How can bi-amping be done right? Have you played around?

[caesar]

I'm looking to bi-amp my MBL 101's. I'm thinking of running tubes for highs and mids and monster powered SS on the bottom to control the current hungry woofers.

Is the biggest key to success finding the appropriate tube and SS amps that have the similar gain? Within how many db does the gain need to match up so the top and bottom will not sound out of sync?


Is there anything else to getting this right?

 

[GaryProtein]

First, select a good active crossover.

The two amps DO NOT need to have the same gain because you can adjust their relative volume outputs with your active crossover.

Good analog crossover options are the PassLabs XVR1 (I love mine) which you can make as many "way" (2-way, 3-way, 4-way, more-way) as many you want, and the Bryston 10B-STD. If you want to go digital, there is the Accuphase.

Once you snip the wires in the speaker to separate the woofers from the midrange and tweeter, it's fairly straight-forward. Some speakers are easier to do this than others.

 

[caesar]

Thanks, Gary. But I'm not going to be replacing the MBL cross-over. Using the existing crossover, I just want to throw as much power as possible at the speaker, with a lot of SS power on the bottom and tube magic in the mids and highs.

 

[Alrainbow]

Then you need a preamp or source that can drive three amps at once. Now there you got me. As I'm sure it will work but there could be issues that I am not aware of. And if the amps do not have the same gain you have no way of controlling them separately. Just some thoughts.
Al

 

[garylkoh]

The main problem with using two different amplifiers on the top and bottom is that you completely defeat the loudspeaker designer's efforts at coherence if there is a difference in the group delay of the two amps. That is the reason I prevent my speakers from being bi-amped....... although my speakers mostly ARE bi-amped with a servo-controlled woofer amplifier. However, I take the crossover and group delay of the bass amplifier into account when I design the crossover of the mid/high frequencies.

 

[caesar]

The main problem with using two different amplifiers on the top and bottom is that you completely defeat the loudspeaker designer's efforts at coherence if there is a difference in the group delay of the two amps. That is the reason I prevent my speakers from being bi-amped....... although my speakers mostly ARE bi-amped with a servo-controlled woofer amplifier. However, I take the crossover and group delay of the bass amplifier into account when I design the crossover of the mid/high frequencies.

Hi Gary,

What exactly is group delay? Is there a metric that expresses it, or is it just about trying and getting lucky?

And also, what do you think about matching the gain within 3-5 db? How important is it in relation to group delay?

 

[garylkoh]

Hi Gary,

What exactly is group delay? Is there a metric that expresses it, or is it just about trying and getting lucky?

And also, what do you think about matching the gain within 3-5 db? How important is it in relation to group delay?

Group delay is the delay in timing between the signal entering the amplifier and it exiting the amplifier. It should not be matter at all, so I have not seen any specifications at all. The group delay of a transformer-coupled tube amp can be quite high.

http://en.wikipedia.org/wiki/Group_delay_and_phase_delay

You absolutely must at least match the gain of the two amps. Otherwise, the frequency response will be all skewed.

 

[Barry]

I was surprised by the improvement in sound stage of my modded Magnepan 3.6s by level matching right and left channels at the amplifier outputs rather than making adjustments by ear. To Gary K's point, I got even more coherence when I used two of the same exact amps for hi/mids as for the bass panels (I had been using a mix of tube hybrid and solid state class A designs). I think all this is a little less critical if you are talking about adding a subwoofer. I am using a solid state there but it is crossed over at 48 Hz or so. Like Gary P., I'm using a Pass Labs XVR-1-3 (in bypass mode).

 

[Phelonious Ponk]

I believe I'd ask MBL. They'll probably say "don't," but I'd ask. And I'd take their advice, even if it is "don't."

Tim

 

[microstrip]

Caesar,

As far as I remember the MBL 101's were current hungry in all the mid bass and medium frequencies, not specially in the low bass. The only ones I have owned were the old MBL 101c's that were tri-wired. I had a similar idea as the one you refer - two less powerful stereo tube amplifiers for each medium and treble and another very powerful solid state amplifier for the bass, but it was a complete disaster . At that time the best sound I got from them was using the old Mark Levinson ML23.5. But after reading Michael Gindi and friends opinions in magazines we all dreamed about the CAT's ...

 

[Robh3606]

Don't even consider biamping unless you know the correct voltage drives for the high and lowpass filters. If they don't match you are not going to get the same result. Are these 3 way speakers?? If they are and you take out high pass on the midrange driver you are going to have to adjust the remaining poles and potentially any EQ as well. It can be done but not without some work. Best bet would see if you can get the voltage drives and any modifications to the existing network required from the manufacturer.

Rob

 

[DonH50]

Retaining the speaker crossovers defeats one of the main reasons to bi-amp... Directly driving the drivers allows much lower driving impedance and allows you to use a higher-order crossover and processing to align phase and optimize the response.

