Ti10k active stereo bass / XO mod

Having far too little free time in my life, I decided to dedicate what's left of it to revamping my good old JBL Ti10k loudspeakers. Some of you might think this is pointless, as these speakers are quite rare and modding them will ruin their resale value. Maybe so, but because the speakers have already been painted yellow (the don't look so sexy) and I don't plan on selling them in the near future, modding was the way to go. For the sake of the hobby, of course ;)

What I essentially did was replace every electrolytic capacitor with an audio grade polyester capacitor and modify the crossover from 4-way to 3-way, with the dual bass drivers actively driven by a dedicated power amplifier (Parasound Halo A21, 250W into 8 ohms). The rest of the drivers are driven by a Creek 5350SE integrated amplifier (90W into 8ohm) through a 3-way passive crossover network. The creek also works as a pre-amplifier in the system (it has separable pre-amp and power-amp connections). The device that integrates the bass with the rest of the system is a Behringer CX2310 2-way active stereo crossover. The XO point is set to 200Hz, which is the same crossover point as in the passive network.

http://i47.photobucket.com/albums/f1...odified_xo.jpg

To make the original network 3-way, I separated the woofer circuitry and removed a few components from the midbass network. The midbass filter was changed from bandpass to lowpass, and the speaker now sounded quite identical to the original, only with weaker bass (understandably). I was concerned that altering the topology would adversely affect sound near the midbass-midrange crossover point, but with extensive testing with vocal music, my concerns were in vain - the vocals sounded just as sweet as before. The best thing here is that with the bass XO'd at 200Hz, I can use whatever amplifier I can find to drive the 3-way network and it will never run out of power. I can use a watt-hungry power amp to kick the woofers and a sweet-sounding 2 watts tube amplifier for vocals and highs. Biamping FTW!

http://i47.photobucket.com/albums/f1.../equipment.jpg

This picture shows the active crossover. Behringer as a brand may not be regarded highly by audio professionals, but this device does its job well enough. I also use it to control my 11 cubic feet subwoofer. The only drawback is increased hiss because of different input/output voltage levels, but I can live with it. At the bottom you can see half of the parasound amp (all other equipment are not noteworthy, apart from the DIY stainless steel stand ).

http://i47.photobucket.com/albums/f1.../crossover.jpg

Now here's a picture of the original network. As you can see, it's infested with several nasty electrolytic capacitors. Their worst properties (do they even have good properties?) are crappy tolerances in capacitance values, drying with age and high electro-series resistance. All of them got replaced with polyester caps, which are far more reliable in audio use, although bulkier in size.

http://i47.photobucket.com/albums/f1...capacitors.jpg

http://i47.photobucket.com/albums/f1...ectrolytes.jpg

Goodbye, you won't be missed ;)

http://i47.photobucket.com/albums/f1...10k/inside.jpg

This is what the fancy-looking Ti10K cabinets look from inside, through the bottom terminal panel. Note the bitumen damping in the walls and thick internal braces - these cabinets will not begin to resonate even at the loudest sound pressure levels. Also note how the wire gets thinner as we move from bass to tweeter.

http://i47.photobucket.com/albums/f1...connectors.jpg

I took the crossover networks out of the cabinets permanently, making it easier to apply future modifications into them. I didn't want to solder the internal wires to the terminal posts so I used some cheap metal loop connectors. They are prone to oxidation, so I have to replace them in the future with copperized ones.

http://i47.photobucket.com/albums/f1...10k/in_use.jpg

And here's the whole setup. I had not enough time to build cases for the crossover circuit boards, so there's still things to do. I also think about replacing all the polypropylene caps on the board with something of better quality, currently they all are very basic Solen caps.

So how does it sound now? The bass is more deep and controlled, and the mid/highs sound sweet, although a bit too bright, thanks to aural characteristics of the Creek amp. That's the main reason I want a tube amp ASAP! After all, I think this mod was worth the time I put into it, which was one weekend. Having two amps, I felt kind of bad to keep one in disuse. Now everything's in almost perfect synergy.