Bose 901 project

[fill35U 1,847]

Congrats on getting them up and running! 

 

I don't think you'll hurt them by driving them harder, at least with unclipped music signals. 

 

Don't forget that EQ is cutting out a lot of the mids, and boosting the snot out of the highs and lows! They would probably sound a *lot* louder without the EQ. 

 

Here's a chart you can't find on the Internet. EQ curve for a Series VI:

 

 

 

I won't argue that the IV's have a *different* EQ, I know the V's are definitely *slightly* different. But given the similarity of the drivers, III's and IV's should be *pretty much* the same. In any event, look what the user-adjustable controls can do to the response. In theory, those controls are there to help you compensate for the room (presumably floor bounce and wall reflectivity).

 

I don't think the EQ would clip at the input buffer from too high a level- its got +/-15 V supplies. But with 15dB of boost at the first stage, I could see it clipping "along the way". And with better than 20dB of boost available overall, it won't take much at 15kHz to cause problems!

[srinath 34]

 

 

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..

   

  

 

Your room isn't 100% symmetric - much like my HT room. I had a bit of better sound with them backwards. You Have a good reflecting surface though, however the klipsch cabinet is blocking some of it.

Of courseif its fatiguing now - it may throw you into a coma with the thing pointed into the room.

Cool.

Srinath.   

[stevenlevel 146]

Wow Bose my be over priced and slightly over rated but that's more with the lower end speakers and head phones.

 

I would never buy Bose 901s since I don't think they hold their own when compared to modern speakers, but were very good when they first came out on the market.

 

Needing a G.E. to use them just bothers me.

 

That said I would definitely take a pair at a cheap price or if I were given a pair of defective units, take the time to repair them just to have a project to do.

 

I don't hate Bose, I dislike their genius advertising campaign that gets a lot of uneducated speaker buyers to spend way too much on Bose's plastic speakers or surround sound systems that have 2- 3" full range drivers X 5 and a 6" powered sub for $2,000.

 

Bose's 301's are still good bookshelf speakers at a fair price.

 

What bothers me most is they never release any of their speakers SPL ratings or frequency response numbers and that's trickery of sorts.

 

That said, people that like Bose have the right to like them as everyone has a very wide opinion when it comes to speakers.

 

I hope you enjoy your repairs and get them working well. I want to here your thoughts on them?

 

I'm sure if a powered sub is added the 901's that are sold today would be really nice sounding speakers with a really great openness to them that only array speakers can offer.

 

So I may hate their advertising practices but they still make some good speakers.

Steve

[stevenlevel 146]

 

 

 

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..

Your room isn't 100% symmetric - much like my HT room. I had a bit of better sound with them backwards. You Have a good reflecting surface though, however the klipsch cabinet is blocking some of it.

Of courseif its fatiguing now - it may throw you into a coma with the thing pointed into the room.

Cool.

Srinath.

 

Are they supposed to be placed with the 9 main drivers facing you or the rear single driver facing you? Pardon my ignorance but I'm just not familiar with 901's as they are way out of my price range in 1980 and in 2016.

 

[itchitch 4,636]

The single speaker is supposed to be facing towards the listening area allowing the eight drivers to use the back and side walls for reflection (if your room is configured at right angles with no impediments or obstructions.) I use mine mostly for background music or to blow the doors off the house, having mine reversed with the eight drivers pointed toward the listening area.

I do use them in conjunction with a powered sub. Makes a world of difference.

(No highs, now lows, must be BOSE.) 

 

The effect (not for the audio purist) of them configured this way on a track like Wish You Were Here is awesome.

Again, how things sound is an individual assessment. 

 

I bought a few pairs and reformed them. I then bought a really beat up pair for $50 on CL and sent them to Bose... They will send you a brand new pair with equalizer for $500.

 

S 

[RodH 4,866]

To get the "direct/reflecting" effect working as designed they need to be on stands and out away from the walls. Positioning was important.

 

 

Try them either way and go with which ever way sounds better to you!

[kingman 663]

I have ran the 901's and clipped a TFM-75 into them. They can get loud. My opinion...the first series was the best and after series 2 they became non acoustic suspension and required foaming as yours did. I tried the Bose equalizer but never heard much of a difference. Bought an ADC and immediately they took a turn for the better. Use a standard eq on them, run the highs and lows up. add a good sub and go for it! Still have 3 sets back in storage for when I get tired of ribbons...LOL!!!!!!!!

[RodH 4,866]

Only 3?

 

Better look again Wayne!

[PMAT 2,054]

It's good to be .....Wayne.

[Maddmaster 1,023]

They should be 18 inches from the wall if I remember correctly.

[brian darflinger 13]

Well folks, My 901 phase has come to the end. I sold all my 901's. -It just wasnt worth it.. I was putting>1000 watts into them AND a additional Jbl sub with a Crown amp to get the sound I wanted. and even then, it was mediocre. I'll give them credit tho- the vocals and midrange were exceptional. When I used them strictly for mids- they were nice.- but not worth the hassle. No regrets- When I was a kid I thought they were the greatest, and someday I'd get them.- So I had to give it a shot and see for myself if I liked them.,,, and I really cant say I did..