I bi-amped my Maggies for many years but they (Magnepan) specified a low-order crossover even bi-amped, meaning lots of interaction between bass and mid/treble amps and panels. As a result I looked a long time to find a SS amp that would match my tube amp (ended up with an ARC D79 on top and Counterpoint SA-220 on the bottom). I sacrificed some low-end tightness to get a smoother blend. Other speakers I bi-amped, I used a higher-order crossover before the amps and matching amps was much less important. As I've said before, this is quite dated experience so may be irrelevant these days.

As others said, gain matching is easy to do in the crossover. To match phase and group delay you may need to use an active (DSP-based) crossover. I have done it in the analog realm with an all-pass stage, but these days I'd get a DSP-based unit.

FWIWFM - Don

 

[LL21]

I was offered by an engineer who knows Wilsons intimately and was a well-regarded speaker designer to biamp the X1s. After speaking with several professionals I trust, I came to the conclusion (supported unanimously by these professionals) that this individual could do it and the benefits would include greater power, effortlessness and linearity/coherence.

However, we also came to the conclusion that doing so would require me to go back to this individual if we ever moved, or moved the speakers...and certainly if we were try to resell them, we'd need to put them back the way they were.

I have thus declined to move in this direction, but after speaking with many people, they convinced me that if the person doing the work understands the various key technical requirements of the drivers, the phase implications of making these changes, etc...it can be done and to great positive effect.

 

[caesar]

Gentlemen, thanks for the replies. As I understand, MBL only does passive bi-amping. I have no desire to mess around with the speakers. The last thing I want to do is trust some hacker with a soldering iron. As far as I understand, MBL gives 3 amplifier options:

1 - run in a stereo amp
2 - run monoblocks
3 - run 2 pairs of monoblocks

I understand that this is a business, so I know what MBL would tell me: buy more of their amps. I also understand that some people call passive bi-amping "fool's bi-amping". However, having owned very inefficient speakers, I'm of the belief that the fools are the ones who choose not to add enough power to their power hungry speakers. The reality is that power makes the music come alive. When driven by adequate power, the amp's control over the woofer gives you much more realistic dynamics. With enough power, drums that used to sound like pitter-patter can now sound like you are right there with the band. The tubes on top can complement with holography and midrange magic.

I am not a pious man, but I will say prayer and give the tubes on top/ SS on the bottom combo a try.

 

[microstrip]

Caesar,

IMHO, it is not a question of prayer, but of competence and expertise. I have no doubt that it can be done with success. However, if someone just asks in a public forum the very basic questions, and particularly if I know that this person is addicted to the seamless sound of full range single panel electrostatics I feel that the probability of success will be very low, even with the help of Saint Patrick and Saint Cecilia.

 

[DonH50]

To offload the bass from the tube amp (and highs from the SS amp) add an active crossover before the amps. That way you can still drive through the speaker's crossover and get the headroom benefit of bi-amping.

Make sure the amplifier outputs are in phase. IIRC my old ARC inverted phase to the 4-ohm tap, but in general not all amps maintain polarity so it's a good thing to check. If one inverts and the other does not, simply swap +/- connections at the amp or speaker end of the cable for one amp.

 

[ddk]

Gentlemen, thanks for the replies. As I understand, MBL only does passive bi-amping. I have no desire to mess around with the speakers. The last thing I want to do is trust some hacker with a soldering iron. As far as I understand, MBL gives 3 amplifier options:

1 - run in a stereo amp
2 - run monoblocks
3 - run 2 pairs of monoblocks

I understand that this is a business, so I know what MBL would tell me: buy more of their amps. I also understand that some people call passive bi-amping "fool's bi-amping". However, having owned very inefficient speakers, I'm of the belief that the fools are the ones who choose not to add enough power to their power hungry speakers. The reality is that power makes the music come alive. When driven by adequate power, the amp's control over the woofer gives you much more realistic dynamics. With enough power, drums that used to sound like pitter-patter can now sound like you are right there with the band. The tubes on top can complement with holography and midrange magic.

I am not a pious man, but I will say prayer and give the tubes on top/ SS on the bottom combo a try.

You can pray as much as you like Caesar but this is one of those unions that won't be blessed!

Bi-amping/multi-amping has many advantages when done right, specially with power hungry speakers like yours. You can do active or passive bi-amping but you CAN'T mix tubes and ss amps on a full range speaker and expect coherent results, period! We've been selling and setting up multi-amped systems for years and even when adding subs for lower frequencies to a tube driven quality full range speaker there are subtleties involved and audible nuances when trying to mate even the best solid state class A amp with a good tube amp, and this is with lower and low frequencies. If I'm not mistaken the MBL's crossover at above 100hz, you'll hear everything that is wrong with such marriage. Besides I don't know of any tube amplifiers that can properly drive any part of your speaker. In your case and any passive bi-amping you have to use the same amplifiers on both top and bottom. One caveat, if your system is bound up with typical colored audiophile cables, cords and certain tweaks and you're not hearing your electronics anyway you'll probably won't hear the mismatch of the amps either.

david