Some interesting gear from Bose other than the 901

[Mr T]

Hello people,

I am new to this forum and I really appreciate the high technical level, comitment and politeness of most of the contributions about the Bose 901 system. I also liked the absence of the usual bashing those unusual speakers seem to trigger so easily elsewhere. I hope you will excuse mistakes in my english but it's not my native language.

Here's the purpose of my first post : I thought you might find interesting some pages I have put online about fine equipement Bose marketed along with the 901s :

the Bose 901 series II equalizer

The Bose 4401 preamplifier

The Bose 1801 power amplifier (in fact mine has started a second life as a souped-up 1800)

and lastly the Bose 1800 series two Power Station

I enjoy these units every day, some of them since almost 30 years (the Bose 1801) and I am still amazed by the built quality even 35 years after they left the factory. By the way, beside the Bose I also own fine audio equipment from Audio Research, Studer, Revox, IMF and many others so you are not allowed to call me a Bose unconditional fan I use the above equipment with a pair of mint Bose 901 series II and in a vast room I can only confirm that they absolutely need that amount of clean power to give their best results.

Cheers

Mr T

[stan461]

Welcome.

I am about to set up my new 901 series VI.

Did you ever try running the 901 series on anything else but the 1801?

I will be using an Odyssey Stratos amp to start with. It has 150wpc and it handles my AR3as with ease.

I have heard/read over and over that the proper amplification is needed to do these speakers justice.

My biggest concern with purchasing an 1801 is that they are a 30 year old unit and therefore where do I get it serviced?

Since you have 30 years experience with BOSE, I value your comments and opinions.

Thanks for any help and once again a hearty welcome.

[Mr T]

Welcome.

I am about to set up my new 901 series VI.

Did you ever try running the 901 series on anything else but the 1801?

I will be using an Odyssey Stratos amp to start with. It has 150wpc and it handles my AR3as with ease.

I have heard/read over and over that the proper amplification is needed to do these speakers justice.

My biggest concern with purchasing an 1801 is that they are a 30 year old unit and therefore where do I get it serviced?

Since you have 30 years experience with BOSE, I value your comments and opinions.

Thanks for any help and once again a hearty welcome.

HI !

Thanks for the warm welcome.

25 years ago I had a setup made of four BOSE 901 series IV running with the 1801 you see on the pictures. At this time it was looking like a 1801 then, it didn't have the 1800 faceplate it has now.

As the speakers were wired in parallel I had 400 w/pc on the tap, but honestly I never managed to make the amp clip. So yes, the 1801 is more than adequate with the 901, particularly with the early series (I & II) for which it was designed by Bose. These models are really power hungry and need at least 150W/pc to to pass transients with any musical program because of the huge bass boost their EQ provides, thus asking a lot of power from the amp.

That said, the 901 from series III on are a completely different design and are much more efficient than the I & II series. When I bought my first pair of series IV I was surprised to see that a 30w/pc Luxman amp had enough power to play loud music without audible distorsion. The reason is that from series III to series VI the bass boost is nothing compared to what was needed with the 901 series I & II : +18dB @ 30Hz for the early series, a lot less for the successors. I recently got my hands on a 901 series V equalizer that I measured, the bass boost was much lower (didn't keep the curves though) and it is evident that any "good" amp will drive them easily. There is a lot of litterature on the web about this, and you may want to read this Bose 901 buying guide

I sold the two pairs of 901 series IV twenty years ago when I bought real high-end loudspeakers which were light-years ahead of the Bose on any aspect.

However, I always had a nostalgy for these unusual little speakers and a few months ago I got a pair of minty series II, just for fun and recall of the good old time when I was young, the ones with the beige grill you can see on some pictures.

As I own many amps, all being very high quality Class A/B, pure Class A and even modern high-power Class D designs, of course I have tried the 901s II with each of them. Believe me or not, best results were achieved with both my Bose 1800-I & II and also with the 300 w/pc Class D amp.

The other amps, with an output power ranging from 40w/pc to 100w/pc were unable to sustain the power demanded by the 901s II below 50Hz. Result was a fat, distorted, boomy bass with an evident lack of control. Again, the 901 series III, IV, V and VI (which are all the same apart from cosmetic details) will be very happy with, say, 50 to 100W/pc amps.

