JBL 5101B (c. 1975)
The JBL 5101B is a microphone preamplifier. It is a compact 1U unit sold around 1975 for ¥95,700. Documentation is thin, but the spec sheet that survives is clear enough. This was a pro gain block meant to sit ahead of a mixing console or recording chain. It offers 75 dB of gain, a frequency response of 20 Hz to 20 kHz ±1 dB, and total harmonic distortion rated at no more than 0.25%. The S/N figure, quoted as −122 dBm input conversion value unloaded, was the headline feature. JBL's own catalog copy called it a "microphone preamplifier with excellent S/N and low distortion."
The input is high-impedance, and the maximum output is +10 dBm unbalanced. For balanced operation, JBL specified their 5195 matching/bridging transformer. For a low-impedance mic, you add the 5901 universal mic transformer. A 9-pin octal socket on the rear handled the connection (the archive.org scan of the parts list labels it "MIC PREAMP ASSY. 9 PIN. octal socket"). Physically it's standard rack gear: 483 mm wide, 44 mm high, 140 mm deep, weighing 2.6 kg.
Beyond that, the record goes quiet. There are no production years beyond the "around 1975" price context, no circuit topology details, no user reviews, and no market pricing data. A service manual exists (745 kB, parts numbers 661322, 661330, and 722744 are listed), which suggests the unit was meant to be repairable in the field. If you own one, the known facts are these:
- Gain: 75 dB
- Max output: +10 dBm (unbalanced; balance via 5195 transformer)
- Frequency response: 20 Hz – 20 kHz ±1 dB
- THD: ≤0.25%
- S/N: −122 dBm input conversion value (unloaded)
- Dimensions: 483 × 44 × 140 mm; 2.6 kg
It's a niche piece of JBL's professional electronics line. If you have one, or have seen one in the wild, the archive would love to hear from you.
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