Audiopax Model Eighty Eight monoblock power amplifier Page 2
In general, amplifier distortion and speaker distortion will add or subtract in complex ways that are functions of the phase differences between the amplifier and the speaker, speaker phase being variable with frequency. You might say that when it comes to combining amplifier and speaker distortion, more can be less and less can be more. The Timbre Lock bias settings provide a way of fine-tuning the Eighty Eight's distortion spectrum to produce more optimal cancellation of the speaker's distortion.
The resulting amplifier is as unusual in appearance as it is in design principles. Given that each monoblock amplifier is actually two amplifiers in one, it's quite compact but fairly heavy, and the two handles are sensibly located on top. The chassis is made of chrome-plated solid brass, with sides and plinth of lacquered or unlacquered wood (the review samples' blue lacquer matched my Avantgarde Unos). It makes a classy impression. The RCA input jacks and five-way binding posts are plated with rhodium and made by Cardas. Rather than a separate power switch and an AC fuse, a switch at the rear acts as both power switch and circuit breaker, and activates a relay that delays the high-voltage supply to the KT88 tubes for about 30 seconds. Two small toggle switches activate the bias LEDs, and two chrome-plated knobs are used for adjusting bias (Timbre Lock).
The Journey Begins
Having connected the input and output cables (the Audiopax Eighty Eight inverts absolute polarity, so I reversed the speaker cable connections to compensate for this) and turned on the amplifiers, the first thing I noticed was how little noise there was coming through the speakers. With speakers as sensitive as the Avantgarde Unos (+100dB), keeping noise at bay is no trivial matter, and some otherwise admirable amplifiers (such as the Air Tight ATM-211, reviewed in October 2002, Vol.25 No.10) are problematic in this respect. The quietest amplifier I'd had in my system prior to the arrival of the Eighty Eight was the Quicksilver Horn Mono; the Eighty Eight was as quiet or quieter. Mechanical noise from the transformers was also conspicuous by its absence—another welcome characteristic.
The owner's manual has a couple of pages of instruction dealing with the setting of the Timbre Lock controls. The left control is said to determine "definition," with settings in the lower part of the range resulting in a "leaner" sound; going past the 12 o'clock setting is supposed to soften transient impact, attack, and inner detail. The right control is described as affecting overall smoothness and tone: counterclockwise, leaner and drier; clockwise, richer sound.
According to the manual, what's more important than each control's actual setting is the amount of offset, or difference, between the two. Eduardo de Lima told me that he thinks of the level setting of each control knob as analogous to a video monitor's Brightness control, with the offset corresponding to Contrast. The optimal setting will depend on the specific associated components and personal preference, but a suggested starting point is with the left control at 10 o'clock and the right at 2 o'clock.
Following the recommended 20-minute warmup period, that's how I set up the Model Eighty Eights. The sound was good enough that my inclination was to leave the Timbre Lock controls alone and just enjoy the music. When I eventually got around to playing with the Timbre Lock controls, I found that the best sound was indeed produced with an offset between the two controls. Setting both at the same level produced a rather flat, uninvolving sound; my favorite setup was with the left at 11 o'clock, the right at 3 o'clock.