Active Bi-Amping/Tri-Amping FAQ

[Mazeppa1]

Anyone here using a bi-amp setup with just two amps and running the highs and mids together?

Jay

I'm running a horizantal bi-amp using the onboard passive crossover network of my Quartets.

Grant Fidelity TubeDAC tube out > TK2050 T-amp > mid/high section of onboard mid/high passive crossover section.

Grant Fidelity TubeDAC opamp out > Soundcraftsmen A2502 MOSFET amp > woofer section of onboard passive crossover section.

Improvement over either output to a single amp to all passive crossover sections was dramatic. Improvement over either output to both amps in the above described scheme was significant. Oh, digital to the TubeDAC is an older SONY DVD player. I'm very pleased with my system as is, I mean it sounds really good. I can't bring myself to turn it off sometimes, but......

I keep reading, in various forums, so many threads extolling the virtues of active crossovers that I'm having a hard time resisting the temptation to pick up a Behrenger DCX and going full monte. My passive scheme was so successful, but active seems to hold even more potential for mo' betta sound. I may get the credit card warmed up - again. However, I'm intimidated by the prospect of setting the thing up w/o having to get into the whole room EQ software analysis rigamarole (this is where my interest begins to fade) as my system makes me grin as it is. Then there's the unbalanced/balanced thing to deal with as well. All my present equipment is unbalanced only. Still on the fence, here.

[Rudy81]

The DCX2496 should be considered an entry level unit. I still have mine and use it for my subs and center channel. Lot's of folks don't like Behringer for various reasons. I have had good luck with their gear so am not complaining. The quality of the DCX can be improved upon. In my case I settled on an Ashly unit. You can spend anywhere from $200 for an entry level unit, $1200 or so for an Ashly and $5000+ for the more exotic units.

For me, going active was expensive but very much well worth it. It can be a steep learning curve, there are lots of things to consider like crossovers, amps, connection types, noise floor, consumer vs. pro gear integration etc.

[nightcabbage]

Some of this is a tad hard to grasp for a newbie... though I understand the overall concept. I have RF-52 IIs and am about to upgrade to a Yamaha AVENTAGE 7.2 receiver. Those receivers have the ability to "bi-amp" by using the back surround channels as the 2nd outputs for your L/Rs. Would you recommend it with my particular setup? Is there anyone out there that could outline EXACTLY what I need to do, either physically with the speakers (since there's talk of that above) or with settings on the receiver, such as freq/crossover settings related to the bi-amp? Random questions that pop into my head are:

1. Is it true "bi-amping" coming from one receiver?
2. Even if it isn't TRUE bi-amping, will it still have an advantage?
3. Much talk about bi-amping says the two terminals in bi-ampable speakers are for A) tweeter/midrange and woofer sections. I consider the RF-52 IIs to have midranges and a tweeter... so does that mean bi-amping won't be as noticable because of the smaller midrange woofer size?

Any help would be appreciated. Thanks!

[DrWho]

Some of this is a tad hard to grasp for a newbie... though I understand the overall concept. I have RF-52 IIs and am about to upgrade to a Yamaha AVENTAGE 7.2 receiver. Those receivers have the ability to "bi-amp" by using the back surround channels as the 2nd outputs for your L/Rs. Is this option true bi-amping? Would you recommend it with my particular setup? Is there anyone out there that could outline EXACTLY what I need to do, either physically with the speakers or with settings on the receiver? Thanks!

That biamp approach is lovingly referred to as "fool's biamping" and doesn't offer any real performance advantages (which is probably where the term came from).

The problem is that when the xover is after the amplifier, the amplifier is still supplying the full voltage swing at all frequencies. The fact that the tweeter amp is driving less power at lower frequencies doesn't really matter because modern amplifiers only care about the voltage they're putting out....the power drawn is just a means to an end. With that in mind, all the amplifiers in modern amplifiers are usually driven from the same power suppy, so splitting the power load doesn't even make it easier on the power supply.

All that to say, I wouldn't worry about the bi-amp mode built into your receiver.

[BE36]

Nice writeup...you may want to mention the need for amplifiers with no DC bias or turn on/off transients, or the need for a series blocking cap on the MF/HF units. Another advantage is the power load gets spread out so smaller amplifiers can achieve the same SPL as a single bigger amplifier (which usually means better resolution of low level detail, often perceived as cleanness or openness of sound).

Until I understand 1/10 of this statement or someone sets up my system i will remain a pacifist.