As a matter of fact, the more power you have, the more dynamic headroom. After all there's only 3dB difference bewteen a 150w/pc amp and a 300w/pc one, and a 3dB peak can occur very easily in a musical program. A friend of mine is using his 901s/IV with an old BGW750 and he is very very happy with it. The BGW750 is rated 255W/pc and can deliver near 500W when driven into clipping, which the 901 easily stands for short transients.

The Bose 1801 deserves attention, specially if the mod described in a Bose technical service bulletin has not been implemented . It consists in replacing a resistor that overheats and leads to devastating failure if leaved as this. Many 1801s have blow big time, taking the speakers away with themµ. That's because the load sees full DC rail voltage when output stage goes belly-up. See service manual for detailed description, it is an easy one. When mods have been done the 1801 (or 1800, which is the same amp) is totally indestructible, it could be used as an arc welding station.

I hope it helps.

Mr T

[stan461]

I hope it helps.

Mr T

Yes, it sure does. Thank you.

In the 2 months since you posted your response to me, I have been listening to the 901's (VI). Even with the 150wpc Odyssey, I can hear why people say that 250wpc is a good starting point. They seem to suck up more power than the AR3as.

The presentation of orchestral instruments is more life-size than the AR3as. The presentation is a little distant which may be from the reflection properties of the 901. At low volumes it seems the detail is not there but the more you crank the volume you realize that it's all there. Just not exaggerated.

They also don't distort at higher volumes. I haven't pushed them too far, but it something I've noticed.

They are a lot different than anything else I've owned and what I do know is that I'll need much more time spent listening and tweaking before I say these are "it" (for me). So far I'm really enjoying them.

I trust your amp recommendations. No sense in me wasting time and money over carefully covered ground.

I'm concerned that the BOSE 1800 and BGW 750 both have fans. I'm guessing they are pretty quiet.

Also, what model BGW 750 does your friend use? (750A, 750C, etc.)

I'm leaning toward the BGW since they are cheaper and there are more of them in the market.

I would also like to ask you if you felt an Acurus A250 would do the job. I have heard them power a Mirage M3si and combo was magnificent. Full and life-like orchestral reproduction.

And finally, QSC makes a number of "pro" amps. These caught my eye because they pretty much start at 250wpc @8 ohms and go up from there. They seem to have a good reputation and are supposedly very durable/dependable. They too have cooling fans.

Thanks for any further help.

[soundminded]

HI !

Thanks for the warm welcome.

25 years ago I had a setup made of four BOSE 901 series IV running with the 1801 you see on the pictures. At this time it was looking like a 1801 then, it didn't have the 1800 faceplate it has now.

As the speakers were wired in parallel I had 400 w/pc on the tap, but honestly I never managed to make the amp clip. So yes, the 1801 is more than adequate with the 901, particularly with the early series (I & II) for which it was designed by Bose. These models are really power hungry and need at least 150W/pc to to pass transients with any musical program because of the huge bass boost their EQ provides, thus asking a lot of power from the amp.

That said, the 901 from series III on are a completely different design and are much more efficient than the I & II series. When I bought my first pair of series IV I was surprised to see that a 30w/pc Luxman amp had enough power to play loud music without audible distorsion. The reason is that from series III to series VI the bass boost is nothing compared to what was needed with the 901 series I & II : +18dB @ 30Hz for the early series, a lot less for the successors. I recently got my hands on a 901 series V equalizer that I measured, the bass boost was much lower (didn't keep the curves though) and it is evident that any "good" amp will drive them easily. There is a lot of litterature on the web about this, and you may want to read this Bose 901 buying guide

I sold the two pairs of 901 series IV twenty years ago when I bought real high-end loudspeakers which were light-years ahead of the Bose on any aspect.

However, I always had a nostalgy for these unusual little speakers and a few months ago I got a pair of minty series II, just for fun and recall of the good old time when I was young, the ones with the beige grill you can see on some pictures.

As I own many amps, all being very high quality Class A/B, pure Class A and even modern high-power Class D designs, of course I have tried the 901s II with each of them. Believe me or not, best results were achieved with both my Bose 1800-I & II and also with the 300 w/pc Class D amp.

