Bose 901 IV w/ Spacial Control Receiver for FREE!!!

dshoaf · Jul 13, 2008

himm37 said:
The "Spacial Control" is designed for series II & III (I think) 901's specificity. The speakers have 3 terminals, and when hooked up correctly, the receiver allows you to control how much power is applied to each "face" of 4 rear facing drivers. It allows you to control the width of the sound stage.

A minor correction to that: The spacial control's 3rd connection appeared on the Series IIIs and later. I don't know what version ceased to have that feature. The Spatial Control feature wasn't that much of a hit in the late 70s.

I'd also recommend that all of the wire-wrapped connections on the speakers be soldered once they are refoamed. The metal to metal contact oxidizes across time.

Great score, though.

Cheers,

David

Broken.Ears · Jul 14, 2008

tensleep said:
I found this to be a great tutorial on the whole process:

http://audioheritage.org/vbulletin/showthread.php?t=469

Thanks. That should give me good general pointers.

dshoaf said:
I'd also recommend that all of the wire-wrapped connections on the speakers be soldered once they are refoamed. The metal to metal contact oxidizes across time.

Great idea. Do you think it would be safe to use a light gauge sandpaper to clean the post and the wire and then solder?

guptonr said:
Doing a pair of 901 IVs was my first (and so far only) attempt at refoaming. They turned out really well. Because of their small size, I didn't have to remove the dust covers or use shims. I just followed the instructions from the folks that sold me the foam. The first one I did, I left the drivers in the cabinet. This became a pain in the rear because I had to maneuver the whole speaker instead of just the driver while I was working on it. On the second, I was intimidated by the tangle of wires and was worried I would rewire one wrong. So I would remove one driver, refoam it, and then replace it before I pulled the next one. Doing this, you could also test it with the MM.

Do you have the equalizer? It is a must have for 901s although I don't know if it's required if you use the Bose receiver. Besides rotted foam, no EQ may be a reason it sounded bad.

I think this would be the way to go -- taking out one at a time and doing everything to each one. Pull the driver, check for continuity, refoam, clean and solder contacts, reinstall. It may take more time, but also would be a great way of checking as I go.

The Bose Spatial Control Receiver is supposed to have the EQ built in. Apparently, these were sold by Bose as a set. They even have a special switch on the back to engage the equalizer for the 901s.

I don't feel sooo intimidated after reading a few success stories (and no failures so far) on the refoam.

It's been floating between 100 - 115 degrees here. On top of that we have lots of fires giving us awful air quality (reviling Bejing, China for pollution apparently). Those factors are making it difficult to go into my non air conditioned garage, so the actual project will probably wait until it cools off and the forests stop burning before I try and tackle it.

Still, I'm hungry for any experience with these. The more info, the better prepared I'll be.

SkyLounger · Jul 14, 2008

If you're not up to it, you could always send 'em up my way.... (just joking, shipping would be way too costly).

All meant to say, I'd love to stumble upon a free pair of those... I'd keep them for sure! Lucky you!

Broken.Ears · Jul 15, 2008

I started removing the drivers from the cabinets.

The back (or front as Bose likes to label them) cover was easy enough to get off. I pulled all eight drivers and labeled the connections (missed labeling one though).

I tested each driver as well. They all seem to test good, but at ~1.2 ohm instead of the 0.9 ohm as they are supposed to be. I wasn't sure if that was normal, or maybe just my MM.

I can't figure out how to get the front cover off. I can see there are some staples at the corner, but they are incredibly stubborn. There isn't anything to push against for leverage without damaging the veneer. Suggestions?

Anyone point me to a layout for the driver wiring?

avguytx · Jul 15, 2008

I think I ended up using variations of "pick tools" ranging from the right angle one and curled one. After I got them up just a little, I pulled them out with pliers. You are right....they are a biotch. One you have them out, use velcro from there on out! haha

I thought I had that diagram saved as a file somewhere but I guess I'm gonna have to search for it. It might be on the desktop PC at home.

gearhead · Jul 15, 2008

I used a good strong pair of needle nose pliers.

dshoaf · Jul 15, 2008

The wiring diagram is tough to describe but let me take a stab at it:

- Notice you have a Left and a Right designation on the speakers (well, you _should_)
- Then note that you have 3 terminals on the bottom of the speaker.
- The drivers are hooked up all in Series so the wire from one goes to the next one.
- This means that from the + terminal, it will go from one speaker to the next through the whole box until it connects to the - terminal.
- Next, you need to know where that 3rd terminal is connected:
- There is a tap from the connection where the 4 inner speakers connected to this 3rd terminal.
- That is, when you have the 2 speakers setup for L and R, the inner panels of the rear-facing speakers are brought out to that 3rd connection on the bottom. It is _very_ important that you reconnect the speakers correctly when you get done refoaming otherwise the Spacial feature will not work.
- You should have had one of the drivers on the inner panel that had 3 wires connected to it. This is that tap.

