Bose 901 project

[fill35U 1,846]

There are plenty of used drivers on eBay. I don't think the Parts Express drivers have the HVC (edgewound aluminum ribbon voice coils), so efficiency, power handling, and high frequency response might be reduced. In addition, they have stamped steel baskets instead of the injection molded ones. And I believe the factory coated the back of the cones starting with Series IV. Enough things different that I don't think the PE drivers would be equivalent or an improvement. 

 

If it helps, here's the page on diagnostics from the Series VI service manual: 

 

[brian darflinger 13]

Hey Brian when you're getting the drivers ready to put the new surround on, are you supposed to remove the rotted surround and all the old glue or what? I've never done it before but was thinking the old glue would need to come off before applying new glue. 

 

Pindrop-[using a 1/4" or 1/2" sharp chisel]- First you remove all the deteriorated foam and carefully scrape all the glue off the basket then you wet the foam and glue around the cone with rubbing alcohol, and very carefully scrape the loosened glue off.  There's step by step videos on yutube- look for 'speaker refoam'

[zumbini 6,147]

 

 

 

Hey Brian when you're getting the drivers ready to put the new surround on, are you supposed to remove the rotted surround and all the old glue or what? I've never done it before but was thinking the old glue would need to come off before applying new glue. 

 

Pindrop-[using a 1/4" or 1/2" sharp chisel]- First you remove all the deteriorated foam and carefully scrape all the glue off the basket then you wet the foam and glue around the cone with rubbing alcohol, and very carefully scrape the loosened glue off.  There's step by step videos on yutube- look for 'speaker refoam'

 

Toluene or MEK will literaly melt the old glue residue in a flash.

Just be careful to limit exposure as both are EPA listed carcinogens

(I have a couple of quarts left from my days in gravure printing.)

[brian darflinger 13]

Do you guys think my series iv drivers are the same as series v or vi ??? I cant find drivers for series iv,,, onlyfound them for v and vi..

[DaveStL 85]

 

 

Toluene or MEK will literaly melt the old glue residue in a flash.

Just be careful to limit exposure as both are EPA listed carcinogens

(I have a couple of quarts left from my days in gravure printing.)

 

Dom,

 

They are not substances I would use unprotected, but they are not listed carcinogens per IRIS.  I didn't check CA, though--you never know what's listed under Prop 65.

 

All,

 

Always read the MSDS before using a new chemical.  Avoid breathing these two, and getting them on your skin.  Remember styrene model glue?  That stuff used to contain toluene.

 

Folks who have not used chemicals in industry may not realize that those blue gloves from Home Depot don't protect you from many common solvents.  Permeation rate is determined by the combination of the glove material and thickness, and the chemical to be protected against.  Nitrile gloves are marginal for toluene (double-glove thin ones from the box stores, and then just for incidental contact), and they are unsuitable for MEK.  There are glove compatibility charts on the web, e.g. Ansell, but remember that companies that make these available often have industrial-quality gloves, thicker than the ones at HD.

  

[fill35U 1,846]

IMHO you'll be fine with the later drivers. Due to the nature of the beast, I'd put your best two drivers in the fronts. In practice, I don't think you'd notice much difference swapping drivers or EQ between Series III-VI. 

[danowood 2,167]

Well, I have one speaker that's blown... All scratchy, no matter how hard I try to center the cone. Anyone here know where I can get ahold of a factory 901 speaker or two?? I imagine Ill run into another bad one...I know I could buy a replacement from parts express or Dayton, but I'd rather keep them all bose for resale purposes...

 

 You could replace the voice coil, and dust cap, it's not very difficult, if you have had experience re foaming speakers, it's not that much of a step further. Can find here  http://www.simplyspeakers.com/bose-speaker-recone-kit-bose-901-802-rk-b901.html   To center voice coil I've used this trick too.  

.

but for the money and less of a challenge it's prolly cheaper to just drop in a good used one off epray.   And Welcome back.

