The RCA OP-6 was originally introduced in the 1930s and was primarily used for remote, live radio broadcasts.
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The RCA OP-6 was originally introduced in the 1930s and was primarily used for remote, live radio broadcasts. It quickly became a staple in the recording industry where it remained throughout the 20th century. While it sounds amazing, it can be too noisy for some applications and its feature set is quite limited by today’s standards. Retro’s $3,500 OP-6 offers better noise performance as well as the addition of XLR connectors, a quarter-inch high-impedance instrument input, switchable 48 VDC phantom power, switchable polarity, a 25 dB attenuator pad, variable output level control and a VU meter that can also be utilized as a tube checker. Input impedance is switchable between 37 Ω, 150 Ω, or 600 Ω so the pre can be optimized for use with modern- day condensers, classic ribbons, or anything in between. The mic pre provides over 80 dB of gain, making it perfect for quiet sound sources and low-output microphones.

The RCA OP-6 was originally introduced in the 1930s and was primarily used for remote, live radio broadcasts. I recorded several bass guitars through the Hi-Z input and in every occurrence, the result was fantastic. In the instance of a 1960 Gibson EBII Bass, an instrument that always sounds huge but can often become muddy and washy in the low-end, the instrument’s definition and clarity were maintained while still sounding massive. Electric guitars sound wonderful with the OP-6. I had great results with both dynamics (EV RE-20, Heil PR-40, Shure SM57, Sennheiser 421) and ribbons (Royer R-121, Royer R-122 MKII, AEA N22 Nuvo and Beyer M160).

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I should mention that the OP-6 has independent gain and output controls, allowing the preamp tone to be varied by driving it harder but utilizing the output control to maintain a consistent output. The pre sounds the cleanest when the Output is set at the maximum level, but clean isn’t necessarily the desired result as I often found to be the case. Varying the input impedance also provides creative tone control. Driving the mic pre a bit harder when recording vocals lets the vocal pop out of the track even when it’s mixed at a slightly lower volume.

Acoustic instruments are captured beautifully through the OP-6. On multiple occasions, I used the pre in conjunction with the Blue Hummingbird, the Earthworks SR77 and the Audio-Technica ATM450 and had wonderful results in each instance. When recording a particularly bright acoustic guitar, I used the OP-6 along with an AEA A440 active ribbon mic and the pre’s ultra-smooth sound warmed the top end without the need for equalization.

Vocals shine through the OP-6. I had great results capturing female vocals with the Sony C-800G and male vocals with the ADK Z-67. On a tracking session with Steven Curtis Chapman, I used the pre along with a Shure SM7 on the vocal and it sounded wonderful. The pre has gain to spare, making it easy to capture particularly soft vocalists on lower output microphones like the SM7, EV RE-20 or the Coles 4038.

The large price tag makes the OP-6 beyond the reach of many smaller studios, but the box is simply wonderful and it works well with virtually any microphone on any sound source.

Retro Instruments