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Reviewer: Srajan Ebaen
Source: Zanden Audio Model 2000P/5000S
Preamp/Integrated: ModWright SWL 9.0SE; Music First Audio Passive Magnetic; Hyperion Sound BEC-P25T
EQ: Rane PEQ55 active merely below 40Hz
Amp: 2 x Audiosector Patek SE; Yamamoto A-08S; Canary Audio CA-308s; FirstWatt F3 [on review]
Speakers: Zu Cable Definition Pro; Gallo Reference 3
Cables: Zanden Audio proprietary I²S cable, Zu Cable Varial, Gede, Libtech and Ibis; Stealth Audio Cable Indra, MetaCarbon & NanoFiber [on loan]; SilverFi interconnects; Crystal Cable Reference power cords; ZCable Hurricane power cords on both conditioners
Stands: 1 x Grand Prix Audio Monaco four-tier
Powerline conditioning: 2 x Walker Audio Velocitor S
Sundry accessories: GPA Formula Carbon/Kevlar shelf for transport; GPA Apex footers underneath stand, DAC and amp; Walker Audio SST on all connections; Walker Audio Vivid CD cleaner; Furutech RD-2 CD demagnetizer; WorldPower cryo'd Hubbell wall sockets
Room size: 30' w x 18' d x 10' h [sloping ceiling] in long-wall setup in one half, with open adjoining living room for a total of ca.1000 squ.ft floor plan
Review Component Retail: $4,200 with all tubes included as reviewed
SilverTone Audio is a Singapore manufacturer. They specialize in Permalloy line/output transformers, audio chokes and high-quality audio equipment. Their dual-mono single-chassis Model 3.2 stereo amplifier is a zero NFB Western Electric-style 300B parafeed affair. It's also an upscale showcase to demonstrate the refinement of their proprietary Permalloy parts. This uniquely styled amplifier sports a power transformer with a noise reduction electrostatic shield between its primary and secondary windings and two absolutely massive air-gapped silicon-steel-core anode chokes for the 300Bs. These three blacked-out cores (power transformer upfront followed by the chokes) are sandwiched between the stainless steel casings of the discrete channels. Two in-house-wound, non-gapped Permalloy output transformers take pride of place on deck right behind the output triodes. There are two more DC chokes inside each channel chassis, one each for the 9-pin 6C45pi cathode-coupled driver tubes. There are DC filament supplies on the direct-heated triodes to avoid hum. There's two 5U4G valve rectifiers facing the viewer. In toto, there's in excess of 60 pounds of iron in residence behind the architectural laser-cut stainless steel casings with their opaque plexi windows. This assembly makes for an ultra-modern, frosty Scandinavian tube amp aesthetic.
Recounts SilverTone: "For those of you familiar with SETs, the Western Electric 91B was the amplifier responsible for the resurgence of the genre. Having heard a WE91B clone using a pair of original A171 output transformer, WE310 pentode driver and WE300B direct-heated output triode, I finally understood why it was so famous. The midrange produced a seductively rich tone, an excellent match for playing vocal oriented music. The highs were a little soft but free from edginess. The bass was a bit booming and lacked definition, not entirely surprising given that the frequency range in those days was 40Hz to 8kHz. During our prototyping for a parafeed output tranny, we experimented with many winding techniques to optimize high frequency extension. However, listening sessions did not correlate with the nice square wave measurements we achieved. In fact, the best-looking square wave response sounded the most closed in. To achieve a more pleasing tone, we studied the WE91B which elicits the opposite of what we were getting from our design. We noted how its slighty attenuated high frequencies produced a more open soundstage with a warmer midrange. Armed with this insight, we focused on reducing high frequency extension to the point where it did not compromise electrical performance. After all, SETs do not require extension into the 100KHz range since there is no feedback loop to cause circuit instability."

Technical director Gilwin Tan explained how they have operated the Model 3.2 with Lowther front-loaded horns, Tannoy Gold monitors in customized cabinets, Tannoy HPD Eatons, Quad ESL63s and -- by cross-referencing with speakers carried by their retail partners in Singapore -- Hyperion, Almarro and Reference 3A models. "We have also done comparisons with similarly priced 300B amplifiers from famous firms and collected favorable feedback." This was in response to my concern that my customary 101dB Zu Definition Pro speakers would be rather ruthless about exposing hum levels. Gilwin felt that their amp would pass this test with flying colors. So what about the single-minded SilverTone Audio focus on Permalloy cores?

