Details for bi-amping

I am going for a horizontal bi-amping of my system intending to use two tube monoblocs for the mids and the highs and two SS monoblocks for the lows. The issue is that I have to have the same gain of the Pre-amps driving all the four monos in order to avoid a difference. Some Pre-amps have a pair of outputs allowing them to drive two pairs of monoblocks. Would that be a good solution? Would that be a solution at all giving that the tube monos and the SS monos would most probably have different output power? Would the use of a single Pre-amp with two pairs of monos negatively affect the sound quality? Or I should go for two Pre-amps trying to match theeir gains? I will very much apreciate any hint. Tnx.
You do not need two preamps. You can use Y connectors from a single set of outputs, that is what I did when I biamped. Use good quality Ys. It is not clear if you are using 2 matched pairs of amps or 4 different ones. In the first case you will need level controls for the pair of amps that is more sensitive, ie plays louder as a given preamp setting, so you can lower their output. Using mismached amps would require 3 level controls at least and be quite complicated to set up.
Thanks Stan for your quick reply. My ignorance needs a lot of clarification. I intend to use two matched pairs of monos. As you said in this case I will need a level control for the more sensitive pair. Saying "sensitive" do you mean more powerful? If yes, how could I make this setup? Obviously the level control of the single Pre-amp is not useful for that because it would attenuate (lower) the output volume of all the four monoblocks.
Parts Express carries the Harrison Labs fixed inline attenuators in 3, 6 and 12 dB versions. Right now, your guess is as good as mine which you might require but you only need them for the amp with higher gain.

My experience would advise to stay away from variable, potentiometer based units.

Passive volume control attenuators, such as Goldpoint, can be too rough for fine tuning biamping configurations and have fixed input impedance. Which brings up the other consideration of parallel amp impedance getting reduced and whether the preamp can handle that. Usually not a problem for solid state preamps.

Fair warning: Many biamping experiments, passive or active, end in failure because it's far more complicated than most people anticipate or are prepared to understand.
I am concerned that unless you have 4 exact amps, and 2 exact stereo preamps, the sound may be difficult to meld inaudibly.
Its not just a matter of gain matching at a particular frequency, but to track all the sound at any frequency exactly right....and too the dynamics have to be the same or the system will sound different at different sound pressures. If you listen to classical music or jazz at all, this would be of great concern.
Wow, what a bunch of nonreading and confused writing.

The OP first writes that he wants to use tubed amps on the top and SS amps on the bottom; later he writes that he wants to use indentical amps. Which is it? Tubed and SS or 4 identical amps? I suspect it's the former.

One preamps will do, and in fact the use of 2 preamps will complicate matters substantially. Y-connectors work just finely and are almost free. After you decide if you want to continue your experimant, you might look for a higher-resolution solution.

Stanwal is correct that you'll need some way to reduce the Voltage gain (NOT 'sensitivity') of the higher-gain amp(s). Of course, the easiest way to do that is to turn down the level of the higher-gain amp. However most poweramps don't have gain controls, so you'll be stuck having to use the passive attenuators that Ngjockey mentioned.

Good luck. I suspect that you'll decide that it's more trouble than it's worth.
Sorry fot the misspellings; too bad this forum chooses not to have an Edit feature.
The sensitivity of an amp is how much voltage it requires to drive it to full output. For example my Meridian 605s require .5 volt for full output; my CJ 350 takes 2 volts. Since the tweeters will take much less power to drive than the bass section it will probably , but not certainly, be the tubes that need the volume control or attenuation.
JeffreyBehr, I think he means that he wants to use a pair of monoblock solid state amps for the lows, and a pair of monoblock tube amps for the mids/highs.

You are of course making a good point that what needs to be matched is gains, not sensitivities. More likely than not the solid state amps, presumably being more powerful, will have higher gain, and therefore their inputs will probably be the ones having to be attenuated.

I second the comments about biamping being more complex an undertaking than is often anticipated, with there being a substantial possibility of disappointing results.

