Tips and tricks of Bi-Amping.

Bi-amplification or bi-amping is a technique of using two or more separate amplification channels for each speaker.

Although bi-amping requires bi-wiring (that is, using two or more pares of speaker cables for each speaker) as you now understand, bi-amplification is totally different from bi-wiring.


Speaker bi-wirring. The upper terminals lead directly to the crossover’s high pass filters that drive the midrange and the tweeter. The lower terminals lead directly to the crossover’s low pass filter that is connected to the woofers.

Also, bi-amplification is different from bridging (bridged mode is available at some models of stereo power amplifiers so they become mono with increased power and then using one bridged power amplifier per channel). Sure, when bridging an amp you get maximum output level. But remember: the life of your amp becomes harder. At bridged mode, your amp will see an 8 Ohm load like a 4 Ohm load. We want to achieve top performance here, not a maximum decibels so that is why I strongly recommend you for Hi-Fi home use to stick with bi-amplification.



This power amp allows bridged (BTL) operation.

You can have passive or active bi-amping


Passive bi-amping.

• Passive bi-amping relies to the passive crossovers that your speakers have for the frequency separation. Each amplifier channel will see an infinite resistance at a certain part of the audio frequencies. For example, the amplifier’s channel that is connected at the woofer terminals of an X Ohm speaker will see X Ohms at the low end and infinite Ohms at the high frequencies.



Active bi-amping (one channel) with the use of an electronic active crossover.

• Active bi-amping is the ultimate bi-amplification method if applied correctly. It requires that each amplification channel will be driven by an active crossover so you can by-pass the speaker’s crossover – a circuit that is notorious for limiting a speaker performance. It is very common to find this concept at serious car stereo installations where the subwoofer does not have any kind of passive crossover, it is directly connected at a power amp that is driven by an active crossover and this is why the amp is outputting only the low frequencies. Active bi-amping gives you total control but it requires some effort and a lot of adjustments. If you do a mistake like allowing the bass to go out from an amplification channel that is directly connected with a tweeter you can easily burn the tweeter driver.

In this post I will focus on passive bi-amping, something that anybody can easily do if he has two stereo power amplifiers and a pair of speakers that allow bi-wiring. So from now on, whenever I say bi-amping I mean passive bi-amping.

The idea behind bi-amping is to make the life of your amplifier easier. Each amplifier channel will provide power for only a certain part of the audio frequencies and will drive fewer speaker drive units. This way for example, the channel that plays the upper frequencies will not be stressed when there is also a lot of low frequencies.  Also, when the power amp has only one power transformer for both channels, this transformer has to provide the current for the left and the right channel sets of woofers. With bi-amplification, each transformer has to worry only for one set of woofers. Now, in the case your power amp has one power transformer per channel, the advantages of bi-amping are somehow limited. Still, with bi-amping each transformer has to take care of a smaller number of speaker drivers.

Let me point out that it is better to have two identical power amplifiers. If you have different amplifiers, things become complicated. First of all, the amp that will be connected at the woofers needs to have one transformer per channel. You will also have to take care of different input sensitivity that each amplifier has and that will require at least one of your power amps to have attenuator potentiometer. Apart from all that, I prefer the homogeneity in sound that two identical amps can provide. I don’t want to introduce possible phase differences of two different designs.

Before making any connections and disconnections to your amplifiers, please make absolutely sure they are turned off!

So, let’s start first with the simple questions of bi-amplification.

Does bi-amping guarantees that my power amps will play better?

Well, even though it does not guarantee it, chances are that they will. I am aware of only a few exceptions that the power amp did not like bi-amplification and that happened because it did not like to see an infinite resistance at some frequencies. As I said, this is a rare exception.

Another thing is plain economics: let's assume amp model X costs 2k Euro. For two model X amps you have to spend 4k Euro. But maybe, there is model Y from your favorite manufacturer that costs 4k Euro; there is a chance that a single Y model plays better than bi amped model X. I mean, yes, two bi-amped model X amps play better than one model X but hey! In some cases, you better spend your money at buying one unit of model Y rather than two units of model X.

What benefits should I expect from bi-amplification?

You should expect a more relaxed, easy listening but better focused sound. Even at low listening levels, the low end becomes richer and better controlled. You will be able to fully enjoy and feel the music from lower listening levels.

My pre-amp has only one set of outputs, what can I do?

You can use Y connectors so you double the outputs. However, not every pre amp will like that. If a pre-amp has two set of outputs then it is designed to deal with the lower resistance that it will see through these outputs, so you have nothing to worry about. Still, even with one set of outputs, a proper designed pre-amp will have no problem to drive two sets of power amp inputs, so most probably you still have nothing to worry about. However, you have to make a listening test for yourself. Sure thing is that you do not have to worry about damaging the pre-amp – the Y connectors are perfectly safe to use.

Is it better to have long interconnects and short speaker cables, or vice versa?

It absolutely depends from the design of your pre-amp. The safe side is to keep the interconnects short and the speaker cables long. This is because the interconnects carry low level signals that are more vulnerable. However, if your pre-amp is designed to deal with long interconnects please go ahead and place each power amp near to the speaker it drives!

I have power amps with one power transformer. Can I use one power amp for the low end and the other power amp for the high end?

Well, this is the worst thing to do. You see, we don’t want to connect two sets of woofers to one transformer; we will make the life hard for this transformer for no reason at all!

