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Old 9th January 2003, 04:43 PM   #1
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Default Q:balanced output preamps with active crossovers

My question is if you are using a balanced out preamp, e.g. BOSOZ, Aleph P1.7, and active crossovers right after the preamp, don't you need to have balanced active crossover stages, which would probably mean almost double the crossover components? Not to mention the added complexity if you have more buffered stages ? Let's hear from people that had implemented a balanced system with active crossovers.

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Old 9th January 2003, 05:12 PM   #2
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I put a passive LC filter in front of the BOSOZ. This recquires two BOSOZ's, one channel for high and one channel for low times 2. My DAC does not have balanced out.

The BOSOZ then acts as buffer as well as Preamp...what is neat is that you can easily control the levels of the high and low channels using the internal gain controls of the BOSOZ...and you do not change the impedence that the filter is looking into as you change levels.

Doing it this way also elimates all those buffers that you have with active crossovers. The signal goes from DAC to LC filter to BOSOZ to Aleph amps to North Creek Music system Rythm speakers (Scan Speak Revelator tweeter and Scan speak 7 inch woofers)

Bi-amping is clearly the way to go, with out doubt.
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Old 9th January 2003, 09:35 PM   #3
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There are several ways to handle this.
One is to do what Nelson appears to do in the XVR1. Take in a balanced signal. Toss one phase. Do the filtering. Recreate the other phase at the output.
The other is to keep it competely balanced all the way through, which will indeed require more components. As a variation on this you can use one set of caps in a 'flying' configuration that takes care of both phases at the same time. However, you are then forced to use balanced signals always with that layout (unless you want to create a balanced signal, filter it, then throw away the unneeded phase at the output).
Because I am a sick, deviant individual, I intend to build an X crossover. Completely balanced, all the way through, with Nelson's X topology incorporated into every stage. I've done a little work along those lines, but most of my time at the moment goes into the preamp.

Grey
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Old 9th January 2003, 09:50 PM   #4
dms is offline dms
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Default Balanced Pre-Amp plus xover

I am having the same difficulty trying to design a pre-amp with multiple inputs, outputs, any to any switching, and with electronic crossovers on some outputs. This is due to the fact that I want to use the preamp to drive stereo, surround, and background music in my home. My question regarding the balanced crossover is that if you use passive components between buffer stages, do you just duplicate the values for balanced operation? Can anyone shed light on this?
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Old 10th January 2003, 10:04 PM   #5
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In my BOSOZ I've implemented an integrated doughter board to host a passive crossover. The thread is here:
Blue BOSOZ

That was thought as a three-way system (bass-mid-high) and all crossover outputs unbalanced... but then I built the SOZ and found a very very good two way speaker...

So the current setup is with a balanced SOZ (using bass-mid RCA's) and a SE valve triode (unbalanced) amp for upper highs. There is no filtering for the SOZ (as in the original speaker crossover) so things are simpler... but not easy.

Among all the other problems the SE amp is unbalanced, so filtering only the + BOSOZ output lowers it's level while the - one remains unchanged... no way, the SOZ sounds harsh and hard with that. You have to lower the - output by the same amount to make it work as it should. It's some time I'm fighting with this setup and there is not a clear winner yet.

I agree that multiamping a system is the way to go, air, openess, scene, dynamic... almost all improves. The best system I heard was multiamped. But elevating this qualities and still keep the overall feeling of "ONENESS", a homogeneous yet natural sound is another matter entirely. Multiamping can sound impressive easily... but "right" very seldom. In my opinion the tuning work here is almost the "real" work.

In this regard I frankly don't think that active crossovers using op-amps are the way to go. The op-amp itself introduce huge amounts of negative feedback... something that one (at least me)tries to avoid everywhere. I used an active crossover, mind you, I still own one, but it just does not seem to be able to sound "right", no matter what.

ciao,
Roberto Amato
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