Any NHT Classic Four owners biamping?

Mark,
They did not use good components. You will have to take out all the drivers to get to all the crossover parts. I will get you a list of all the values. Just use the original printed circuit boards just soldier on the better parts on and do replace the intrernal wiring. These speakers are a decent design with a great cabinet, decent midrange and woofer. NHT could have had a Giant killer at $4000.00 and would selling them like hotcakes if they would put in a little more effort.

Thanks. A list of what you used would be great. What did you replace the internal wiring with?

I was thinking of removing the subwoofer crossover (really just a low pass filter) after I biamp since I will be using a low pass filter on the amp input.

Mark

Is there any chance of getting the mods you did as my classic four drivers are dying 

I have the NHT Classic 3's which are similar to the Classic 4... just missing the woofer that extends the low-end response, I believe, but with the same mid-woofer, dome midrange, and dome tweeter.

I have pulled out the passive crossovers and tri-amped them, using 2 dbx 234s active electronic analog crossovers. The system is quad-amp since I am also using 2 Rythmik subwoofer.

The NHT Classic 3 (and, I believe, Classic 4) (mid)woofer to mid/tweeter crossover is in the lower "basket" accessible from the rear. The midrange to tweeter crossover is accessible from the front by removing that whole unit.

They sound great now. Going to a multi-amp active crossover system added many advantages:

For one, I discovered the midrange driver is very efficient - I removed a couple power resistors that previously throttled their output to match the woofer better along with those crossovers - so I am able to use a low-power SET tube amp for the dome midrange drivers for enhanced midrange clarity. I use another tube amp for the tweeters and a NAD 2700 THX solid state amp for the woofers.

It seems odd to me that the midrange & tweeter (referred to above as "tweeter and super tweeter" could be replaced by an Aurum Cantus G2Si  https://www.parts-express.com/Aurum-Cantus-G2Si-Ribbon-Tweeter-276-400. According to that Parts Express link, the Aurum Cantus G2Si Ribbon Tweeter goes down to 1700 Hertz but the woofer for the NHT crosses over to the mid at 800 Hz. Either the woofer is being asked for an extra octave up (can't sound great there, I imagine) or you'll likely have a fried ribbon tweeter in short order.

Or, maybe I'm missing something? It's been a decade since the original post but these speakers are now a great value on the used market and I imagine there's a need for knowledge on how to modify and/or repair them that will last some time.

It looks like this other Aurum Cantis has the ability to go to a lower crossover frequency, but it still seems too high to match up well with that woofer https://www.parts-express.com/Aurum-Cantus-G1-Ribbon-Tweeter-276-420?gclid=CjwKCAiAgc-ABhA7EiwAjev-j....

Cheers

Chris