Who Here is Vertical Bi-Amping?

I recently tried vertical bi-amping and I am very impressed with the results. For the record, I am using “vertical” to refer to using two stereo amplifiers (one amp per speaker) where each amp uses one channel for the midrange/bass driver(s) and the other channel for the tweeter. I am using passive crossovers between the amps and speakers.

My first impression is that there is a noticeable increase in detail and a large reduction in treble harshness at higher listening levels. This makes sense to me because now the tweeter is independent of what the midrange/bass driver is doing. (Technically its “independence” is equal to the channel separation spec of the amplifier.) When the mids call for lots of power which can stress the performance of that channel, the tweeter performance isn’t affected. 

After reading what I could online, I was hesitant to even try vertical bi-amping since I saw lots of mixed reviews on bi-amping in general. I decided I had to try it after reading this post on another forum by Mark Donahue of Sound/mirror Inc. (no affiliation):

“...We have been vertically biamping the speakers here in our mastering studios for 25 years and have yet to find a monoblock that delivers better performance than a pair of stereo amps.
Going back almost 20 years we were looking for a big solid state amp to drive the brand new at the time B&W 801 II. What we found at the time was that the larger monoblock amps from B&W (MPA-810) and Threshold (SA-1000) did not sound nearly as good as the similar stereo amps in a vertical biamp configuration. Every couple of years we would try out the new big monoblock de jour (Krell, Spectral, Cello.....) and every time we found that the stereo sibling of the big monoblock yielded better imaging and lower overall distortion.
Recently we went through the entire routine again. I finally had to retire my five trusty old Threshold S-500 series II due to the need for true balanced inputs. I tried the Classe CAM400 and was underwhelmed with the imaging and clarity. I then replaced them with the (Less Expensive!!) CA-2200 stereo amp and the difference was shocking. Better imaging, better impact and smoother frequency response from my Dunlavy SCV’s.”

I’m very glad I tried it as my system is sounding much better! Does anyone here vertically bi-amp their speakers? If so, what has been your experience and do you find it better/the same/worse than monoblocks, stereo amps, horizontal bi-amping, etc.?
Horizontal: how easy is it to truly gain-match two different amps? How much does it limit your choice of components?
If you really want to have success biamplifying, it's best to use an active crossover. That solves level and amplifier matching problems, and allows fairly easy horizontal biamplification.
When you can match a 200 watt amp for the bass, and a 50 watt (of higher quality) for the mids and highs.
A point to keep in mind when horizontally biamping using two amps having much different maximum power capabilities, without using an electronic crossover "ahead" of the amps (i.e., using the amps in a passive horizontal biamp configuration), is that chances are you won’t be able to utilize a lot of the power capability of the higher powered amp.

While a passive horizontal biamp configuration reduces the amount of current and power the high frequency amp must supply at low frequencies, it and the low frequency amp must (to a close approximation) both put out equal voltages, corresponding to the full frequency range of the signal. If they are not set up to do that the amps are not properly gain matched.

And if there is a large disparity between the power capabilities of the two amps chances are very good that the lower powered amp will not be able to supply as much voltage as the higher powered amp, without clipping. Therefore the user will probably not be able to turn the volume control up high enough to utilize all or even most of the power capability of the higher powered amp without driving the lower powered amp into clipping.

An electronic crossover "ahead" of the amps would eliminate that concern, as well as providing the benefits @cleeds referred to above.

@d2girls, that issue is likely to be particularly pertinent with the combination of an MC462 (450 watts) and an MC275 (75 watts) that you referred to. In terms of listening it might not be a problem, of course, depending on speaker sensitivity, listening volume, etc. But at the very least you would be paying for a lot of watts with the MC462 which couldn’t be utilized in that situation.

-- Al
After rebuilding my two Dynaco ST-70s with the VTA mods, I stumbled into Bob Latino’s suggestion to do vertical bi-amping. It obviously requires two identical amps. After having them hooked up that way for a few months now, I can definitely say that it makes an easily audible improvement in separation, imaging, clarity through the mids and highs, and dynamics vs using just one of the single stereo amps, and even vs using one channel of each amp as monoblocks.

Like any system upgrades or changes, how audible an improvement is depends a lot on the other variables in the system. Some components are simply more revealing of changes than others....for better or worse.

My speakers have passive crossovers, so that’s the route I pursued as a path of least resistance. I’m getting excellent results with them in the vertical bi-amp configuration, so am reluctant to head down the rabbit hole of active crossovers, but maybe someday for curiosity sake. I’d assume there are good and bad examples of both, so likely pros and cons with each.

I don’t know if this subject has been mentioned, but one of the benefits of vertical bi-amping with tubes amps is the ability to tailor the tubes with one matched set that has deeper tighter bass on the channels that go to the woofers, and a different set that has more open and clear mids and highs on the other channels. "Mismatched matched" sets on each side, with both amps setup identically of course.
Knotscott, that’s an interesting concept with the “mismatched” tubes. It makes a lot of sense.

I started with a stereo amplifier and then went to two stereo amplifiers in monoblock configuration (only using one channel on each amp). I really appreciated the step up from one stereo amp to “monoblocks.” It was a big improvement. I wasn’t there long before I tried vertical bi-amping and finding that I really like the results.

I use left and right channel tube preamplifiers. I could definitely try something somewhat similar to what you described with your stereo amp “mismatched” tubes concept. Thanks for the suggestion.