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Maximinus. As MSB have championed for years with their own products and with advanced modules for OEMs—and as French DIYer-gone-pro Vincent Brient had accomplished by hand with his TotalDac project to nearly gain a contract with a major firm—the Thrax eschews even true multi-bit integrated converter chips like the famous BB 1704. Instead it accomplishes the task with a discrete resistor array by way of MSB's embedded DAC IV board below. This is switched by very fast control logic via custom firmware. This DAC swings 3.6V peak to peak to generate 1.27Vrms which past the permalloy Tamura TK-135 output transformer becomes ~1V on RCA/XLR. Output impedance is ~550Ω. The 32/384 USB transceiver is MSB issue and powered from their motherboard. A forthcoming firmware update will enable the newer DSD-over-USB standard. The machine's layout already includes an option-board slot. "We have two spare S/PDIF and two I²S interfaces. By changing the control board firmware, we can add specific options which comply with our sonic and technical quality standards. In response to client requests the currently planned options are alternate USB like the Edel ABC/PCB, a LAN/UpNP client, HDMI, FireWire and by special request even custom I²S where we'd have to know the transport to be connected. We're also investigating a suitable AirPlay module to make the machine compatible with streaming iTunes. With the fast-moving changes in this sector, we're committed to leaving all our options open."

"One of our core philosophies has always been to keep all sources galvanically isolated from the inner workings of our products. Thus upstream ground and common-mode noise can't contaminate our own ground planes. With the Maximinus we isolate the twin coax, twin AES/EBU, USB and Ethernet inputs with very special SC947-02 'super' transformers which offer the very best possible performance. Their only drawback is costing more than most converters. The twin optical inputs are isolated by optocouplers. Performance of the Toslink standard is known to be less serious and here was merely added to accommodate Apple TV and similar sources.


"In the Maximinus all incoming noise has been comprehensively stripped to deliver a pure clean signal to our MSB board where DSP accomplishes a few things. If enabled it upsamples incoming signal to 352.8 or 384kHz at 32 bits. If enabled it also reclocks the data to the internal clock over a digital flywheel. A second DSP stage handles digital filtering which affects pulse energy and bandwidth. Because we couldn't decide which filter sounded best—it depends on the music—we left in several user-selectable options. The filtered signal then is sent to our quad converters over ultra-fast optocouplers to again maintain a pristine interface between the digital front end and the mixed signal plane of the DAC modules."

"The four fully discrete converters process our phase-inverted data. To prevent conversion-generated currents and noise from leaking into the ground plane or the power supply, we tap the signal from each channel's two conversion ladders by directly loading each output with the other. Hence all ground and PSU-induced noise ends up in common mode to the output transformer to be utterly ignored. The transformer also provides necessary impedance matching. The converter stage's true floating balanced outputs then feed our analog RCA or XLR directly without any buffers, opamps or I/V conversion.


"For all this galvanic isolation to work requires separate power transformers for the control logic, DSPs, DAC modules, clock and option boards each with their own silicon-carbide rectifier, high-performance regulator and our own constant-current load. Nasty digital clocks go right through most regulators. The only proper way of screening various downstream circuits is to power them independently. We developed our constant current load technology to reduce to insignificance all load variations and the effect which the load-generated noise has on the DC power lines of our boards. This eliminates a major source of EMI/RFI noise inside the component's case. In short, we use MSB with their extreme number-crunching know-how for the very best R2R converter modules money can buy and cook everything else ourselves. The hidden meaning of the name Maximinus refers to how a 'barbarian' Thracian ruled the Roman empire like us analog guys now rule the digital domain."
Heros assembly
Heros. This 30kg heavy 100-watt into both 8Ω and 4Ω monaural design marries a CSS-loaded single 5687 twin triode with grounded cathodes for differential voltage gain to a cascaded Jfet/Mosfet current buffer. This creates fully differential signal processing between phase-splitting input transformer and push/pull summing output transformer from Plitron's toroidal 4144-00 range. It floats the entire gain circuitry for full immunity from outside interference. The output-stage power supply exploits the latest in silicon-carbide rectifier diodes to keep constant noise-free voltage on the Ixys power Fets. The massive enclosure with its internal subdivisions for different sub circuits acts as a singular monolithic heat sink to dissipate class A heat whilst doubling as resonance-suppressing platform.

Thrax and Magico at HighEnd Munich 2012
Besides the expected single pair of speaker terminals on the back there are three small switches for the XLR/RCA inputs, hi/lo gain as 2/4V input sensitivity and two transformer taps which show about 0.4Ω for the 8Ω tap and slightly less for the 4Ω tap. Even for a rarer hybrid the Heros still manages to carve out its very own path. This is most unexpected with the output transformer. Aside from the famous autoformers which McIntosh use, an output transformer is a rare sight behind transistor output stages since their native low output impedance doesn't require down conversion by magnetics. Aside from isolation, Rumen also cited far higher efficiency for their class A output stage. 230-watt power consumption for 100-watt output is unexpectedly green.

Thrax and Wilson at HighEnd Munich 2010
"Apart from the output stage, practically nothing else consumes power. The driver and logic circuits run on 3-4 watts, the Jfet has a very low voltage drop and the Mosfet is a depletion-mode device. Hence we swing 96% of the power supply's voltage. Our efficiency is as good as it gets from this arrangement or about 45% (we lose 2% from the output transformer's resistance)." The amps' name derives from Heros Karabazmos, an ancient god of the underworld usually depicted as a horseman slaying a beast with a spear to be the likely precursor of St. George.

Extrapolating from the above gets us at another Thrax statement. "A few other audio companies compete with us on sound. Nobody does on silence." What Rumen & team consider their decisive difference—what silence signifies—is pursued with transformer coupling on all inputs and outputs and maximally filtered regulated power supplies. Meanwhile the actual signal-path circuitry is kept as simple as possible. This reflects in a single stage for the preamp and the absence of reconstruction filter, buffering or I/V conversion stages in the DAC. Those who believe that power supplies make 90% of the final sound will applaud. Likewise those who believe that additional gain stages create higher-order distortion products. Another takeaway from the specs is low source gain and low amplifier input sensitivity. At 1V the Maximinus outputs half the industry standard. Many balanced sources deliver 4V or more. The Heros is switchable between 2/4V. Most modern amps reach full output at 1V or less. Coupled to high source gain, high amplifier input sensitivity usualy 'overloads' a preamp's volume control range to go from mute to too loud in a few clicks. Here the transformer volume of the Dionysos is limited to 23 steps below unity gain. Just how would this manifest without its stable mates whose specifications are naturally copasetic with the Thrax preamp?