AMP6 T-Amp DIY Class-T Amplifier Kit
Introduction - AMP6 T-Amp DIY Class-T Amplifier Kit from 41hz.com
In late 2004 and early 2005, raving reviews about the $30 Sonic Impact T-Amp started to surface. Some called it a "Giant Killer", some did not like it, but most agreed it was an inexpensive amplifier that sounds pretty darn good. The favorable reviews had me wondering about Class-T amplifiers so I decided to try one on for size. Taking the DIY route, I opted for a $39 AMP6 kit from 41hz.com.
The AMP6 is a small amplifier that uses the Tripath TA2020 chip and includes an on-board regulated power supply. The manufacturer, Tripath Technology, Inc. describes Class-T amplifiers as offering both the audio fidelity of Class-AB and the power efficiency of Class-D amplifiers.
Figure 1: Tripath TA2020 Distortion vs Power Output
DIY Class-T Amplifier Kit
The kit components came neatly packaged in small Ziploc bags which identified the contents. The PCB is double weight, double sided copper and very compact.
Photograph 1: Contents of the AMP6 Kit
As you can see from the contents, the toroids need to be hand wound. I somehow managed to break a wire while I was winding one and it was promptly replaced by 41hz.com. The instructions are decent, but expect you to have a basic understanding of electronics and some soldering skills. However, there is an error on the PCB to be aware of. The polarity of the large bulk capacitor C99 is reversed on the PCB. The rectangular pad on the PCB should be positive, the round pad negative. Be careful with this one as wrong polarity of electrolytic capacitors can cause them to explode! This error is identified in the documentation, so be sure to read though the manual before you break out the soldering iron.
Construction - AMP6 T-Amp Kit
Assembly of the board is fairly straight forward. I always start with the smallest components and work upwards in size. The polarity markings on the diodes can be hard to see, so if you are uncertain, use a multimeter to determine their polarity. Also, don't forget to isolate the regulator from the heatsink. The amplifier chip does not need to be isolated.
Photograph 2: Assembled AMP6 PCBs
The transformer was salvaged from a dead computer UPS. I don't know the power rating, but it is a sizable chunk of iron and much larger than required. The documentation recommends a transformer rated at 80VA for 4 ohm loads and 40VA for 8 ohm loads. The heatsink was salvaged from a dead computer power supply which also provided the IEC socket, power switch and fuse holder. As it turns out, it is the voltage regulator that sizes the heatsink required as the amplifier chip does not produce much heat. The small aluminum chassis was purchased from a surplus store and was unmarked, but appears to be a Bud Chassis. Note that I had to move the tank capacitor to the underside of the PCB in order to have room to fasten the regulator to the chassis.
Photograph 3: Underside View of Finished AMP6 Kit
The kit comes with 3.3 uF electrolytic capacitors for input (DC blocking), but I opted to use 3 uF film capacitors instead. The volume control (not supplied with the kit) is a 100k Alps Blue Velvet. Input is through inexpensive gold plated RCA jacks with inexpensive gold plated binding posts used for the output. A small toggle switch on the front allows you to switch between on and sleep (standby) mode.
Photograph 4: Finished AMP6 - Front View
Measurements and Listening Impressions
I checked the frequency response into a 4.5 ohm resistive load and it was flat from 10 Hz to about 6 kHz, up 0.2 dB at 10 kHz and up 1 dB at 20 kHz. The measurements are similar with those by Michael Mardis. See Michael's site for measurements of SNR, distortion and crosstalk.
I tried the AMP6 with my BD-Pipes and while I was impressed with the detailed midrange and top end, I found the bass a little dry and lacking. I experimented by adding an additional 4900 uF to C1819 with the result of seemingly less bass. I came to the conclusion that the stiff (low Xmax) 40-1197 drivers in the BD-Pipes prefer amplifiers with a low damping factor which allows them resonate more and help fill in the bass.
Photograph 5: Finished AMP6 - Rear View
The AMP6 was a very nice match With a pair Paradigm Mini Monitors (2-way bookshelf). The bass was very tight and accurate. The AMP6 had nice crisp and detailed highs. Overall a very nice amplifier for the low cost. Another positive is the low power consumption of the AMP6 kit which will work well with battery power supplies. Now for the big question - How does the AMP6 kit sound relative to other low cost IC based amplifier kit? I still find that my favorite IC based amps are the LM3886 IC chip amplifier (gainclone) kits. There is something about the LM3886 chip amps kits that make the music more involving over the AMP6. This is not to say I think the AMP6 is bad, in fact, I think it is a fantastic value and sets the bar high for a low cost off the shelf kit. Higher resolution photographs of the AMP6 kit are available in the Photo Gallery: AMP6 DIY Class T Amplifier Kit.