Onix SP3 Amp Overview and Design
Design and Construction
The Melody SP3 is an attractive retro design recalling the art deco era. The amplifier will certainly draw attention and start conversations if prominently displayed; perhaps as much attention from audiophytes who know very little about audio gear and have no idea what the SP3 is as well as Audioholics who know exactly what type of amplifier is before them. The SP3 has a lacquered silver finish with Onix in black lettering and one blue power LED centered on the faceplate. Rather than boxing the internal hardware, it is featured as part of the esthetics: on the top of the unit, to the front, are four larger tubes that are flanked by six smaller tubes with a pair of bulging output transformers at the back of the unit. All the covers and cages for the tubes are easily removable, allowing one to bask, if you will, in the warm glow of the tubes under power.
The SP3 is a ten tube stereo design that takes a minimalist approach; features are few which leads to a simplified audio path that many consider a source of improved fidelity. There are only three controls to operate and two inputs: the on/off rocker switch on the left side, an input selector rocker switch on the right side, the volume knob in the center of the faceplate, a CD input, and an auxiliary input.
On the back there are six binding posts to hook up four speaker leads: two black and four red. A pair of red binding posts is grouped with each of black connectors, one post labeled 8 ohms and the other 4 ohms, relating to the two options for the output transformers. The two inputs are stacked vertically with the left and right channels at the outside of the chassis. The SP3 also has a detachable power chord that mounts at the center of the back panel.
The tube compliment includes the four larger 5881 tubes in a push pull (AB) design and the six smaller tubes that include two each of 12AX7, 6922, and 12AU7 type tubes. The 5881 tubes are housed under a common cage attached to the chassis using banana plugs while the smaller tubes each have their own housing on spring clips.
Adjustable bias controls are provided for the left and right channels on the respective sides behind the rocker switches. There are two adjustment dials and three probe leads. Biasing adjustments for tube amplifiers regulates a negative voltage across the output tubes to optimize their performance. Typically, biasing is adjusted because sonic performance is dependant on these settings: new tubes need to be tuned because of tolerance issues even within the same specifications, as tubes age the specifications drift with deterioration requiring retuning for optimum performance, and audiophiles who really like tubes need something to play with. Care should be taken with bias adjustments where too much current across the tubes will damage them and too little will cause audible distortion.
This unit is fairly heavy; at 56 lbs, the SP3 easily outweighs most seven channel A/V receivers on the market and some two channel audiophile amplifiers. One issue that I would like to mention: the support feet, there are only three, two in the back and one in the front. This is a meta-stable support condition that leaves the unit more prone to tipping while moving it. The saving grace is that the large output transformers on the back do provide a resisting moment to counterbalance this condition to some extent. It would be a good idea to make sure that the SP3 s properly seated and upright any time it is relocated.
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