Roll Out The Barrel...Snip Out The Caps...Your Tweeters Ain't Burnt Series IIMar 26, 2012 (Updated Apr 18, 2012) Write an essay on this topic.
Popular Products in Home Theater Speakers and SubwoofersThe Bottom Line I cannot emphasize it enough. When buying used speakers that require woofer refoaming...replace those wornout capacitors also. Experts claim that these caps should be replaced every ten years!
Author's Footnote & UPDATE:
It has only been a few days since my "Caps" article broke and yet I have received some rather interesting and valuable information from not only BA A70 lovers but also dedicated vintage owners of other two-way systems as well.
Firstly...the commonly seen Owner's Manual notation "Design Modifications and Specifications subject to change without notice due to model improvements " applies to the A-70 Series I which includes the "T/V" models.
Apparently Mr. Kotsatos along with Boston Acoustics used different makes and values in their crossover capacitors. One A70 Series 1 owner found his crossover capacitor by pulling the rear speaker terminal plate off whereas the cap almost fell out. This is opposed to my model where the crossover board [although mounted and sealed on the rear side] is better accessed via the woofer hole.
He may have an early production arrangement where the tweeter was mounted above but slightly to the right of the woofer...in other words...off center as opposed to mine & later production models which have their tweeters directly centered above the 8" driver. This particular enthusiast found the typical Texas Instruments TI Part # 12K 6.0 uF cap in one speaker and the not so typical 4.7 uF cap in the other!...as O.E.M. The A70 was not sold in pairs necessarily.
He replaced both caps with a 5.9 uF one and all was absolutely hunky dory. H.D.8 owners should note that their caps are located behind the speaker terminal plate which is easily removed via four phillips head screws in the manner this gentleman removed his whereas the crossover network is mounted directly on the back of said plate. There are two yellow Boston Acoustics branded electrolytic capacitors used in this model...a 4.7 uF & 8.2 uF. Try to replace these with equal or as close to original value as possible. If you are off by a couple of tenths on either one...it's probably no big deal. Do your best to stay close though. I investigated further into the tolerances of capacitors and have come to the following conclusion...
A tolerance or variance of 20% is quite commonly accepted amongst speaker/electronics designers when dealing with high quality caps. It must be said though that the superior slightly more expensive Dayton 6.2 uF 250V Polypropylene capacitors are significantly better and more durable with a 5% rating. Therefore I must conclude from my own experience with the 5.5 uF Richey capacitor that this particular cap will absolutely work well as a suitable on-hand test part because of its low bulk price with the Dayton as a better long term cap part as the A70's single pass capacitor.
PLEASE! PLEASE! PLEASE! DO NOT be put off by the smaller physical size of the Richey cap. Richey has been around for over forty seven years and has the technology to produce & supply superior capacitors to the industry. Certainly advancement in component structure includes the making and miniaturization of superior electrolytic fluid filled caps especially compared to those available to Andy and Boston Acoustics in 1979. Still...the considerably larger Dayton will render superior performance for five bucks a pop as opposed to the eighty-five cent Richey. Have NO FEAR...DO IT! You can!
I only state this here because so many youngsters in these audiophile threads seem to be so tentative about attempting the project yet they have no problem facing the challenge of replacing their woofer surrounds and caps.
Oh...and that's another sometimes misunderstood situation. Woofer caps and crossover caps are two separate things when rejuvenating classic loudspeakers. However...You can do both while you're in there. The rewards will be great and you'll LOL to yourself for days afterward after you hear the results. I still am amazed how this little X-over cap fix made all the difference in the world with my own reference BAs.
This is an important subject for the many vintage lovers out there as well as for the young one who just picked up a pair of wonderful classic Allison Fours for seven bucks from the local Goodwill store...true story...I just spotted the thread on the internet yesterday. So please feel free to add your own comments here. We need this info badly and if you wanna criticize my report in any way...well that's OK too. Go ahead...beat me up. I can take it.
So PLEASE LEAVE YOUR COMMENTS or if you are shy...just email me and I'll be most happy and willing to assist you in any way possible. God bless all!...PJSII
After tinkering around with dufferent value caps from the Richeys to the Daytons...I woundup replacing the entire crossover board inthe A-70T with a Dayton two-way 2.5khz one for thirty bucks each. Apparently some corrosion was evident on the other components in the board and I just decided to replace the whole business while upgrading the internal wiring and rear speaker terminals. I'll post the results when the project is completed.
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