The other amps, with an output power ranging from 40w/pc to 100w/pc were unable to sustain the power demanded by the 901s II below 50Hz. Result was a fat, distorted, boomy bass with an evident lack of control. Again, the 901 series III, IV, V and VI (which are all the same apart from cosmetic details) will be very happy with, say, 50 to 100W/pc amps.

As a matter of fact, the more power you have, the more dynamic headroom. After all there's only 3dB difference bewteen a 150w/pc amp and a 300w/pc one, and a 3dB peak can occur very easily in a musical program. A friend of mine is using his 901s/IV with an old BGW750 and he is very very happy with it. The BGW750 is rated 255W/pc and can deliver near 500W when driven into clipping, which the 901 easily stands for short transients.

The Bose 1801 deserves attention, specially if the mod described in a Bose technical service bulletin has not been implemented . It consists in replacing a resistor that overheats and leads to devastating failure if leaved as this. Many 1801s have blow big time, taking the speakers away with themµ. That's because the load sees full DC rail voltage when output stage goes belly-up. See service manual for detailed description, it is an easy one. When mods have been done the 1801 (or 1800, which is the same amp) is totally indestructible, it could be used as an arc welding station.

I hope it helps.

Mr T

I bought the original Bose 901 in 1970 and still have them. They have held up well except for two minor problems which I easily repaired. The speaker surrounds have remained in excellent condition but the putty used to seal the drivers to the cabinet had hardened, cracked and was probably no longer air tight. Rather than replace it, I ran some clear GE silicone calking around all of the rims of the drivers and on the screw heads. This seems to have restored them to air tightness and it can easily be removed if I ever have to replace a driver. The input and ouput jacks did not have their ground pins wired. Instead they relied on a press fit to make a ground connection. This occasionally resulted in a hum. Eventually after I took it apart and looked at it (I'd always assumed it was bad interconnect cables) I spent a few minutes wiring them together and the problem disappeared. Otherwise, manufacturing quality was very good to excellent.

Putting a resistor in series with a transformer to reduce voltage is a very bad engineering choice IMO. Bose should have used a different transformer instead for its European export versions. I'm not aware of anyone else who has done what they did. That alone should have been sufficient to correct the problems. I have not noticed any problems with my equalizer that would suggest recapping it would matter audibly.

I agree with Gordon Holt's review in Stereophile Magazine it at least one respect. The 4" drivers we now call "midwoofers" (the term didn't exist AFAIK back when) have too high inertial mass to be a good tweeter. IMO they cannot reproduce the top octave satisfactorily. If you can't hear that octave anyway due to hearing loss it doesn't matter. But if you can, it is very noticable. Therefore no amount of treble equalization will overcome its lack of high frequencies. But even if it could, a 4" driver would beam all of its high frequencies on axis. This would not matter as much for the rear drivers but the front driver where the precedence effect creates the apparent directional source and high frequencies play a major role would suffer anyway. I've re-engineered mine into two way systems using six 3/8 polydome tweeters per channel. Less than 5% of the treble energy is directed forward, the bulk of it is backwards and upwards. IMO this has made a great improvement without any sacrifice to the special spatial qualities inherent in the design.

I heard the Series VI briefly about a year ago at a Bose store in a shopping mall in California. It had the same dull high end to my ears as other versions of 901. This was not all that different from other speakers in the 1960s and 1970s. I don't know if the ported design can reach anywhere nearly as low as the original acoustic suspension design but given its dimensions, I doubt it. I'd guess it probably rolls off at around 40 hz. This would make it much more efficient though requiring only a low powered amplifier. Series 1 (or II) will suck up 138 wpc at bass frequencies like it was nothing. For this reason and because the speaker seems to exhibit a 6db per octave rolloff starting at around 250 to 500 hz where it has about a 7db peak with respect to 1khz in my room, additional equalization and lots of power are required IMO to get the full potential from this design. When properly equalized for the room and the source as a 2 way design, it has proven to be IMO the most accurate speaker I have heard. AR9 has more powerful bass but in other regards, it would be very hard to beat this speaker system now.