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Srajan Ebaen
Financial Interests: click here
Source: Apple iMac 1TB running OSX 10.6.6 with AIFF files up to 24/192 and Pure Music 1.74 in memory playback with pre-allocated RAM; Burson Audio HA160D as DAC, Weiss DAC2, iPod Classic 160GB, Onkyo ND-S1 digital-direct iPod dock
Preamp/Integrated: Esoteric C-03 (transistor), Bent Audio Tap-X (AVC passive), ModWright LS100 (tubes)
Amplifier: FirstWatt J2, ModWright KWA-100 SE
Speakers: ASI Tango R
Full-size headphones: Audez'e LCD-2, beyerdynamic T1, Sennheiser HD800, AKG-K702 (all rewired by ALO Audio); HifiMan HE-5LE & HE6, audio technica ATH W-5000 'Raffinato'
Inner-ear headphones: Ortofon EQ7
Headphone amps: Woo Audio Model 5, Trafomatic Audio Experience Head One, Burson Audio HA160D
Cables: Complete loom of ASI Liveline, Crystal Cable Ultra, Zu Audio Event, Furutech GT2 and WireWorld Starlight USB A-to-mini-B cables [on loan], LaCie and Entreq Firewire 800 cables, Black Cat Cable Veloce S/PDIF cable [on loan]
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 1 x GigaWatt PF-2, 1 x Furutech RTP-6
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: $3.995

Craig Uthus' Eddie Current brand is craftily named. His Balancing Act is just as cunning a linguist. It's also that rare linestage and headphone amp to use direct-heated power triodes. Manley has a 300B linestage, Coincident a 101D version. So did Supratek. The companion preamp for the Trafomatic Kaivalya monos might become one. But there aren't many.

Moth Audio Xana tube amp - 102 lbs. of class A1 tube circuitry "direct-coupled via monstrous paper and oil capacitors."

The Balancing Act—BA for short and bachelor of audio perhaps—can be set up for either 45/2A3 or 300B/PX4 but not both. Let's start at the beginning. "This is a line/headphone amp featuring 3 x RCA and 1 x XLR line inputs and XLR and RCA pre-outs. For headphones there's one 6.3mm output on the front for standard drive, two three-pin XLR plus one 4-pin XLR for balanced. The amp drives all headphones including the new less efficient planars. Features include a lustrously polished top, laser-etched nomenclature and a retro Davies control knob. There are partial silver EI-core OPTs and a quiet outboard supply with two power trannies and two 6X4 rectifiers. This PSU also has dual regulated  B+ supplies; a discrete 18-watt 40kHz heater power amp; and a meter with voltage adjustment for the output tube heaters. The amplifier comes standard with ElectroHarmonix platinum-matched 300Bs, a Russian-made Tung Sol 6SN7 driver and two JAN 6X4 rectifiers. The main unit is all point-to-point wired. The power supply has three boards - one for the B+ regulation, one for the heater-supply power amp and one surface-mount board for the oscillator circuit that piggybacks on the power amp board." [A visual precursor for the Balancing Act is the Xana at left which Craig built during his tenure at Moth Audio.]


Craig also shared that over the last year he'd been working on a tube hybrid bipolar amplifier. "That is a dual mono integrated which makes 11.3V at clipping, i.e. 16 watts into 8Ω, 30 watts into 4Ω and 2.5 watts into 50Ω. It really handles my AKG K1000 and Audez'e LCD-1. The former is a tricky load of course. I've found that if the amplifier will drive 10Vrms with a source resistance of less than 1Ω and have enough gain to make up for the K's low efficiency, you're good to go. The Eddie Current Hybrid meets that criteria. For current gain I use six high-frequency bipolars per side and a 10,000uF cap on top of each. All voltage gain is handled by the 12AX7. The Hybrid amp is great on speakers and headphones." Now we get to question the BA concept.

Why DHT preamps are rare: "Most likely cost. One 6SN7 per channel for gain plus cathode follower is cheap and does the business just fine [that would be my ModWright LS100 below - Ed.]. The problem with DHTs is their low mu and relatively high plate resistance. A 6SN7 as a cathode follower has a source resistance of about 200 ohms. It does not have to drive a load and the power supply can be simple. A 300B meanwhile has a plate resistance of about 900 ohms.

Moth Audio M304TL 35-watt SET mono.

"The gain is less than 4 and—once you consider the heater requirements—the power supply is much more elaborate. 900Ω is really too high for a line amp. Driving the capacitance of interconnects becomes an issue. One solution is transformer coupling. A 3KΩ:600Ω transformer with a 300B has a through-put gain of about 3dB to require an additional tube in front for more voltage gain. 

"If one is going to have a good output transformers and a driver tube, one has really built not a preamp but integrated amplifier that drives loudspeakers directly*. The Balancing Act needs to drive 16Ω but not to speaker level power. Then the gain as a line amp is just right  Great care was taken to get the most from the DHTs. If you think about how they work, the heater is the cathode. Ideally the cathode wants to run on AC. This isn't just for longer tube life but to have an even electron cloud around the cathode so that the grid-to-plate control works symmetrically."

* And that's exactly what my above Woo Audio Model 5 300B SET with 6SN7 drivers is - an 8wpc integrated with headphone outputs rather than a line stage with earspeaker sockets like the Eddie Current.