Biamping Triode Tubes No Feedback With Solid State

Using the integrated amp (IA) for 2 channels of power and a SS poweramp for the other 2 channels sounds plenty OK. But depending on how the speakers are crossed and how much tubed power you buy, you might not have enough tubed power.

Two-way speakers almost always have a high crossover, sending only treble to the 'high' half of the speaker. The vast majority of tubed IAs will have plenty of power for the high half of that kind of speaker, even in trode mode. Most 3-way speakers send MR and treble thru the high terminals of the crossover, sending only bass thru the low terminals. IF you use one of these 3-ways and IF you buy a relatively low-powered tubed IA and IF the speaker's sensitivity is lower than average, your tubed IA may NOT have enough power for the high 'half' (or, in this case, about two-thirds) of the speaker. Of course it'll be easier to drive a separate poweramp if the IA has jacks for driving poweramps.

All this could be done without an active crossover, but you'd need some way to adjust the volume of the more-sensitive poweramp to match levels between the 2 sections of the speaker. An active crossover facilitates improving sound quality by bypassing most if not all of the components in the speaker's crossover, but that REQUIRES wiring around the speakers' crossovers.

So it's not quite as simple as it might seem, but it's doable, and you might end up with the harmonic glories of triodes driving your MR and treble.
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I wouldn't even THINK about it until I found a speaker I absolutely loved AND an intergrated amp I absolutely loved, both of which I wanted to make a little better. IMO, the only situation in which biamping is easy is when you're using 2 identical stereo amps (or the identical channels of a multichannel amp) and you simply feed them with 4 identical signals from the preamp and connect the amps with 4 chunks of speakercable to existing double terminals. The next less-easy situation is when one pair of amp channels is more sensitive than the other and 'all' you need is a volume adjuster. After that, it gets lots more complicated.

Here's my story. I fell in love with a pair of new Eminent Technology LFT-8s, hybrid planar-magnetic systems with coned woofers, that are biwirable. (They replaced a pair of excellent-sounding Quad 989s.) I had and loved a pair of 50-Watt SETs, ASL 805s. The ASLs had not nearly enough power for the 8s and barely enough for the MR/treble panels. I had a 7-channel Outlaw poweramp. I tackled, first, the bass. I dug up an old Dalquist DQLP1, an electronic crossover with an active, second-order, lo-pass section and a passive hi-pass section. I removed and tossed the lo-pass inductor that was the woofer's filter, hardwired speakercable all the way back to the amp*, and started tweaking the DQ's level, crossover, and bass-boost controls. I observed changes in frequency response using a Phonic Audio Assistant II, a hand-held real-time analyzer, a tool that's HIGHLY valuable in this tweaking process. Then I contacted Bruce Thigpen of ET to determine the target range of crossover points for the MR/tweeter high-pass filter, calculated the value necessary for my 100K-Ohm-input-impedance amps, and bought and installed those caps**. That allowed me to remove the huge (475μF) electrolytic cap that was in the crossover. WOW!!! What a difference that made. This removal caused what is still the largest single sonic improvement in a music-reproduction system, caused by changing a ‘passive’ component, I’ve ever heard. That left only the MR lo-pass and the tweeter hi-pass filters in the crossover, and they’re still there, populated with higher-quality components***.

Conclusions? 1. Usually it’s not easy, and it’s sure not quick--all this took weeks, and I'm retired. 2. Going to active filtering still doesn’t necessarily allow one to remove all passive crossover components from your speakers. 3. I now have the BEST BASS I’ve ever heard in my largish (3200CF) room, and all from 2 little 8" woofers. 4. Most-real and attractive-sounding MR and treble I’ve ever heard in my system, in my room. 5. Was it worth it? ABSOLUTELY. 6. Should someone else do it? Only God knows, and He ain’t tellin’! 7. Would I go back? Never, with this system.

* That is, there are NO mechanical or solder joints after the woofer and before the spadelugs attaching to the amp. The cable runs out a hole I drilled in the enclosure's bottom and then sealed

** I chose Cardas Golden Ratio caps and I'm VERY pleased with their nonsound.

*** Those are a Solo copper-foil inductor and a SoniCap-1 shunt cap in the MR lo-pass filter, with a Cardas GR cap as the tweeter hi-pass filter. I think I'd use a Solen Perfect-Lay inductor next time.

I agree with Matrix's point that biamping with passive crossovers and 2 different kinds of amps is difficult.

I disgree that one needs--or even that it's a good idea--to strip all passive 'crossover' components when actively biamping. Doing so with a 3-way speaker requires one to triamp; biamping actively is difficult enough. Also, most 3-ways have band-pass filters--those that block lows from the bottom and highs from the top--on the midrange driver. Removing it from the crossover requires one in the active crossover.

Also, some speakers have equalization networks in them to level their response. Removing all passive components eliminates the very real benefits of these eq. networks.

I'm all for biamping actively, 2-way, and with the fewest number of components and IC cables and mechanical and solder joints, all of which degrade the quality of the sound to varying degrees. My active high-pass filter has NO mechanical connections and only one extra solder connection per channel. The four pieces of interconnect cable are hardwired to my Dalquist low-pass filter; that eliminates 4 mechanical and at leat 4 solder connections from the low-frequency section. Those who think that active filtering is all good and has NO negative affects on sound quality are wrong IMO.

Good listening.
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