Incorporating Sub into two channel stereo

I am interested in adding a powered subwoofer to my two channel stereo system which includes Krell KAV 250a and 250p with B&W 804 matrix speakers. I have no idea how to do this as there is no subwoofer output on either the amp or preamp. Any help would be much appreciated.

Thank you.

With many subs you can connect the subwoofer to the speaker outputs on your amplifier. REL subwoofers actually prefer this method of connection and are great subwoofers. Your regular speakers remain hooked up the same way.
Rel subs, and I assume other can hook up directly to your power amp. Small gauge wires that do not make hooking up the speaker wires to your B&W's a problem. I have always thought this was the best way to hook up a sub. I am sure others will disagree.

Good luck
i can't believe they would not put you a sub out on that equipment, but krell is not about sub woofers, with the 804s i don't know why, but we all have out listening needs and sometimes want to explore, as i have many times, so in saying that , use the record out and use a bw sub to try and match crossover...if your speaker goes down to 40 , then put the crossover on the sub at 40...hope this helps...record out should give you an output to the amplified subwoofer
The record out is fixed level and will be a royal PITA to set the sub level manually for each listening session. Any sub that has a high level (speaker) input will work.
The nice thing about B&W is that they publish distortion figures for the 800 series. The 804, though a floorstanding speaker, would do well using bass replacement.

My suggestion is to pick up an NHT X2 filter and insert it between your preamp and amp. The X2 produces a summed mono output for the sub and high-passed outputs for the main amp/speakers.

I would not set the crossover below 80Hz. The distortion specs for your speakers are very good above 90Hz. Pick up an SPL meter and the test tones from either the M&K archived web site or the current Blue Sky web site to correctly match level between the 804s and your sub.

Which sub you choose is another question... Oh, for good information on placement and wiring options for a sub, download the manual for the Revel B15a sub.
If you use the balanced outputs from the preamp into the amp you can use the unbalanced preamp outputs into the sub. Some prefer using speaker connections and others prefer preamp connections. If you have the option, you should try both to see which works best for you.

Would using the unbalanced outputs cause distortion b/c the balanced outputs are utilized (i.e. no pin)? I think I read somewhere that this is an issue..... I dunno....


I guess I would be leaning towards hooking the sub to the amp binding posts.... Seems easier.... Any sound quality disadvantage to doing it this way?

I will check out the revel manual.

As far as the sub with the 804's.... Although they are floorstanding and generally have good bass response (great midbass punch and decent slam for their size), lower end bass response is not great and I have a big, solidly built room to fill.

Thanks for the input, guys... Any other suggestions?
I'm not certain whether or not both outputs of your preamp can be used simultaneously but the one preamp I owned with both sets of outputs could be used that way. You should check the manual on it to be sure.
I guess I would be leaning towards hooking the sub to the amp binding posts.... Seems easier.... Any sound quality disadvantage to doing it this way?

Potentially, yes with your speakers. You can not take the bass load off of your main speakers using speaker level connections, so depending upon the level and the frequency your main speakers will produce more distortion than necessary. If you were using the B&W 803 instead this would be much less of an issue, because the 803 is good to 50Hz versus 90Hz for the 804. That 3rd woofer makes all the difference.

Whether this will bother you or not is anyone's guess.
Running your speakers fullrange, and then trying to blend in a subwoofer with them, depends on a few things.

Blending a subwoofer into the system, without use of a hi-pass filter on the mains, only works...sometimes.

Many speakers have 10-15db peaks at "just above" the point where roll off will never get a good blend with these have to use a hi-pass filter with these.

Ported systems...along with, panel types, (Apogee, Maggie come to mind)...probably Soundlabs?...although I have never measured a pair of Soundlabs.