One of the most common misconceptions about passive biamping (i.e., biamping without an active line-level crossover) is that it makes sense to use a powerful solid state amp on the bottom, and a much less powerful tube amp on top. In addition to the possibility of that resulting in a sonic mismatch, what is commonly not realized is that much of the power capability of the solid state amp will not be utilizable, because how much of its power capability can be utilized will be limited by the clipping point of the lower powered amp. In a passive biamp arrangement, the mid/hi amp(s) have to output just as large a voltage swing as the bass amp(s).

-- Al
"...what is commonly not realized is that much of the power capability of the solid state amp will not be utilizable, because how much of its power capability can be utilized will be limited by the clipping point of the lower powered amp."

Maybe so, but one still has more power available than if using only one pair of amp channels of whichever you had first, because each amp channel's power is not consumed driving a full-range signal.

Do understand that 'after filtering' (by the crossover's filters) is as effective in power saving as prefiltering, in that, for instance, the upper-frequency amp simply isn't able to/doesn't have to deliver current required by low-frequency signals. Said another way, if one starts this biamping (NOT 'bi-amping') process with a 50WPC tubed amp and adds a 100WPC amp for the bass, the 50WPC amp no longer has to consume the power of its powersupply driving low frequencies into the 'bottom half' of the speaker. So maybe we don't have 150WPC available, but we do have lots more than 50WPC available.

Passive biamping can be very effective, but it also can be excessively complex if one starts with the wrong amps and especially if one can't balance levels correctly.
Agreed, Jeffrey. The thoughts we have expressed are not inconsistent, as what I was referring to was the use of a "MUCH less powerful tube amp on top" (emphasis added), resulting in "much of the power capability of the solid state amp" not being utilizable, due to the voltage swing limitations of the lower powered amp.

-- Al
The amount of relative power of amps used in a biamp setup is very much related to the crossover point.
Take a crossover of 10khz. How much power, as a %age of total does music contain above the crossover? Maybe 10% or 15%?
Likewise, if you crossed over at 100hz, you may need MORE power to the mid/hi amp than the bass amp. Above crossover may end up as 80% of total power needed.
Depending on crossover point, it may actually be appropriate to mate a relatively small amp on 'top' with a more powerful amp for the lows....

3 way designs would just complicate the heck out of it!
As an example:: The Braun Tri-Amp.....maybe early late '70s / early '80s? had three amps per speaker. 55watts=bass 35watts=mids 15watts=highs. Wacky expensive for me at the time, I looked but didn't touch!

The OTHER issue I never see addressed is what I call latency. How long does it take a signal to get thru amp 'a' vs amp 'b'? What is the effect at crossover if one amp is a hi feedback design (for bass=hi df) vs an amp with less feedback used above crossover? How will those distortion products interact at crossover +- 1 octave?
Excellent points, Magfan. To further clarify my point about power, though, what I was basically saying is that for passive biamping voltage swing capability needs to be considered as well as power capability, particularly if there is a large disparity in the power capability of the two amps.

Using your extreme hypothetical example of a 10kHz crossover, the amount of power that would have to be provided by the high frequency amp is extremely small. However, if say a 50W amp were used for the highs and a 500W amp were used for the lows, the 500W amp would in effect be no more powerful than, for example, perhaps 75 or 100W. Asking it to provide more power than that would cause the OTHER amp to clip, resulting in lots of extraneous non-musical high frequency energy going into the tweeter.

Good point about latency, aka propagation delay. You're right, that never seems to be addressed. Not sure how it would play out quantitatively under typical circumstances.

Best regards,
-- Al
If you are planning on passive crossovers, then unless the amps are identical, you will have gaps or mismatch is high/low output of the amp/speaker setup. Some speakers (Martin Logan's for instance) have switches that allow you to adjust the input of the amps to the speakers for just such an occurance.

However, it appears to me that if you want to bi-amp, then you can;
1) get identical amps for high/low inputs

2. Get an active crossover which allows you to adjust the levels of the amps.

There are some very good active crossovers out there and even your speaker manufacturer may have or suggest an active crossover for you also.

Have we noticed that Nikmilkov hasn't posted a word since the original message? Probably he's so confused and discouraged from our audiobabble that he'll either never try passive biamping or never ask a question here again! :-)

Nik, the biggest and IMO-only-important issue is gain matching the 2 different amps. Resolve that and you're well on your way.