[brian darflinger 13]

Using rubbing alcohol works great.. I dont see the need for using such aggressive chemicals. in fact, I tried to take the brand-new surround off a blown speaker and it was impossible- the new surround was bonded so well to the cone.

dampen the old glue and foam with rubbing alcohol and its softens it up into a paste that comes of very easily and completely. maybe other surround materials require stronger chemicals, -but for foam I cant imagine it going any easier.

[srinath 34]

Well, I have one speaker that's blown... All scratchy, no matter how hard I try to center the cone. Anyone here know where I can get ahold of a factory 901 speaker or two?? I imagine Ill run into another bad one...I know I could buy a replacement from parts express or Dayton, but I'd rather keep them all bose for resale purposes...

 

4 drivers are same as 3.
And IMHO, atleast from the 6's research I did I think nothing else will work.

The freq response of the 6's was 85 hz - 15K hz. And .9 ohm.

1 and 2 are a bit easier to substitute. Sony made a few back in the 70's that were close.

 

Cool.

Srinath.   

[brian darflinger 13]

I just need to make sure which ever bose901 driver I buy is 1 ohm ..

--Another question- Is the front driver the same as the rear 8 drivers??

 

[Maddmaster 1,001]

 

 

IMHO you'll be fine with the later drivers. Due to the nature of the beast, I'd put your best two drivers in the fronts. In practice, I don't think you'd notice much difference swapping drivers or EQ between Series III-VI.

 

There is actually a big difference between the III and VI EQ's. I had both back in the day.

 

 

[nascar03 25]

I just need to make sure which ever bose901 driver I buy is 1 ohm ..

--Another question- Is the front driver the same as the rear 8 drivers??

Hi Brian...

I have a set of BOSE901 series II.  I'm assuming the newer versions follow the same build parameters although with newer drivers and equalizers.

I believe the Bose901 drivers are 6-8 ohms each and thru use of proper series/parallel circuit wiring will ultimately show a 6-8 ohm total load to the amplifier. They are not 1 ohm each. Be sure to follow the internal wiring connections within each cabinet.

The front driver is the same as the other drivers in the cabinet.

I don't envy you having to do 18 foam surrounds... Good on you.

Graham

[fill35U 1,846]

I just need to make sure which ever bose901 driver I buy is 1 ohm .. 

--Another question- Is the front driver the same as the rear 8 drivers??

Hi Brian...

I have a set of BOSE901 series II.  I'm assuming the newer versions follow the same build parameters although with newer drivers and equalizers.

I believe the Bose901 drivers are 6-8 ohms each and thru use of proper series/parallel circuit wiring will ultimately show a 6-8 ohm total load to the amplifier. They are not 1 ohm each. Be sure to follow the internal wiring connections within each cabinet.

 

Series I & II used 8 ohm drivers, wired as three parallel strings of three drivers in series each: 

 

 

The drivers in Series III through VI are nine 0R9 drivers in series:

 

 

[nascar03 25]

I'll be darned! Thanx for posting the diagrams.

I wonder where the yellow wire goes?

 

Graham

[fill35U 1,846]

I'll be darned! Thanx for posting the diagrams.

I wonder where the yellow wire goes?

 

You're welcome! 

 

The yellow wire doesn't exist for the Series V & VI, despite the drawing's title. 

 

The Series III & IV bring the yellow wire out to a third terminal. This was intended to be used with the Bose Spatial Control Receiver:

 

 

This stereo receiver actual had *four* channels. Not only did it incorporate EQ for the 901's, it allowed the user to adjust the signal sent to the inner drivers of each 901. Probably mixed in/out the mid & high components of the L-R difference signal?:

 

 

FWIW, the 601 Series II, which had inner and outer sets of drivers, also had the third terminal. 

[srinath 34]

 

 

[ 

 

FWIW, the 601 Series II, which had inner and outer sets of drivers, also had the third terminal. 

 

This is the truest picture of sound from a 901.

It will go all over the place and hit your ear like soup.

Some kinda weak and bland soup.

You'd be temped to look under the speaker in case there is some kind of beaver or badger eating up all the good parts of the soup.

In all honesty though, if your room was this geometric, and you have no stupid furniture in the way, and no drapes, no curtains no cabinets and had perfect symmetry, it may sound OK.

