JBL 5600-2B Mixer/Preamplifier
A rack-mount broadcast mixer with a spec sheet engineers actually trusted.
Overview
The JBL 5600-2B is not a hi-fi component. It's a solid-state mixer/preamplifier built for the Professional Division of James B. Lansing Sound, Inc. at 8500 Balboa Boulevard in Northridge, California - the same address stamped across the company's studio monitor line. Most JBL gear of the era was destined for a living room. The 5600-2B was destined for a rack, and JBL's authorized-dealer advertising of the period promoted the company's subwoofers to hi-fi buyers, as seen in the pages of Audio (January 1985, p.179). It occupies three EIA standard rack spaces, measures 5¼ inches tall by 19 inches wide by 10 inches deep, and weighs 12¼ pounds net. The chassis finish is non-glare baked enamel in light gray, which suits a control room better than a showroom.
The architecture is the interesting part. As shipped, the 5600-2B combines four microphone channels and two program channels. Each microphone input is unbalanced high impedance, fed through a three-pin female XLR receptacle. Each can be converted to accept a low-impedance microphone by dropping a 5901 accessory transformer into a socket provided for that purpose. The two program channels are wired for 50,000-ohm unbalanced operation and have both screw terminals and an alternate phono jack, so a single channel can serve either a tuner or one side of a stereo source. Any microphone channel can be turned into an unbalanced 50,000-ohm program input, with the same sensitivity as the standard program channels, by inserting a 5904 T-pad.
Expansion needs no soldering iron. The 5190B microphone preamp expander module mounts on the main chassis and adds two more microphone channels, for a total of six mic plus two program. Installation is simple. The audio output and power connections route through a single five-pin plug, and the labeled cutouts for the added level controls ("MIC 5" and "MIC 6") sit concealed behind a removable plate at the upper left-hand corner of the front panel. The manual says the added channels are identical to the originals, with the same performance characteristics and the same accessory compatibility.
The measured performance backs up the intent. Output is +18 dBm maximum and +8 dBm nominal, with frequency response of 20 to 20,000 Hz, ±1 dB direct out. Total harmonic distortion is specified at less than 0.25% at +18 dBm from 30 to 20,000 Hz, and intermodulation distortion at less than 0.5%. Equivalent input noise is quoted at -122 dBm over a 20 kHz bandwidth, with output noise at -85 dBm. Microphone channel isolation runs 60 dB. Gain is 57 dB at high impedance, or 83 dB at low impedance with the 5901 transformer installed. Input overload doesn't arrive until -27 dB at 1 kHz and 5% THD, referenced to 0.775 volts with controls at the minimum usable setting.
The control surface is sparse. Power is an on-off toggle. Microphone, program, and master gain are all audio-taper. The tone controls offer cut at 150 Hz and boost or cut at 7 kHz, with midrange material deliberately unaffected. The bass control sits flat at "7" and the treble flat at "3." A green pilot lamp indicates power, and the VU meter is factory-set so 0 VU reads +8 dBm, with an internal, continuously variable calibrate trim. The Cue/Normal switch turns the program output on and off without disrupting the monitor, which lets an engineer audition a mix before committing it to the feed. The monitor output lives on a front-panel jack and can drive headphones or an auxiliary amplifier. It is not affected by the Cue/Normal switch.
The output stage is built around a 600-ohm unbalanced line available at a rear-panel phono jack. Drop a 5195 transformer into the provided socket and you get a 600-ohm balanced output on screw terminals, while the original unbalanced output remains usable to drive loads greater than 10,000 ohms. Semiconductors throughout are all silicon. Power draw is 10 watts from 120 VAC, 50/60 Hz, fused at 0.25 amps slow-blow. Operating temperature is rated to 131°F (55°C). JBL warranted the unit for two years and listed it with Underwriters' Laboratories. Accessories documented alongside the 5600-2B include the 5190B expander, the 5191 magnetic phono/tapehead preamp, the 5195 matching/bridging transformer, the 5901 universal microphone input transformer, and the 5904 T-pad.
For anyone shopping one today, the manual notes that JBL reserved the right to make minor component changes without notice. Internal revisions exist, and two units from different production runs may not match part-for-part. The mixer is also a 120 VAC, 50/60 Hz design as specified, so anyone outside North America should confirm the transformer situation before plugging in. A 5600-2B without its 5195, 5901, or 5190B is a functional but limited mixer.
One caution on sourcing: the model designation appears on the chassis as "5600-2B," and the manual uses that full form throughout. Buyers searching only "JBL 5600" may miss listings, and listings using the short form may or may not include the B-suffix revisions. The 5600-2B is a professional broadcast tool from JBL's Northridge professional division, not a hi-fi preamp.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.