This review page is supported in part by the sponsors whose ad banners are displayed below
Both engineers on the iQube design team had their own specific tasks assigned. Bruno's knowledge and experience with class D is unique in the world. Add to that his extensive knowledge of other technologies like tubes and it was clear that he had to set up the heart of the amplifier and size it. Guido then took that design and added other features, the first a turn-on transient suppressor. This was of great importance seeing how certain ear-canal headphones have up to 119dB of sensitivity at 1mW. Guido's solution limits max power on/off noise to 100uV to protect the user's hearing - a task that proved easier said than done. A related demand was operational noise which had to be extremely low while eschewing conventional noise suppressors. The circuit itself had be ultra low noise since using noise suppressors would have been putting the horse behind the cart as Guido put it.

The next addition to Bruno's central amplifier board was for Guido to fit it with the battery charger. Once finished on a bread board, the works had to be transferred to PCB. Here Guido used the skills of long-time audio partner Peter van Vegchel and after three iterations, the PCB was electronically and mechanically up to the required high standard. With a working prototype now, the fine tuning could begin. In one-on-one exchanges between Hans and Guido, the latter translated Hans' specific sonic feedback into the correct components on the board. The end results of these listening and component swap sessions are carbon composite resistors throughout the signal path, Vishay/BC Components Series 036 capacitors in the power supply and an Alps attenuator. The DC-coupled design required no coupling capacitors and typical offset is less than 0.5mV.

During the voicing sessions, Hans used a wide variety of headphones - a Grado GS1000 open design, an Ultrasone ED9 closed design and a set of Ultimate Ears 11 Pro custom in-ear monitors. Hans was able to detect the small and delicate changes the swapping of electronic component made. Guido added a more radical way to judge the amplifier by using it as a line stage between his Tent Labs CDP and 300B SET power amplifier into a set of Ensemble Reference monitor speakers.

When studying the PCB, one discovers two OPA2376 op amps. These work as integrators which, according to Guido, is a completely different task than amplifying an analog signal. The aural effect of these operational amplifiers - um, operates in another league than when used in linear circuits. A LT1671 handles phase inversion and a Linear Technology LT1512 IC handles battery charging. Eight paralleled 74AC240 inverters per channel appear in the output stage. This means the iQube could drive a 100dB+ 8-ohm loudspeaker.

This image opens in a new window at 2000 x 1312 and 202KB

From the technical specification sheet, we quote an input impedance of 10kOhm and a voltage gain of 2 or 7 depending on the switch setting. Maximum output is 160mwpc at 16 ohm, 80mwpc at 32 ohm and 12mpwc at 200. Output impedance is <0,1 ohm below 5 kHz and <1.5 at 20kHz. Total harmonic distortion is typical 0.01% at 200mV output and maxes at 0.03% while unweighted output noise is 10uV. The battery charger accepts any DC voltage between 5 and 20 volt and draws a current of 0.3 amps. Charging time is typically 3 to 4 hours.

The iQube is packed in a box very similar to the iPod shipping box. They are the same in size, with the iQube's a bit thicker. Another visual difference but a big one in user friendliness are the two thumb holes in the outer box that made pulling out the inner box a jiffy compared to getting at the inner iPod box.

The inner flip lid box held the iQube in a foamed compartment on the right while a closed envelope-like compartment contained an interconnect, the owner's manual and a black elastic band. On the iQube amplifier itself, a bright yellow sign warns that alkaline batteries are preinstalled and to not connect the iQube to a charger or USB port before changing the batteries to rechargeables. This warning is repeated twice in the manual.

With a weight of 204 grams including batteries and a size of 10cm (10.7cm with attenuator knob) x 6.3 x 2.3, the iQube rekindled that small, relatively heavy nostalgia. This was enhanced further by the black paint on the top and bottom covers which isn't smooth but rubbery. Its slightly rough surface prevents the iQube from sliding and protects the back of an iPod when strapped to the top of the amplifier with the supplied elastic band. This band by the way is another example of the thorough design brief. It is not just a plain rubber band. It's like the popular yellow wrist bands of Lance Armstrong fighting cancer. The iQube band states "iQube. power to the music".

Other design features are the not fully clear anodized aluminum casing. The color has a brownish haze which in combination with the black panels gives the iQube a very classic, almost roaring '20s style. The reminiscence of a period gentleman's pocket flask with its silver and black leather is striking. When placed upright, the attenuator knob is like the screw top of the flask, negated only by the fact that to the left of the knob sits the main on/off switch and a tiny green control light. To its right, in perfectly symmetrical fashion, sits the gain switch and battery charger indicator. Only four engraved marks are present on the front indicating the setting for both switches. The attenuator knob has no visible markers.