[Horsehead]

I've been doing a lot of good old two channel listening lately and I am thinking about using my second Pass X350 that I use for my surrounds to biamp my main RM40s.  Question is- should I use one X350 for the bass and the second X350 for mids/highs (horizontal biamping) or use one X350 for each RM40 (vertical biamping).  I know Julian runs the ultimate setup with his RM/Xs biamping with four Ampzilla 2000 monoblocks.  I'm leaning towards the horizontal biamping as cable setup would be easier, and also the X350 used for the mids/highs would almost always remain in full Class A operation, while the X350 used for the bass could do its power thing (700 W/4ohms) into Class AB on demanding bass passages.

I'm going to upgrade my Placette RVC to the Placette Passive Linestage which will provide 2 sets of fully balanced outputs for easy biamping (no "Y" cables needed).  

I am also leaning towards this setup in the event I upgrade to a pair of RM/Xs which benefit from biamping.

So, give me your best opinion on which way to biamp the RM40s.  I'm really starting to like the idea of Pass pure Class A power going to the Neo mids and (one day) FSTs.

[JoshK]

Question,

When the amp goes into Class AB, do both channels go?  Second, I think I read somewhere that the Pass were dual mono, am I right?  Each channel has its own transformer?  

If it is a true dual mono design, I don't think it will matter which way you go.  If it isn't and the channels are linked somehow, either by sharing a transformer or coupled to go class ab at the same time then it might matter.   If they share a transformer but aren't coupled then vertical biamping would probably be best, if the opposite were true (would seem weird though) then horizontal would be better I would think.

I haven't tried biamping yet but did read up a bit on the matter.  I would probably just experiment with something really dynamic.

[Sedona Sky Sound]

My vote would be for the Horizontal bi-amping. The only drawback I see is that it will require slightly longer speaker cables than if you went Vertical and could place each amp right next to the speaker (assuming Interonnect length would be roughly the same in each case).

You would definitely never get out of Class A on the mid/tweeter amp. In my RM/X set-up, the mid/tweeter amp never gets warmer than it does at idle. However, the bass amps can get overly warm (but not quite hot) to the touch when playing really dynamic, bass heavy music. By going Horizontal, you also never have to worry about sucking the power supply dry and thus affecting the current the mid/tweeter capacitors see. The end result is that the clipping SPL might be a few dB less than if you went Vertical (but still incredibly loud), but the overall sound should be better.

Ultimately, I plan to use the Son of Ampzilla for the mids/tweeters and the Ampzilla 2000s for the bass.  

Julian

[Horsehead]

Thanks guys. I think when the amp goes AB, both channels go. The X350 uses a single, but HUGE 4Kva transformer.  I'm leaning towards horizontal biamping and letting one amp remain pure Class A to feed the mids/tweeters.  Even at idle, the amps run fairly warm due to the heavy Class A bias, so both amps will always be "warm" to the touch.  
Actually with the Placette, I need keep the amps nearby so I can use short interconnects, so even if I did vertical biamp, I'm not sure I could move them closer to each speaker to use shorter speaker cables.  The input impedance on the X350 is only 22Kohms, so I need to keep the interconnects from the Placette as short as possible (1/2 meter).

[ekovalsky]

With the crossover @ 166 hz, your mid/treble amp may be putting out as much or more power than the bass amp.  Unlike the mid/treble section, the bass amp will need to have a high damping factor (i.e. solid state) to adequately control the woofers.

Obviously if you want to use different amps for bass and mid/treble, then horizontal is the only option. Best results will usually be with two identical amps.  Using different amps introduces new problems, such as mismatch with phase and sensitivity, that may require a high end active crossover to work around.

Vertical biamp has its advantages -- full channel separation (effective monoblocks) and placement flexibility (short speaker cables).  If identical amps are used, passive biamp works well and is simple to implement.

[Val]

I agree with ekovalsky, the mid/treble amp will work just as hard or harder and vertical biamping is the way to go in your case.

[Horsehead]

I e-mailed Pass Labs and they suggested vertical biamping as well.  They also suggested if I did want to dedicate one amp for the bass, then an electronic crossover would be the way to go.  I guess I can always experiment, but I'll try the vertical way first.