Question about byamplification

Hi guys

A question for those with experience and knowledge.


I'm thinking about experimenting on byamping with my valve amp, the Line MagneticLM-508, and a class D power amp I have, both driven by my Audio-GD HE-1 preamp.


As my speakers, the Q Acoustics Concept 500, have two pairs of binding posts, I was thinking about connecting the LM-508 to the highs binding post and the class D to the lows ones of the speakers.


I don't have an active external crossover, so I was suggested on splitting the RCA output of my preamp to both amplifiers. I know that I will probably have trouble matching the gains of the amps as they are likely different, but I have tubes with different gains and also the LM508 has a knob with different negative feedback settings (different gains) so I can try to match them, at low volume levels of course.


The one millon dollars question is if I'm risking on blowing a tweeter with the LM-508? The speakers manufacturer said I should be careful since the LM-508 will only be running the tweeters and it could "see" a high impedance load at frequencies below the crossover point (2.5 Khz).


On the other hand, people with experience on byamping told me that it should not a risk, I should only start with low volume levels and go up carefully.


Has anyone experienced something similar? Am I risking the tweeters or the amps?


Any thoughts or suggestions are appreciated.


Get a crossover. The DBX is a very affordable unit and works great. Model 223XS. I run a similar unit on my big system and it works good and solves all crossover issues. 

Well, there is something I don’t quite understand.

If I connect one amp to the highs binding posts and the other amp to the lows binding posts, the internal crossovers of my speakers will divide the frequencies at 2.5 Khz. So, what’s the point on adding an external crossover if I won’t be able to change the crossover point at the end of the chain.

I guess external crossovers are for speakers without internal crossovers. Am I missing something?

I guess external crossovers are for speakers without internal crossovers. Am I missing something?

Setting levels for two different amps.

To do it right, you need an external electronic crossover, like a Marchant crossover (see link below). You are going to have to disconnect at least the bass driver from the passive crossover. Not sure if your speakers are 2-way or 3. If 3-way, you can leave the tweeter and mid connected to the passive crossover. You going to have to find a way to deal with the gain level between the two amps. When you are done, your speakers will sound like they cost at least 5 times what you paid for them, I kid you not.  The point of the electronic crossover is that it will address the weakest link of your speakers, namely the passive crossover.

Thanks for the answers.

Yes, that's a good idea, but for now I would like to know if I can try byamplifing with the passive crossover of the speakers without risking the tweeters or the amps.

The point of biamplification is to allow the amps concentrate on the frequencies specific to the load. So you need to cross over the signal before it gets to the amplifiers. You need the electronic crossover if you are to do this right. 

plga--I used a similar amp to yours, the JAS Array 2.1, also using 300B and 805 tubes for several years.  I used it in a biamp set up using Legacy Focus clones and it drove the midbass, midrange, and tweeters beautifully.   I never ran it full range so have no idea of the bass quality but it reproduced the best mids I've ever heard in my system(s) and could float a most tangible 3D soundstage.  However, it, and the other tubed amp(s) I had,  the VAS Citation II, weren't the best at reproducing extended treble.  Both amp nailed the critical midrange and had surprisingly dynamic mid bass but neither seemed to fully reproduce the top end.  It seemed slightly truncated although never veiled.  So, with that in mind, I must ask if running your Line Magnetic just to the tweeters might not loose much of that 805/300B magic that makes these amps so wonderful to listen to?

With regards to biamping using the LM and a Class D amp for the woofers, you can  do it without an outboard/electronic crossover by having another volume control.  For me, it was an integrated amp for the woofers so I could control their output and later a small Kingrex preamp driving a D-Sonic M3 600S.  I would dial in the bass level via the Kingrex pre and control the system level using my DAC volume control.  You could pick up a small preamp to do this as well, maybe even a headphone amp/preamp although the extra circuitry and interconnects might reduce the transparency of your system.  After all, that's one of the major benefits of using  SET amplifier. 


I recently bypassed the crossover in my speakers to the woofers running them directly to the binding posts and using an electronic crossover, the NHT X1 and it was a noticeable  step up plus the NHT X1 has a volume control on it so I pulled the extra preamp out of my system.   Either way  should let you biamp.  You might not appreciate having the Class D amp reproducing the mids though.  Best of luck with experiment.

you don't need external crossovers to biamp so long as the most powerful amp has gain control. Many will tell you that you do.  Those of you who think your internal crossovers should do the job are correct.   

As I interpret the OP question, and i don't know  the answer, since his speakers are 2 way, and the tube amp will just be powering the tweeter, so  the tube amp will sometimes have very little load on it.   can it be damaged from that (like a tube amp can damage transformers if running without a load on them). 



Yes you can. That’s perfectly safe. Most refer to this as bi-wiring. By the way, it’s bi-amping not by-amping. But people who have actually done both would tell that bi-amping is the next level. In fact, it’s not even close, the difference is noticeable and worth the trouble. Good luck. 

your speaker’s crossover is prepared for biamp. you only need a volume control for the strongest amp, cut it to match the other amp.

I would buy an in-expensive SPL meter to help with the adjustment.

hole for tripod mount at seated ear height, ...

better yet, find a remote volume control.


later (or now), sell your class D, get a pair of mono-blocks with volume control on them.


another way is to control the volume after the amp, on the way to the speakers


made for adjusting levels of amps of car woofers



Here's an article from JBL about BI- Amplification that might help.



So, what’s the point on adding an external crossover if I won’t be able to change the crossover point at the end of the chain. I guess external crossovers are for speakers without internal crossovers. Am I missing something?

A bi-amp or tri-amp systems are a big-boy playground. There are a number of reasons to use a proper crossover even on a loudspeaker that has an internal crossover. Most have already been discussed. A proper crossover will give you flexibility that a mere volume control can't do. You can affect the built-in crossover to some limited extent and you can simply bypass the internal crossover for full control. Running both amps full range is eliminating one of the reasons to bi-amp in the first place. There is a difference between being ABLE to do something and doing something the right way. If you are going to all that effort to bi-amp you should want to get the maximum out of that configuration. 

OK, I said my piece.   



There are two ways to BI- AMP a loudspeaker, you can passive BI-AMP or

active BI-AMP, the article below explains the two ways. I prefer active




There are actually 3 ways, passive, passive line level and active line level.