When Retro Instruments first announced the brand’s new 500PRE ($799), we knew we were in love before we ever even heard it. After all, what’s not to love about bringing the Sta-Level design to the 500 Series world and packing three tubes into that compact module. Little did we know, we had something to do with the inspiration for it.
“It was inspired by the Vintage King April Fools’ Day post on the 500 Series Fairchild 670,” says Retro Instruments Owner/Designer Phil Moore. ““The performance of the 500PRE exceeded my expectations. It’s based on professional tube console program amplifiers from the era of the Sta-Level and 176. It’s got 75 dB of gain and no compromises.”
While the 75 dB of gain will make the 500PRE a great tool for tracking sessions, the 500 Series module can also be vital during the mixing process.
The 500PRE is Retro’s third 500 Series module, joining the original DoubleWide I and the updated DoubleWide II–both dual-slot, single-channel tube compressors. The 500PRE incorporates the same basic double-balanced Class-A circuit topology as in the company’s Sta-Level limiter.
WHAT DO WE HAVE HERE?
The 500PRE works both as microphone preamp and line-level amplifier; it has an input operating range of -72 dB to +12 dBu. The output clips at +18 dBu, with maximum output at +24 dBu. The 500PRE has two switchable gain ranges: high gain at 75 dB using all three of its TAD 12AT7 tubes, or low gain at 48 dB using just two of the tube stages.
SOME TECHNICAL DETAILS
The total slot current drain for the 500PRE is 160 mA. This exceeds the allowable current drain in the API Audio VPR Alliance specification of 130 mA for a single-slot module. A check in a tube manual shows that the 12AT7 requires 150 mA filament current each, and there are three.
Taking an idea from old ’50s tube television sets, the three tube filaments are wired in series and powered directly from the 500 rack’s +/-16-volt rails, or 32 volts total–that’s nearly 11 volts DC for each tube. The tubes’ plate voltage is supplied by the 48-volt phantom power supply, and the current drain is just 3 mA.
If your Lunchbox or rack does not have phantom power, the 500PRE will still work, albeit with reduced headroom as the plate voltage will automatically switch over to the +/-16-volt rails.
I ran the 500PRE in an API 8P High Current 500 rack (250mA per slot) and..