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).
THIS IS WHERE THE MAGIC LIVES.
The Symph EQ would have been an awesome sculpting tool just as it has been described above, but it turns into a monster piece with the following 3 additions:
- It features the same exclusive Carnhill input transformers made in Oxford found in the Successor.
- Its outputs are driven by 73-type Class-A output amplifiers, built with the same Carnhill St´Ives output transformers as the rest of the family.
- Most importantly and, here is where the Symph EQ really shines, it has built in Mid Side (M/S) capabilities.
M/S EQUALIZING CANNOT BE RIVALED.
Nothing comes close to M/S equalizing a mix. It allows the user to process the center and the sides independently. The benefits of such processing are hard to believe. You can brighten your mix without making your vocals sound harsh, or even tighten the stereo-image’s bass content without making your bass or kick sound weak! These are just a few examples of the Symph EQ M/S power!
The response of the Side high pass filter has been made elliptical as in the vintage disk cutters for precise frequency response.
THIS IS WHAT YOU GET WITH THE SYMPH EQ
- Custom Carnhill Oxford input transformers, and custom Carnhill St Ives output transformers, both exclusively made for Heritage Audio.
- A high-end, 73-style Class-A output stage.
- All controls use high-quality rotary switches for 0.5dB precision equalizing.
- Mid-side processing allows for precise center bass management and high boosting hard panned sources without affecting center ones such as vocals, snare, etc. Side high-pass filter turns into elliptical type when in M/S, as implemented in vintage disk cutters.
- Stereo and M/S inputs and outputs, all balanced and ground free (unbalanced compatible) on gold plated XLRs.ON, M/S or stereo mode and individual hard BYPASS per channel.
- Fully manufactured in the EU.
- 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.
- 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.
Well, I´ve finally gotten around to writing a review for this absolutely stellar preamp… it only took me three years! At least you know that I actually had time to give it some use before writing my review. Since, winning my 73Jr in an online writing contest, it has made valuable contributions to all of my recordings. Everything about the 73Jr is well made and I can’t say enough about its build quality. It´s based on the vintage 1073 preamp and it adds a warm, creamy clarity to vocals and it makes digital keyboards/synthesizers sound less digital before hitting the DAW. My 73Jr does what it is meant to do and it does it flawlessly. BONUS: when pushed it adds some really sweet breakup to clean guitar. I never imagined that a mic preamp could actually contribute to a recording… I mean, all they do is raise the volume of a signal, right? Hahaha! I was wrong and I’m glad I was wrong! Had I not won my 73 Jr in a contest, I would have never found out how truly necessary a good preamp is to making a quality recording. I have to admit that, my first thought was to sell it for some quick cash – I didn’t own a Lunch Box and my prize was going to require the purchase of a Series 500 chassis. But, ha! I’m a gear freak and the 73Jr now sits next to an harmonic exciter and a compressor. I’m glad I spent the money on a Lunch Box because the 73Jr is a keeper!!!! If you are in the market for a 500 Series preamp, the Heritage Audio 73Jr will make you a very happy camper.
It´s a truly special unit. It´s a best in class considering its price, having ahpf, and line in onboard. Without all of those things it still wins, as it´s exactly what you´re looking for sound-wise. I´ve tried several other sub 1k iterations of this circuit. Up until now, nothing has gotten me this close. Shines on vocals, and synths. I´m frantically trying to save to get another unit, and will eventually add the eq’s as well. This is the real deal folks. My Sweetwater Rep, Brian Loney was dead-on with this one!
It’s the real deal… been tracking vocals on this thing with an SM7b and Warm Audio 1176 after in the chain before printing in Protools… excellent. Just recently tracked a kick drum with it and it was surprising very transient and punchy accompanied with API 550A/560 EQ within the Protools DAW. Incredible piece that is a MUST in your U-rack.
I’m completely loving this preamp after a couple of weeks of ownership. Dialing in a good sound is straightforward. I have gotten thickly saturated sounds from a DI improving tone on my Fender P bass and allowing the bass to be heard easily in a mix. Playback on my iPhone speakers still produced the clear sound of the bass recordings. With a cheap mic I was able to dial in a clean sound by keeping the input transformer subdued and cranking the squeaky clean output transformer. By the way, the pad is in the chain before the input transformer so engaged you can crank the input harder. Also lots of success with my Alpha Juno 2 analog synth. It sounds huge. I will likely invest in the 73eq down the line. Tone galore.
Can´t go wrong with this Pre. The amount of tonal variation the gain knob provides will make it easy to fit any source you throw at it. Great on Vocals – just sounds simply expensive. I usually record guitars direct and this thing gave my Axe Fx 2 a new life. ( Never thought the sound of the Axe fx needed any more but this preamp just gives the sound an extra level of clarity ) Can’t wait to get at least another one of these units for a stereo pair.