To all the Polk wizards. I need guidance.....Please

pumpkinman

Today I picked up a pair of Boston Acoustics A-400's. (FREE) I was told that one of the speakers didn't sound right. I hooked them up and one speaker is producing little to no bass out off either of the bass drivers.
I swapped bass drivers and still the same. So I'm assuming the 8'' drivers are OK and that issue is somewhere else.

Suggestions please on how to procede.

Thanks
P-man

F1nut

Check the crossover.

cnh

I agree.

Here's another thought. I believe the A400s have Bi-amping wires/jumpers in an unusual configuration on the back. Check to see that everything is connected!

I see in the pic below they do. Make sure those upper terminals are tied together as shown in photo.

headrott

My first thought was also the crossovers. As cnh suggested, check the jumpers are connected/working correctly. If they are, check the crossovers.

[Deleted User]

Nice score! I like the BA sound. Real nice.
Did you take any pics of the insides?
On a flier, I'm guessing the jumpers are what
make this a 4ohm speaker? 8ohm woofers in parallel...
Anyway the specs say 4 ohm. (so be careful)

More Captain Obvious:
On another note and judging by the picture, you do have over 4000 records
That makes you four times crazier than I.

pumpkinman

Thanks guys
I did check the jumper wires and moved the moved the 8" drivers into the working speaker where the drivers worked. I'll remove the crossover later today and look for anything obvious. Beyond that I'll need professional help. Haha in more ways than the crossover.

pumpkinman

rednedtugent wrote: »

Nice score! I like the BA sound. Real nice.
Did you take any pics of the insides?
On a flier, I'm guessing the jumpers are what
make this a 4ohm speaker? 8ohm woofers in parallel...
Anyway the specs say 4 ohm. (so be careful)

More Captain Obvious:
On another note and judging by the picture, you do have over 4000 records
That makes you four times crazier than I.

No Red I'm 6 1/2 times crazier than you. LOL

[Deleted User]

Someone opines:
"Keep in mind that they are designed to be put up against the wall, so the footprint is relatively small."

"I just refoamed mine so I have experience with the dust covers. The ones on the midrange are vented, as the pole piece is not. The ones on the woofers are, as the poles are vented. They seem to be of the same material, but the ones on the woofers have a coating of some sort."

Here is a mod:

[Deleted User]

Here is the manual copied from AK forum

pumpkinman

Thanks Red
I can find very little info about them on the net. The drivers where refoamed but it's a horrible looking job.

[Deleted User]

you are welcome PMan. Happy 4th!
Here is a nice review.

Msabot1

pumpkinman wrote: »

rednedtugent wrote: »

Nice score! I like the BA sound. Real nice.
Did you take any pics of the insides?
On a flier, I'm guessing the jumpers are what
make this a 4ohm speaker? 8ohm woofers in parallel...
Anyway the specs say 4 ohm. (so be careful)

More Captain Obvious:
On another note and judging by the picture, you do have over 4000 records
That makes you four times crazier than I.

No Red I'm 6 1/2 times crazier than you. LOL

Ha...at last count..I had well over 2k and growing...I guess that makes me a little less crazy!! LOL!!...but seriously..check the low pass on the X over...nice find!!

[Deleted User]

I'm proud to say I did a better job refoaming my A40's.
Sold them to a guy who lives in the same town. He spent a
lot of time listening to them before buying. (at my cost)

Anyway, the crossover was impressive even in the BOL
Boston's. Again, real nice score and good luck!

drumminman

If it was me I'd pull the Xovers and look for signs of failure: bulging caps, broken solder joints, burned resistors - anything that looks amiss. You could also take pics and post them here. I'm sure some of the folks here could provide some guidance.

motorstereo

That's a damn fine pick up for free. I'm betting one of the 8'' drivers is wired out of phase. Use a d battery to verify which one it is. The crossovers on the 400's can take lots of abuse and I'm doubting that's your problem. They're great speakers with plenty of bass when they're up and running correctly (I had a pair).

leftwinger57

Bill, congrats. The journey paid off and I'm sure even if you or someone else rebuilds the x-overs (if that's the problem) you'll have a great looking set of that famous east coast sound. Red says they aren't all that big they sure looked way too big for my apt. Maybe 'doc' Hardy if not away on vacation could lend a suggestion.

motorhead43026

Good score, here is a pair they want $500.00 for.

http://cincinnati.craigslist.org/eld/5070947573.html

pumpkinman

motorhead43026 wrote: »

Good score, here is a pair they want $500.00 for.

http://cincinnati.craigslist.org/eld/5070947573.html

$500
For me that's to steep

pumpkinman

I put the speaker back together and I'm thinking it must be the crossover. I think I had set OK and not out of phase

Schurkey

Connect speakers to amp as usual. Put on your favorite tunes, (better yet: FM interchannel hiss) turn the volume up just beyond comfortable listening level. Turn the balance knob to the defective speaker so the room isn't overly loud.

How much AC voltage do you have at the speaker terminals at the back of the cabinet? (First guess: 2--3--4 volts, but this could be high or low. All depends on where the volume knob is set.)

How much AC voltage do you have at the bass driver(s)? (You'll have to pop the driver(s) out of the cabinet to test voltage at the wires connected to the driver(s).)

You could compare to the "good" speaker if you reposition the balance knob to be centered.

pumpkinman

Not much new to report on the A400's. I took the bass crossover out and unsoldered all it's components. Took the parts to a friend of mine with a Fluke meter so he could test the parts. The 100uf cap tested at 111uf and the 60uf cap tested at 66uf. Still I'm told by others the caps still could be the culprits. So I ordered 4 caps and they were mailed out today, so I'm thinking mabye next week I'll have them. The actual work is not nearly as diff. as I thought it would be. Still I don't like not fully understanding what I'm doing.


I've posted in the past how much I hate speakers with the old spring clips. Although many will most likely think what I purchased aren't much better. I went to eBay and found an inexpensive drop in replacement with binding posts. New jumpers made from 12 gauge OFC cable.

motorstereo

I think that's a nice upgrade over the old spring clips. The big caps in the lower crossovers are shunts and won't solve your bass problem but it certainly won't hurt to replace them. I used polys on mine and had to fashion a new board as the old one wasn't big enough.
Someone on another forum also had the same symptoms as your bass shy problem. It turned out to be one of the woofers was out of phase.

pumpkinman

I checked the woofers for out of phase as Motorstereo suggested but in the end it was the caps. I replaced the 2 in the one xover and now it's playing fine. Next up is to remove the other xover and replace those caps too.

motorstereo

Glad to hear it all worked out for you and your bass problem is solved. So you say you had 2 bad caps in the top crossover that were the culprit?

pumpkinman

Motorstereo
When I got home I checked the woofers with a battery as you suggested and they both checked out and they were in phase. Since I had already received the 4 caps for the lower xover I installed them. Hooked them up up on the floor outside the speaker cabinet and every thing worked fine. Last night I finally put all the stuffing and new gaskets in.
They're playing fine at least for now. Fingers crossed
P-man

pumpkinman

pumpkinman wrote: »

Motorstereo
When I got home I checked the woofers with a battery as you suggested and they both checked out and they were in phase. Since I had already received the 4 caps for the lower xover I installed them. Hooked them up up on the floor outside the speaker cabinet and every thing worked fine. Last night I finally put all the stuffing and new gaskets in.
They're playing fine at least for now. Fingers crossed
P-man

pumpkinman

Next thread new stands for the A400's

When I'm finished with my new stands you can have the old ones if you want them Red.

P-man

soundfreak1

If you want to and have an "extra amp" try bi-amping. It might chang your life. LOL