Gyraf Audio G23-S Stereo Tilting Equalizer

The Gyratec 23-S Tilting equalizer is a tone control based on a somewhat different concept. Instead of going with standard 6dB/oct "first order" filters with their inherent phase/group delay around cutoff frequency, we approximate a 1dB/oct filter which distributes the (necessary) phase clutter over eight octaves. This results in a very unobtrusive response - even at extreme settings the material will tend to stay in balance and subjectively sound unprocessed.

On top of the tilting tone control, we have added a very-gentle Baxandall tone control with shelving lows and highs and a bell mid, each with three selectable corner frequencies.

Our interpretation of the the "Tilting" equalizer does not have selectable corner or rotation frequencies, as the linear approach makes this unnecessary.

The -S addition for the G23 designates an added solid-state architecture – with the bypass switch in the “S” position, we bypass the usual transformers and tubes, and wrap the tone control circuits in servo-balanced active circuits instead. This for situations where you need the enhanced cleanliness or huge drive capabilities of solid-state.

The main feature of the unit is the "Linear Tilting" knob . At centre position it acts bypassed, providing linear transfer through the unit. Turning the knob clockwise will gradually boost higher frequencies while attenuating lower frequencies - and the opposite way when you turn it counter-clockwise. At the end of the knob travel you have a maximum of 1dB/oct - which equals to ca. +/-4dB at the outer ends of the audio spectrum.

On top of this, we have the simple Baxandall tone control with three boost/cut controls, centre detented and neutral when centered. The available boost/cut amount is +/-6.5dB on lows, +/-2dB on mids, and +/-4dB on highs. The curves are VERY gentle, a wide bell for the mids and wide shelves for the high/lows. The desired frequency range of the Baxandall part is set by the frequency controls, each with three selectable frequencies.

No, we won't tell you where the frequencies are - but we spent a good deal of time on optimizing both frequencies and boost/cut range for best performance in the "unobtrusive" category… is your Bypass switch – it select solid-state (“S”) or tube technology (“IN”)- and when set to “OUT”, it takes the entire electronic circuit out of your audio path, and shorts the input XLR's directly to the output XLR's by means of a relay. You don't want eq, you don't get any.

The "Trim" control is a control for fine-tuning the gain of your processed material, making it easier to perform a same-level comparison for judging sonic performance.

Last, the Power switch to turn off the unit when it's not in use. Tubes last long, but not forever.

This Tilting-Equalizer is based on two closely-matched ECC88 output stages in the feedback chain of a linear cutoff slope filter, and the topology is pure class-A. Lundahl audio transformers with internal electrostatic shielding are used for both in- and output interfacing, giving a true floating input impedance of about 10KOhm, and an output impedance of less than 1KOhm. Solid-state part behaves like such should.

This unit was originally intended for use with our analogue tape recorders, which means that the optimum operating levels are around that of +4dBu – and at this point you still have some 14dB up to the point where the tube side of the unit starts to get tired, which happens around 15Vpp AC output – and then some before it starts sounding bad. This means, however, that you should consider checking your levels if you’re running a modern-day DAW, which often comes factory set to extremely-high levels like +24 or +28 for 0dBfsd. Those kinds of levels are aimed at keeping a good safety-margin before running into digital-clip, but at the same time it’s common practice to try getting as close to clip as possible for loudnesswarrific reasons.

A good level for use with the G23-S (and for most analogue gear in general) is somewhere around +10dBu to +15dBu analogue for 0dBfsd (full scale digital). Note, that the solid-state path of the unit does not really care much about working levels – but listening tests indicate that even this sounds best at levels discussed above.

Our audio path, in “real mode”, consists of ONLY transformers, tubes, and passive components. The power supply circuits, and off course the solid-state audio chain when selected, are solid-state based though.

The tubes should last for at least a couple of years - and often much longer than that. If and when changing tubes, contact Gyraf Audio for instructions on matching and proper adjustment of the unit.