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Oram Hi-Def 35 Limited Edition

Equaliser By Hugh Robjohns
Published March 2000

Oram Hi-Def 35 Limited Edition

To mark 35 years in the business of audio design, Oram have launched a special limited edition 'Hi‑Def' equaliser. Hugh Robjohns tries out this attractively priced derivative of the famed HDEQ2.

John Oram has had a long and illustrious career in the design of audio equipment and mixing consoles. His name is linked with the Vox AC30 and 'Super Beatle' amplifiers and, during 14 years as consulting designer with Trident Audio, he played a major role in the development of the much sought‑after Trident TSM and Series 80 mixing consoles. His company, Oram Professional Audio, today produce a wide range of high‑end analogue signal processing equipment and mixing consoles — everything from compact 8:4:2 broadcast mixers up to some very serious, fully automated recording consoles.

Their rackmount products include a metering and measuring unit, a 'microphone work station', a stereo compressor and a range of eight‑channel units such as a mic preamp, equaliser, fader panel and line mixer. However, perhaps the best‑known element of the Oram lineup is the HDEQ2 'Hi‑Def' equaliser. For those readers unfamiliar with the HDEQ2, it is a dual‑channel device occupying 3U of rack space to provide eight bands of extremely flexible equalisation. Popular in mastering circles and top recording studios, the 'Hi‑Def' incorporates low‑ and high‑pass filters along with switchable‑turnover low and high shelf equalisers, plus four overlapping bell‑shaped equalisers, all with switchable bandwidth and swept centre frequencies. All Oram rack products are a distinctive sky‑blue colour, and most units feature a sculpted front‑panel design with recessed bevels around the base of each control.

The subject of this review, the Hi‑Def 35, is, apparently, exactly the same in circuitry terms as the far more costly HDEQ2, and differs only in the absence of the expensive (and unnecessary) three‑dimensional sculpted front panel. In celebration of his 35 years in the professional audio industry, John Oram has produced this limited‑edition design with a substantially reduced price tag which is actually less than half the list price of its antecedent. It may therefore be regarded as something of a bargain!

Connectors & Controls

The rear panel of the equaliser is plain, with two channels of electronically balanced inputs and outputs on both XLRs and TRS quarter‑inch sockets. Mains power is interfaced via the usual IEC mains connector which contains an integral fuse holder. A voltage selector is also present.

The front panel, however, is a rather more complex affair. The two channels are ranged horizontally, one above the other, with vertical alignment of the corresponding controls. Whilst this arrangement is entirely logical, its industrial design, for want of a better term, makes the markings and layout surprisingly indistinct, perhaps because of the regular, mathematical spacing of identically sized knobs. This profusion of knobs and switches, with little in the way of panel markings or physical segregation to identify the relevant bands or channels, makes the machine a little intimidating to use at first. Familiarity helps to overcome this stumbling point to a large extent but, even so, I think most users will frequently find themselves double‑checking the small and congested panel legends.

Starting at the left‑hand side, the first control in the signal path is an input gain knob offering a ±20dB range either side of a central unity gain click‑stop. An associated red LED indicates signal peaks at +10dBu, a level which leaves a very comfortable headroom margin for the following equalisation stages. The machine is capable of a maximum balanced output level of +28dBu. The first equalisation stage is a continuously variable 12dB/octave high‑pass filter extending between 5 and 300Hz. The final knob of the equaliser at the right‑hand side of the control surface provides a complementary low‑pass filter covering the range between 1.5 and 80kHz. These two filters may be engaged or bypassed (as a pair) independently of the rest of the equalisation, through a white button and associated yellow LED at the far right of the panel.

The remaining six bands of equalisation are ordered across the panel as low sweep and shelf, low and high swept mids, and high shelf and sweep. All are equipped with cut/boost controls providing an expansive ±18dB range, with a central click‑stop unity gain position. A black button adjacent to each control (labelled 'Detail') reduces its gain swing to a more pragmatic ±6dB, allowing for much greater resolution and finesse in adjusting the equalisation.