We learn that in 1914, Gustav Elmen of Bell Laboratories discovered that the 20/80 iron/nickel Fe-Ni alloy exhibited higher magnetic permeability than silicon steel and christened it Permalloy. In 1923, Elmen found that magnetic permeability could be dramatically enhanced when Permalloy was heat treated. While known as Permalloy in Japan, it is standardized as Fe-Ni Alloy. It is also known as Mo-Permalloy, Mu-Metal, M-1040, Supermalloy, Ultraperm and yet other names. It is used for transformer laminations and anisotropic magnetoresistive (AMR) sensors. With a 78% nickel content, Permalloy "has the highest permeability and the lowest coercive force" and is used for tape record head cores, GMR heads for the data storage industry and CRT shield covers". With a 45% nickel content, Permalloy "has the largest saturation induction and is used for sensitive relays and AC transformers." [From Nakano Permalloy]. "Permalloy is deposited from a plating bath using nickel sulfate, nickel chloride, ferrous sulfate, boric acid, sodium saccharin and a wetting agent. The alloy as deposited has very useful magnetic properties and is used in many different types of devices, including logic devices, thin-film recording heads and shielding devices. Other materials may be deposited with the iron and nickel. Cobalt and indium are examples." [From Arthur S. Kushner Electroplating School].

It is generally acknowledged that Permalloy transformers offer reduced HF losses and thus enjoy far superior sensitivity to micro signal fluctuations that elude their silicone-steel brethren. On the flip side, they
saturate at lower magnetic flux levels. This means reduced power handling for the equivalent cross sections of regular cores. Seeing that power requirements in audio compound in the bass, Permalloy cores carry a reputation for compromised LF control. Hence transformer inductance is often raised to compensate for core saturation under high signal (sometimes by up to 90% over an equivalent steel core). As per their website, SilverTone Audio uses 350 Henries @ 115Vrm/ 50Hz with no DC current. Bandwidth for this non-gapped parafeed output transformer is given as 10Hz to 40KHz -3dB @ 1Wrms/8ohm when coupled to a 3.9uF parallel-feed cap and a 32H anode choke.

How has the Model 3.2 circuit been tweaked to guarantee superior bass performance from Permalloy core output transformers? Technical director Gilwin Tan explained: "The Model 3.2 stereo amplifier is a single-ended triode design with Permalloy output transformers. Each non-magnetic stainless-steel enclosure houses a single channel. Each channel consists of a 5U4G tube rectified pi-filtered power supply stage and a high gain 6C45pi driver stage direct-coupled to a parallel-feed 300B output stage to produce 8 watts per channel. The circuit is laid out to provide for the shortest signal paths and noise isolation.

The 6C45pi is a relatively high gain tube yet retains low output impedance when supplied with sufficient bias current. The low output impedance is important of course to prevent HF attenuation when coupled to the relatively high capacitance of the 300B input grid. Unfortunately, this high bias current limits the plate load necessary for good linearity. To overcome this, we employ an anode choke instead of the more commonly used low-value plate load resistor. Another unique design element is that the power supply for this driver stage is tapped off the 300B cathode. This prevents the driver stage from overloading the 300B under dynamic conditions. In actual listening, you will notice very little compression and no hard clipping when the amplifier maxes out."
The output stage is also unconventional as it uses a parafeed design. In the past, parallel-feed designs were used to minimize costs and weight. In our case, the direct opposite is true. The size of our anode choke alone is already bigger than many output transformers of competing amps. This high inductance is necessary to properly load the 300B down to the lowest octave. We have measured the -3dB point at 12Hz for full power. Our main objective in using parafeed is to eliminate DC in the output transformer and allow the use of superior Permalloy core material. The signal path only sees the 300B, our Permalloy output transformer and a big oil capacitor instead of detouring through the power supply.

Permalloy evidences very different magnetic properties than silicon steel. To help us achieve better transformer designs, we have built proprietary test equipment that allows us to measure the transformer under realistic load conditions. Each prototype is placed into the circuit and listened to. From our listening comments, we then improve on every prototype until we're satisfied. As you can appreciate, it is quite impossible to find 3rd party transformer vendors who'd be willing to accommodate us on this endless one-up prototyping process. Remember the saying: "If you want it your way, do it yourself". That's why all SilverTone Audio Permalloy transformers are designed in-house. The recommended retail price for the Model 3.2 is $4,200 and includes a pair of Sovtek 5U4G rectifiers, a pair of EH6C45pi and a pair of gold-pin mesh plate Full Music 300Bs. We are currently expanding our dealer network and welcome any interested dealer."

The 300B tube sockets are deliberately oriented not only to have the full breadth -- rather than sliver-thin depth -- of the mesh plates face the viewer but also to turn the Full Music silk screen rearwards and thus out of sight. Once ambient light conditions are low enough, you'll bask in the full romantic glow cast by these sexy bottles.

Another thoughtful feature are the 4/8-ohm switchable taps. They don't necessitate a disconnect of speaker cables. They can be evaluated on the fly. This helps to determine which connection sounds better. After all, most speakers present anything but a stable load impedance. Optimal power transfer might occur at a setting different from what the so-called nominal speaker impedance would suggest. Experiment.

Permanently marked just below the terminals are the basic specs: 8wpc max output power; 100K input impedance; 1.2Vrms input sensitivity for full output -- and on the other half with the power inlet -- 3.0/1.5A for the externally accessible mains fuse at 115/240 of line voltage respectively