Shinobu Karaki of Japan's Aurorasound thinks out of the box. His Pada EL34 tube power amp for example uses transistor drivers. Except for KR Audio and Nagra with their 300B integrated, I'm not aware of other brands who practice this reverse hybrid approach. For his 10.8kg Preda preamplifier, he's not using any tubes even though its Cada precursor did; 3A5/DCC90 direct-heated 7-pin double triodes no less. But he uses 54-step Slagleformers without step-up gain option. And, he brackets those OEM modules with discrete DC-coupled buffers for constant 56kΩ input impedance and constant 47Ω output impedance.

Bandwidth is 5Hz to 100kHz -1.5dB. The bandwidth of the output stage is 12MHz for exceptional speed. It's reportedly capable of driving 110dB of open-loop gain. It claims THD+N of 0.0003% and a slew rate of 28V/µs. One Preda uses six of these amplifier modules on gold-plated PCB and with vintage NEC and Toshiba transistors of which Karaki-San has a large NOS inventory. The Preda also gets dual-mono power supplies and for Rhodium-plated connectivity 4:2 RCA:XLR inputs and one each RCA/XLR output.

The familiar Chapman remote controls volume, balance, mute, display on/off, input selection and polarity inversion. On the frontal belly, there's a -16dB low-gain switch*. That moves the entire gain/attenuation range downward, perfect for perhaps late-night SPL, high-gain systems and/or very efficient speakers. Next to said gain-cut button, there's also the power mains. Relocating those two controls declutters the face without having to reach 'round back. And having the green indicator LED face down to be primarily seen as a shelf reflection, there's no annoying iris attack. Whilst the Preda is not a passive preamp—it uses active buffers to properly terminate its autoformers—its concept and Karaki-San's 28 years with Texas Instruments of Japan did suggest a relentless pursuit of ultimate neutrality plus uncompromised drive: a passive with guts if you will. At least that was my read on its concept. It's squarely why I requested this assignment.
Shinobu with Per Lundahl whose output transformers power his Aurorasound Pada tube amp. Lundahl's very first tube amp output transformer account was Shindo Labs of Japan by the way.

* This switch essentially turns the Preda into a negative gain device (its circuit's 10dB of voltage gain is set 6dB below the incoming signal). That still doesn't make it a passive; except that by now operating 6dB below unity gain at full output, it virtually behaves like one.

Two Preda preamplifiers under assembly in Shinobu's atelier.

When I sent Shinobu the preceding copy for corrections and additions, he responded with "I am surprised by how well you described Preda in detail although you do not have it yet. There is no misunderstanding! I will send a short summary about my background, my objectives and my sonic ideals later. Also, I'll send some hidden technical details about the design."

With their wood casings, Shinobu's Vida phono stage and Heada balanced headphone amplifier embody a vintage aesthetic unlike the more modernistic Preda. This lack of unified cosmetics is more typical of a smaller enthusiast's operation than a mainstream electronics house.

Now the hand of Lady Circumstance tore asunder the Heavens to reach down from on high. Actually, it was Aurorasound's UK distributor Guy Sergeant of PureSound playing his hand: "I do have a Preda I can loan you although it needs to go to a prospective customer for a few weeks first. I do also have the two-box fully balanced TBSP version which you'd be welcome to try. That one hasn't been reviewed anywhere yet." Given that true balanced ups the usual game to two of everything to transcend the ancient joke about the Buddhist monk ordering his burger from a NYC street vendor (make me one with everything); and given how we'd already seen just how stuffed the standard Preda box is... two boxes really are mandatory to house the additional modules. That's a lot of material excess for home audio. Our cable lengths are a fraction of the hundreds of metres in recording studios which mandate the inherent noise rejection of balanced lines. Just so, companies like Balanced Audio Technologies do stake their entire product catalogue on the superiority of balanced even for home use. Others call the inherent complexity and costs of doing it right unnecessary for our purposes. Or they claim that to create a truly balanced signal—one whose independently amplified phase halves are 100% identical—is essentially impossible. Of course so-called push/pull circuits rely on the very same matching first with their phase splitters, then with their subsequent counter-phase circuitry. Seeing how push/pull amplification is in the vast majority over single-ended, the "imperfectly balanced" argument might hobble on just one foot.

All this by way of keeping a cooler head on the subject of balanced circuitry. Particularly so-called balanced preamps often cheat with stereo rather than quad volume controls. The two-box Preda does not. Does that make it sufficiently better than the standard Preda which already is balanced past its attenuators to justify the price hike? We'll just pose that question for further head cooling, not to pursue an actual answer. Suffice it to say that TBSP stands for true balanced signal path; and that the two-chassis necessity has the fringe benefit of moving the entire dual-mono power supply—discrete-channel supplies for both digital and analog circuits—into the second 'dirty' box. That leaves the upper control box clean for just music signal. And because the TBSP is literally twice of everything, its power consumption doubles and so does price. It seems fair to call this extremist gear for the rare take-no-prisoners customer pursuing end-game hardware. All published performance specs like bandwidth, THD+N and i/o impedance are identical to the standard Preda. The number of inputs and output differs. Instead of single RCA/XLR outputs, the TBSP gets a second XLR and instead of 2 balanced inputs, it gets six. The four RCA inputs of the one-box unit carry over. That gives the two-box unit 10 inputs and three outputs.