Heritage Audio SYMPH-EQ – Master Bus Stereo Asymptotic Equalizer

70 YEARS AFTER ITS CREATION, THE BAXANDALL EQ GETS A DEFINITIVE UPDATE.

Baxandall equalizer’s topology, introduced to the public by Peter Baxandall in 1952, was a very ingenious way of obtaining high and low shelves with boost and cut option without using expensive rotary switches. This affordable circuit was soon adopted by hi-fi and console manufacturers for its simplicity, where parametric options aren’t needed.

Heritage Audio has successfully replaced the Baxandall topology with a functional equivalent — a much more musical one, implemented as a one rack space, master bus/ mastering type unit.

The Stereo Asymptotic Equalizer, affectionately known as Symph EQ, takes its name from the shape obtained by its shelf curves; where the boost or cut amplitude grows up until the asymptotic value is reached, keeping the ultra highs and sub lows always controlled.

Its sound can only be described as tight, sweet, and natural, and its use of parallel equalizing to obtain the desired response curves makes it to have exceptional low phase deviation and artifacts.

SHELVING WITH SURGICAL, BUT MUSICAL PRECISION.

A smart circuit layout allows for a maximum boost/cut of 10.5 dB in 0.5 dB steps. The main rotary switch sets 1dB steps whilst the 0.5 button adds half a dB to the main reading. The CUT button turns the boost amount into cut. Six strategically selected frequency choices per band are available (8, 10, 12, 15, 20 and 24 Khz on the high shelf, and 470, 360, 220, 110, 60 and 20 Hz on the low shelf).

2-POLE HIGH AND LOW PASS FILTERS

In order to keep the sub-low and ultra-high frequency content well under control, further high-pass and low-pass filters have been added on dual concentric rotary switches, at 12dB/octave. 5 frequency choices plus OFF are available on each one (10, 12, 18, 22 and 30 Khz on the low-pass, and 160, 82, 47, 20 and 15 Hz on the high-pass).

• <> Carnhill based, transformer coupled balanced inputs and outputs for added character and vintage vibe.
• <> 73 style class A output stages bring the desired 73 sound to your mix or instrument buses.
• <> Stepped controls for easy recall of settings.
• <> Input impedance: 10 Kiloohms bridging. Input is transformer balanced and floating.
• <> Output impedance: Less than 75 Ohms, transformer balanced and floating, to drive a load of 600 ohms (factory terminated).
• <> Maximum output: Greater than +26dBu into 600 ohms.
• <> THD: Less than 0.025% at 1 Khz, less than 0.05% at 100Hz.
• <> Frequency response: 20Hz ( +0.3dB ) to 20Khz (-0.2dB)
• <> Noise: Less than -89dBu , EQ flat.
• <> ASYMPTOTIC EQUALIZER SECTION:
• <> Hi Frequency shelving: Frequency selectable 8, 10, 12, 15, 20 and 24 Khz.
• <> Boost / Cut: 10.5 dB maximum, in steps of 0.5dB.
• <> Lo Frequency shelving: Frequency selectable 470, 360, 220, 110, 60 and 20 Hz.
• <> Boost / Cut: 10.5 dB maximum, in steps of 0.5dB.
• <> FILTER SECTION:
• <> 12dB/octave high pass filter, -3dB point selectable at 160, 82, 47, 20 and 15 Hz.
• <> 12dB/octave low pass filter, -3dB point selectable at 10, 12, 18, 22 and 30 Khz.
• <> Side filter automatically turns into elliptical topology when M/S is engaged, as in the disk cutters, at 6dB/octave.