Now we got the basics, let’s see the tips and tricks of bi-amplification. Bi-amping gives you the opportunity to make a nice fine-tuning at your system in order to deal with the below tolerances:

• Preamp balance tolerances: Except in the case your pre-amp has a ladder volume control, every pre-amp has a slight different output per channel, meaning that one channel plays a little louder than the other.

• Power amp balance tolerances: Almost always you will see that the power amp has a little different sensitivity between the two channels, meaning that one channel plays a little louder than the other.

• Tolerances between two identical power amps: Almost always you will see that even two identical power amp have a little different sensitivity between them, meaning that one power amp will play a little louder than the other when they are feed with the same input signal.

With bi-amping you have the chance to minimize the effect of these tolerances. Also, you will have the chance to micro-fine tune the sound of your system. For example, if you find that sometimes you wished for a little softer sound, then just drive the mids / tweeters with the most insensitive channel of each power amp. So, let’s see what I call the ultimate guide in the art of bi-amping.

You will need an accurate multimeter and a reliable signal generator (or you can download a signal generator app at your smartphone, tablet or laptop).

Disconnect the speaker cables from the power amps. Unplug the power amps signal interconnects from the preamp and connect your signal generator at a stereo line input of your pre-amp. If your signal generator has only one RCA output, use a Y cord and double it. When you have “tone bypass” or “line direct” function at the preamd, please use it. Do make sure that your signal generator (or smartphone / tablet / laptop) is connected to the mains; we do not want the discharging of the battery to create variations at the output level of the signal generator.

Connect your headphones to the preamp. Choose a frequency of 1kHz, turn the preamp’s volume up to a usual listening point (so we can measure volume potentiometer’s channel tolerances at the point of your average listening level) and start increasing the output level of the signal generator until you get a normal listening volume from your headphones. The aim of this is to make sure that you will not overload the input of your preamp, neither have a very low signal. So, when you are done with the volume settings, disconnect the headphones and turn on the pre amp’s line output.

Now, with the help of a naked RCA plug, measure the output level in Volts AC of preamp's left and right channel. Make sure that you will not short circuit by mistake the output of the preamp.

By now you know which preamp channel sounds louder.

Now, with the power amps turned off, connect the signal generator directly at the stereo input of one power amp. If your power amp has attenuators, put them all at 0 positions – that is, the loudest position. Put the signal generator at 0 volume and then turn on the power amp. Start measuring the output level in Volts of the speaker outputs. Increase the volume of the signal generator until you get around 10 Volts at the speaker output. Make sure that you will not short circuit by mistake the output of the preamp. Wright down the values you measure and proceed to the other power amp without changing the output volume of the signal generator at all. Please remember to turn off the power amps during connection and disconnection of the signal generator.

By now you also know the sensitivity of each channel of each power amp.

So, let’s see an example:

• The pre amp output is louder at the R channel.
• Power amp 1 has output 10.06V at L channel and 10.12V at R channel.
• Power amp 2 has output 9.41V at L channel and 9,34V at R channel.
• You would like the sound of the system to be a little softer on the high end.

So, ideal set up for the example above would be:

• Power amp 2 goes to the R channel - we connect the most insensitive power amp at the channel where the preamp gives a higher output.
• Power amp 1 goes to the L channel - we connect the most sensitive power amp at the channel where the preamp gives a lower output.
• Power amp 1 gets the midrange / tweeter at his L channel and the woofers at his R channel - since we wanted the high end to sound a little softer, we connect the midrange and the twitter to the power amp's channel that is less sensitive.
• Power amp 2 gets the midrange / tweeter at his R channel and the woofer at his L channel - since we wanted the high end to sound a little softer, we connect the midrange and the twitter to the power amp's channel that is less sensitive.

So, here it is. You have set up your system for bi-amping in the best possible way.

Now, you might think why all this fuzz, if the power amps have attenuators you can use them to compensate for possible intolerances. Well, doing so is not the best way. You see, correct designed attenuators at the 0 position are like a short circuit, they virtually don’t exist. You do want to take advantage of that. Also, you don't want your pre amp to see different loads between his stereo outputs. The above connection method gives you optimum results without any kind of side effects.

A last tip for the few owners of power amps with two power transformers and selectable Class A / Class AB operation.


Power amp with one power transformer per channel.

In the past, my good friend Panos had two Pioneer M-73 power amps. Those wonderful amps have one transformer per channel, selectable Class A / Class AB operation and the same sensitivity at both Class A and Class AB mode – meaning that for any given input signal of X volts you get Y watts output, no matter if you are at Class A or Class AB operation. Class A had of course less output RMS power.

The Pioneer M-73 power amp has a Class A / AB selector.

All these mean that you can connect one power amp for the woofers of both channels (since you have two transformers per power amp, even at this case each transformer takes care of only one set of woofers) and the other power amp at the mids /tweters of both channels. This gives you the advantage of selecting Class AB at the power amp that drives the woofers and Class A at the amp that drives the mids / tweeters. So you have the dynamism of Class AB for the low end and the warmth of Class A at the mid & high end. This setup is a very versatile one.

This same amp is very good for bi-amping your center channel at your home cinema. You can instantly choose Class A for a musical or a jazz concert and Class AB for an action film.

Happy listening as always!

Christos