Bi-Amping Options B&W 801 Series 2

New to me Bowers & Wilkins floor-standing full-range monitors with two sets of binding posts.
Currently have dual MC252 solid-state amps (with autoformers) connected as follows: (1) to both bass drivers and (1) to midrange and treble drivers.

Meanwhile, I have a Rogue Audio Stereo 100 sitting idle (although I could hook it up to my vintage Warfedales). I’m wondering if I would be better served by bridging both the MC252s and putting them both on bass duty (500 Watts to each driver), and put the Stereo 100 to use driving the midrange and tweeters. What do you think?

Especially interested to hear from someone with experience driving this particular speaker, which sounds wonderful, by the way. My system is fully described (but not well pictured) under my profile in Virtual Systems. And, if anyone has a lead on an original Bass Alignment filter, I’m all ears.


Try the Rogue by itself and see if you like the sound. Not sure you will even need the Mac amps unless you are trying to bust the windows.

If you’re looking for more bass, a bigger amplifier is not going to do it. Do you need to add more base with the tone control. I bet you’re fine if you look at the meters, you’re probably only using about 10 watts during a typical listening session

I've got the 803 D3s. Just like mine yours dip down to 3 ohms.

They need current. The more the better.

You need the headroom for dynamic peaks.

Strap the Macs for mono for the bass and use the Rogue for the mid/treble.

For biamping you’ll need an external crossover or passive volume device to match the gain between top and bottom drivers. Is that what the Shiit Freya is for or can this be done with the Mac control processor?

You have a beautiful system, btw.

tomcarr is mistaken; your speakers do not dip to 3 Ohms; they have a minimum impedance of ~ 5.5 Ohms at ~ 10 KHz. This speaker has very benign impedance and phase angle curves which make for a very easy to drive speaker. Regrettably, I consider tomcarr to also be mistaken in stating that they need current. At chez xeno, our North Creek cross-overed Matrix 801 Series 2 speakers are driven by 75 lb. custom tube monoblocks that use 2 BL7 and 4 KT77 tubes, making about 100 watts. The system can play much louder than I would ever want.

Suffice it to say, I agree with russ69, try the Rogue 100. I bet it sounds great :).

Saw your system photos; I’m curious about your 801’s crossovers; what are they? They look great...good for you for upgrading from the week link factory x-overs. Oh, and forget about the bass alignment filter, at least the B&W one; it steals the incredible detail that these speakers have without it. The Krell version is thought by some to avoid this problem, I don’t know, but I do know that I’m not willing to put anything between these amazing speakers and our amazing amps other than Silversmith’s amazing Fidelium speaker cables :)

Enjoy your great speakers!


@russ69 A single MC-252 got better highs and better lows than the Rogue Stereo 100 from the Warfedales, in my opinion. I had issues with very dissonant distortion from an Electric Light Orchestra recording when running both the Freya and the Stereo 100, although the main issue was with my cartridge & Numark turntable & arm, as I recall.  Taking the Freya out of tube mode removed the distortion. I actually came to prefer the buffered mode for the Freya. 
The B&W have a lot more top end than my vintage Warfedales, ARs, and KLH models, so I was thinking that with the B&W speaker, I wouldn’t mind a bit of roll-off on the top end. 

@raysmtb1 I am using at least one tone control now, the ‘Environmental’ equalizer McIntosh MQ-107, and although I haven’t attempted to ‘curve’ it as yet, I am boosting the bass at ‘2’ out of 5 or 6 (I can’t recall exactly), but I’ve had to turn it down from ‘rattling the windows’ on some recordings. I would say you’re correct, although you can hear the bass without the EQ boost, you can hear it a lot better with it. 
More to your point, I’m not sure what more power will do for me. The manufacturer describes the bass driver as “12 inch (300mm) high-power polymer-cone woofer,” and I have read comments about what a nice speaker it is (was), but that it required a lot of power. When I have it turned up to ‘loud’ I’m 21 dB consuming about 25 Watts. But the amp experts always talk about having enough reserve in either the choke or the capacitor bank to deliver high amounts of current in a short amount of time to properly deliver the ‘transients’ that make for dynamic playback. 
But I think the also say that twice the power takes ten times the Watts, so . . . how much is enough, and how much is too much? That’s kind of my question. 