And DO NOT--DO NOT--DO NOT combine passive biamping with an electronic crosover; ONE crossover network per speaker is just the right number.
Plan 'b' would of course be to can the biamp idea and get a single amp per speaker of high enough capability to render biamping unnecessary.

Maybe something like the Spectron offering? Or the kilowatt Pass amp?

Put any extra funds into a whole house lightning / surge protector, dedicated circuits to the amps and listening area and top it off with the appropriate room treatments and a couple 'o subs.

Back to the OP.
Before you even start choosing amps, I'd get the preamp thing sorted out. Some preamps have balanced AND single ended outputs which may allow use of both...simultaniously.
I'd like some additional information.
Where (frequency) is the proposed crossover? Are the speakers 2-way or more than 2-way?

Synergy will be critical and as others have pointed out, may be difficult to pull the trigger on.
Thanks, guys, for your help and instructive suggestions. Frankly I didn't expect so many advises which obviously is because the biamping option is highly attractive for many but also because it is a complicated issue. At least for me. I didn't post a single word since yesterday because of the 7 hours of time difference. But it gave me some time to think. So for sure I'll gonna go for a simple solution. Probably the use of 4 identical amps driven by a single pre-amp. Under this setup the advantage of the SS's in the lows will obviously be lost. (Just because I prefer tubes.) Another element of a simple solution seems to be the passive biamping but I am still doubtful to what extend it worths the effort - the result is modest compared to the investment. For summarizing - going for a simple solution I will loose the main advantages of the biamping option. The questions are 1) does it still worth the efforts and the money and 2) are the risks of messing up the things bigger than the modest output that can be expected.
Well, now I'M confused, by your summary.

So you plan to biamp passively with 4 identical tubed monoamps?

Two STRONG advantages are that the gains will be identical and that you'll have 3dB more power. Another advantage will be slightly less IM and harmonic distortion.

Good luck.

One advantage not yet mentioned is that if your speakers split the frequencies between bass (NOT including midrange) and MR/treble, you can use a high-gage-but-inexpensive cable on the bass. If your speakers split the frequencies into bass/MR and treble--2-ways do this--I recommend equally-high-quality cable on both legs.
crossover point of 'stock' speakers is still unknown.

Just for example, my 2-way panels split at 600hz.....

And indeed, Nik, the cost / benefit is really up for grabs. To be factored in is the cost of you time (therapy would be cheaper) to tune your proposed setup in. You may even have to resport to measurements.
Magfan is right. If you're dealing with a 2-way with a 2K crossover we could have saved a lot of time and called you nuts to begin with. On the other hand, if you're talking about an Infinity Kappa9, that's another kettle of fish.
Some more thoughts/issues.

Yes, you do need to match gain; IMHO, the amps don't need to be of equal power but should be in the ballpark; and I would not use any Y-cable from a preamp.

Most people using a bi-amp setup will use an active crossover between the pre-amp and the 2 pairs of monoblock power amps (a la Pass Labs XVR1). This is so that each pair of monoblocks will be dedicated only to amplify a certain portion of the audio band - either the low freq's for the woofers or the mid/high freq's for the midrange/tweeters.

Contrastingly, if you bi-amp with a passive crossover (e.g., use the crossovers built into the speakers), then each pair of monoblocks will amplify the full audio band. For example, the monoblocks for the woofer will be amplifying the full audio band but at the passive crossover, the mid/high freq's will be filtered out and essentially lost (the same thing happens for the monoblocks for the midrange/tweeter, except that the low freq's. will be filtered out and essentially lost).

Passive is not very efficient. Active is more efficient because only the specific part of the audio band is being amplified. This latter method leads to what, to me, appears to be more headroom - that is bi-amping my 100W Aleph 2 monos and my 125W Threshold SA/6e monos sounds much more than `100W full bandwidth.

So, let's say you now want to use an active crossover. In doing that, you also need to remove the passive crossover from the signal path. Otherwise the signal will be going through 2 filtering networks - first the active and then the passive crossover. This should be a consideration if you ever want to sell your speakers. In some speakers, removal of the passive crossover can be reversible; others not.

