While looking at these connectors, I realized there are independent power connections for the left and right channels, and these are actually electrically isolated inside, not just paired together where the connector meets the pcb. Each channel uses a separate 20-amp fuse, power supply toroid, and associated rectification, so you must connect both B+ cables and both grounds to get both channels working. Studying the connections further, I learned the amp isn't bridgeable. It's designed to only provide a signal to your main stereo speakers and isn't designed to drive subwoofers. In fact, the minimalist -12dB crossover is highpass only. There are no bass EQ controls, subsonic filters, phase knobs or any of the other fairly common features - more suggestions that this amp is designed to appeal to the purist. My only nitpick on the fit and finish was the ATC fuse holders. They didn't hold the fuses as securely as I would've liked, and they are both mounted crooked in the heatsink. This is a fault of the fuse holder's design, but I would've expected better at this price level.
When you first power up the amp, blue LEDs illuminate the area around the vacuum tubes, as an indication that the amp is not yet ready for use. After about seven seconds, the LEDs turn red and the amp will pass a signal. Also, unlike some other amps I've tested, these tubes are not just for looks. They actually pass audio signals. I checked.
Circuit DesignInside the Ultimate TA2, I found more high-end, top-quality components. The pcb itself is a heavy-duty, double-sided, plated-through, glass/epoxy type board, very much like pcbs found in military-spec equipment. The independent power supplies each use a pair of 2,200F caps on the input, and filtering is used at the outputs of the separate toroids to minimize ripple and noise in the secondary rail voltages. The rails use a total of eight 4,700F caps - four on each channel - as well as what appears to be a smaller "bypass" cap to speed the current delivery. Very nicely done.
The power supplies use a total of 12 high-current capable International Rectifier IRZ44 Mosfets, and the outputs are complementary pairs of 2N6488 and 2N6491 bi-polar transistors, with each transistor rated for 75 watts, so there is plenty of headroom designed into the output section. All of the Mosfets and output transistors are sandwiched between the pcb and the heatsink to take advantage of the heatsink's maximum surface area.
Another high-end feature that I believe greatly affects sonics are the capacitors used in the low-level signal path. In this case, the DLS TA2 uses some of the best-quality parts available in the world at any price. All the "small signal" passing caps are ultra high-quality polystyrene or polypropylene, some from WIMA, and some evidently proprietary to DLS. This type of attention to detail represents a "cost be damned" approach to sound reproduction, and helps to justify the amplifier's price tag.
PerformanceThe DLS Ultimate TA2 performed very well on the revealing Cogent bench. Measured distortion plus noise at rated 4-ohm power was an ultra low 0.01 percent, and the signal to noise (referenced to full 4-ohm power) was also very good at -99.9dBA.
At a test voltage of 14.4 volts the amp developed 170 watts into 4 ohms, and 290 watts per channel into 2 ohms, easily exceeding all the published specifications. It also exceeded the published power specs with an input voltage of 12.5 volts. So rest assured you'll get the power you paid for.
Frequency response was very flat from below 10Hz all the way to 130kHz. I've measured respectable home amps with less bandwidth!