As for resoldering the driver terminals. Be careful as the metal will get hot fast and the plastic basket will melt around it quickly. This means you have to be good and fast to make a solid solder connection _and_ not trash your drivers.

As for using something to remove the oxidation, not a bad idea. I'd actually recommend using new wires, if possible. This all depends on your soldering skills to some degree but can be done by anyone with a bit of practice.

Hope that helps.

Cheers,

David

Broken.Ears · Jul 15, 2008

avguytx said:
I think I ended up using variations of "pick tools" ranging from the right angle one and curled one. After I got them up just a little, I pulled them out with pliers. You are right....they are a biotch. One you have them out, use velcro from there on out! haha

I thought I had that diagram saved as a file somewhere but I guess I'm gonna have to search for it. It might be on the desktop PC at home.

Got the front cover off. That was a tough one. Unfortunately, one speaker cabinet now has some minor impressions from trying to use the wrong tools. What ended up working was a flexible putty knife and mini-prybar. I used the putty knife to lift the cover away from the cabinet and then inserted the prybar. From there I muscled it away by pulling straight up. Once I got a corner open the rest was easy.

If you can find that diagram, it would help a lot.

Broken.Ears · Jul 15, 2008

dshoaf said:
The wiring diagram is tough to describe but let me take a stab at it:

- Notice you have a Left and a Right designation on the speakers (well, you _should_)
- Then note that you have 3 terminals on the bottom of the speaker.
- The drivers are hooked up all in Series so the wire from one goes to the next one.
- This means that from the + terminal, it will go from one speaker to the next through the whole box until it connects to the - terminal.
- Next, you need to know where that 3rd terminal is connected:
- There is a tap from the connection where the 4 inner speakers connected to this 3rd terminal.
- That is, when you have the 2 speakers setup for L and R, the inner panels of the rear-facing speakers are brought out to that 3rd connection on the bottom. It is _very_ important that you reconnect the speakers correctly when you get done refoaming otherwise the Spacial feature will not work.
- You should have had one of the drivers on the inner panel that had 3 wires connected to it. This is that tap.

As for resoldering the driver terminals. Be careful as the metal will get hot fast and the plastic basket will melt around it quickly. This means you have to be good and fast to make a solid solder connection _and_ not trash your drivers.

As for using something to remove the oxidation, not a bad idea. I'd actually recommend using new wires, if possible. This all depends on your soldering skills to some degree but can be done by anyone with a bit of practice.

Hope that helps.

Cheers,

David

Yes my speakers are labled "Part 1" and "Part 2".

I see the three terminals at the bottom of the cabinet. From the inside of the cabinet the wiring for the terminals is this:

Red = + (Pos)
Black = - (Neg)
Yellow = Spacial

Throughout the cabinet, there are sets of different colored wire (yellow, red, black). I labeled the connections on the speakers (to make it easier to reassemble). Following it through, it makes sense -- everything is wired in series. Here is how my Part 2 speaker is setup:

Code:

Y    B      B    K     R    B      B    Y
+ 1  -      + 2 -      + 3  -      + 4 -
   
- 5 +       - 6 +       - 7 +      - 8 +
Y    B      B    R      K    B     B    Y

I need confirmation that the back array of eight speakers is the same between both cabinets. I forgot to label one driver when it was pulled and while I'm 99% sure it's the same, I want to make sure.

The front driver for the spacial feature is different between cabinets. The cabinet labeled "Part 1" has the spacial driver like this:

Code:

YR   K 
 - 9 +

The cabinet labled "Part 2" is like this:

Code:

R   YK 
- 9 +

I'm guessing that the spacial feature is some sort of phase adjustment for the front driver. Maybe?

As far as soldering, I thought about getting some crimp spades to solder the wire to and then slide over the terminals. Thought this might be especially helpful if I wire something incorrectly.

Pics of the front spacial driver, empty cabinets and labeled drivers attached.

Please let me know if something looks or sounds amiss. Thanks!

Rat44 · Jul 15, 2008

Hope it all works out. Thats a lot of work.
I know Bose gets no love around here but the combo you have is a good set.
A room mate had that same setup he bought in Korea and it sounded good.
Of course proper setup is crucial.
The reciever was one of Boses better products.
Good luck.

tensleep · Jul 15, 2008

I see a 901 expert in the making - way to tackle the job!:thmbsp:

Broken.Ears · Jul 16, 2008

tensleep said:
I see a 901 expert in the making - way to tackle the job!:thmbsp:

Thanks!

Broken.Ears · Jul 16, 2008

I started cleaning the drivers. The basket is pretty simple and cleans quick. The cones are a different story. The attached photo shows the cleaned on the right and the untouched on the left. The foam is like tar. I gently scraped for over ten minutes to get it in that condition.

