Any NHT Classic Four owners biamping?

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

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

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

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.

Cool thanks for the response. The tweeter mod is a little more than I want to tackle right now, but I would consider upgrading the crossovers. DO you have a parts list of what you used?

I keep meaning to pop the back off and take a look at the crossovers. Did the stock crossovers use decent components?

Mark

I was shocked when I hooked the modified Classic 4s up to my Pass Labs X350.5 before I delivered the speakers to my friend. Difference is they now disappear. They have such a natural tonal balance. The timing is perfect. The sound stage is deep and wide. They sure make my audio friend's shake their heads in disbelief. The moded classic 4s had a much better sound than a set of Focal Utopia Divas. The only speakers in my system that sounded better was my highly modified set of Apogee Duettas and a stock set of B&W 802Ds.

My friend who owns a pair of classic 4 and runs them with two Rotel RB 970BX amplifiers with great results. Since both amps are in exactly the same. He uses one stereo amp for each speaker. One channel runs the lows and the other channel runs the highs. They sounds better than I could ever imagine for a $2000.00 set of speakers . He uses the stock designed passive crossovers which I modified. The crossovers are now set up with sonicaps, Alphacore 12 awg copper foil inductors, Cardas speaker connectors and better internal wiring. I also replaced the dome tweeters and super tweeters with a new set of Aurum Cantus 2GSIs ribbon tweeters. This also required the removal of super tweeter crossover frequency point. This really made the highs much better. The highs extend way up, and now sound natural and much faster. It was a crazy mod but it made this a world class speaker system. I had to use several resistors to get the new tweeters to blend. I had a machinist machine new faces out of billet aluminum for the Aurum Cantus Ribbon Tweeters so that they would fit in the stock factory NHT holes. I also lined the insides with Dynamat, and had better stands made out of steel, filled sand. It is crazy good. In fact I am going to build my self a set sometime this summer.