JBL 3133A (c. 1981–1983)

Name: JBL 3133A
Brand: JBL

The JBL 3133A is a three-way dividing network. It's the external crossover box that sat between amplifier and speakers in some of JBL's top studio monitors of the early 1980s. Japanese period catalogs listed it at ¥55,000 (around 1981) and ¥72,000 (around 1983) per unit. It's the crossover specified for the JBL 4333A, 4333B, and L300 Summit. It crosses over at 800 Hz and 8.5 kHz and handles 150W continuous program. The odd part is the impedance: only the midrange section is 16 Ω, while the low and high frequency sections are 8 Ω.

The network is built to professional standards. JBL described it as using non-inductive, non-polar capacitors with large current capacity, developed specifically for network use. The inductors are low-loss and adjusted one by one, and the switches and resistors are heavy-duty. It has continuously variable level controls and a selector switch for 2-way multi-amplifier drive. The input terminals and level controls are independent, so the whole assembly can be mounted into an enclosure instead of being racked.

Documentation on this model is thin. There's no official service manual in circulation, and no definitive list of every speaker model it appeared in, though the 4333A/4333B and L300 Summit are consistently named. Forum discussion at audioheritage.org notes that the internal wiring is 18 or 16 gauge copper, possibly tin-plated if it looks silver. People often confuse the 3133A with the crossover inside the L300. Per forum sources, the L300 uses completely different components, and the 3133A is its own distinct network.

These are rare and collectible. One forum user described a single unit appearing on eBay as "generally nonsense" - they're expensive by themselves and almost never sold individually. A pair sold on eBay in July 2012 for $228 plus roughly $100 shipping. The same forum user advised bidding around $500 "to be sure," estimating a pair might appear once a year and cost no less than $600 plus $200 shipping. Recent listings show a used pair at $500 and a single unit at $773.29. Condition varies: one Reverb listing noted the crossovers had been painted by a previous owner and were sold untested.