-- Onto the next-- I'm putting together a Jb pro Cinema 2-way.. got the mid/lows, now I need to find some horns...

[Nahash5150 10,928]

Good to see you Brian!

 

Let us know how the new speaks work out. 

[aslan7 955]

"now I need to find some horns..."

 

 

How about ribbons? 

[Eddy Currents 0]

Hello all,

I'm new here and I just want to introduce myself and say what a wonderful site this is. If memory serves, I recall Bob Carver taking an amplifier he made in a coffee can to a McIntosh clinic and blowing them all away! The man never ceases to amaze. I was just rereading "The Carver Challenge" in Stereophile. He made his amp sound better than the C-J reference!

Anyway, Bose. Amar, Amar. His beloved 901 continues to inspire controversy. But what is with all the foam rot? Haven't they heard of butyl rubber surrounds? Driver technology has made such strides one would think the guys in their famous R & D department would have thought about using real full range drivers instead of "inexpensive" paper cone midranges. Also, the great Jim Thiel figured how to mechanically put a tweeter in the center of the midrange for a point source arrangement (no electrical crossover). Something like that would be a neat thing to have on the front baffle. One could do away with EQ. Does anyone here know of such a DIY project?

[aslan7 955]

Hello all,
I'm new here and I just want to introduce myself and say what a wonderful site this is. If memory serves, I recall Bob Carver taking an amplifier he made in a coffee can to a McIntosh clinic and blowing them all away! The man never ceases to amaze. I was just rereading "The Carver Challenge" in Stereophile. He made his amp sound better than the C-J reference!
Anyway, Bose. Amar, Amar. His beloved 901 continues to inspire controversy. But what is with all the foam rot? Haven't they heard of butyl rubber surrounds? Driver technology has made such strides one would think the guys in their famous R & D department would have thought about using real full range drivers instead of "inexpensive" paper cone midranges. Also, the great Jim Thiel figured how to mechanically put a tweeter in the center of the midrange for a point source arrangement (no electrical crossover). Something like that would be a neat thing to have on the front baffle. One could do away with EQ. Does anyone here know of such a DIY project?

 

Hey Eddy.  Welcome to the CarverSite!!!  

 

I fell in love with Carver after hearing the Amazing's in 1990 and reading the same story you did.  What a genius Bob is.  Sounds like you have the same addiction-OCCD 

 

We have some experts here who can answer your Bose question and your DIY project q's.  Incredible talent that never ceases to amaze me on this site.

 

As always, we LUV pics of ANY audio gear--of course we are partial to Carver products.  If you are able to post some, please do.

 

Welcome aboard my friend    

[Eddy Currents 0]

Thank you aslan7,

Re: "Partial to Carver products"

I have just purchased a C-1 preamp in near mint condition. Very excited, I can't wait for the amp to arrive before I try it out. I've read many pages on this site about the BillD mods which I'm sure would dramatically improve the stock unit, especially as it is in "vintage" territory. I'll hold off with the mods for now because I'd like to get my stereo up and running; I'd also like to get a sense of what the C-1 sounds like as is. I do have a question for forum members regarding the mm three position switch on the back. Does it affect the gain of the cartridge? I'm using a Shure V15 MR (last model before they ceased production). On my HK integrated I have to turn the volume knob to near 12 for adequate sound. Any suggestions would be most appreciated. Thanks all.

[aslan7 955]

Thank you aslan7,

Re: "Partial to Carver products"

I have just purchased a C-1 preamp in near mint condition. Very excited, I can't wait for the amp to arrive before I try it out. I've read many pages on this site about the BillD mods which I'm sure would dramatically improve the stock unit, especially as it is in "vintage" territory. I'll hold off with the mods for now because I'd like to get my stereo up and running; I'd also like to get a sense of what the C-1 sounds like as is. I do have a question for forum members regarding the mm three position switch on the back. Does it affect the gain of the cartridge? I'm using a Shure V15 MR (last model before they ceased production). On my HK integrated I have to turn the volume knob to near 12 for adequate sound. Any suggestions would be most appreciated. Thanks all.

 

Hey Eddy, you might want to start a NEW post with this preamp repair question as it may have gotten lost here in the Bose 901 topic post.

 

If desired, click on "preamp repair" in the middle of the home screen and then select "new topic" at the top right.  Then re-post your q..  Someone will be along to answer your C-1 question (unless they find it in this topic before that).  

 

 

[aslan7 955]

Ahh. I see your q was answered now under the "preferred cartridge" post. Disregard above.

 

Enjoy EC!

[MORE CARVER'S PLEASE 99]

Well folks, My 901 phase has come to the end. I sold all my 901's. -It just wasnt worth it.. I was putting>1000 watts into them AND a additional Jbl sub with a Crown amp to get the sound I wanted. and even then, it was mediocre. I'll give them credit tho- the vocals and midrange were exceptional. When I used them strictly for mids- they were nice.- but not worth the hassle. No regrets- When I was a kid I thought they were the greatest, and someday I'd get them.- So I had to give it a shot and see for myself if I liked them.,,, and I really cant say I did..

