New Gear Review: API 535-LA Line Amplifier

The API 535-LA Line Amplifier is their console’s 325 booster card packaged in a 500-module. The 535-LA supplies either a gain boost from 6dB to 45dB or a gain loss and that is the key to its utility. It can both amplify or attenuate incoming and outgoing signals and provide API’s trademark sound in the process.

The 535-LA has a balanced input, a polarity switch, a -20dB pad for incoming signal attenuation and an Output Ratio toggle switch for three different output transformer windings and levels of gain.

I liked that there are separate “Cal” or calibration pushbuttons for both the input and the output stages that switches the front panel controls over to recessed trim pots. The API 535-LA is useful anywhere signal levels need adjusting such as from keyboards, audio playback and processing devices without level controls.

I tried two 535-LA Line Amplifiers as buffer amplifiers for recording a Waldorf synthesizer’s line level output directly into Pro Tools. I connected the synth’s output to the patch bay TT inputs of the studio’s 500 rack with pair of 535s installed.

The Output Ratio control is handy for quickly establishing gain staging from the Waldorf’s hot output and the Clip LED monitors for potential overloading of both the 2520 output the 2510 input amps.

I found the 535-LA to be super quiet, transparent and solid sounding. The 535-LA sells for $595 MSRP.


Barry Rudolph is a recording engineer/mixer who has worked on over 30 gold and platinum records. He has recorded and/or mixed Lynyrd Skynyrd, Hall & Oates, Pat Benatar, Rod Stewart, the Corrs and more. Barry has his own futuristic music mixing facility and loves teaching audio engineering at Musician’s Institute, Hollywood, CA. He is a lifetime Grammy-voting member of NARAS and a contributing editor for Mix Magazine. barryrudolph.com