.audiokarma.org/forums/showthrea...coustics+series

Something was telling me I should open them up first, but I got a little bit lazy. Thanks for your timely post and references.

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Something was telling me I should open them up first, but I got a little bit lazy. Thanks for your timely post and references.

Sorry--I was not aware there were different versions :rolleyes: . You only placed the order today, so maybe you could phone or email Mad and ask them to hold the order until you check.

OTOH maybe you'll get lucky.

Kent

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  • 2 months later...

Finally back to A150 recap. Opened them up for look see at the xover and it does seem to be different than the schematic given earlier in the thread.

Bear in mind that I'm a long time electrician with a bare smattering of electronics knowledge. I checked and rechecked my schematic against the xover itself until I was cross eyed. As I'm unfamiliar w/crossover design I'm asking those more knowledgeable to check me as best as can be done with the pic. and not too pretty schematic.

I'm still trying to determine which cap.s are just for bypassing (C3 & C4?) so I can use electrolytics for those and polyesters for all in series signal path positions. Any and all help will be appreciated.

post-103392-1248737401.jpg

post-103392-1248737308.jpg

First attempt at anything but text, is this the way to go?

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Just a suggestion--you might want to scale down those jpg files.

So there are 4 caps: two 60uF, one 10uF and one 6uF

It's a little crowded in there but you can parallel 3 Carli 20uF caps for the 60s, use a Carli 10uF and a Carli 6uF.

Or... use Solen 60uF (they are $19 each) :lol:

Or... use Bennic non-polarized electrolytics. 65uF is under 2 bux

They still have those surplus caps for .60 each, but you'd end up with 13 10uF caps plus the 6uf in each box. It can be done, but may be a bit of a hassle.

btw--after you pry all those components out of the hot-melt glue you might want to replace the resistors too. Eagles from Madisound are just $1.20 each.

good luck

Kent

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  • 3 weeks later...

I thought I'd throw in my 2 cents on A150s. I refoamed on recapped mine also. I believe mine are Sries I and have a completely different compliment of capacitors than the Series II and IIIs already discussed.

Each of mine has one each 5, 8, 13, 42 and 60 mfd caps.

I recapped them using Parts Express house brand Dayton poly film capactiors. I noticed an incredible difference is sound. Only real issue is that the larger poly caps are large. I wound up hhot glueing them to the back of the speaker cabinet, because there was no way they would fit on the crossover board.

I wish I could share the crossover diagram, but after going completly cross-eyed I couldn't figure out how to get it down on paper. :blink:

Bugs

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The use of 12X12X2 inch thick foam block in New Large Advents was very common. Five of them in fact.

I've done some comparison work on two NLA's now using OCFG vs the original foam blocks and each time the FG has performed better a 1 lb/cu.ft. stuffing or-so stuffing density. Lower Fc and smoother impedance & phase response.

See posts #1 and attachment at #12 here http://www.classicspeakerpages.net/IP.Boar...c=2895&st=0

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Just a suggestion--you might want to scale down those jpg files.

I'll have to figure that out. What scale will still provide usable defintion?

So there are 4 caps: two 60uF, one 10uF and one 6uF

It's a little crowded in there but you can parallel 3 Carli 20uF caps for the 60s, use a Carli 10uF and a Carli 6uF.

Or... use Solen 60uF (they are $19 each) :P

Or... use Bennic non-polarized electrolytics. 65uF is under 2 bux

They still have those surplus caps for .60 each, but you'd end up with 13 10uF caps plus the 6uf in each box. It can be done, but may be a bit of a hassle.

btw--after you pry all those components out of the hot-melt glue you might want to replace the resistors too. Eagles from Madisound are just $1.20 each.

good luck

Kent

Thanks for the suggestions. The difference in price between the 60uf Solens and the 65 uf Bennic NP electrolytic very well illustrates why I was trying to confirm which cap.s are series in signal path (Solens) or parallel (Bennic).

