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Onix SP3 Amp System Setup


System set up is minimal for the SP3, but may be hampered by the included manual for some.  To say that the manual for the Melody SP3 is thin is an understatement.  Not only is it thin but the manual also has very little printed on the few pages that are present.  Fortunately, there are only three controls and they are labeled; if the user does not take notice of the labeling on the sides of the chassis, identifying the controls is left it up to trial and error.

One issue that may come up: with no information in the manual, those, who like me, own speakers with a 6 ohm nominal impedance are left to their own judgment as to which connection to make.  In the case of the 6 ohm speaker, it may be prudent to use the 4 ohm lead to minimize the possibility of a higher current draw than the 8 ohm lead may be designed to safely provide.

The specifications provided on AV123’s web site indicate that the unit features a manually adjustable bias.  There are two bias controls and three probe points on each side of the amplifier behind the rocker switches.  The owner’s manual again gives no indication of such a feature (though we were told AV123 is now shipping a supplementary sheet explaining this function) or advice on how and why one would want to make this adjustment.  Moreover, because the external control for the adjustment requires a voltmeter, anyone interested in making this adjustment should keep in mind safety when messing with high voltage sources, such as tube amplifiers, as it is potentially risky for those unfamiliar with the innards of electronic devices.  Incorrectly adjusting bias can damage the tubes and the amplifier and a lack of basic safety procedures can be damaging to the one making the adjustment.

As a nice touch, the SP3 comes with a pair of white glove with the Melody name embroidered on them.  Since the manual does not discuss why gloves are included, I will for the benefit of those who don’t already know.  Use the gloves any time the tubes need to be directly handled, as with halogen lamps, any skin oil on the glass tubes will cause a localized temperature concentration that may cause them to crack under power.

Another item that perhaps should be included in the manual are manufacturer recommendations as to the what, where, and when for the tubes.  Tubes occasionally get broken and they also deteriorate sonically over time.  Because this product is intended as an introduction to the ‘wonderful world of tubes’, some information on electrical requirements for replacement tubes, the names for suppliers of compatible tubes, and recommendations on the useful life of the tubes supplied might be in order.  Valuable information if this is a first experience owning and maintaining tube based gear.  Granted, all the tubes that come stock with the unit say ‘Melody’ on them, but I saw no listing for replacement tubes under products on either the Melody or the AV123 websites.

As a public service, I am including some links to information regarding vacuum tubes and bias that I have found on the web.  Many relate to musical instrument amplifiers but that is inconsequential.  Keep in mind that I do not necessarily endorse anything said in these pages but provide them as a source of information for tube audiophytes.

Basic tube information:

Information on tube bias:

Tube types and manufacturers:


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