2. amps-preamps
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Passive bi-amp question

I understand this might have been discussed in the past, but wanted to get some better insight as to doing it correctly. I am looking to biamp (passive only, not crazy about active biamp) my speakers. I have MA PL500II, and after discussing with monitor audio, they strongly recommend passive biamping. Trust me, these speakers are already amazing with just stereo amp driving them now. I am trying to push the envelope to see if I can get best out of it. 
I am looking to use different amp brands for biamp. I know, ideal will be to use same amp or at least same company amp, but wanted to see if anybody have done passive biamp with different brand and what was their experience, pros, cons and how did you guys made decision while selecting different amps.
What are the amp specs that needs to be matched (or closely matched). Is it gain, input sensitivity, input impedance, watts per channel. Or in other words will results be still good if the amps have different gain, impedance, sensitivity and wattage. Anything else should I be looking for. Any valuable thoughts will be appreciated. I will be using same power cords and speaker cables in both (including the lengths). 
Currently I have thrax dionysos preamp with audia flight strumento no.4 mk2. 
romney80
georgehifi's avatar
georgehifi
10,312 posts
 
romney80 OP

Yogiboy is correct, just use a $49 Schiit Sys https://www.schiit.com/products/sys on the louder amp if both amps are not the same gain, so you can make them the same with it.
Then drive the lot with your main preamp.
Here is how to wire it up https://ibb.co/x6dKF0N

Cheers George
romney80 OP
150 posts
 
Ok. 
The gain of my current amp is 29 db, input sensitivity is 1.4 volts RMS, impedance is 7.5 kohm, damping factor (at 8 ohm) >1000, power output 250 watts at 8 ohms.

I am considering Luxman M-900u, which also has gain of 29 db, input sensitivity of 1.24V/150W (8ohm), input impedance of 34 kohms (balanced), damping factor of 710, power output 150 watts at 8 ohms. 

The gain seems to be matched and input sensitivity seems to be close (even though different watts power at 8 ohms). Will this be acceptable for biamp with my current amp ?.
georgehifi's avatar
georgehifi
10,312 posts
 

romney80 OP

Yes close, you may not need the Sys, but get it anyway as it comes with a trial period, so you can send it back, it is only $49

If it’s on the bass amp, then you "can" raise it slightly for those "bass shy albums", or lower it slightly if it’s on the treble amp.

And yes I’m also against active bi-amping as it sterilizes the mids and highs, it’s ok on the bass though and use the speakers passive xover on the mids and highs.

Cheers George
romney80 OP
150 posts
 
@yogiboy and @Georgehifi. 
Thanks for those suggestions. I would rather not do that, unless that is the only option. But, in the meanwhile, I will dig deep into this. 
erik_squires
16,164 posts
 
The thing to keep in mind, with amps, is that the gain specification measurement is just not that important to makers.

That is, maybe they will specify 29 dB but maybe it’s 28.5 and maybe it’s 29.7.  It's rarely 29.00 dB

Since 99.9999 of their customers will use 1 stereo amp, accuracy here is just not that important. I’m sure it is consistent among the same model but across different models or makers probably not.

So, good to have some way of measuring the relative gain and adjusting if wrong.
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