Sonic Impact T-Amp - The Truth

[UPDATE: Tripath went out of business last year. Several manufacturers are still offering their chipsets in new equipment, but they may be using "new old stock" parts.]

I mentioned the $29 Sonic Impact T-Amp yesterday. It's an extremely low cost digital amplifier that has been generating quite a bit of excitement around the web. I've done a bit of digging, and it appears this is one of those rare cases where you get considerably more than you pay for.

The Low-Down

1. The T-Amp uses a Tripath TA2024B digital audio power amplifier. This respected chipset is incorporated into LCD TVs from Samsung, Sharp and several others. They use it because it sounds good, doesn't require expensive low-pass filtering, and is extremely efficient (~90%), which means it produces less heat and doesn't require a bulky heat sink.

2. Tripath chips (TK2050) are used in the Sonos Digital Music System as well as hi-fi integrated amps from Bel Canto. Car stereo manufacturers are also beginning to take notice -- several manufacturers are using Tripath chips, includingPanasonic

3. Tripath introduced the TIO Digital Amplifier card [warning: pdf link] for PCs in 2000. It was a clever idea: mount a TA2024 audio amplifier on a PCI card that connects between a soundcard and some good passive speakers. Sadly, it didn't catch on.

4. The Sonic Impact T-Amp appears to be designed around a low-cost version of Tripath's reference board for the TA2024 chipset. This explains the T-Amp's almost non-existent feature set (a single set of inputs, one plain-Jane volume knob/power switch). But remember - simple designs are great for DIY tweaks.

5. In the audio world, there's no such thing as a "Class T" amplifier. This appears to be a trademarked Tripath buzzword. The design appears to be a highly modified Class D circuit that resolves some of the traditional problems associated with digital amplifier design.

6. The T-Amp design works best in small rooms driving extremely efficient (>90dB) speakers.  THD+N (distortion & noise) is quite respectable until you drive the Tripath chip above 5W output per channel. If you crank it up, THD+N rises to an icky 10% at full-power (15W into 4 Ohms).

7. For best results, use a stabilized AC power adapter that puts out no more than 13.2V DC at 1.2 amperes. The Tripath chip *will* be damaged if you overdrive the voltage. While we're in warning mode -- continuous operation at high volume *will* shorten the life of this amp - the circuit board doesn't have a heat sink and will get quite warm if you pump a lot of power through it.

Conclusion

The T-Amp is basically the same design as the $125 Tripath TA2024B evaluation board, but selling at a bargain price. Sonic Impact cut corners on the case and connectors (and perhaps quality control - several people report receiving DOA units), but the internals are  top-notch.

You'll have to put in a bit of DIY effort to make the T-Amp really sing. I suggest attaching a good stabilized power supply, installing an ALPS volume knob, and upgrading to gold-plated RCA inputs and speaker posts. Make these changes and you'll be impressed as long as you keep the volume to moderate levels and use high-efficiency speakers. Rumor has it that Sonic Impact will introduce more powerful models based on other Tripath chips in 2006. I can't wait!

Buy a T-Amp from Amazon (support Retro Thing & get free shipping over $29)
Manufacturer's product page
DIY tweaks for the T-Amp (tnt-audio.com)
T-Amp review (tnt-audio.com)
Another T-Amp review (audio-ideas.com)