Speading the power load and narrowing the band that the amp has to work on seems staight forward the other stuff?

When goong active would there be signifcant benifit from selecting different amps that specialize in low or mids etc.?

[Chris A]

When going active would there be significant benefit from selecting different amps that specialize in low or mids etc.?

Clearly, many here would say that tube electronics are mid-high frequency friendly, while SS amps of the BJT (bipolar) persuasion tend to have snappier bass response (and lower output impedance).

However, I'm not a tube aficionado - I prefer Nelson Pass's approach using FETs for power amplification. There are many benefits and virtually no burdens to this approach.

Chris

[The Dude]

When going active would there be significant benefit from selecting different amps that specialize in low or mids etc.?

Clearly, many here would say that tube electronics are mid-high frequency friendly, while SS amps of the BJT (bipolar) persuasion tend to have snappier bass response (and lower output impedance).

However, I'm not a tube aficionado - I prefer Nelson Pass's approach using FETs for power amplification. There are many benefits and virtually no burdens to this approach.

Chris

I was thinking of trying something along the lines of a tubed amp on the hf/mf section and a ss on the bas bin of the Khorns. I will be using the passive between the tweeter and squawker, and a active between them and the bass bin.

1. will this work

2. If I am using a lower power tubed amp and a higher power ss amp is there going to be some delay issues that need to be addressed with something like a eq.

[Chris A]

I was thinking of trying something along the lines of a tubed amp on the hf/mf section and a ss on the bas bin of the Khorns. I will be using the passive between the tweeter and squawker, and a active between them and the bass bin...1. will this work?

Yes.

is there going to be some delay issues that need to be addressed with something like a eq.

I'd put in a 6.0 ms delay on the tweeter/midrange channels.

Another really, really big thing to try is to simply remove your tweeters from their top-hat locations (still attached to their crossovers) and place them on top of their cabinets, set back from the front with their magnet/horn throat areas aligned within 1/2 inch of the K-55 midrange driver beneath them. You don't need to wait to bi-amp to try this.

Trust me: your imaging performance will dramatically improve if you do this. You may need to set the tweeters on top of a book or some sort of spacer to raise them slightly, but only if you sit below the level of the midrange horns when listening to your Khorns.

An active crossover's EQ can be used to address bass bin FR peaks below 250 Hz, and perhaps some issues around 4-7 KHz. The Richard Heyser review of the Khorn will detail these issues.

Chris

Edit: Here is the tweeter time-alignment trick, except using a La Scala:

[DrWho]

However, I'm not a tube aficionado - I prefer Nelson Pass's approach using FETs for power amplification. There are many benefits and virtually no burdens to this approach.

I'm a fan of Pass's designs too, but I wanted to throw this out there....

Tubes actually have a larger linear region than the best solid state transistors. Pass has some very elegant transistor solutions, but you do get more linearity in the active stage from a tube. I'm pretty sure Pass would agree with that too.

That said, the design challenge with tubes is that they are high voltage, low current devices, which means you need a transformer if you want to take advantage of that linear region. Ironically, the transformer then dominates the linearity of the amplifier, and it gets progressively worse as you go lower in frequency.

[Chris A]

Tubes actually have a larger linear region than the best solid state transistors. Pass has some very elegant transistor solutions, but you do get more linearity in the active stage from a tube. I'm pretty sure Pass would agree with that too.

Mike,

I believe that Mr. Pass's notes on modified cascode design is apropos here (i.e., "modulated cascode" on highly loaded power FETs) - that is the real contribution that enables Pass's power FET designs. His designs are also pretty elegant, i.e., simple, and avoid the following issues that tubes have:

1) high output impedance (requiring feedback to lower) that usually results in having to add more amplifier stages.

2) exceedingly low tube reliability for my tastes (in fact, it's just silly).

3) resulting even harmonic distortion of low-gain single-ended tube designs with low dynamic headroom, or the not-so-good effects of cascaded push-pull gain stages in order to achieve sufficient feedback to lower the output impedance to something tolerable.

4) cost to achieve a really good amplifier design.

These are important considerations.

I urge listening to one. I've got one in the D/FW area... []

Chris

[Islander]

Some listeners have said that with bi-amped setups that use SS for bass and tubes for treble, that you can hear the tonal difference between the two power amp types, and that it distracts from the music.

Has anyone else experienced this?

My setup uses Class D amps for both bass and treble and it sounds pretty smooth.