-- Onto the next-- I'm putting together a Jb pro Cinema 2-way.. got the mid/lows, now I need to find some horns...

 

Well Brian I'm glad to see your madness has ended with the Bose  lol lol ..... Now I would be a liar if I said I never owned any. My 1st "real" system was 901 II's got em used for $200 some 30 years ago... I also snagged 3 901 V1's several years ago, cheap... no EQ but I got one from the e-bay for $75. I had those hanging in my shop for a few years... and yea I liked em for a shop system. Ran an old Adcom GFA-1A amp to em. 

 

Now I gotta ask.... whats up with the Klipsch..... now us hard core Klipsch guys don't allow Klipsch and Bose in the same room much less put a 901 on a Klipsch speaker...lol lol..... Just poking at ya my man... Are those Forte's??? You like em... heck you got horns....

 

You said your looking at some horns???? ever check out any of the Pro-Klipsch line... The KP's....OMG.... or may be a Chorus II with that tractrix horn..... I fell in love with Klipsch some 25 years ago....

Best of luck with your next project...

 

MCP :-) 

[Dav-Em 335]

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

I wonder where the yellow wire goes?

 

Graham

 

It's like a ballast resistor wire (as in an ignition system) to 'correct' the impedance of the entire speaker - trimmable. The wiring is very different from the acoustic versions.

[fill35U 1,847]

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

I wonder where the yellow wire goes?

 

Graham

 

It's like a ballast wire to 'correct' the impedance of the entire speaker - Trimable. The wiring is very different from the acoustic versions.

 

While the idea of using the yellow wire to change the impedance of the speaker is intriguing, that purpose is completely undocumented, AFAIK unprecedented, and IMHO generally impractical.

 

The answer I gave IN THIS IMMEDIATE FOLLOWUP POST is the widely documented and accepted purpose and use of the yellow wire. The Bose Spatial Control Receiver has four amp channels. They can be set to series bridged in pairs, but for Spatial Control with 901's, the "yellow wire" goes to ground, and a separate amp channels drive the + and - terminals. The Spatial Control scheme only affects frequencies above 1kHz. 

 

Now, I'm no expert, and we're all here to learn.  So I'd love for you to provide info showing that yellow wire was intended to be used to trim impedance. Or how anybody ever did so. Like I said, intriguing! 

 

However, I think it's generally impractical. There are only so many ways to add impedance to the system, and none of them make sense. 

 

First off, the 901 uses full-range drivers. Any impedance you added would have to cover the full audio range, or it would change the speaker's frequency response. Granted, you could cut the mids to help even it out, but that's a waste of amp power in passives and a drop in efficiency, and the active EQ does this far better. A full-range passive network would be big, expensive, a harder amp load, and wasteful of power. Plain resistors would be much smaller, cheaper, and easier.

 

So what can you possibly do with resistors? With three speaker terminals, basically two possibilities:

 

1. Put resistance across the normal + and - terminals. This has no effect on the speaker's performance. All it does is make the amp see a *lower* impedance load, never a good thing. The amp works harder to maintain the same voltage at more current, the extra current just goes into heating the resistor. This gets significant as the resistor's value drops near or below the speaker's impedance, it could dissipate the hundreds of watts (or more!) the speaker is consuming.  Let's add "dangerous" and/or "bulky" to the disadvantages. Using rheostats or switch networks only makes things worse.

 

   Putting resistance from both the + and - terminals to the "yellow wire" (terminal marked " * ") accomplishes the exact same thing, if the two resistances are kept balanced to the driver groups they parallel. Which leads to the only other possibility:

 

2. Put resistance from the * terminal to the + and/or - terminal in a manner that doesn't balance the driver groups they parallel. In other words, put 100 ohms across * to +, and 10 ohms across * to -. This changes the voltage division between the two groups of drivers, and their relative volume. You'd effectively be doing some of what the Bose Spatial Receiver did. However, the effect would only be significant when the resistance approached the impedance of the driver groups. So again you'd have the drawbacks of #1 above. In the extreme case of zero resistance (short * to + or -), there's no resistor necessary, but now you've got a ~4 ohm speaker- more sensitivity, but the radiation pattern is radically different from design, and you're wasting half the drivers. If you short the group containing the front driver, it's *really* not going to sound good! 

 

If  you're suggesting using the yellow wire as one terminal, and tying the + and - together as the other terminal, think about polarities, and what the resulting impedance would be...

 

Do you have any info on whatever device or accessory Bose or anybody else made to accomplish this "impedance trim"?

 

FWIW I've never heard of anything like this for the pro 802's either, where impedance adjustment might make more sense.  

 

BTW I wonder if the whole Spatial Control Receiver concept died because nobody could find 3-conductor speaker cable... 

[fill35U 1,847]

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.

 

Previously posted Series VI EQ curve:

 

 

 

From the Spatial Control Receiver service manual:

 

 

 

 

So Series III and IV have identical EQ. Compare the Series IV and Series VI (middle curve) EQ's above.  About 3dB difference at the 35Hz and 14kHz peaks, definitely significant. But less so in view of the adjustability of the controls. 

[kingman 663]

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