Also note that a few passive crossovers not only filter the lows/mids/highs, but also act as an rudimentary equalizer. If you go the active crossover route, you will lose the equalization that was inherent in the passive crossover. Might be better, worse, the same, or just different.

Also, someone mentioned using XLRs and RCAs for the 2 pairs of monoblocks. You don't have that problem with an active crossover because it will split the signal from the pre-amp. Also, if you do use the XLRs and RCAs from the pre-amp, note that there usually will be a gain difference from these outputs from a fully differentially balanced pre-amp.

In sum, a lot of things really need to be looked into. But if you can get it set up correctly, the bi-amped active crossover method works real well.

FWIW, from time to time, I bi-amp with an active crossover my Aleph 2 (for mid/highs) and Threshold SA/6e (lows). When set up right, they sound amazing - the liquidity of the Alephs on top with the bass authority of the Thresholds.

Also, be forewarned, if you like to setup your system once and not touch it, the bi-amp & active crossover may not be for you. The level of adjustment and permutations available with such a set up leads to constant fiddling. =) Some like it, some don't.

"Contrastingly, if you bi-amp (SIC) with a passive crossover (e.g., use the crossovers built into the speakers), then each pair of monoblocks will amplify the full audio band. For example, the monoblocks for the woofer will be amplifying the full audio band but at the passive crossover, the mid/high freq's will be filtered out and essentially lost (the same thing happens for the monoblocks for the midrange/tweeter, except that the low freq's. will be filtered out and essentially lost)."

A common misconception. Yes, the entire frequency band is presented to each poweramp, but the 2 ends of the frequency band are NOT amplified equally, because the crossover presents a rapidly rising impedance within the filter (rolled-off) band. That's why one 'saves' amp power when passively biamping.
Either way, passive or active, you have to decide if you want seams or holes in your system response or whether you want it "tunable" with an active crossover. As mentioned previously, if you can remove the passive built-in crossover easily from your speaker, then, since you plan on spending some serious money on amps, I would imagine that an active crossover isn't outside your price rance, then definitely go for active. If you don't want active, then you would need amps of equal specifications or the same amps. otherwise you definitely will have seams that you will notice. So, after all the posts, the choices are really simple. Active, you can get different amps for low/high and adjust with the crossover. solid state for the low and tube for high depending on your listening desires. Passive, you get the same amps for high/low or amps that are pretty close in specifications and you are good to go. It really isn't rocket science. It is only complicated if you allow it to be. You have two choices.

If you can easily remove the passive crossover, like my Martin Logan Monolith III's it is simple to remove them, since they are external passive crossovers and insert an active crossover to the system (which is what I did), and borrow an active crossover and amps and experiment to make your decision. I am a strong believer that when one is paying a large amount of cash for this type of equipment, borrow equipment first and take it home, insert it into your system and hear how it sounds in your system before purchasing. Asking others for their opinion is okay, however, that is what it is, their opinion. Your's is the only one that matters.

Find good dealers and stores that will allow you to take equipment home for a home demo first. They will have used/consignment/demo equipment or new equipment and take your credit card info. give you the equipment for a week or so and allow you to make an educated decision based on home listening.

Also, get on-line and check. I would bet that there are some active crossovers out there specifically designed for your speakers.

Realy tempted to try the active option as more efficient. I have two pairs of speakers PD 80 by Tyler acoustics and von Shweikert VR 4 Jr on two systems. As all of you, guys, know both are 3 way. One pair will be biamped depending on which one is easier to eliminate the built in crossovers. My choice may also depend on and I may take into consideration also other specs and details for each one pair of speakers leading to more rewarding results. I will address the manufacturing companies. My preference now is for the PD's because they are very efficient and easy to drive with less powerful tube amplifiers. A low output tube amplifier can be built on a very simple scheme which could result in a very clear and detailed sound. Last but not least a low output tube amp is usually cheaper than a high output tube amp of the same quality. You see the future set up should be built around the speakers that are already in place. Have heard both Ty and Albert are willing to help by advising. Unfortunately my remote location will not allow these companies to perform the crossover's bypass. But if I won't be 100% sure in advance that the things are doable the active way I will go passive. That's my strategy by now. Thank you again for your competent advise.