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Weiss Engineering A1

Microphone Preamplifier & De-esser By Hugh Robjohns

Weiss Engineering A1

500-series modules aren't usually this expensive — but they aren't usually designed by Swiss legend Daniel Weiss...

Swiss manufacturers Weiss Engineering are known for very high-quality digital audio processors that are intended mainly for the professional mastering and high-end hi-fi markets. Their product line includes stereo A-D and D-A converters, a sampling frequency converter, a combined de-noiser, de-clicker and ambience digital processor, a seven-band equaliser and a dynamics processor with de‑esser. The latest addition to the fold is not only the company's first foray into the buoyant API 500-series modular market, it's also the first Weiss product to have only analogue inputs and outputs!


The new A1 is a combined microphone preamp and de‑esser in a 500-series single-slot format, built to the exemplary standards and with the advanced technology we've come to associate with Weiss. Of course, digital technology has not been eschewed altogether; the side-chain control is done with a digital signal processor (DSP) for supreme accuracy and precision, and the gain-controlling element is an MDAC (see below).

Housed in a fully screened module, the A1 has a substantial, white-painted front panel with small but clear black markings and control legends. The module requires up to 150mA of current from the standard 500-series' ±16V power rails, which I assume to be a total figure, rather than per rail. (The original API spec allows 130mA per rail, but most racks are capable of far more these days.) In any event, I used the A1 in an old API 'Lunchbox' rack without any problems.

The preamp's gain control is a large, black rotary switch, with 3dB steps between +15 and +60 dB. A trio of LEDs alongside indicates the output level: a green 'signal present' LED illuminates at -19dBu, an amber LED lights at +1dBu, and a red LED comes on at +18dBu, although the unit has a generous headroom margin as the maximum output level is a whopping +27dBu.

Below the gain control are three miniature toggle switches. The first activates 48V phantom power — although there is no warning/status lamp — and the last introduces a -24dB pad, allowing the A1 to accept line-level inputs. The maximum input level with the pad is higher than the +26dB range of my Audio Precision test set; the specifications claim a massive +29.7dBu.

The middle toggle is a three-position type which controls an active second-order (12dB/octave) high-pass filter with three turnover frequencies of...

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Published February 2020