Wednesday, August 13, 2008
DIY class T amplifier
A class T amplifier is an audio amplifier which uses Tripath (since insolvent) chip based on Class D topology instead of being a different class of amplifier. It is a high order switching chip amplifier that uses a spread spectrum PWM technique to generate the audio output. This output is then filtered through a simple second order low pass passive filter to remove the ultrasonic switching residue and leave the audio signal to be sent to the loudspeakers.
I have come across numerous rave reviews on class T amplifiers and that their excellent sonic qualities far exceed many other amplifiers costing 100 times their price. Review 1: http://www.stereophile.com/solidpoweramps/1006sonic/ Review 2: http://6moons.com/audioreviews/trends/ta10_2.html plus many others. Nothing transpired and this information only remained at the back of my mind until the recently concluded KLIAV Show 2008 where I finally got to hear a class T amplifier myself. It is an amplifier in wood casing named Charlize with Tripath TA2020 chip (max output of 10W into 8Ω / 20W into 4Ω) driving a pair of horn speakers in diyParadise room. I thought to myself how natural the sound was.
I gathered more information at diyParadise and diyForum websites and even chatted with Yeo as I was keen to buy an unit of Charlize in kit form for RM350 (diyParadise also sells Charlize as finished product for RM1,000). I like the idea of assembling my very own Charlize in a small wooden jewellery box just like what was featured in their website but with RCA connectors and speaker binding posts fitted in more properly instead of them sticking out midway from the wooden casing. Just before I could place my order, I chanced upon another class T amplifier also in kit form but uses Tripath TA2024 chip (max output of 6W into 8Ω / 11W into 4Ω, both ratings @ 0.10% THD) being retailed at a hard-to-resist price of RM55. Given its price, I thought the capacitors and resistors must be of inferior quality which may need to be replaced for this class T amplifier to really sing properly. I have since ordered this kit and would need to listen to it with my loudspeakers to assess whether the 11W output is sufficient for my applications before I replace any of its components. I hope not to go overboard and work within my original budget of RM600 for the finished amplifier.
The TA2024 is a stereo bridged amp. This could be seen from the schematic in the dual push pull transistors for each channel and the 2 sided output filters. The chip is designed to run off 12V DC, so the bridged mode is needed to squeeze more power out of the 12V. It cannot be bridged further. Most of those who have written about this amplifier rave about its sound qualities, often comparing it favorably to valve amplifiers. What is the difference of TA2024 from Charlize (TA2020)? I have only heard Charlize once and never did any direct comparison between the two but after reading the comments of many others who have written on these Tripath chips, TA2020 seems to have a smoother, fuller sound and a bigger soundstage than TA2024. There is also slightly more power from TA2020 before clipping. TA2024, however, is the winner for micro details, the magical thing that valve amplifier lovers seek.
What would I be driving my class T amplifier (hereinafter referred to as T-amp) with? Most probably a pair of 86dB/1W/1m Q Acoustics 1010 bookshelf loudspeakers that I picked up during KLIAV Show 2007 meant for my second system in the bedroom/study although I also have another mint pair of audiophile loudspeakers in Epos m5. I only intend to set up a small system for nearfield listening with no intention for yet another hifi system as I already owned a decent-sounding system at home which I enjoy listening to immensely. Listening to my main system has always put back a smile to my face whenever I am feeling a little down from work pressure.
After I sold off my Sony TA-F5000 integrated amplifier, I had always fancied buying a Musical Fidelity X-80 (40W) integrated amplifier for my bedroom/study because of its looks and small footprint. Sonic quality is decent. The local agent, LTB Enterprise has some brand new units but still maintained their selling price at RM3,200 each, too pricey as far as I am concerned. I then lowered my choice to a NAD C315BEE integrated amplifier but felt its sound is a little too harsh to my ears and its full equipment size rather unsuitable. All these until the T-amp came along.
I have maintained in LYN forum from day one even before I received my first T-amp board that I am not expecting it to sound as good as the resident amplifier in my system. My first T-amp fitted with a discrete attenuator actually sounded very good and far exceeded my expectation so much so I later built another unit for my office. I am quite a perfectionist and have taken great pain to select the peripheral parts and assemble both my T-amps. Read about my listening to the T-amp where I have dedicated a separate article on it. An interesting article where TA-2020 chip based T-amp is built DIY, detailing parts used, the process and rationale: http://ta2020.huuryuu.com/index_e.html
Further thoughts: If only the JVC SX-WD1KT wood cone single driver loudspeakers could be gotten at a more affordable price, I am of opinion that these are even better suited for my T-amp based system for my bedroom/study. The system would probably be the only system I ever need to accompany me to my sunset years if they could last that long.