JBL 3131A
The JBL 3131A is a two-way dividing network, a passive crossover, made for JBL's professional monitor loudspeakers of the early 1980s. Documentation is thin, and most of what survives comes from period Japanese equipment listings rather than original JBL literature. Here is what the record shows. It crossed over at 800 Hz and was rated for 150W continuous program input. It had a continuously variable attenuator for the high-frequency section. The low-frequency section is 8Ω and the high-frequency section is 16Ω. The Japanese database entry gives the weight as 4.3kg. At least one resale listing claims roughly double that, but the factory figure is likely the more reliable one.
JBL specified carefully selected parts for the network: high-voltage non-polar capacitors, low-loss inductors, and resistors. It also had a changeover switch for 2-way multi-way configurations, which suggests some flexibility in how it could be deployed. The original price in Japan was ¥49,000 per unit around 1981. A later 1983 listing shows ¥70,000, apparently a price revision rather than a separate model. It is known to have been used with the JBL 4331 studio monitor, and the 800Hz crossover frequency fits the 4331's two-way design.
Beyond that, the record is essentially silent. No original manual, no schematic, no dimensions and no period reviews have surfaced. The 3131A appears in Japanese audio databases and occasionally in resale listings, some described as all-original and unmodified. No substantive reception or collectibility data exists.
Known specs:
- Two-way dividing network (crossover)
- Crossover frequency: 800 Hz
- Allowable input (continuous program): 150W
- Impedance: 8Ω (LF), 16Ω (HF)
- HF attenuation: continuously variable
- Weight: 4.3 kg
- Original price: ¥49,000 (c. 1981, per unit)
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