The RCA LMI 32215 preamplifier was designed to be used in conjunction with RCA's LMI 32216 power amplifier but could be matched to any preamplifier capable of supplying the required plate and filament voltages.

The circuit consisted of three stages employing a low noise pentode (EF86) and two double triodes (ECC81). The first stage included a feedback loop and was used when pickups and microphone inputs were selected. It also provided equalisation for the different recording characteristics of the day.

Radio and tape inputs were fed directly into the second stage, arranged as an anode follower. The third stage incorporated a low pass filter with 10Kc/s, 7Kc/s and 5Kc/s cut-off frequencies along with a continuously variable slope which was achieved by the variation of feedback around the filter valve.

Controls included an input selector for correct equalisation of the four main recording characteristics of the day. they were: R.I.A.A., LP, A78 (American 78 rpm recording) and B78 (British 78 rpm). Additionally, the input selector had a GND position for reproduction from radio/tape inputs, and isolated the first stage of the preamplifier. The MIC position selected when reproduction from a microphone was desired.

This model was improved upon in 1958 and renamed LMI 32215A.

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