What's a good cartridge for infinity black widow?

Actually- The weight of the cartridge is not what's important. The Black Widow is a VERY low effective mass arm, and needs a high-compliance cartridge. The Blue-Point(at 12x10-6cm/dyne) is considered a fairly low compliance cartridge. Here's a good treatise on compatibilty: (http://www.gcaudio.com/resources/howtos/tonearmcartridge.html) But then- That's science and physics, which don't ALWAYS apply when it comes to audio.

This site has a formula that you may find useful: (http://www.theanalogdept.com/cartridge___arm_matching.htm)

Shure V15 was made for that tonearm. My friend has that combination and it sounds great

Mr J- Which V15? The V15 series began in 1964, and there have been a plethora of variations since, with many differing compliances.

Rodman is right, not only is the widow ridiculously low mass,it is also a double knife edge bearing (like the early SMEs).These were once thought to "chatter" if too low a compliance cartridge is used.Most moving coils would be out of the question! Over the years I found the Shures (type III or newer),ADC XLM,Sonus Blue,Empire 2000 EII, B+Os,and AKG P8 all suitable. This was when the industry was on a "low mass" kick.BTW,you will notice that there are almost no arms available today that are this low mass.You might be better served to look for a used MMT or Audioquest PT,that way you would have more cartrige choices. These are usually available at a pretty reasonable price.The BP works well with the MMT.