@tomcarr I like the way you think. I’m probably goin to try it, regardless, but I thought I would ask the question here, to gain knowledge from experts and those more experienced than myself. I’ve got a good deal of money tied up in the system at this point, so there isn’t a lot of room for ‘playing around’ in ways that failures go in the trash can. Ben there, done that, got the T-shirt and a few damaged amps and speakers to prove it. :-)


@lowrider57 Thanks for the compliment on my system, I’ve certainly been all-in since COVID struck which coincided with my retirement and my wife’s death May she rest in peace. 
Regarding the crossover, the speaker comes with two sets of speaker terminals, so that to drive them from a single amp, I would need strap the two positive terminals together and strap the two negative terminals together as well so that the power from the two wires could get to all four terminals and from there to all three drivers. 
It is my understanding that each original set of speaker terminals were connected to their own crossover network, and the drivers receive their signal from the crossover network internal to each speaker, but external to the amplifier. I include a picture of the crossover networks in my virtual system photos. Both crossovers inhabit the same circuit board, so it is difficult to distinguish them. 
I can definitely vouch for the fact that if I turn the one amp off driving the midrange and tweeter, all I hear is muffled bass notes, not at all distinct or loud; likewise, if I turn the amp feeding the bass drivers, all I hear is faint ‘tinny’ treble, again, not very distinct or loud. But when both amps are turned on I hear much more than the sun of the separate parts, the notes are clear, distinct, and loud, there is a sound stage (speakers disappear) instruments are well-placed within it, and there is plenty of ‘air’ around the instruments. As one listener noted, “I feel as if the musicians are in the room with me.” It is truly astonishing, and I didn’t have that kind of sound until I brought the B&W 801 speakers into the mix. They are truly a magnificent speaker: what you have (in the recording) is what you hear, no doubt. 

@xenolith Let me assure you, I am enjoying my new (to me) speakers. I bought the speakers used from a dealer in northern New Jersey. I won’t give their name because previous posts on this forum that referenced them were removed silently. Suffice to say that they would have been perfectly capable of replacing the original, if what I have is not original. I have seen some crossovers on eBay that are much heftier than mine, but I think I will hold what I’ve got for now.
I find your configuration interesting. I haven’t, as yet gone the mono-block route, I was already on the dual-mono path before I found out about it.
Your knowledge of this speaker ‘system’ (it’s really more than just a speaker, isn’t it?) far exceeds mine, but you seem to know what you’re talking about, and I like what I hear about it being easy to drive. The original designer, from accounts I’ve read was trying to correct the ‘muddy’ bass of the original series by going with a an intentionally stiffer material for the cone. The function of the optional bass alignment filter was to boost the signal to the bass and ‘wake it up’ as it were, as well as provide 6th order Butterworth filtering. Most people were happy with speaker as it was. B&W also offered 11” stands for them, but again the original designer said that was just to lift them up over furniture found in a typical recording studio, they weren’t necessary for use in the home.
Anyway, as I said, I’m enjoying them, and I’ll try driving them with the Rogue Stereo 100 and see what I think.

Thanks for the response, and that goes to everyone who has responded thus far. I really appreciate it.

@oldrooney  I'm so sorry for your loss.

I saw the pic of the crossover network, perhaps you can ask the dealer to explain the design. They are impressive speakers and it's great that they sound as good as they look.

My earlier comments were about adding the Rogue to drive the highs/mids where an external crossover or gain control is needed. You would need to verify that the internal crossovers are truly discreet; top and bottom drivers are separate.  

