Amplification Reviews

That's what I wondered about those big, gleaming amps at Theta's home-theater-centered demo a CES or two back. Yes, they made a nice sound, but I know Theta as a premier producer of digital preamplifiers, digital disc players, DACs, and, more recently, multichannel preamplifier-processors. Naïvely, I assumed that these new power amps were actually OEM units wearing Theta badges.

Wrong. Theta's amps are originals endowed with some fairly innovative design ideas. The line includes the imposing Citadel 400W monoblock that Jonathan Scull reviewed in May, the heavyweight Dreadnaught with two to five 200W channels, and the 58-lb baby of the bunch, the five-channel, 100Wpc Intrepid.

All Theta amps share the brushed-silver styling of the company's other components and feature fully balanced, differential channels through the driver and output stages. Not surprisingly, they also feature balanced inputs and outputs. Inside, the amps are built of three discrete stages—input, driver, and output—with no global feedback linking them.

The input stage is a complementary common-source differential amplifier constructed of matched pairs of JFETs. This voltage amplifier, with a gain of about 2.5, also provides a reasonably high input impedance. The second stage is similar in construction to the input stage, and it, too, functions primarily as a voltage amplifier, but with a gain of 19. The output stage is a fully balanced differential complementary emitter-follower with eight high-power bipolar transistors per channel to provide the current needed to drive speakers. The total current capability of devices in this stage is 128 amps for each 100W channel! A DC servo, on the output stage only, eliminates manual trimming of output offset.

In the Intrepid, each channel is a physically independent assembly that, in parallel with the others, spans from the rear panel to a rack about 8" behind the front panel. While each amp has its own onboard capacitor bank, all channels share the control and regulation circuitry, the huge, 1100VA power transformer, and a large output-stage diode bridge located in the front of the chassis. This arrangement is distinct from more modular multichannel amps, in which each channel has its own transformer and power supply and shares only the chassis, power switch, and AC cord. Theta reasonably argues that, except on the test bench, the demand on the power supply is never simultaneously equal from all channels, and that the large common supply makes extra reserves available to the channels that need it. In any case, the Theta is specified for 100Wpc, all channels cooking.

The build quality and parts selection were impressive, fore and aft, inside and out; only the lack of latches on the XLR jacks surprised me.

Five Channels Minus Three...
As usual, I took an easy first shot and installed the Intrepid in the system that includes the Revel Studio loudspeakers. I used only two of the Theta's channels, fed via balanced lines from the preamp. The sound was sweet and smooth but seemed a bit lightweight, even though there was no overt tonal imbalance. There was no lack of bass extension if one listened for those special moments, but subjectively, the lows never demanded my attention, even when I expected them to do so. The spatial representation was open and deep, and voices had an immediacy that few amps could rival. Midrange and highs were essentially pure and free of grain, benefiting the reproduction of upper strings and brass.

I confirmed these observations when I replaced the Revels with B&W's even more critical and power-hungry Signature 800s that I reviewed in June. Strangely, while there was more bass via the S800s (two 10" vs two 8" drivers per side), the lack of bottom-end authority was equally noticeable, especially in comparison to the Bel Canto eVo monoblocks. Had I the alchemy to do it, though, I'd love to have combined the eVo's bottom-end slam with the Intrepid's clarity and smoothness throughout the rest of the spectrum. And, while the Revels and B&Ws are not what this amp's 100W channels were designed to drive, the Intrepid successfully faced off the eVo and the McCormack DNA-1 Rev.A, and faced up to the Sonic Frontiers Power-3 monoblocks in everything but power output and sheer bass whomp.