Each of the four swept equalisers provides a bell‑shaped response curve with switchable bandwidth, courtesy of white buttons adjacent to each frequency control. The bandwidths are not published, but the 'narrow' setting is usefully surgical while the 'broad' setting maintains a sensible and highly musical area of control. The low sweep extends between 35 and 500Hz, nicely sharing an overlapping octave with the low‑mid which covers 250‑2500Hz. Similarly, the high‑mid spans 1 to 9kHz and the high sweep, 5 to 18kHz. In practice, each control covers a usefully contained frequency range, allowing unusual precision in adjustment.

The four high and low shelf controls feature a different knob design from all the others, and therefore stand out amongst the other 24 controls. They determine the turnover frequencies of the shelf equalisers, with low options of 35, 60 and 200Hz and high settings of 3, 6 or 20kHz. The far more customary 100Hz and 10kHz settings are notably absent. All six equalisation stages may be engaged or bypassed en masse by a black button (and associated green LED) on the right‑hand side, next to the filter bypass switch.

A pair of vertical LED bar‑graph meters show the output level for each channel in regimented 3dB steps. The central indicator is labelled as 0VU, with the top and bottom lights showing +12 and ‑15 respectively — I assume these figures relate to dBu. The final operational control at the extreme right is a solid rocker switch to power the unit.

Internally, the machine is constructed to a very high standard. Two main circuit boards are visible, one for each channel, and they are populated almost exclusively with surface‑mount devices. A toroidal transformer is fixed to the right‑hand side of the well‑engineered case. There is also evidence of careful attention being paid to the earthing of potentiometer cases, presumably to minimise noise and crosstalk.

Hi-Def 35 In Use

The first thing I became aware of, from the moment the Hi‑Def 35 was inserted in the signal path, was the subtle 'presence' it introduced — even when all equalisation was bypassed. After careful investigation, I found a small HF tilt in the frequency response of the machine which I thought, at first, was the result of a mismatch in input and output impedances. However, a little research revealed this to be a deliberate sonic characteristic; apparently it is a hallmark of the Oram design.

Using the equaliser was a pleasure, and everything behaved precisely as it should. The filters, shelf equalisers and sweeps are all exactly as you would expect to find on any decent console or outboard EQ, except that here we have a plethora of them, all available simultaneously, and all sounding particularly musical. I found the adjustability of the shelf turnovers surprisingly useful, as was the ability to park a bell equaliser on top of a shelving slope, on occasions.

During the time I had the Hi‑Def on review I developed an approach to setting the machine up which started with adjusting the filters to define (or tame) the frequency extremes. I then established any necessary overall spectral shaping with the shelf equalisers. This left the four swept bands to address specific issues, such as notable colorations, resonances and room modes. This extraordinary level of flexibility proved to be a real boon and the obvious musicality and 'rightness' of its sound character makes it a very usable tool indeed.

Overall, however, I found the Hi‑Def 35 to be an extremely competent and unusually flexible and powerful equaliser. It was also clear from the outset that its technical specifications are to the very highest standards in terms of noise and distortion. Aside from my concerns over its role in processing stereo material and my earlier observations on its ergonomic design, there is nothing to criticise, and its quality of sound deserves the highest praise. If you are looking for a very serious equaliser, this may well be the bargain you have been waiting for.


The Hi‑Def 35 is a particularly flexible unit, but there is one case in which this could be a weakness. An important issue, particularly given its designation as a "reference equaliser for the mastering, broadcast and live sound environments," is the inability to guarantee matching of EQ between the two channels. This is a shame since the exemplary technical and sonic performance of the machine makes it absolutely ideal for the mastering of stereo material. Unfortunately, with so many infinitely variable gain and frequency controls, matching the two channels precisely is virtually impossible, even with careful visual alignment. Whilst this may not be a practical or significant issue for some, the professional mastering fraternity generally prefer rotary switch controls rather than continuously variable ones, specifically to guarantee channel matching and repeatability.


  • Filters, bells and shelf equalisers all in one box.
  • Eight simultaneous bands of musical EQ.
  • Exemplary technical specifications.
  • Attractive value for money — a bargain, even!


  • Indistinct control layout.
  • Impossible to guarantee stereo matching.


A mechanically reworked HDEQ2 providing eight beautifully engineered bands of equalisation on each of its two audio channels, with a 50 percent price reduction. The combination of filters, shelf and bell equalisers provides the utmost flexibility and permits total creativity.


£1499 including VAT.

Published March 2000