Yes, so sorry for your loss. May your memories of her remain vibrant and detailed for all of your days.

My best advice with these speakers is to give them tubes and the best of those that you can; yes, this means to disregard the advice to give them big solid state power; I’ve done both; with respect to sound quality, the former far exceeds the latter.

And most importantly, give them the cleanest path between them and their power...magic is then possible.

@xenolith Thank you. I just hooked up the Rogue Stereo 100 to the ‘High Frequency’ taps and the sound is so sweet. I prepared a long post to update everyone on this thread, but lost it all on an errant finger click trying to preview it. Oh well. The 2nd MC252 has Ben removed from the temporary system downstairs to drive the McIntosh XRT20s that are being installed on the ‘New System’ upstairs. If the XRT20’s need another MC252 to get off the ground they’ll get it. Testing the XRT20‘s revealed that they need a lot of juice to move the woofers; haven’t hooked up the tweeters yet: we’ll see. Again, thanks for the sympathy and advice. 

@lowrider57 Thank you for the kind words. As best I can tell, the crossovers are, and always have been separate. From the response I’m getting on this thread they may well not be stock. In any case there are others for sale, so I’m not as worried about the ‘Bass Alignment’ option as I once was. The bass is powerful and clean without any additional equalization. Thank you for your concern. 

B&W states a minimum impedance of 3 ohms.

I've heard my 803 D3 with amps rated at 150/300 w/ch and amps rated at 600 w/ch.

They sound better with higher power amps.

They love current. They devour it and want more!

You can't have too much power, but you can sure have too little.

With identical amps you are better off splitting them horizontally.  That is, one amp per side.  This spreads out any current demands on the power supply more evenly.  The alternative puts all the strain on the bass on one amplifier's power supply.

Also, PS - Bass alignment filters can be fully compensated for in Roon using the DSP features.

@erik_squires Hi Erik.

Paul McGowan did a video on horizontal and vertical 

bi-amping. He said horizontal configuration is better for using different amps, one for the mids/tweeters and one for the woofers.

He said vertical configuration is better for identical amps, one for the left channel and one for the right channel.

@tomcarr I’ve never seen an impedance curve for the 801 S2, but I checked the user manual specs and found that while they are rated at ‘Nominal 8 Ohms’ in parantheses immediately following it reads “not falling below 4 Ohms.” I expect the drooping impedance would most likely occur in the lower frequencies. I think I’ll try the MC252 taps for the low frequencies over from 8 to 4 Ohms. 
I also checked the specs on the MC252. Since it has autoformers, it can deliver max power however you hook it up: 250 Watts in stereo and 500 Watts in mono continuous sine wave with up to peaks of 50 Amps to each speaker. We’re I to go back to using both MC252s on the B&Ws I could run them either bridged or parallel into 4 Ohms. The parallel configuration would deliver the most current, I would think. One day I may try it, but after lugging that 96 lb. beast upstairs yesterday, it’s not going back down for a while. It seems perfectly suited to drive the XRT20s. 

@erik_squires Point taken on using identical amps as monoblocks. To be honest I was a bit intimidated at the prospect, I was afraid I might blow something up. But there is plenty of protection built into the McIntosh amps. I may try to source an MC2255 for the XRT20s and move the MC252 back downstairs for the B&Ws, or possibly bring the 65 lb. Rogue upstairs for the XRT20s, although the XRT20s could bring the Rogue 100 into clipping, and does NOT have the protection the McIntosh units provide. I think my current configuration makes the best use of the power I have available. 

OP- I LOVE the idea of using both 252s for your 801s!

Do it, and report your impressions.

I'm betting the sound will be effortless, and sublime!

Where one amp drives the left speaker and the other amp drives the right speaker.

I mixed up horizontal and vertical. I meant to say vertical when using identical amps, but I described my intention correctly.

That is, if using 2 identical stereo amplifiers, relegate each amp to a single channel (Left or Right) to maximize the power supply available and minimize crosstalk.