Is it clean enough for refoam, or is there something else I should try?

tensleep · Jul 16, 2008

I have used Goo Gone as a solvent for the surround adhesive on a JBL. It did make the adhesive easier to remove; however, I had to take extra care because some of the cone material wanted to come away as well:

MEK is supposed to work very well, but it is a powerful solvent and may discolor the cones. I have some MEK, but have not tried it yet. I found both at Home Depot. MEK is the acronym for Methyl Ethyl Ketone, BTW. Watch that stuff - very toxic, very flammable, requires either great ventilation or a six-pack, depending on your allegiance.

Broken.Ears · Jul 16, 2008

tensleep said:
I have used Goo Gone as a solvent for the surround adhesive on a JBL. It did make the adhesive easier to remove; however, I had to take extra care because some of the cone material wanted to come away as well

Thanks for the suggestion. I tried some 94% isopropyl alcohol and it worked well. The cone isn't completely clean, but it's very close, with most of the discoloration coming from the broken down foam staining the cone. In the pic bottom is the alcohol cleaned cone, top left is scraped and top right is untouched.

tensleep said:
MEK is supposed to work very well, but it is a powerful solvent and may discolor the cones. I have some MEK, but have not tried it yet. I found both at Home Depot. MEK is the acronym for Methyl Ethyl Ketone, BTW. Watch that stuff - very toxic, very flammable, requires either great ventilation or a six-pack, depending on your allegiance.

Ventilation? :beerchug:

tensleep · Jul 17, 2008

Very nice! I'll have to try the alcohol - that is cheaper and easier to find, for sure. Well, you're even with me - I still have to order my surrounds. I have been working on a privacy fence, so I have several audio projects on hold, including finishing my surrounds. Good luck to you with the rest of your project - I'll be watching your progress with interest.

Broken.Ears · Aug 6, 2008

Finished! At last!

I've working on a lot of audio projects (with this being the major one). Usually I enjoy refurbishing vintage audio, but this project has been almost like a full time job. Between the cleaning of the eighteen drivers, refinishing the cabinets, cleaning up the receiver and putting on the new surrounds, it was a lot of work to get it done. Honestly, this one burned me out for awhile.

That said, the results turned out really well. The sound is amazing. I'm hearing stuff in music I haven't heard before. The sound is huge. The bass can go very, very low. Moves the walls when called for. Unbelievable dynamics.

Tested out with some Vivaldi concertos and Miles Davis Bag's Groove -- man, the speakers just sing. Incredible, beautiful sound -- very full with lots of detail. Hearing minute incidentals like an a bow getting positioned on strings before the note or a breath and sound of lips on the reed before the solo on the saxophone. Astounding!

Another song I tested out was Heart's Barracuda. Had a stressful moment when listening to it, thinking I had a rubbing driver (meaning I would need to go back and find the bad driver and redo the surround). I went through the intro five separate times hearing the same scraping and distortion. Finally pulled out the headphones and played it on another system and also the ipod. After very careful listening, it turned out to be in the song itself. I was hearing distortion from an overloaded mic during recording!

The only downside for me is the system really requires more room than I have. In order to get the best sound, I need more space. Space I don't have. I could put it in the living room, but I would need to rearrange the whole room around the system. The wife will not go for that. My mancave room is too small (at ~ 10 x 10). I actually get a better listening experience standing in the hall.

So, I made a decision. The system is going to my dad's place, as he has a large open floor plan at his house -- perfect for setting this unit up. He's going to reimburse me the layout for refinishing and repairs. I'll get to hear it every once and a while, so it'll make for a nice treat.

The real downside to the situation is I am now incredibly spoiled. I don't know if/when I'll run into another speaker that will floor me as much as this. I've had a decent number of speaker setups, some that I thought sounded really, really good. But this kills them all. Maybe it's the combo of the speakers, specialized stands and Bose receiver. I don't know. I do know that while listening to it, it went from the normal enjoyable and pleasurable to an experience -- I was living the music. Sounds weird, but it was that good.

Well, anyway, I attached some pics of the finished system. Certainly a memorable project.

gearhead · Aug 6, 2008

Glad to hear your results were positive!
So much for the oft-repeated "no highs, no lows" wheeze, huh?

Broken.Ears · Aug 6, 2008

gearhead said:
Glad to hear your results were positive!
So much for the oft-repeated "no highs, no lows" wheeze, huh?

Thanks! As far as the "no highs, no lows" business, I can see where that comes from when listening to the more modern systems (cube systems and such), but this thing has INCREDIBLE sound. I had a couple of other pair of Bose speakers (bookshelf size) and they were nothing to write home about, but this setup is a dream. The only limitation is room size and placement. Two things I have going against me unfortunately.

Bose 901 IV w/ Spacial Control Receiver for FREE!!!

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