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Some lessons are learned only to be forgotten again. I'd experimented with passive preamps before and ended up with what I consider to be activated passives. My versions thereof are Esoteric's C-03 and Wyred4Sound's STP-SE. The former can be set to zero voltage gain to operate exclusively below or at unity gain. Naturally it then still runs off the same voltage rails which the 12/24dB active gain settings employ. The Wyred applies no gain until the source output voltage is crossed. Neither machine has issues with driving long interconnects. Both offer full remote facilities. For occasions requiring tubular intercession, I also keep a two-box ModWright on hand.
This story would end there had Shigeki Yamamoto not solicited me to review his AT-03-1A passive volume controller. It's built up of surface-mount precision resistors on a quality Elna switch with very short hookup wires. In association with my Yamamoto A-09S 300B amp, the results were stunning. Drawbacks? No remote; and the necessity for short cables to the amp. On the sonic shopping list of 'measurable' attributes, nothing really changed between my usual C-03 set at zero gain and the Yamamoto. Yet the subjective listening experience was quite different. The passive removed tension and grippiness to feel nearly limpid. On this sublimely relaxed canvas, the tone color magic of 300B persuasiveness unfurled in ways I found most compelling - to such an extent in fact that my flagging interest in such valve amps rekindled.


Put differently, my 'conversion' to transistors at the hands of the F5 and J2 models from Nelson Pass' specialty FirstWatt stable had sensitized me to the coagulation effects of 2nd-order harmonic distortion. This interferes with the transistors' crystallized lucidity to sound less resolved and direct. Things feel more 'buffered', distanced and a bit hazy in fact. Lo and behold—and I'd been there before but forgotten it—Yamamoto's passive removed these in-between veils which the same amp suffered when preceded by my active preamps. Presto, I found myself straight at the heart of SET. You know it when it happens. Naturally, heavily driven rhythmic fare with challenging bass and multi-layer complexity was still better served by the sand amps. But I had reconnected with what makes valves special in a way that kept specific liabilities at bay which had in the meantime divorced me from the genre in general.

The same hallelujah transferred intact to my custom-commissioned Trafomatic Kaivalya monoblocks. Designer Sasa Cokic took great pains to strategically trim the THD behavior of particularly the 12AU7 triode driver. An unusual local feedback loop between that and the EL84 inputs through the interstage transformer applies an apparently inconsequential 0.3dB of NFB. Sasa however claims that this merest whiff of feedback is responsible for a 30% reduction of THD. That's significant. For his class A push/pull output stage, he too applied local feedback through the double C-core output transformer, this one at 4dB.


The Kaivalya was thus deliberately disciplined to shun typical 300B-type THD. So deliberate and dialled are the resultant sonics at least to these ears that any intrusion, dilution or shifting by way of a preceding active preamp of even very high pedigree undermines this allure by degrees. It's like the brilliant clarity of pure water sparkling in an expertly cut decanter. It gets slightly opaque when one slips in a heavier infusion which, though translucent itself, creates some cloudiness. Sonically this manifests as thickening; as a slowing of reflexes; and an insertion of distance and subtle cotton batting one must now work through. The Yamamoto passive completely removed that 'stuff'.

Until Sasa authors his own matching preamp in 2011, I feel faced with needing a superior passive to really hear my new Kaivalyas at their very best. With a deliberately low 3V input sensitivity on them, my hi-gain 5.45V max Weiss DAC2 already is the perfect source. How about creature features of remote control, fine 1dB steps, balance control and input switching?


Canvassing the net shows numerous transformer volume controls, autoformer volume controls, standard resistive solutions and variable resistors set by the light intensity of a diode. The perhaps most extreme acknowledgement for how resistive passives don't like long output cables is manifested in TweakAudio's $350 Ultimate Attenuators [above]. Dual mono, those devices ride RCA or XLR connectors which jack directly into the amp. Forget convenience of course.


Daniel Weiss' newer ATT 202 remote-controlled passive looks very appealing but is currently under revision to incorporate automatic impedance matching [his clutch-driven custom volume control is shown at left].

I'd already owned the Music First Audio Passive Magnetic whose all-out remote version is very pricey. Ditto for the SMc Audio. The Promitheus Audio from Malaysia lacks remote. The forthcoming Audience Wavemaster does have it but is projected to sell for around $12.000. The design itself is apparently based on John Chapman's OEM Slageformers, 61-tap autoformers packaged very compact [right] to avoid the rat's nest in my former MFA.

To not compete with his OEMs, Chapman has righteously discontinued manufacture of his own turnkey Tap-X preamp. That incorporated similar relay-switched AVC modules to what Audience will use. Incidentally those multi-tapped autoformers were co-developed with expert winder Dave Slagle when Music First cancelled their former licensing agreement with Bent Audio for their popular TVC modules. (Audience supplies special OHNO wiring for their autoformers and Dave Slagle optimized his winding geometry to suit the new wire. There's also a custom buffer stage designed by Roger Sheker, costly WBT NextGen connectors, a headphone output and more.)


Still in the colonies, the Sonic Euphoria is no more while Placette Audio's $1.595 remote-controlled passive with Vishay resistors is very much kicking and offering a very stout 125 steps. Nelson Pass has a basic buffered resistive passive in his FirstWatt stable. Ed Schilling from The Horn Shoppe sells his photo-cell, not optocoupler The Truth preamp. The Magnequest collaboration with Steve Eddy might be in production by now. The AVTAC Pasiphae has all possible bells and whistles and a price tag to match. Going East to Serbia, Dragan Solaja's SA-TVC-1 comes with remote control but his relay-switched transformer secondaries offer only 24 steps. Farther East there's Opera/Consonance with their TVC and DIY Hifi Supply with their Django. And there surely are lots more. This isn't a comprehensive survey of the breed's present offerings by any stretch. It's merely a reflection on current goings-on in Casa Chardonne. Those were precipitated by remembering, in the actual listening seat, just how fabulously purist valve amps get along with passive volume controllers. Passives clearly aren't for everyone nor for all systems. But for tube amps whose interaction with properly matched speakers is so locked as to not want any alterations—just an invisible means to control volume—they can be especially attractive. Time will tell what I end up with for these very particular purposes...
PS: Swiss reader Walter Stähli reminded me of two others I'd forgotten and two more I'd never heard of before: Two 48-step attenuators from Khozmo for $189; a 41-step unit from Acoustic Dimension for €200; the STA-522 TVC unit from Thailand's Silk Transformers; and the $2.500 Magnetic Enigma preamp from Stereoknight.