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Recently I was looking into the BOSE 301 speakers and came across a webpage (german though) which showed the inside of the speakers. Every BOSE speaker has this " Automatic Protection Circuitry" which prevents the speakers from being "overdriven".I didnt know what it was but now looking at the pictures and doing some translating, apparently a lightbulb turns on inside the speakers when the voice coil gets hot? This is very interesting!
http://www.avguide.ch/index.cfm/show/page.view/uuid/392EFDF8-8A11-97B0-4619C4153CA42F96
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I worked in a store in the 70s, the owner of which was one of the early Bose dealers. I believe the 301s were the 3rd speaker Bose introduced after the 501 and the 901. Both the 501s and 301s suffered from tweeter burnout in the Series 1 and 2 versions mainly from overzealous customers overdiving their receivers. BTW, in those days a 60 watt receiver was considered top-end gear which was well underpowered enough to cause lots of tweeter damage. Note that this wasn't a problem with the speakers - Bose did really have one of the best quality control systems I'd seen to date - they even marketed it as the Syncon II - you'll see reference to it on old Bose speaker shipping boxes.For the record, the Bose service department supported me as a warranty station and *never* questioned all the tweeters I replaced in the early series of these speakers. I'm sure all the replacements they shipped me were just a small indication of the number they replaced under warranty. The real problem was that the speakers sounded good because they were punchy and sounded 'clear' to most non-techie consumers. We sold tons of them for that reason.
So, I'm quite sure that those engineers in Framingham finally addressed the problem of blown tweeters with the light bulb - a rather elegant and simple solution from the repair-man's perspective - which certainly helped the number of warranty repairs I didn't do after they started shipping sometime in the late 301 Series Is and the 501 Series IIs. I really hated having to pull the 501 grilles off to get to those old tweeters.
BTW, anyone with old 301/501/601s should go in an resolder the wire-wrapped connections on the terminals and on the speaker posts - they will have oxidized after all these years.
Hope that helps.
Cheers,
David
Disclaimer: This is a factual report of my own experiences with Bose service in the mid-70s - there is no intent to incite Bose comments pro or con.
I've got a pair of 101 indoor/outdoor speakers...Actually when I got them (used) the drivers (like a single 901 driver, one in each) were dead so I pulled them out. (I think they were left outside for years) inside there is some kind of contouring network and a small U shaped lamp like one you see in a strobe light. I guess the previous owner liked it loud because the poly fill touching the lamp was melted! I always thought it would be cool if B*se made their plastic cabinet speakers in translucent colors so you could see the bulbs glow...
--Matt
"Cold Turkey isn't as delicious as it sounds..." --Homer Simpson
I used to work at CC and during slow times we used to get really bored. On day our manager told us how he used to purposly blow car subs (forgot his reasoning) at work by hooking them up via a power cord with bare wire on the ends. He would just hook the bare wire into the subs and then plug them into the wall and viola, a blown sub. We decided to try this with some speakers to see how much punishment they could take. For some reason we could never blow Bose, the polks took the longest but eventually the woofers went, but the Bose never did. We tried with the 202s and some of the small cubes, neither of which worked. Guess this explains why.
As the current gets greater, the filament heats up and the resistance increases. It is of course non linear which is the whole point. The trick is to choose a lightbulb with just the right characteristics to match the speaker you want to protect.
Looks like its a good quality thing BOSE corporated into their speaker systems and does this prevent distortion? What do I have to do to activate this bulb....crank it?
which is utilized on a brand new set of Monarch "Firefly" bookshelfs I just purchased from www.soundsmith.com. which are rated at 400 WPC. The designer incorporated a General Motors dome lamp into the tweeter circuit which serves a dual purpose both protecting the tweeter from being blown, as well as an amplifier clipping indicator.
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