Retro Instruments 500 PRE

Retro Instruments 500 PRE is a microphone preamplifier that fits the Sta-Level circuit topology into a single 500-series slot. A three-tube gain stage on three 12AT7s keeps the detail and depth of the company's full-sized designs. A gain switch selects between a two-stage configuration at 48 dB and a three-stage configuration at 76 dB, while a continuously variable output attenuator sets the level going into whatever comes next in the chain.

A preamp that becomes a limiter after the session

Rather than clipping hard, the tubes limit gracefully from +18 dBu with headroom to +24 dBu, and that behaviour was kept in the design deliberately. In practice the same module you track a vocal through can work at mix time as a high-energy limiter for fattening tracks. The output attenuator lets you overdrive the tube stage without clipping the gear downstream, so tone is chosen independently of the level sent to a converter. In the LOW position the two-stage configuration accepts signals up to +10 dBu without overload, which makes it a useful line stage for finished tracks.

Mind the rack power budget

The module draws 160 mA, slightly above the 130 mA allowed by the VPR specification, so the manufacturer recommends racks with a quiet linear supply, the API models among them. With that condition met the circuit runs reliably for years, and soft-start circuitry limits stress on the tubes and the supply at switch-on. Warm-up to full performance takes under a minute, so the module does not force you to power up long before a session. The 12AT7 tubes are available both in current production and as new old stock, which leaves room for tailoring the sound.

KEY FEATURES

• Sta-Level circuit topology in a single-width 500-series module
• Three 12AT7 tubes in the gain path
• Gain switch: 48 dB two-stage, 76 dB three-stage
• Graceful tube limiting from +18 dBu
• Continuously variable output attenuator for overdriving the stage without clipping the chain
• Phantom power and polarity switch on the front panel
• Soft-start circuitry, warm-up under a minute
• 600 Ohm transformer balanced output

TECHNICAL SPECIFICATIONS

• Gain: 48 dB two-stage, 76 dB three-stage
• Total harmonic distortion: below 0.05% at +4 dBu output, 20-20,000 Hz
• Frequency response: +/- 0.25 dB, 20-20,000 Hz
• Equivalent input noise: -128 dB with 150 Ohm termination
• Typical output level: +4 dBu
• Tube limiting threshold: +18 dBu, clipping headroom to +24 dBu
• Input level range: -72 dBu to +12 dBu
• Input impedance: above 1000 Ohms, 20-20,000 Hz
• Output impedance: 600 Ohms, transformer balanced
• Power consumption: +/-16 V at 155 mA and 48 V at 3 mA
• Controls: input level, gain select, phantom power, polarity, output level
• Weight: 1.1 kg