What resistor value to put in an NHT X2 Balanced Crossover

[BonkM]

Hey guys and gals,

so I've got an NHT X2 balanced, active crossover. I haven't had my speakers shipped here yet, but I'll be hooking it up via XLR to a pair of Emotiva Pro Stealth 6s and a pair of SVS SB-13 Ultras via XLR for the low end.

I've read here and there that adding resistors to the crossover in certain places can make them sound better. I've got no clue, and the crossover wasn't too expensive, so I'd like to fiddle with it. I'll also be putting a toroidal transformer in it at some point, so get rid of its wall-wart brick. But that's for another thread at another time.

So, what should I do for resistor values? I'll be hooking the entire time up via XLR cables, so there's not too much point in discussing what to do with the RCAs or single ended stuff. Here's a schmatic of the NHT X2, on page 3 of the link. There's also a little typo, there's 2 "L HP Out"s, one of them is clearly supposed to be a "R HP Out".
http://www.nhthifi.com/site/pdf/X2_Manual.pdf

The resistor brand I have in mind is PathAudio, and I'll be getting a discount on them, so the price is more reasonable.
resistors_path.html

There's also a neat thread here, where the guy replaced the OP-amps, which I'd also take a shot at if I had it opened up and were messing with it anyway.
Modded NHT X2 crossover - AudioKarma.org Home Audio Stereo Discussion Forums

So, please give me some tips about the resistors; where, how many, and values. And anything else you might be worth while~ :-D

Thanks,
Ben

 

[SY]

I've read here and there that adding resistors to the crossover in certain places can make them sound better.

You need to find better places to read. If the crossover frequencies and slopes are correct for the speakers you will be using, leave it alone. If you need to add EQ, change the frequency range, or otherwise alter the transfer characteristics of the crossover, it's a major job that will likely cause the crossover to no longer work unless you know what you're doing. It's also a major job to determine exactly what the target will be, which involves careful speaker measurement and analysis.

Changing brands of resistors will make the crossover work not even a little bit better and risks destruction. The NHT units are very well engineered, and the likelihood that some random guy posting on the Internet has come up with a significant improvement that the smart engineers there hadn't thought of is remote.

Here's an example of the sort of thing I'm talking about:

Biamping the NHT M3.3, p3

There is a specific target, analysis of what has to change to hit that target, and the modifications were cross-checked with the NHT guys who designed the unit in the first place.

 

[AndrewT]

read up on the Sallen and Key filter topologies.
Then look at the filtering in your bought in crossover.

The X2 has put all it's efforts into the bass channels/s

There are two tiny areas for the two main sound channels and all it shows is a stepped variable filter for all the upper bass, mid and treble.

This is not really a crossover.
It is a low bass processor/ driver.

 

[SY]

Andrew, that is not correct. It very much is a crossover, with a specific set of HP transfer functions. The bass channels add EQ and phase control to the LP filter. Topologies are a mix of Sallen-Key and gyrato/NICr.

 

[AndrewT]

Are you sure?
There appears to be switchable HP filtering @ 50, 80 and 110Hz
There is no other information nor front or rear panel controls for the HP sections.
These are the two Satellite channels.

All the rest is for processing the low bass channel/s

 

[BonkM]

I'm still digesting what you guys have said and I'll have to answer later, but for now, here's a MUCH more detailed schematic from a guy that was posting on here about replacing the LM833 OP-amps.

http://www.diyaudio.com/forums/analog-line-level/205533-replacement-lm833-active-crossover.html

 

[SY]

Are you sure?

Since I have one, yes. All that's needed for the HP is the filters.

 

[SY]

...here's a MUCH more detailed schematic from a guy that was posting on here about replacing the LM833 OP-amps.

See the schematic at my link above.

I would very much recommend against changing out the opamps- very easy to screw up the boards, the result may or may not be stable, and the audible performance will likely not be better.

 

[AndrewT]

Since I have one, yes. All that's needed for the HP is the filters.

Since you have one, can you confirm this is a Low Bass only processor/driver?

Can you confirm that the satellites are fed with a wideband signal starting with the High Pass Filter set to 50Hz or 80Hz or 110Hz and there is no crossovers for the satellites, no EQing for the satellites, no processing to massage the satellite acoustic frequency response to the desired crossover handover to the low bass speaker/s?

 

[SY]

Since you have one, can you confirm this is a Low Bass only processor/driver?

I cannot confirm this because it's untrue.