high pass filter options

Hi all, long time reader here- first time posting
I recently added a sub to my 2 channel system. I have been enjoying it for awhile but want to experiment a bit. Im working with Canton vento 9k bookshelves, my amp is Mcintosh ma5200 (various sources hooked up). the sub is a canton 12.3. room is treated as best as possible. I have always kept the sub crossover and volume low so it just be there to supplement the speakers. I want to instead run the speakers in high pass (100hz preferred) and keep the lows for the sub to deal with. I know its a debate to do this or not but figured to try it out. The speakers do not have a crossover on board as some canton's do, I just have them bi-wired straight to the amp. The amp itself is an integrated so im having trouble figuring out how to make it work without connecting an active external crossover. I have read Connecting an external crossover it may alter soundstage that im used to coming from the Mc. 
I don't want to run the speakers thru the sub, even if I could because the sub does not have a hpf output. It only has low pass input/out rca's and line level inputs. I currently have the sub tapped into the output posts of the Mc.
Options im considering is a couple rca line hpf crossovers from the preamp output of the amp to the pwramp input. Though with this option I don't know how I would then connect the sub as the speaker outputs would lack the low end that the sub is connected to. 
Another is to use a y-splitter at the preampt output to run the sub then connect the hpf after, but I am concerned this would degrade the sound in the end.
Lastly is it possible room correction or something like it could work? a more pricey choice like a lyngdorf I could run the speakers and sub independently while using its crossover, but again I would be investing in something that could take away the natural sound of the Mc amp. I want to keep it all simple as possible but cant figure this one out.
Any input or suggestions are much appreciated. Matt
 Putting a digital crossover in between the preamp/amp ports is indeed the best route.

A MiniDSP SHD is <$100, includes DIRAC (though REW to get it initially setup still needs to be done), and it’s DAC clean enough (SINAD better than 109dB, it’s like Signal-to-Noise Ratio, this also includes distortion) and powerful enoguh (2Vrms, your McIntosh only needs 1Vrms).

I always recommend DSP for subs in a quality setup (unless you aren’t tech-savvy), as dual/ten/quad subs and even a good amount of bass traps still won’t be perfect (neither is DSP, but helps get you there).
I use this HSU high pass filter. It works fine in my system!
Hi OP!

What I suggest instead is that you use a MiniDSP to optimize your sub's output.

The contra of this solution is a single one: Your main amp and speakers won't gain any headroom.  Unless dynamic headroom is an issue for you, this is a good feature to loose.

However, the pros are numerous, like staying out of your main audio chain, and optimizing the subwoofer, letting you raise the level, and blend in seamlessly.  The MiniDSP will act as a crossover AND digital EQ, letting you clip the peaks. If used in conjunction with bass traps you may even be able to fix nulls.

If you must have an inline high pass filter, the Hsu is probably good enough, but it's another set of opamps and cables, and power supply, along with not being able to EQ your sub, a feature most rooms sorely need.


Mcintosh ma5200

To make a passive HP filter.
Your Mac has a steady fixed input impedance of 20k, using this you could do a simple 1st order filter with just one component (a capacitor) on this by putting a
0.068uf cap in series with the input, that will roll off the bass a 117hz -3db.
or a 0.1uf will be 80hz -3db
or a 0.033uf will be 240hz -3db.
or 0.082uf will be 97hz  -3db
Or using the 20kohm input you can work out more complex and steeper 2nd order, 3rd or 4th.

Cheers George
Yogi, how do you use the HSU filter in your system? 
I run a pair of ICs from my preamp into the inputs of my sub. I run a second pair of ICs from my preamp into the HSU. I run another pair of ICs out of the HSU into my amp. This made a big difference instead of running my speakers full range. I use these y adapters on my preamp to give me the two outputs that is needed to accomplish this!
Great, I will see which way will work best and go from there. Thank you all for the replies