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Hux Balanced Buss Summing Amplifier

This unit was custom built for David Spearritt (Brisbane), it is fully balanced buss summing amplifier. The brief was to make the signal path as uncluttered as possible, with as much headroom as possible (with a conventional power supply), with as low a noise floor as possible and with as clean a sound as possible. I am still waiting for David to send me some good in-use pics and will update this page when I get them.

This is a very high end summing amp, it features a passive input stage onto an balanced active mix buss. The unit has an electrically short signal path and has only one capacitor in line with the signal (per channel), it has an industrial build (it should be very hard to break) and is as small as possible (David plans to carry it in a backpack).

There are 4 x stereo balanced inputs on 5-pin XLR and 2 x stereo floating balanced outputs on 3-pin XLR. The first pair of outputs are at unity gain and the second pair are set for unity less 10dB to suit the input of the Nagra V portable digital recorder (owned by David Spearritt). The measured clip point is +29dBu. The only user controls are input mute switches. Inputs are LCR with C requiring the use of a "mono" input cable. Panning of a mono input signal is not catered for but it is possible by using input cables modified for the task.

The VU metering is driven by meter drive electronics with true VU ballistics. The LED between the VU meters normally glows green, if the true clip point detector senses clipping then several things happen, the LED turns red, the meter backlights are blanked and the VU meters are muted (audio remains unaffected). Later meter drive versions (if I build others) will have the meter and backlight mute set at 10dB over 0VU so that the meters are muted for signals that would cause them to pin, this will enable testing and use at high input levels without meter damage.

Not the greatest shot but it shows the essential look when the unit is powered up.

Back to the egg. The empty box before being loaded with bits. It was a tricky job to get the board with the mute switches into this space and I wasn't sure if I could stack three PCB's horizontally in there at this stage (well I knew that I would find a way), I had to lay capacitors down sideways on the meter board to make it fit.

The above shows the nearly finished summing amp, the left hand side shows the passive input switching, the green circuit board (center) is the left channel of the balanced summing and output stage, mounted below is the right channel and below that is the clip detector and meter drive electronics board, there is a lot crammed into this box, all internal signal cabling is Mogami installation cable, the VU meters (right side) are backlit with warm white LED's and have true VU ballistics

The nearly complete Hux Summing Amplifier and its overbuilt power supply. The power supply also outputs +48 volts as it is identical the one that powers David Spearritt's "Hux Box" mic pre-amp (which is the original version of the Hux TC Pre but built into a small diecast box). Some info on the Hux Box can be found on here (scroll down to the third photo and onwards)

A comment from the owner, David Spearritt, who commissioned the little beasty : "This little mixer is a real gem. I am astonished at the sound improvement over Mackie and indeed the Nagra mixer which sounds as nice but is noisy in comparison. The noise floor with 5 mics we had last night, 2 into AMEK, 2 into Gold Channel and 1 spot from Hux box is simply the lowest I have heard and there is this silky air in the sound which is beautiful. I was pretty sure all that extra circuitry in typical mixers with controls was undesirable but the extent was not expected. I am going to use this as the centerpiece of all my chamber music recording from now on."