Bass Player Magazine
By Scott Malandrone
Are you a tube fan? If so, Demeter's VTHF-300M all-tube mono-block power amp is to die for. This wonderful-sounding amplifier adds delicious depth and detail to either tube or solid state preamps. Of course it's not cheap, but most hi-fi tube amplifiers aren't.
The VTHF-300M delivers loads of power from its eight Ruby Tubes 6550s and custom JEC toroidal power transformer. We wired the amp into one of our reference systems, which includes a Demeter VTBP-201DBL preamp, a Hafler pro 5000 mosfet power amp, and an Eden D410XLT 4 by 10. Although we love the fast attack and dark punch of the Hafler, the musical, deep tone of the 300M defines what bass is all about. The Demeter stays round all the way down to a 5-string's low B, and it has smooth, polished top end that's never brittle. The amp sounded equally impressive connected to an Alembic F-1X preamp, with a thicker low end that makes you want to play James Brown funk, Family Man reggae and Tommy Shannon blues (this amp loves flat wounds). Pushing the preamp's volume control makes the amp slide into fat compression with the touch of great sounding overdrive.
The black, brushed aluminum front panel looks sharp. The amp is beautiful inside, too: point-to-point wiring, WIMA capacitors, thick bundled wires and shiny solder joints show a high attention to detail. The rear panel sports three gold-plated banana jacks: one common, one for 8 ohm loads and one for 4 ohm loads. Odd detail: the amp doesn't have a standby switch, James Demeter comments, "Since a standby switch removes voltage from a tube's plate, it can deplete the life of a tube, especially if the amp is left in standby mode for a long period of time."
Removing the small panel labeled amplifier controls reveals several adjustment switches and pots. The first toggles between pentode and triode modes, which cuts the power in half and changes the amp's feel (because it has less headroom, triode mode adds compression when pushed harder). The feedback knob a small circuit to reduce distortion adjusts from low to high. We found the amp had a softer, fatter bottom in low, while turning the trim pot to high increased the gain and made the upper mids more pronounced (a setting of 12 o'clock seemed to please most testers). Another cool feature: the user-adjustable bias controls (proper biasing provides longer tube life and lower distortion and noise).
Demeter provides a voltmeter with each 300M; adjusting each tube's bias is as easy as plugging the black probe into ground and the red (positive) probe into the desired tube input connector. adjust each tube to 300 millivolts and presto! No more trips to your amp tech for costly adjustments.
It's hard to go back to a solid-state power amp after listening to the VTHF-300M's heavenly sound. this powerhouse is also one of the few pieces of professionally audio gear that's equally at home kicking out a 4-string funk as it is filling a living room with Mozart. You'll probably have to save a ton of pennies to afford one, but it will put a smile on your every time you use it.
Made in: U.S.A.
Power rating: (Pentode) 300 watts RMS into 4/8 ohm; (triode) 150 watts RMS in 4/8 ohm
The controls for output mode, fan speed, feedback level, and output-tube bias are located under a small front door. The bias is user adjustable.