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Howard & Carl,

Foam blocks for cabinet stuffing not so rare, eh? No end of things to learn it seems.

I already had a notion to try stuffing my A150s w/fiberglass just to see, hear rather, if there was an improvement over the stock polyfill. Got the idea from a very interesting report on the differences in acoustic performance of various cabinet stuffing materials. Carl, I believe you provided the link in a thread about stuffing vintage ARs. Fiberglass was found to be generally superior over acoustic polyfill and Wal-Mart poly pillow stuffing.

Knowing how I am, my test mule A150s may find themselves stuffed w/foam blocks some of these days.

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Howard & Carl,

Foam blocks for cabinet stuffing not so rare, eh? No end of things to learn it seems.

I already had a notion to try stuffing my A150s w/fiberglass just to see, hear rather, if there was an improvement over the stock polyfill. Got the idea from a very interesting report on the differences in acoustic performance of various cabinet stuffing materials. Carl, I believe you provided the link in a thread about stuffing vintage ARs. Fiberglass was found to be generally superior over acoustic polyfill and Wal-Mart poly pillow stuffing.

Knowing how I am, my test mule A150s may find themselves stuffed w/foam blocks some of these days.

OCFG was also superior to the foam blocks - FYI

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  • 6 months later...
Howard & Carl,

Foam blocks for cabinet stuffing not so rare, eh? No end of things to learn it seems.

I already had a notion to try stuffing my A150s w/fiberglass just to see, hear rather, if there was an improvement over the stock polyfill. Got the idea from a very interesting report on the differences in acoustic performance of various cabinet stuffing materials. Carl, I believe you provided the link in a thread about stuffing vintage ARs. Fiberglass was found to be generally superior over acoustic polyfill and Wal-Mart poly pillow stuffing.

Knowing how I am, my test mule A150s may find themselves stuffed w/foam blocks some of these days.

Getting the correct surrounds on the BA woofers makes a huge difference. Sir Boyd (AudioKarma) convinced me of this this a while back, not long after I had refoamed mine w/ generic 1/2 roll surrounds. Bass output was lacking in both SQ and SPL. That was my first refoam, it turned out technically correct, and I was so proud of myself, but the speakers just didn't sound very good. Bass output was too low, speakers were very unbalanced, all mids & highs. I tried replacing the polyfill w/fiberglass, which seemed to make little, or no difference. In the closet they went for a while.

It took me a month to get around to ordering the correct surrounds and another 7 months (just did it last week) to convince myself to cut the other ones out. That was a job I wouldn't wish on anybody. I can't imagine any way to make a really good job of it, but I managed to get them off w/out damaging the cones. In went the correct surrounds. Recapped the x-over with PartsExpress Poly's bypassed w/film types while I was in there. But they were still way bass shy, I thought, good grief, that was a lot of trouble for absolutely zero gain, dammit. Then I decided to go back in and reinstall the polyfill.

Wowsers! Now we're talking. The bass is better in every way, SQ and SPL both, vintage East Coast bass w/some slam! Just outstanding. The recap had the usual amazing improvement of mids & highs. Now my A150's are a delight to listen to, I just love 'em now.

BTW, the correct surrounds are not only shaped slightly differently (see sketch) than the generic 1/2 roll, the material is thinner and more flexible, it takes much less force to move the cone than with the generic.

gzsanka@comcast.net - Source for correct foams, thank you, Sir.Boyd.

Sketch showing difference in surrounds discussed.

http://s713.photobucket.com/albums/w...ion=postupload

In retrospect, the fiberglass probably didn't get a fair trial. I'd guess I had too much in the enclosure. Were I to experiment further, I'd progressively reduce the amount I had in there. I didn't weigh it, just filled it w/out cramming it in. When I put the polyfill back in I noticed that the enclosure wasn't quite full. So, if fiberglass is a more effective stuffing material than fiberfill, I may have had way too much in there. They sound too good for me to want to mess with them now, though.

__

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