I had much better sound keeping pointy side toward you. Both on the 1/2 and the 6's.

 

Cool.

Srinath.   

 

[srinath 34]

I have a series 2. No third wire in mine.

Maybe the 2 continental had it ?

Cool.

Srinath.

[cwad8505 102]

http://www.parts-express.com/replacement-speaker-driver-for-bose-901-4-1-2-1-ohm--290-922

[srinath 34]

That 83-15k is really close to bose's specs for their drivers. May even be exact.

 

1 ohm is a bit high, bose said .9 ohm if I recall - but for the 6's. I'm not sure about 3-5.

91.5 db sensitivity is a bit lower than the bose specs, I think they said 93 for the 6's.

 

It probably is close enough for matching with the ones that have some age on them.

 

The best bit, it looks like the bose item. And probably acts and sounds very very close.

 

Cool.

Srinath.

[RodH 4,866]

0.9 vs 1.0 ohms...? All but the best multimeters can't make that distinction.

A couple feet of wire could make a bigger difference. A new driver for $19 a driver, why even bother trying to fix the old ones?

 

 

 

[brian darflinger 13]

 

 

0.9 vs 1.0 ohms...? All but the best multimeters can't make that distinction.

A couple feet of wire could make a bigger difference. A new driver for $19 a driver, why even bother trying to fix the old ones?

 

 

 

 

 My guess is that - since they're wired in series, they specifically made the drivers .9 ohm to hit the 8ohm mark almost perfectly.. So- yes 1/10th of a ohm IS a big deal if you were to put 9 of them in series. If I'm replacing only one- then it wouldnt make much of a difference

 

[B-Man 4,780]

Out of all the parameters that define a driver's characteristics, the impedance is probably the least important in your scenario.

 

As Rod said, .1 Ω is nothing to worry about, even if you did replace all the drivers. Remember, it is an impedance rating, not a resistance rating.

[RobertR 847]

Everybody's talking about the Bose 901's imaging (Why talk about something they had so very little of?) and the impedance (I think I remember somewhere reading 0.89 ohms each - fairly silly, I'd say) - it doesn't much matter, as long as all the drivers are about the same.  

A far more concrete problem was what occurred in the mid-1980's as CD's took over the market. The equalizers were not engineered for input levels of two volts, and would crank out terrible clipping distortion on the loudest passages on maxed-out, highest spec modulation CD's.  At least my V's  (whose foam did disintegrate over a decade go) were like that...had to place the EQ after the preamp's gain control; running in a tape loop they were a disaster. 

 

Lots of components had a problem with the higher output of CD's - a good portion of the early complaints about "digital" distortion may have been just the same sort of thing.  Many will remember that Bob's Phase Linear 1000 had the same issue, neatly solved by a mod from jvdtexas.

 

RobertR 

[srinath 34]

My 6's obviously didn't have that issue - post CD design.

The series 1's - I have never run a CD player with it. LOL.

 

Cool.

Srinath.   

 

[brian darflinger 13]

Ok- So I got all the drivers done, and I'm taking them for a quick spin.. 

14' x 25' living room set-up single speaker forward, on the short wall 

Running them with my M-1.0t's in mono,  Mp3 signal feed through  my sunfire theatre Grand III -   a dusty series iv bose equalizer , and If i need to equalize further I'll run the signal through my ADC eq additionally.

  I started listening to A Perfect Circle, and I have to say that I'm very surprised with the depth.

 When I was aligning the drivers with my signal generator, I didn't think I'd get ANY low end. but there's plenty- certainly no need for my Sub

 So far my first impressions are pretty good..  Although I'm dumping a TON of power into these things.. - Can I really crank the hell out of these?- because I'm already lighting up my amp meters without the decibels I've been expecting. It seems to me that the 450 watt max rating isn't going to relate to db's when there's so much power pushing those poor little 4.5" drivers to get the range I want. If it was just mid-range, I'm sure they would blow the windows out. 

 - single driver forward is noticeably better sounding- deeper sounding, and when they face backwards, sound is very fatiguing ..

 I need to mess around with these things for a while more.. and not this late at night when the neighbors are probably trying to relax..