[djk]

"Has anyone else experienced this? "

Yes.

The pace, rhythm and timing of an amplifier (PRAT) need to match.

PP and SET do not match up well.

Amps with no global feedback do not match up well with amps with global feedback.

[Taz]

Ignorance is my claim. Is this difficult to do with 60s and 70s amps.

I would presume in my case that Fisher 400 should be used for tweets

mc30s for mid range

and sansui or marantz SS for base, 100 + watt unit?

[*-)] I have read of digital active units. Confused. Output from CD player is analog as is turntable.

[Quiet_Hollow]

The pace, rhythm and timing of an amplifier (PRAT) need to match.

How would you recommend I accomplish this?

[Chris A]

The pace, rhythm and timing of an amplifier (PRAT) need to match.

How would you recommend I accomplish this?

Here is a link. This is too much of an esoteric subject for my contributions (note the UK spelling used):

http://www.audioenz.co.nz/2008/archive_storyofprat.shtml

It's been fascinating to watch the noted UK hi-fi reviewer Martin Colloms (

Hi-Fi News

) explore the same territory over the past couple of years. Colloms referred to "pace, rhythm and timing", which one

Hi-Fi News

reader cleverly dubbed "PRAT". So PRAT is how I now label these phenomena.

Before delving any further into the subject of PRAT, it would be useful to define a few terms.

Pace

Pace refers to the apparent musical tempo. I use the word

"apparent" with care, for if a metronome was used, the tempo would

remain the same no matter the hi-fi. Yet in different hi-fi systems, the

group of musicians can sound as if the ensemble are playing at

differing speeds. In some hi-fi systems, it can sound as if the

musicians are playing at a slower tempo or pace – downbeat instead of

upbeat.

This appears to correlate with impaired interest or involvement

in the music by listeners. Interestingly enough, in my experience hi-fi

equipment never makes music sound as if the tempo is too fast. The

effect of hi-fi equipment on tempo, if any, seems to be only to reduce

the pace or tempo of music.

Rhythm

Much music in our culture is built upon a rhythmic base. And yes,

hi-fi components can affect our perception of the rhythmical lines in

music. Way back in the December 1990 issue I wrote about the Creek 4140

amplifier’s ability to unravel rhythmical lines.

Although through a number of other competing amplifiers the piano

sounded tonally more accurate, through the Creek the musical lines, the

playing with time that a good composer and musician can bring, were

laid bare.

In comparing CD players and amplifiers over the years, I have

been perplexed at how there was more than just "sound"; that through

some products the music the music made sense.

A few years ago a friend was building an amplifier. Often he

would bring the latest version, along with an amplifier at the previous

stage, over to compare. One of my friends favourite albums was Peter

Gabriel's

So

. At one stage of the amplifier modifications, the Fairlight bass doodlings on one track (

Sledgehammer

from memory) suddenly stopped being merely tonal colouring, and became part of the rhythmic structure of the music!

Timing

If pace referred to the musical ensemble as a whole, timing refers to the individual musical parts.

"If the musicians are pleasing us we often say they were 'hot',

or 'the band were smokin'!", wrote jazz reviewer John Paul in the

February 1993 issue. A large part of this is down to the synchronisation

of the musicians or, as it is often described in the classical world,

their ensemble.

A group of musicians that are playing well tend to lock into each

other, creating music that is more than the sum of its parts. This is

as apparent in rock music, where the band can ride a groove, as it is

with a string quartet.

Yet some hi-fi equipment can dilute this musical energy.

Sometimes the lack of timing can be frequency dependent, as if the

drummer was playing the cymbals out of synchronisation with the rest of

the drum kit (or band, for that matter).

At its worst, it can be as bad as one system I heard playing the Oscar Petersen Trio's album

We Get Requests

.

On this hi-fi system, it sounded as if there were three separate

recordings: each member sounded as if they were playing vaguely the same

tune, at vaguely the same time. But they weren't playing together.

The audiophile dilemma

Many audiophiles have trouble getting to grips with these

concepts. I know I did, until I realised that PRAT was describing how

music exists in reality. The reason many audiophiles have trouble

grasping these concepts, I believe, is largely due to the training' they

receive. Reading hi-fi magazines, talking to audiophiles and conversing

with the staff in many hi-fi stores, reinforces that hi-fi is all about

the reproduction of tone and of space.

