Antique Sound Labs Line I DT Preamp, Mini Phono II DT, and AV-25 DT Monoblock Amplifier

From a popular Chinese manufacturer, three pieces of tube gear priced for the workingman.

Antique Sound Labs (ASL) makes a wide variety of tube electronics ranging from affordable to moderately expensive. The ASL Hurricane DT won TAS’ Best Tube Amplifier of the Year award in 2002, and the ASL AQ1006 845DT won a Golden Ear in 2000.

This past spring I took the company’s budget gear—a pair of $690 baby monoblock amplifiers, a $345 linestage preamp, and $345 phonostage—for an extended test drive. I initially set up all the ASL pieces on a library table, using an older Marantz DVD-910 disc player as a source and for speakers, a pair of Silverline Audio SR-11 mini-monitors on 30" metal stands. For several weeks, the ASL/Silverline setup served as a secondary system until I began individually experimenting with the pieces in my main system, including using the monoblocks to drive my big, custom-made Montana loudspeakers, a larger version of PBN Audio’s highly regarded EPS.

AV-25 DT Monoblocks

The Wave AV-25 monoblock is a narrow- profile, three-tube single-channel power amp that uses one ASL-brand 12AT7 as input gain stage and driver for a pair of 6L6 output tubes. A slotted metal cage protects the tubes. Behind it sits the output transformer, and behind that, the power transformer. Each back panel has a gold-plated RCA jack, one pair of five-way binding-post speaker terminals, and an IEC mains connector with built-in fuse holder. Painted to look like brushed aluminum, the front panel sports an on/off switch and indicator light. There are two top-mounted output bias adjustments with test points.

I set the bias according to the owner’s manual and left it at that setting for the duration of the audition. On my test bench, with AC voltage at 120, both AV-25s showed onset of clipping at 14.5VRMS into 8-ohm resistive loads. That translates to an output power of 26.28 watts, slightly higher than the manufacturer’s spec.

When I first set up the ASL/Silverline system, each AV-25 sat right next to a speaker. Every time I turned the amps on, I got a loud, annoying feedback buzz that could only be stopped by pressing my hands on the tube cages. Once the amps reached operating temperature, they worked fine and didn’t misbehave. Moving them away from the speakers solved the problem. There was no audible feedback with music, regardless of how loudly it played.

I’ve always had mixed feelings about tube amplifiers’ warm, rich harmonics and hollow, underdamped bass. I’ve owned several, from the requisite modified Dynaco Stereo 70 to the Red Rose Model 2 Silver Signature, which I used for years in a bi-amp setup with a big, solid-state power amp of my own construction driving the bottom end of the Montanas. It’s a setup that worked well because of the two amps’ in-phase operation, and the efficient Montanas’ steep 24dB/octave crossover. (With this kind of speaker it’s possible to bi-amp without an external crossover. It doesn’t work well with speakers using first-order [6dB/octave] crossovers. In my experience, bi-amping with tubes on top and solid state on the bottom can yield an incredibly musical result.)

Used alone to drive the Montanas via a pair of Nordost SPM speaker cables, the AV-25s played with surprising dimensionality, although as expected, the bass had that hollow sound characteristic of amps with poor damping capability. I dug my old solid-state amp out of the garage and set the two up in the bi-amp configuration that I had enjoyed with the Red Rose, and was delighted to find that the AV-25s offered plenty of image depth, instrumental detail, and harmonic richness, without any objectionable shortcomings.

Disregarding its sins of omission, ASL’s baby monoblock offers an amazing amount of performance for not much money. It can deliver the goods with an efficient speaker—especially if you’ve got another way to generate bass. In a budget system, it would be a good choice to drive a pair of bass-shy monitors, with low end provided by a decent powered subwoofer.

Mini Phono II DT

The cute little Mini Phono II DT connects to its hefty external power supply via a two-foot umbilical cord. The business of amplifying and equalizing the phono signal is done by a pair of Russian-made Electro-Harmonix 12AX7EH tubes that are protected by a small cage. Beneath the cage is a single circuit board for both channels.

The dimensions of the power supply suggest that it’s an ideal base for the preamp, but don’t be tempted—the II DT hums when you do that. It’s best to set the phono section as far away from the power supply as possible—and also away from any other potential source of AC radiation, such as power transformers in other equipment—to keep it as quiet as possible. I put the power supply on the floor and set the II DT on a Shakti stone next to my turntable, a Rega Planar 2 with Sumiko Blue Point cartridge.

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