To make things worse, many of the products that perform well in

PRAT parameters have often performed less than wonderfully in the

traditional hi-fi checklists, sometimes sounding quite strident.

It has recently been put to me that the pace, rhythm and timing

that some hi-fi components reproduce is because they often aren't

wonderful tonally. In other words, that PRAT is a distortion.

So far, no

one has been able to explain to me how this 'distortion' manages to

find its way into live music performed by real people.

Listening for PRAT

Back in the early '80s, Linn's Ivor Tiefenbrun suggested that the

ability to tap your feet to the music, and to hum and sing along with

the tune, were among the most important attributes to listen for when

buying hi-fi. As often happened with Tiefenbrun's pronouncements, these

comments were widely dismissed by many in the audio industry. Even

though Tiefenbrun was right.

Although inexpertly put, Tiefenbrun's suggestions basically came

down to this: react to music played on a hi-fi the same way you would to

live performers. Instead of straining to hear the hi-fi parameters that

is the approach of most audiophiles to hi-fi, react to the music on an

emotional level. I now find that pace, rhythm and timing have become

necessary – but not sufficient – conditions for me to enjoy my music

through hi-fi equipment.

"Music, I feel, must be emotional first and intellectual second,"

said composer Maurice Ravel. So don't over-intellectualise hi-fi. Enjoy

it instead.

(Contents are copyright to AudioEnz 1986-2011. All rights reserved.)

[DrWho]

Haha, "PRAT" is just a term used by those afraid of the technical language of things like phase, distortion, frequency response, and all sports of other time-domain phenomenon that are difficult to put in the form of a spec (like power supply sagging and that rejection, for one). It is so much easier to just use the same amp on the HF as the LF, and I would argue will always sound more natural since they gotta blend perfectly at the xover frequency.

[djk]

"Haha, "PRAT" is just a term used by those afraid of the technical language of things like phase, distortion, frequency response, and all sports of other time-domain phenomenon that are difficult to put in the form of a spec (like power supply sagging and that rejection, for one). It is so much easier to just use the same amp on the HF as the LF, and I would argue will always sound more natural since they gotta blend perfectly at the xover frequency. "

99% of the readers are not engineers, and 99% of engineers cannot explain why two identical amplifiers running with different amounts of feedback will have different PRAT.

The best test equipment made is a poor substitute for the ear.

For the readers out there that do not have the time, money, and education for the test equipment route (that won't give you the answer you seek anyway):

"The pace, rhythm and timing of an amplifier (PRAT) need to match.

PP and SET do not match up well.

Amps with no global feedback do not match up well with amps with global feedback. "

[Colin]

Another difficulty is the enormous complexity of selecting
just the right cross-over points when active tri-amping. There are endless permutations
available and I am not aware of low-cost tools to automate this arduous task.

[Colin]

Passive dual-amplifiers does not bring the all of the benefits

of active bi-amping, but it does bring a lot of them.

In my case, the crossover

allows the bass bins to run a full-range signal. This means that separating the

Khorn bass bins from the crossover allows them to be run with a solid-state amplifier.

Even a small solid-state amplifier has better impedance control over the woofer

than many moderate price range tube amplifiers. Therefore, matching a solid-state

amplifier with a tube amplifier of the PROPER WATTAGE RATIO (ten to one) allows

the listener to enjoy tubes on the mid and high horns with solid-state on the

bass.

This configuration sounds better with either my vintage Harmon Kardon

330B receiver ($5 at yard), cheap class T amplifiers, massive Pioneer class A amplifier

($250) or even small Trends tube amps. It most certainly IS worth the minor expense

of the extra amplifier. It comes close to sounding as good as a $4k Pass X250

on my Big Ole Horns.

[Chris A]

Another difficulty is the enormous complexity of selecting just the right cross-over points when active tri-amping.

There are endless permutations available and I am not aware of low-cost tools to automate this arduous task.

For my tri-amped Belle center, I use approximately the same crossover points as the original passive networks, but with added crossover filter between the midrange driver and tweeter that is actually missing in the stock Belle crossover. It just takes seconds to change the settings to move the crossover points, relative driver gains, and parametric EQ filters, and most importantly, the relative delay of the drivers in order to time align them. This is a really big deal that you get only with digital active crossovers - delay correction due to differing horn path lengths.

Once I got my Belle dialed in, and not the least including the proper time delay setting between midrange and tweeter, the Belle blended in seamlessly between the two big Jub K-402/TAD TD-4002s.

Chris